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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
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3 | @c Copyright (C) 1990-1993, 1998-1999, 2001-2013 Free Software |
4 | @c Foundation, Inc. | |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
ecc6530d | 6 | @node GNU Emacs Internals |
b8d4c8d0 GM |
7 | @appendix GNU Emacs Internals |
8 | ||
9 | This chapter describes how the runnable Emacs executable is dumped with | |
10 | the preloaded Lisp libraries in it, how storage is allocated, and some | |
11 | internal aspects of GNU Emacs that may be of interest to C programmers. | |
12 | ||
13 | @menu | |
14 | * Building Emacs:: How the dumped Emacs is made. | |
333f9019 | 15 | * Pure Storage:: Kludge to make preloaded Lisp functions shareable. |
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16 | * Garbage Collection:: Reclaiming space for Lisp objects no longer used. |
17 | * Memory Usage:: Info about total size of Lisp objects made so far. | |
18 | * Writing Emacs Primitives:: Writing C code for Emacs. | |
19 | * Object Internals:: Data formats of buffers, windows, processes. | |
d92d9c95 | 20 | * C Integer Types:: How C integer types are used inside Emacs. |
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21 | @end menu |
22 | ||
23 | @node Building Emacs | |
520f2425 | 24 | @section Building Emacs |
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25 | @cindex building Emacs |
26 | @pindex temacs | |
27 | ||
28 | This section explains the steps involved in building the Emacs | |
29 | executable. You don't have to know this material to build and install | |
30 | Emacs, since the makefiles do all these things automatically. This | |
d15aac68 | 31 | information is pertinent to Emacs developers. |
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32 | |
33 | Compilation of the C source files in the @file{src} directory | |
34 | produces an executable file called @file{temacs}, also called a | |
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35 | @dfn{bare impure Emacs}. It contains the Emacs Lisp interpreter and |
36 | I/O routines, but not the editing commands. | |
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37 | |
38 | @cindex @file{loadup.el} | |
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39 | The command @w{@command{temacs -l loadup}} would run @file{temacs} |
40 | and direct it to load @file{loadup.el}. The @code{loadup} library | |
41 | loads additional Lisp libraries, which set up the normal Emacs editing | |
42 | environment. After this step, the Emacs executable is no longer | |
43 | @dfn{bare}. | |
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44 | |
45 | @cindex dumping Emacs | |
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46 | Because it takes some time to load the standard Lisp files, the |
47 | @file{temacs} executable usually isn't run directly by users. | |
48 | Instead, as one of the last steps of building Emacs, the command | |
49 | @samp{temacs -batch -l loadup dump} is run. The special @samp{dump} | |
50 | argument causes @command{temacs} to dump out an executable program, | |
51 | called @file{emacs}, which has all the standard Lisp files preloaded. | |
52 | (The @samp{-batch} argument prevents @file{temacs} from trying to | |
53 | initialize any of its data on the terminal, so that the tables of | |
54 | terminal information are empty in the dumped Emacs.) | |
55 | ||
56 | @cindex preloaded Lisp files | |
b578c9cc | 57 | @vindex preloaded-file-list |
d15aac68 CY |
58 | The dumped @file{emacs} executable (also called a @dfn{pure} Emacs) |
59 | is the one which is installed. The variable | |
60 | @code{preloaded-file-list} stores a list of the Lisp files preloaded | |
61 | into the dumped Emacs. If you port Emacs to a new operating system, | |
62 | and are not able to implement dumping, then Emacs must load | |
63 | @file{loadup.el} each time it starts. | |
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64 | |
65 | @cindex @file{site-load.el} | |
b8d4c8d0 | 66 | You can specify additional files to preload by writing a library named |
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67 | @file{site-load.el} that loads them. You may need to rebuild Emacs |
68 | with an added definition | |
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69 | |
70 | @example | |
71 | #define SITELOAD_PURESIZE_EXTRA @var{n} | |
72 | @end example | |
73 | ||
74 | @noindent | |
520f2425 GM |
75 | to make @var{n} added bytes of pure space to hold the additional files; |
76 | see @file{src/puresize.h}. | |
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77 | (Try adding increments of 20000 until it is big enough.) However, the |
78 | advantage of preloading additional files decreases as machines get | |
79 | faster. On modern machines, it is usually not advisable. | |
80 | ||
81 | After @file{loadup.el} reads @file{site-load.el}, it finds the | |
82 | documentation strings for primitive and preloaded functions (and | |
83 | variables) in the file @file{etc/DOC} where they are stored, by | |
84 | calling @code{Snarf-documentation} (@pxref{Definition of | |
85 | Snarf-documentation,, Accessing Documentation}). | |
86 | ||
87 | @cindex @file{site-init.el} | |
88 | @cindex preloading additional functions and variables | |
89 | You can specify other Lisp expressions to execute just before dumping | |
90 | by putting them in a library named @file{site-init.el}. This file is | |
91 | executed after the documentation strings are found. | |
92 | ||
93 | If you want to preload function or variable definitions, there are | |
94 | three ways you can do this and make their documentation strings | |
95 | accessible when you subsequently run Emacs: | |
96 | ||
97 | @itemize @bullet | |
98 | @item | |
99 | Arrange to scan these files when producing the @file{etc/DOC} file, | |
100 | and load them with @file{site-load.el}. | |
101 | ||
102 | @item | |
103 | Load the files with @file{site-init.el}, then copy the files into the | |
104 | installation directory for Lisp files when you install Emacs. | |
105 | ||
106 | @item | |
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107 | Specify a @code{nil} value for @code{byte-compile-dynamic-docstrings} |
108 | as a local variable in each of these files, and load them with either | |
109 | @file{site-load.el} or @file{site-init.el}. (This method has the | |
110 | drawback that the documentation strings take up space in Emacs all the | |
111 | time.) | |
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112 | @end itemize |
113 | ||
114 | It is not advisable to put anything in @file{site-load.el} or | |
115 | @file{site-init.el} that would alter any of the features that users | |
116 | expect in an ordinary unmodified Emacs. If you feel you must override | |
117 | normal features for your site, do it with @file{default.el}, so that | |
118 | users can override your changes if they wish. @xref{Startup Summary}. | |
119 | ||
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120 | In a package that can be preloaded, it is sometimes necessary (or |
121 | useful) to delay certain evaluations until Emacs subsequently starts | |
122 | up. The vast majority of such cases relate to the values of | |
123 | customizable variables. For example, @code{tutorial-directory} is a | |
124 | variable defined in @file{startup.el}, which is preloaded. The default | |
125 | value is set based on @code{data-directory}. The variable needs to | |
126 | access the value of @code{data-directory} when Emacs starts, not when | |
127 | it is dumped, because the Emacs executable has probably been installed | |
128 | in a different location since it was dumped. | |
129 | ||
130 | @defun custom-initialize-delay symbol value | |
131 | This function delays the initialization of @var{symbol} to the next | |
132 | Emacs start. You normally use this function by specifying it as the | |
133 | @code{:initialize} property of a customizable variable. (The argument | |
f003f294 | 134 | @var{value} is unused, and is provided only for compatibility with the |
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135 | form Custom expects.) |
136 | @end defun | |
b8d4c8d0 | 137 | |
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138 | In the unlikely event that you need a more general functionality than |
139 | @code{custom-initialize-delay} provides, you can use | |
140 | @code{before-init-hook} (@pxref{Startup Summary}). | |
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141 | |
142 | @defun dump-emacs to-file from-file | |
143 | @cindex unexec | |
144 | This function dumps the current state of Emacs into an executable file | |
145 | @var{to-file}. It takes symbols from @var{from-file} (this is normally | |
146 | the executable file @file{temacs}). | |
147 | ||
148 | If you want to use this function in an Emacs that was already dumped, | |
149 | you must run Emacs with @samp{-batch}. | |
150 | @end defun | |
151 | ||
152 | @node Pure Storage | |
520f2425 | 153 | @section Pure Storage |
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154 | @cindex pure storage |
155 | ||
156 | Emacs Lisp uses two kinds of storage for user-created Lisp objects: | |
157 | @dfn{normal storage} and @dfn{pure storage}. Normal storage is where | |
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158 | all the new data created during an Emacs session are kept |
159 | (@pxref{Garbage Collection}). Pure storage is used for certain data | |
160 | in the preloaded standard Lisp files---data that should never change | |
161 | during actual use of Emacs. | |
b8d4c8d0 | 162 | |
d15aac68 | 163 | Pure storage is allocated only while @command{temacs} is loading the |
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164 | standard preloaded Lisp libraries. In the file @file{emacs}, it is |
165 | marked as read-only (on operating systems that permit this), so that | |
166 | the memory space can be shared by all the Emacs jobs running on the | |
167 | machine at once. Pure storage is not expandable; a fixed amount is | |
168 | allocated when Emacs is compiled, and if that is not sufficient for | |
169 | the preloaded libraries, @file{temacs} allocates dynamic memory for | |
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170 | the part that didn't fit. The resulting image will work, but garbage |
171 | collection (@pxref{Garbage Collection}) is disabled in this situation, | |
172 | causing a memory leak. Such an overflow normally won't happen unless | |
173 | you try to preload additional libraries or add features to the | |
174 | standard ones. Emacs will display a warning about the overflow when | |
175 | it starts. If this happens, you should increase the compilation | |
176 | parameter @code{SYSTEM_PURESIZE_EXTRA} in the file | |
177 | @file{src/puresize.h} and rebuild Emacs. | |
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178 | |
179 | @defun purecopy object | |
180 | This function makes a copy in pure storage of @var{object}, and returns | |
181 | it. It copies a string by simply making a new string with the same | |
182 | characters, but without text properties, in pure storage. It | |
183 | recursively copies the contents of vectors and cons cells. It does | |
184 | not make copies of other objects such as symbols, but just returns | |
185 | them unchanged. It signals an error if asked to copy markers. | |
186 | ||
187 | This function is a no-op except while Emacs is being built and dumped; | |
999dd333 | 188 | it is usually called only in preloaded Lisp files. |
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189 | @end defun |
190 | ||
191 | @defvar pure-bytes-used | |
192 | The value of this variable is the number of bytes of pure storage | |
193 | allocated so far. Typically, in a dumped Emacs, this number is very | |
194 | close to the total amount of pure storage available---if it were not, | |
195 | we would preallocate less. | |
196 | @end defvar | |
197 | ||
198 | @defvar purify-flag | |
199 | This variable determines whether @code{defun} should make a copy of the | |
200 | function definition in pure storage. If it is non-@code{nil}, then the | |
201 | function definition is copied into pure storage. | |
202 | ||
203 | This flag is @code{t} while loading all of the basic functions for | |
333f9019 | 204 | building Emacs initially (allowing those functions to be shareable and |
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205 | non-collectible). Dumping Emacs as an executable always writes |
206 | @code{nil} in this variable, regardless of the value it actually has | |
207 | before and after dumping. | |
208 | ||
209 | You should not change this flag in a running Emacs. | |
210 | @end defvar | |
211 | ||
212 | @node Garbage Collection | |
520f2425 | 213 | @section Garbage Collection |
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214 | |
215 | @cindex memory allocation | |
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216 | When a program creates a list or the user defines a new function |
217 | (such as by loading a library), that data is placed in normal storage. | |
218 | If normal storage runs low, then Emacs asks the operating system to | |
219 | allocate more memory. Different types of Lisp objects, such as | |
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220 | symbols, cons cells, small vectors, markers, etc., are segregated in |
221 | distinct blocks in memory. (Large vectors, long strings, buffers and | |
222 | certain other editing types, which are fairly large, are allocated in | |
223 | individual blocks, one per object; small strings are packed into blocks | |
224 | of 8k bytes, and small vectors are packed into blocks of 4k bytes). | |
225 | ||
226 | @cindex vector-like objects, storage | |
227 | @cindex storage of vector-like Lisp objects | |
228 | Beyond the basic vector, a lot of objects like window, buffer, and | |
229 | frame are managed as if they were vectors. The corresponding C data | |
230 | structures include the @code{struct vectorlike_header} field whose | |
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231 | @code{size} member contains the subtype enumerated by @code{enum pvec_type} |
232 | and an information about how many @code{Lisp_Object} fields this structure | |
233 | contains and what the size of the rest data is. This information is | |
234 | needed to calculate the memory footprint of an object, and used | |
235 | by the vector allocation code while iterating over the vector blocks. | |
b8d4c8d0 | 236 | |
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237 | @cindex garbage collection |
238 | It is quite common to use some storage for a while, then release it | |
239 | by (for example) killing a buffer or deleting the last pointer to an | |
240 | object. Emacs provides a @dfn{garbage collector} to reclaim this | |
241 | abandoned storage. The garbage collector operates by finding and | |
242 | marking all Lisp objects that are still accessible to Lisp programs. | |
243 | To begin with, it assumes all the symbols, their values and associated | |
244 | function definitions, and any data presently on the stack, are | |
245 | accessible. Any objects that can be reached indirectly through other | |
246 | accessible objects are also accessible. | |
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247 | |
248 | When marking is finished, all objects still unmarked are garbage. No | |
249 | matter what the Lisp program or the user does, it is impossible to refer | |
250 | to them, since there is no longer a way to reach them. Their space | |
251 | might as well be reused, since no one will miss them. The second | |
252 | (``sweep'') phase of the garbage collector arranges to reuse them. | |
253 | ||
254 | @c ??? Maybe add something describing weak hash tables here? | |
255 | ||
256 | @cindex free list | |
257 | The sweep phase puts unused cons cells onto a @dfn{free list} | |
258 | for future allocation; likewise for symbols and markers. It compacts | |
259 | the accessible strings so they occupy fewer 8k blocks; then it frees the | |
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260 | other 8k blocks. Unreachable vectors from vector blocks are coalesced |
261 | to create largest possible free areas; if a free area spans a complete | |
262 | 4k block, that block is freed. Otherwise, the free area is recorded | |
263 | in a free list array, where each entry corresponds to a free list | |
264 | of areas of the same size. Large vectors, buffers, and other large | |
265 | objects are allocated and freed individually. | |
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266 | |
267 | @cindex CL note---allocate more storage | |
268 | @quotation | |
269 | @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not | |
270 | call the garbage collector when the free list is empty. Instead, it | |
271 | simply requests the operating system to allocate more storage, and | |
272 | processing continues until @code{gc-cons-threshold} bytes have been | |
273 | used. | |
274 | ||
275 | This means that you can make sure that the garbage collector will not | |
276 | run during a certain portion of a Lisp program by calling the garbage | |
277 | collector explicitly just before it (provided that portion of the | |
278 | program does not use so much space as to force a second garbage | |
279 | collection). | |
280 | @end quotation | |
281 | ||
282 | @deffn Command garbage-collect | |
283 | This command runs a garbage collection, and returns information on | |
284 | the amount of space in use. (Garbage collection can also occur | |
285 | spontaneously if you use more than @code{gc-cons-threshold} bytes of | |
286 | Lisp data since the previous garbage collection.) | |
287 | ||
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288 | @code{garbage-collect} returns a list with information on amount of space in |
289 | use, where each entry has the form @samp{(@var{name} @var{size} @var{used})} | |
290 | or @samp{(@var{name} @var{size} @var{used} @var{free})}. In the entry, | |
291 | @var{name} is a symbol describing the kind of objects this entry represents, | |
292 | @var{size} is the number of bytes used by each one, @var{used} is the number | |
293 | of those objects that were found live in the heap, and optional @var{free} is | |
294 | the number of those objects that are not live but that Emacs keeps around for | |
295 | future allocations. So an overall result is: | |
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296 | |
297 | @example | |
f24f2e22 | 298 | ((@code{conses} @var{cons-size} @var{used-conses} @var{free-conses}) |
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299 | (@code{symbols} @var{symbol-size} @var{used-symbols} @var{free-symbols}) |
300 | (@code{miscs} @var{misc-size} @var{used-miscs} @var{free-miscs}) | |
301 | (@code{strings} @var{string-size} @var{used-strings} @var{free-strings}) | |
302 | (@code{string-bytes} @var{byte-size} @var{used-bytes}) | |
303 | (@code{vectors} @var{vector-size} @var{used-vectors}) | |
304 | (@code{vector-slots} @var{slot-size} @var{used-slots} @var{free-slots}) | |
305 | (@code{floats} @var{float-size} @var{used-floats} @var{free-floats}) | |
306 | (@code{intervals} @var{interval-size} @var{used-intervals} @var{free-intervals}) | |
307 | (@code{buffers} @var{buffer-size} @var{used-buffers}) | |
308 | (@code{heap} @var{unit-size} @var{total-size} @var{free-size})) | |
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309 | @end example |
310 | ||
311 | Here is an example: | |
312 | ||
313 | @example | |
b8d4c8d0 | 314 | (garbage-collect) |
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315 | @result{} ((conses 16 49126 8058) (symbols 48 14607 0) |
316 | (miscs 40 34 56) (strings 32 2942 2607) | |
317 | (string-bytes 1 78607) (vectors 16 7247) | |
318 | (vector-slots 8 341609 29474) (floats 8 71 102) | |
319 | (intervals 56 27 26) (buffers 944 8) | |
320 | (heap 1024 11715 2678)) | |
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321 | @end example |
322 | ||
74934dcc DA |
323 | Below is a table explaining each element. Note that last @code{heap} entry |
324 | is optional and present only if an underlying @code{malloc} implementation | |
325 | provides @code{mallinfo} function. | |
b8d4c8d0 GM |
326 | |
327 | @table @var | |
74934dcc | 328 | @item cons-size |
39670ef4 | 329 | Internal size of a cons cell, i.e., @code{sizeof (struct Lisp_Cons)}. |
74934dcc | 330 | |
b8d4c8d0 GM |
331 | @item used-conses |
332 | The number of cons cells in use. | |
333 | ||
334 | @item free-conses | |
74934dcc DA |
335 | The number of cons cells for which space has been obtained from |
336 | the operating system, but that are not currently being used. | |
b8d4c8d0 | 337 | |
74934dcc | 338 | @item symbol-size |
39670ef4 | 339 | Internal size of a symbol, i.e., @code{sizeof (struct Lisp_Symbol)}. |
74934dcc DA |
340 | |
341 | @item used-symbols | |
b8d4c8d0 GM |
342 | The number of symbols in use. |
343 | ||
74934dcc DA |
344 | @item free-symbols |
345 | The number of symbols for which space has been obtained from | |
346 | the operating system, but that are not currently being used. | |
347 | ||
348 | @item misc-size | |
39670ef4 | 349 | Internal size of a miscellaneous entity, i.e., |
74934dcc DA |
350 | @code{sizeof (union Lisp_Misc)}, which is a size of the |
351 | largest type enumerated in @code{enum Lisp_Misc_Type}. | |
b8d4c8d0 GM |
352 | |
353 | @item used-miscs | |
74934dcc DA |
354 | The number of miscellaneous objects in use. These include markers |
355 | and overlays, plus certain objects not visible to users. | |
b8d4c8d0 GM |
356 | |
357 | @item free-miscs | |
358 | The number of miscellaneous objects for which space has been obtained | |
359 | from the operating system, but that are not currently being used. | |
360 | ||
74934dcc | 361 | @item string-size |
39670ef4 | 362 | Internal size of a string header, i.e., @code{sizeof (struct Lisp_String)}. |
74934dcc DA |
363 | |
364 | @item used-strings | |
365 | The number of string headers in use. | |
366 | ||
367 | @item free-strings | |
368 | The number of string headers for which space has been obtained | |
369 | from the operating system, but that are not currently being used. | |
370 | ||
371 | @item byte-size | |
372 | This is used for convenience and equals to @code{sizeof (char)}. | |
373 | ||
374 | @item used-bytes | |
375 | The total size of all string data in bytes. | |
376 | ||
377 | @item vector-size | |
39670ef4 | 378 | Internal size of a vector header, i.e., @code{sizeof (struct Lisp_Vector)}. |
74934dcc DA |
379 | |
380 | @item used-vectors | |
381 | The number of vector headers allocated from the vector blocks. | |
382 | ||
383 | @item slot-size | |
384 | Internal size of a vector slot, always equal to @code{sizeof (Lisp_Object)}. | |
385 | ||
386 | @item used-slots | |
387 | The number of slots in all used vectors. | |
388 | ||
389 | @item free-slots | |
390 | The number of free slots in all vector blocks. | |
b8d4c8d0 | 391 | |
74934dcc | 392 | @item float-size |
39670ef4 | 393 | Internal size of a float object, i.e., @code{sizeof (struct Lisp_Float)}. |
74934dcc | 394 | (Do not confuse it with the native platform @code{float} or @code{double}.) |
b8d4c8d0 GM |
395 | |
396 | @item used-floats | |
b8d4c8d0 GM |
397 | The number of floats in use. |
398 | ||
399 | @item free-floats | |
74934dcc DA |
400 | The number of floats for which space has been obtained from |
401 | the operating system, but that are not currently being used. | |
402 | ||
403 | @item interval-size | |
39670ef4 | 404 | Internal size of an interval object, i.e., @code{sizeof (struct interval)}. |
b8d4c8d0 GM |
405 | |
406 | @item used-intervals | |
74934dcc | 407 | The number of intervals in use. |
b8d4c8d0 GM |
408 | |
409 | @item free-intervals | |
74934dcc DA |
410 | The number of intervals for which space has been obtained from |
411 | the operating system, but that are not currently being used. | |
b8d4c8d0 | 412 | |
74934dcc | 413 | @item buffer-size |
39670ef4 | 414 | Internal size of a buffer, i.e., @code{sizeof (struct buffer)}. |
74934dcc | 415 | (Do not confuse with the value returned by @code{buffer-size} function.) |
b8d4c8d0 | 416 | |
74934dcc DA |
417 | @item used-buffers |
418 | The number of buffer objects in use. This includes killed buffers | |
39670ef4 | 419 | invisible to users, i.e., all buffers in @code{all_buffers} list. |
74934dcc DA |
420 | |
421 | @item unit-size | |
422 | The unit of heap space measurement, always equal to 1024 bytes. | |
423 | ||
424 | @item total-size | |
425 | Total heap size, in @var{unit-size} units. | |
426 | ||
427 | @item free-size | |
428 | Heap space which is not currently used, in @var{unit-size} units. | |
b8d4c8d0 GM |
429 | @end table |
430 | ||
999dd333 | 431 | If there was overflow in pure space (@pxref{Pure Storage}), |
b8d4c8d0 | 432 | @code{garbage-collect} returns @code{nil}, because a real garbage |
9658dc2a | 433 | collection cannot be done. |
b8d4c8d0 GM |
434 | @end deffn |
435 | ||
436 | @defopt garbage-collection-messages | |
437 | If this variable is non-@code{nil}, Emacs displays a message at the | |
438 | beginning and end of garbage collection. The default value is | |
999dd333 | 439 | @code{nil}. |
b8d4c8d0 GM |
440 | @end defopt |
441 | ||
442 | @defvar post-gc-hook | |
443 | This is a normal hook that is run at the end of garbage collection. | |
444 | Garbage collection is inhibited while the hook functions run, so be | |
445 | careful writing them. | |
446 | @end defvar | |
447 | ||
448 | @defopt gc-cons-threshold | |
449 | The value of this variable is the number of bytes of storage that must | |
450 | be allocated for Lisp objects after one garbage collection in order to | |
74934dcc DA |
451 | trigger another garbage collection. You can use the result returned by |
452 | @code{garbage-collect} to get an information about size of the particular | |
453 | object type; space allocated to the contents of buffers does not count. | |
454 | Note that the subsequent garbage collection does not happen immediately | |
455 | when the threshold is exhausted, but only the next time the Lisp interpreter | |
456 | is called. | |
457 | ||
458 | The initial threshold value is @code{GC_DEFAULT_THRESHOLD}, defined in | |
459 | @file{alloc.c}. Since it's defined in @code{word_size} units, the value | |
460 | is 400,000 for the default 32-bit configuration and 800,000 for the 64-bit | |
461 | one. If you specify a larger value, garbage collection will happen less | |
462 | often. This reduces the amount of time spent garbage collecting, but | |
463 | increases total memory use. You may want to do this when running a program | |
464 | that creates lots of Lisp data. | |
465 | ||
466 | You can make collections more frequent by specifying a smaller value, down | |
467 | to 1/10th of @code{GC_DEFAULT_THRESHOLD}. A value less than this minimum | |
468 | will remain in effect only until the subsequent garbage collection, at which | |
469 | time @code{garbage-collect} will set the threshold back to the minimum. | |
b8d4c8d0 GM |
470 | @end defopt |
471 | ||
472 | @defopt gc-cons-percentage | |
473 | The value of this variable specifies the amount of consing before a | |
474 | garbage collection occurs, as a fraction of the current heap size. | |
475 | This criterion and @code{gc-cons-threshold} apply in parallel, and | |
476 | garbage collection occurs only when both criteria are satisfied. | |
477 | ||
478 | As the heap size increases, the time to perform a garbage collection | |
479 | increases. Thus, it can be desirable to do them less frequently in | |
480 | proportion. | |
481 | @end defopt | |
482 | ||
483 | The value returned by @code{garbage-collect} describes the amount of | |
484 | memory used by Lisp data, broken down by data type. By contrast, the | |
485 | function @code{memory-limit} provides information on the total amount of | |
486 | memory Emacs is currently using. | |
487 | ||
b8d4c8d0 GM |
488 | @defun memory-limit |
489 | This function returns the address of the last byte Emacs has allocated, | |
490 | divided by 1024. We divide the value by 1024 to make sure it fits in a | |
491 | Lisp integer. | |
492 | ||
493 | You can use this to get a general idea of how your actions affect the | |
494 | memory usage. | |
495 | @end defun | |
496 | ||
497 | @defvar memory-full | |
d15aac68 | 498 | This variable is @code{t} if Emacs is nearly out of memory for Lisp |
b8d4c8d0 GM |
499 | objects, and @code{nil} otherwise. |
500 | @end defvar | |
501 | ||
502 | @defun memory-use-counts | |
503 | This returns a list of numbers that count the number of objects | |
504 | created in this Emacs session. Each of these counters increments for | |
505 | a certain kind of object. See the documentation string for details. | |
506 | @end defun | |
507 | ||
508 | @defvar gcs-done | |
509 | This variable contains the total number of garbage collections | |
510 | done so far in this Emacs session. | |
511 | @end defvar | |
512 | ||
513 | @defvar gc-elapsed | |
514 | This variable contains the total number of seconds of elapsed time | |
515 | during garbage collection so far in this Emacs session, as a floating | |
516 | point number. | |
517 | @end defvar | |
518 | ||
519 | @node Memory Usage | |
520 | @section Memory Usage | |
521 | @cindex memory usage | |
522 | ||
523 | These functions and variables give information about the total amount | |
524 | of memory allocation that Emacs has done, broken down by data type. | |
525 | Note the difference between these and the values returned by | |
01a6dcc8 | 526 | @code{garbage-collect}; those count objects that currently exist, but |
b8d4c8d0 GM |
527 | these count the number or size of all allocations, including those for |
528 | objects that have since been freed. | |
529 | ||
530 | @defvar cons-cells-consed | |
531 | The total number of cons cells that have been allocated so far | |
532 | in this Emacs session. | |
533 | @end defvar | |
534 | ||
535 | @defvar floats-consed | |
536 | The total number of floats that have been allocated so far | |
537 | in this Emacs session. | |
538 | @end defvar | |
539 | ||
540 | @defvar vector-cells-consed | |
541 | The total number of vector cells that have been allocated so far | |
542 | in this Emacs session. | |
543 | @end defvar | |
544 | ||
545 | @defvar symbols-consed | |
546 | The total number of symbols that have been allocated so far | |
547 | in this Emacs session. | |
548 | @end defvar | |
549 | ||
550 | @defvar string-chars-consed | |
551 | The total number of string characters that have been allocated so far | |
9658dc2a | 552 | in this session. |
b8d4c8d0 GM |
553 | @end defvar |
554 | ||
555 | @defvar misc-objects-consed | |
556 | The total number of miscellaneous objects that have been allocated so | |
9658dc2a | 557 | far in this session. These include markers and overlays, plus |
b8d4c8d0 GM |
558 | certain objects not visible to users. |
559 | @end defvar | |
560 | ||
561 | @defvar intervals-consed | |
562 | The total number of intervals that have been allocated so far | |
563 | in this Emacs session. | |
564 | @end defvar | |
565 | ||
566 | @defvar strings-consed | |
567 | The total number of strings that have been allocated so far in this | |
568 | Emacs session. | |
569 | @end defvar | |
570 | ||
571 | @node Writing Emacs Primitives | |
520f2425 | 572 | @section Writing Emacs Primitives |
b8d4c8d0 GM |
573 | @cindex primitive function internals |
574 | @cindex writing Emacs primitives | |
575 | ||
1df7defd | 576 | Lisp primitives are Lisp functions implemented in C@. The details of |
b8d4c8d0 GM |
577 | interfacing the C function so that Lisp can call it are handled by a few |
578 | C macros. The only way to really understand how to write new C code is | |
579 | to read the source, but we can explain some things here. | |
580 | ||
581 | An example of a special form is the definition of @code{or}, from | |
582 | @file{eval.c}. (An ordinary function would have the same general | |
583 | appearance.) | |
584 | ||
585 | @cindex garbage collection protection | |
586 | @smallexample | |
587 | @group | |
588 | DEFUN ("or", For, Sor, 0, UNEVALLED, 0, | |
d15aac68 CY |
589 | doc: /* Eval args until one of them yields non-nil, then return |
590 | that value. | |
591 | The remaining args are not evalled at all. | |
b8d4c8d0 GM |
592 | If all args return nil, return nil. |
593 | @end group | |
594 | @group | |
595 | usage: (or CONDITIONS ...) */) | |
b88746ba | 596 | (Lisp_Object args) |
b8d4c8d0 GM |
597 | @{ |
598 | register Lisp_Object val = Qnil; | |
599 | struct gcpro gcpro1; | |
600 | @end group | |
601 | ||
602 | @group | |
603 | GCPRO1 (args); | |
604 | @end group | |
605 | ||
606 | @group | |
607 | while (CONSP (args)) | |
608 | @{ | |
7d2d7cc0 | 609 | val = eval_sub (XCAR (args)); |
b8d4c8d0 GM |
610 | if (!NILP (val)) |
611 | break; | |
612 | args = XCDR (args); | |
613 | @} | |
614 | @end group | |
615 | ||
616 | @group | |
617 | UNGCPRO; | |
618 | return val; | |
619 | @} | |
620 | @end group | |
621 | @end smallexample | |
622 | ||
623 | @cindex @code{DEFUN}, C macro to define Lisp primitives | |
624 | Let's start with a precise explanation of the arguments to the | |
625 | @code{DEFUN} macro. Here is a template for them: | |
626 | ||
627 | @example | |
628 | DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc}) | |
629 | @end example | |
630 | ||
631 | @table @var | |
632 | @item lname | |
633 | This is the name of the Lisp symbol to define as the function name; in | |
634 | the example above, it is @code{or}. | |
635 | ||
636 | @item fname | |
d15aac68 CY |
637 | This is the C function name for this function. This is the name that |
638 | is used in C code for calling the function. The name is, by | |
639 | convention, @samp{F} prepended to the Lisp name, with all dashes | |
640 | (@samp{-}) in the Lisp name changed to underscores. Thus, to call | |
641 | this function from C code, call @code{For}. | |
b8d4c8d0 GM |
642 | |
643 | @item sname | |
644 | This is a C variable name to use for a structure that holds the data for | |
645 | the subr object that represents the function in Lisp. This structure | |
646 | conveys the Lisp symbol name to the initialization routine that will | |
647 | create the symbol and store the subr object as its definition. By | |
648 | convention, this name is always @var{fname} with @samp{F} replaced with | |
649 | @samp{S}. | |
650 | ||
651 | @item min | |
652 | This is the minimum number of arguments that the function requires. The | |
653 | function @code{or} allows a minimum of zero arguments. | |
654 | ||
655 | @item max | |
656 | This is the maximum number of arguments that the function accepts, if | |
657 | there is a fixed maximum. Alternatively, it can be @code{UNEVALLED}, | |
658 | indicating a special form that receives unevaluated arguments, or | |
659 | @code{MANY}, indicating an unlimited number of evaluated arguments (the | |
660 | equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are | |
9658dc2a GM |
661 | macros. If @var{max} is a number, it must be more than @var{min} but |
662 | less than 8. | |
b8d4c8d0 | 663 | |
84ebefe9 | 664 | @cindex interactive specification in primitives |
b8d4c8d0 | 665 | @item interactive |
84ebefe9 XF |
666 | This is an interactive specification, a string such as might be used |
667 | as the argument of @code{interactive} in a Lisp function. In the case | |
668 | of @code{or}, it is 0 (a null pointer), indicating that @code{or} | |
b02b5481 GM |
669 | cannot be called interactively. A value of @code{""} indicates a |
670 | function that should receive no arguments when called interactively. | |
84ebefe9 XF |
671 | If the value begins with a @samp{"(}, the string is evaluated as a |
672 | Lisp form. For example: | |
673 | ||
b02b5481 | 674 | @example |
84ebefe9 | 675 | @group |
b02b5481 GM |
676 | DEFUN ("foo", Ffoo, Sfoo, 0, UNEVALLED, |
677 | "(list (read-char-by-name \"Insert character: \")\ | |
84ebefe9 XF |
678 | (prefix-numeric-value current-prefix-arg)\ |
679 | t))", | |
680 | doc: /* @dots{} /*) | |
681 | @end group | |
b02b5481 | 682 | @end example |
b8d4c8d0 GM |
683 | |
684 | @item doc | |
685 | This is the documentation string. It uses C comment syntax rather | |
686 | than C string syntax because comment syntax requires nothing special | |
687 | to include multiple lines. The @samp{doc:} identifies the comment | |
688 | that follows as the documentation string. The @samp{/*} and @samp{*/} | |
689 | delimiters that begin and end the comment are not part of the | |
690 | documentation string. | |
691 | ||
692 | If the last line of the documentation string begins with the keyword | |
693 | @samp{usage:}, the rest of the line is treated as the argument list | |
694 | for documentation purposes. This way, you can use different argument | |
695 | names in the documentation string from the ones used in the C code. | |
696 | @samp{usage:} is required if the function has an unlimited number of | |
697 | arguments. | |
698 | ||
699 | All the usual rules for documentation strings in Lisp code | |
700 | (@pxref{Documentation Tips}) apply to C code documentation strings | |
701 | too. | |
702 | @end table | |
703 | ||
b88746ba | 704 | After the call to the @code{DEFUN} macro, you must write the |
d15aac68 CY |
705 | argument list for the C function, including the types for the |
706 | arguments. If the primitive accepts a fixed maximum number of Lisp | |
707 | arguments, there must be one C argument for each Lisp argument, and | |
708 | each argument must be of type @code{Lisp_Object}. (Various macros and | |
709 | functions for creating values of type @code{Lisp_Object} are declared | |
710 | in the file @file{lisp.h}.) If the primitive has no upper limit on | |
711 | the number of Lisp arguments, it must have exactly two C arguments: | |
712 | the first is the number of Lisp arguments, and the second is the | |
713 | address of a block containing their values. These have types | |
39670ef4 | 714 | @code{int} and @w{@code{Lisp_Object *}} respectively. Since |
74934dcc DA |
715 | @code{Lisp_Object} can hold any Lisp object of any data type, you |
716 | can determine the actual data type only at run time; so if you want | |
717 | a primitive to accept only a certain type of argument, you must check | |
718 | the type explicitly using a suitable predicate (@pxref{Type Predicates}). | |
719 | @cindex type checking internals | |
b8d4c8d0 GM |
720 | |
721 | @cindex @code{GCPRO} and @code{UNGCPRO} | |
722 | @cindex protect C variables from garbage collection | |
723 | Within the function @code{For} itself, note the use of the macros | |
d15aac68 CY |
724 | @code{GCPRO1} and @code{UNGCPRO}. These macros are defined for the |
725 | sake of the few platforms which do not use Emacs' default | |
726 | stack-marking garbage collector. The @code{GCPRO1} macro ``protects'' | |
727 | a variable from garbage collection, explicitly informing the garbage | |
728 | collector that that variable and all its contents must be as | |
729 | accessible. GC protection is necessary in any function which can | |
730 | perform Lisp evaluation by calling @code{eval_sub} or @code{Feval} as | |
731 | a subroutine, either directly or indirectly. | |
b8d4c8d0 GM |
732 | |
733 | It suffices to ensure that at least one pointer to each object is | |
d15aac68 | 734 | GC-protected. Thus, a particular local variable can do without |
b8d4c8d0 | 735 | protection if it is certain that the object it points to will be |
7d2d7cc0 | 736 | preserved by some other pointer (such as another local variable that |
d15aac68 CY |
737 | has a @code{GCPRO}). Otherwise, the local variable needs a |
738 | @code{GCPRO}. | |
b8d4c8d0 GM |
739 | |
740 | The macro @code{GCPRO1} protects just one local variable. If you | |
741 | want to protect two variables, use @code{GCPRO2} instead; repeating | |
742 | @code{GCPRO1} will not work. Macros @code{GCPRO3}, @code{GCPRO4}, | |
743 | @code{GCPRO5}, and @code{GCPRO6} also exist. All these macros | |
744 | implicitly use local variables such as @code{gcpro1}; you must declare | |
745 | these explicitly, with type @code{struct gcpro}. Thus, if you use | |
746 | @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}. | |
b8d4c8d0 GM |
747 | |
748 | @code{UNGCPRO} cancels the protection of the variables that are | |
749 | protected in the current function. It is necessary to do this | |
750 | explicitly. | |
751 | ||
b8d4c8d0 GM |
752 | You must not use C initializers for static or global variables unless |
753 | the variables are never written once Emacs is dumped. These variables | |
754 | with initializers are allocated in an area of memory that becomes | |
755 | read-only (on certain operating systems) as a result of dumping Emacs. | |
756 | @xref{Pure Storage}. | |
757 | ||
b8d4c8d0 GM |
758 | @cindex @code{defsubr}, Lisp symbol for a primitive |
759 | Defining the C function is not enough to make a Lisp primitive | |
760 | available; you must also create the Lisp symbol for the primitive and | |
761 | store a suitable subr object in its function cell. The code looks like | |
762 | this: | |
763 | ||
764 | @example | |
7d2d7cc0 | 765 | defsubr (&@var{sname}); |
b8d4c8d0 GM |
766 | @end example |
767 | ||
768 | @noindent | |
7d2d7cc0 | 769 | Here @var{sname} is the name you used as the third argument to @code{DEFUN}. |
b8d4c8d0 GM |
770 | |
771 | If you add a new primitive to a file that already has Lisp primitives | |
772 | defined in it, find the function (near the end of the file) named | |
773 | @code{syms_of_@var{something}}, and add the call to @code{defsubr} | |
774 | there. If the file doesn't have this function, or if you create a new | |
775 | file, add to it a @code{syms_of_@var{filename}} (e.g., | |
776 | @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all | |
777 | of these functions are called, and add a call to | |
778 | @code{syms_of_@var{filename}} there. | |
779 | ||
780 | @anchor{Defining Lisp variables in C} | |
781 | @vindex byte-boolean-vars | |
782 | @cindex defining Lisp variables in C | |
783 | @cindex @code{DEFVAR_INT}, @code{DEFVAR_LISP}, @code{DEFVAR_BOOL} | |
784 | The function @code{syms_of_@var{filename}} is also the place to define | |
785 | any C variables that are to be visible as Lisp variables. | |
786 | @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible | |
787 | in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int} | |
788 | visible in Lisp with a value that is always an integer. | |
789 | @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp | |
790 | with a value that is either @code{t} or @code{nil}. Note that variables | |
791 | defined with @code{DEFVAR_BOOL} are automatically added to the list | |
792 | @code{byte-boolean-vars} used by the byte compiler. | |
793 | ||
7d2d7cc0 GM |
794 | @cindex defining customization variables in C |
795 | If you want to make a Lisp variables that is defined in C behave | |
796 | like one declared with @code{defcustom}, add an appropriate entry to | |
797 | @file{cus-start.el}. | |
798 | ||
b8d4c8d0 GM |
799 | @cindex @code{staticpro}, protection from GC |
800 | If you define a file-scope C variable of type @code{Lisp_Object}, | |
801 | you must protect it from garbage-collection by calling @code{staticpro} | |
802 | in @code{syms_of_@var{filename}}, like this: | |
803 | ||
804 | @example | |
805 | staticpro (&@var{variable}); | |
806 | @end example | |
807 | ||
808 | Here is another example function, with more complicated arguments. | |
809 | This comes from the code in @file{window.c}, and it demonstrates the use | |
810 | of macros and functions to manipulate Lisp objects. | |
811 | ||
812 | @smallexample | |
813 | @group | |
814 | DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p, | |
7d2d7cc0 GM |
815 | Scoordinates_in_window_p, 2, 2, 0, |
816 | doc: /* Return non-nil if COORDINATES are in WINDOW. | |
817 | ... | |
b8d4c8d0 GM |
818 | @end group |
819 | @group | |
7d2d7cc0 GM |
820 | or `right-margin' is returned. */) |
821 | (register Lisp_Object coordinates, Lisp_Object window) | |
b8d4c8d0 | 822 | @{ |
7d2d7cc0 GM |
823 | struct window *w; |
824 | struct frame *f; | |
b8d4c8d0 | 825 | int x, y; |
7d2d7cc0 | 826 | Lisp_Object lx, ly; |
b8d4c8d0 GM |
827 | @end group |
828 | ||
829 | @group | |
7d2d7cc0 GM |
830 | CHECK_LIVE_WINDOW (window); |
831 | w = XWINDOW (window); | |
832 | f = XFRAME (w->frame); | |
833 | CHECK_CONS (coordinates); | |
834 | lx = Fcar (coordinates); | |
835 | ly = Fcdr (coordinates); | |
836 | CHECK_NUMBER_OR_FLOAT (lx); | |
837 | CHECK_NUMBER_OR_FLOAT (ly); | |
838 | x = FRAME_PIXEL_X_FROM_CANON_X (f, lx) + FRAME_INTERNAL_BORDER_WIDTH(f); | |
839 | y = FRAME_PIXEL_Y_FROM_CANON_Y (f, ly) + FRAME_INTERNAL_BORDER_WIDTH(f); | |
b8d4c8d0 GM |
840 | @end group |
841 | ||
842 | @group | |
7d2d7cc0 | 843 | switch (coordinates_in_window (w, x, y)) |
b8d4c8d0 | 844 | @{ |
7d2d7cc0 | 845 | case ON_NOTHING: /* NOT in window at all. */ |
b8d4c8d0 GM |
846 | return Qnil; |
847 | @end group | |
848 | ||
7d2d7cc0 | 849 | ... |
b8d4c8d0 GM |
850 | |
851 | @group | |
7d2d7cc0 | 852 | case ON_MODE_LINE: /* In mode line of window. */ |
b8d4c8d0 GM |
853 | return Qmode_line; |
854 | @end group | |
855 | ||
7d2d7cc0 GM |
856 | ... |
857 | ||
b8d4c8d0 | 858 | @group |
7d2d7cc0 GM |
859 | case ON_SCROLL_BAR: /* On scroll-bar of window. */ |
860 | /* Historically we are supposed to return nil in this case. */ | |
861 | return Qnil; | |
b8d4c8d0 GM |
862 | @end group |
863 | ||
864 | @group | |
865 | default: | |
866 | abort (); | |
867 | @} | |
868 | @} | |
869 | @end group | |
870 | @end smallexample | |
871 | ||
872 | Note that C code cannot call functions by name unless they are defined | |
1df7defd | 873 | in C@. The way to call a function written in Lisp is to use |
b8d4c8d0 GM |
874 | @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since |
875 | the Lisp function @code{funcall} accepts an unlimited number of | |
876 | arguments, in C it takes two: the number of Lisp-level arguments, and a | |
877 | one-dimensional array containing their values. The first Lisp-level | |
878 | argument is the Lisp function to call, and the rest are the arguments to | |
879 | pass to it. Since @code{Ffuncall} can call the evaluator, you must | |
880 | protect pointers from garbage collection around the call to | |
881 | @code{Ffuncall}. | |
882 | ||
883 | The C functions @code{call0}, @code{call1}, @code{call2}, and so on, | |
884 | provide handy ways to call a Lisp function conveniently with a fixed | |
885 | number of arguments. They work by calling @code{Ffuncall}. | |
886 | ||
887 | @file{eval.c} is a very good file to look through for examples; | |
888 | @file{lisp.h} contains the definitions for some important macros and | |
889 | functions. | |
890 | ||
891 | If you define a function which is side-effect free, update the code | |
7d2d7cc0 | 892 | in @file{byte-opt.el} that binds @code{side-effect-free-fns} and |
b8d4c8d0 GM |
893 | @code{side-effect-and-error-free-fns} so that the compiler optimizer |
894 | knows about it. | |
895 | ||
896 | @node Object Internals | |
520f2425 | 897 | @section Object Internals |
b8d4c8d0 GM |
898 | @cindex object internals |
899 | ||
74934dcc | 900 | Emacs Lisp provides a rich set of the data types. Some of them, like cons |
f24f2e22 | 901 | cells, integers and strings, are common to nearly all Lisp dialects. Some |
74934dcc DA |
902 | others, like markers and buffers, are quite special and needed to provide |
903 | the basic support to write editor commands in Lisp. To implement such | |
904 | a variety of object types and provide an efficient way to pass objects between | |
905 | the subsystems of an interpreter, there is a set of C data structures and | |
906 | a special type to represent the pointers to all of them, which is known as | |
907 | @dfn{tagged pointer}. | |
908 | ||
909 | In C, the tagged pointer is an object of type @code{Lisp_Object}. Any | |
910 | initialized variable of such a type always holds the value of one of the | |
911 | following basic data types: integer, symbol, string, cons cell, float, | |
912 | vectorlike or miscellaneous object. Each of these data types has the | |
913 | corresponding tag value. All tags are enumerated by @code{enum Lisp_Type} | |
914 | and placed into a 3-bit bitfield of the @code{Lisp_Object}. The rest of the | |
39670ef4 | 915 | bits is the value itself. Integer values are immediate, i.e., directly |
74934dcc DA |
916 | represented by those @dfn{value bits}, and all other objects are represented |
917 | by the C pointers to a corresponding object allocated from the heap. Width | |
918 | of the @code{Lisp_Object} is platform- and configuration-dependent: usually | |
39670ef4 | 919 | it's equal to the width of an underlying platform pointer (i.e., 32-bit on |
74934dcc DA |
920 | a 32-bit machine and 64-bit on a 64-bit one), but also there is a special |
921 | configuration where @code{Lisp_Object} is 64-bit but all pointers are 32-bit. | |
922 | The latter trick was designed to overcome the limited range of values for | |
923 | Lisp integers on a 32-bit system by using 64-bit @code{long long} type for | |
924 | @code{Lisp_Object}. | |
925 | ||
926 | The following C data structures are defined in @file{lisp.h} to represent | |
927 | the basic data types beyond integers: | |
928 | ||
929 | @table @code | |
930 | @item struct Lisp_Cons | |
931 | Cons cell, an object used to construct lists. | |
932 | ||
933 | @item struct Lisp_String | |
934 | String, the basic object to represent a sequence of characters. | |
935 | ||
936 | @item struct Lisp_Vector | |
937 | Array, a fixed-size set of Lisp objects which may be accessed by an index. | |
938 | ||
939 | @item struct Lisp_Symbol | |
940 | Symbol, the unique-named entity commonly used as an identifier. | |
941 | ||
942 | @item struct Lisp_Float | |
943 | Floating point value. | |
944 | ||
945 | @item union Lisp_Misc | |
946 | Miscellaneous kinds of objects which don't fit into any of the above. | |
947 | @end table | |
948 | ||
949 | These types are the first-class citizens of an internal type system. | |
950 | Since the tag space is limited, all other types are the subtypes of either | |
951 | @code{Lisp_Vectorlike} or @code{Lisp_Misc}. Vector subtypes are enumerated | |
952 | by @code{enum pvec_type}, and nearly all complex objects like windows, buffers, | |
953 | frames, and processes fall into this category. The rest of special types, | |
954 | including markers and overlays, are enumerated by @code{enum Lisp_Misc_Type} | |
955 | and form the set of subtypes of @code{Lisp_Misc}. | |
956 | ||
957 | Below there is a description of a few subtypes of @code{Lisp_Vectorlike}. | |
958 | Buffer object represents the text to display and edit. Window is the part | |
959 | of display structure which shows the buffer or used as a container to | |
960 | recursively place other windows on the same frame. (Do not confuse Emacs Lisp | |
961 | window object with the window as an entity managed by the user interface | |
962 | system like X; in Emacs terminology, the latter is called frame.) Finally, | |
963 | process object is used to manage the subprocesses. | |
b8d4c8d0 GM |
964 | |
965 | @menu | |
966 | * Buffer Internals:: Components of a buffer structure. | |
967 | * Window Internals:: Components of a window structure. | |
968 | * Process Internals:: Components of a process structure. | |
969 | @end menu | |
970 | ||
971 | @node Buffer Internals | |
520f2425 | 972 | @subsection Buffer Internals |
b8d4c8d0 GM |
973 | @cindex internals, of buffer |
974 | @cindex buffer internals | |
975 | ||
7d2d7cc0 | 976 | Two structures (see @file{buffer.h}) are used to represent buffers |
1df7defd | 977 | in C@. The @code{buffer_text} structure contains fields describing the |
7d2d7cc0 GM |
978 | text of a buffer; the @code{buffer} structure holds other fields. In |
979 | the case of indirect buffers, two or more @code{buffer} structures | |
980 | reference the same @code{buffer_text} structure. | |
b8d4c8d0 | 981 | |
c773345a | 982 | Here are some of the fields in @code{struct buffer_text}: |
b8d4c8d0 GM |
983 | |
984 | @table @code | |
985 | @item beg | |
c773345a | 986 | The address of the buffer contents. |
b8d4c8d0 GM |
987 | |
988 | @item gpt | |
c773345a CY |
989 | @itemx gpt_byte |
990 | The character and byte positions of the buffer gap. @xref{Buffer | |
991 | Gap}. | |
b8d4c8d0 GM |
992 | |
993 | @item z | |
c773345a CY |
994 | @itemx z_byte |
995 | The character and byte positions of the end of the buffer text. | |
b8d4c8d0 GM |
996 | |
997 | @item gap_size | |
c773345a | 998 | The size of buffer's gap. @xref{Buffer Gap}. |
b8d4c8d0 GM |
999 | |
1000 | @item modiff | |
c773345a CY |
1001 | @itemx save_modiff |
1002 | @itemx chars_modiff | |
1003 | @itemx overlay_modiff | |
1004 | These fields count the number of buffer-modification events performed | |
1005 | in this buffer. @code{modiff} is incremented after each | |
1006 | buffer-modification event, and is never otherwise changed; | |
1007 | @code{save_modiff} contains the value of @code{modiff} the last time | |
1008 | the buffer was visited or saved; @code{chars_modiff} counts only | |
1009 | modifications to the characters in the buffer, ignoring all other | |
1010 | kinds of changes; and @code{overlay_modiff} counts only modifications | |
1011 | to the overlays. | |
b8d4c8d0 GM |
1012 | |
1013 | @item beg_unchanged | |
c773345a CY |
1014 | @itemx end_unchanged |
1015 | The number of characters at the start and end of the text that are | |
1016 | known to be unchanged since the last complete redisplay. | |
b8d4c8d0 GM |
1017 | |
1018 | @item unchanged_modified | |
c773345a CY |
1019 | @itemx overlay_unchanged_modified |
1020 | The values of @code{modiff} and @code{overlay_modiff}, respectively, | |
da6062e6 | 1021 | after the last complete redisplay. If their current values match |
c773345a | 1022 | @code{modiff} or @code{overlay_modiff}, that means |
b8d4c8d0 GM |
1023 | @code{beg_unchanged} and @code{end_unchanged} contain no useful |
1024 | information. | |
1025 | ||
1026 | @item markers | |
1027 | The markers that refer to this buffer. This is actually a single | |
1028 | marker, and successive elements in its marker @code{chain} are the other | |
1029 | markers referring to this buffer text. | |
1030 | ||
1031 | @item intervals | |
c773345a | 1032 | The interval tree which records the text properties of this buffer. |
b8d4c8d0 GM |
1033 | @end table |
1034 | ||
c773345a | 1035 | Some of the fields of @code{struct buffer} are: |
b8d4c8d0 GM |
1036 | |
1037 | @table @code | |
7d2d7cc0 | 1038 | @item header |
74934dcc DA |
1039 | A header of type @code{struct vectorlike_header} is common to all |
1040 | vectorlike objects. | |
b8d4c8d0 GM |
1041 | |
1042 | @item own_text | |
c773345a CY |
1043 | A @code{struct buffer_text} structure that ordinarily holds the buffer |
1044 | contents. In indirect buffers, this field is not used. | |
b8d4c8d0 GM |
1045 | |
1046 | @item text | |
c773345a CY |
1047 | A pointer to the @code{buffer_text} structure for this buffer. In an |
1048 | ordinary buffer, this is the @code{own_text} field above. In an | |
1049 | indirect buffer, this is the @code{own_text} field of the base buffer. | |
b8d4c8d0 | 1050 | |
74934dcc DA |
1051 | @item next |
1052 | A pointer to the next buffer, in the chain of all buffers, including | |
1053 | killed buffers. This chain is used only for allocation and garbage | |
1054 | collection, in order to collect killed buffers properly. | |
1055 | ||
b8d4c8d0 | 1056 | @item pt |
c773345a CY |
1057 | @itemx pt_byte |
1058 | The character and byte positions of point in a buffer. | |
b8d4c8d0 GM |
1059 | |
1060 | @item begv | |
c773345a CY |
1061 | @itemx begv_byte |
1062 | The character and byte positions of the beginning of the accessible | |
1063 | range of text in the buffer. | |
b8d4c8d0 GM |
1064 | |
1065 | @item zv | |
c773345a CY |
1066 | @itemx zv_byte |
1067 | The character and byte positions of the end of the accessible range of | |
1068 | text in the buffer. | |
b8d4c8d0 GM |
1069 | |
1070 | @item base_buffer | |
1071 | In an indirect buffer, this points to the base buffer. In an ordinary | |
1072 | buffer, it is null. | |
1073 | ||
c773345a CY |
1074 | @item local_flags |
1075 | This field contains flags indicating that certain variables are local | |
1076 | in this buffer. Such variables are declared in the C code using | |
1077 | @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored | |
1078 | in fields in the buffer structure itself. (Some of these fields are | |
b8d4c8d0 GM |
1079 | described in this table.) |
1080 | ||
1081 | @item modtime | |
c773345a CY |
1082 | The modification time of the visited file. It is set when the file is |
1083 | written or read. Before writing the buffer into a file, this field is | |
1084 | compared to the modification time of the file to see if the file has | |
1085 | changed on disk. @xref{Buffer Modification}. | |
b8d4c8d0 GM |
1086 | |
1087 | @item auto_save_modified | |
c773345a | 1088 | The time when the buffer was last auto-saved. |
b8d4c8d0 GM |
1089 | |
1090 | @item last_window_start | |
c773345a CY |
1091 | The @code{window-start} position in the buffer as of the last time the |
1092 | buffer was displayed in a window. | |
b8d4c8d0 GM |
1093 | |
1094 | @item clip_changed | |
c773345a CY |
1095 | This flag indicates that narrowing has changed in the buffer. |
1096 | @xref{Narrowing}. | |
b8d4c8d0 GM |
1097 | |
1098 | @item prevent_redisplay_optimizations_p | |
c773345a CY |
1099 | This flag indicates that redisplay optimizations should not be used to |
1100 | display this buffer. | |
b8d4c8d0 | 1101 | |
c773345a CY |
1102 | @item overlay_center |
1103 | This field holds the current overlay center position. @xref{Managing | |
1104 | Overlays}. | |
1105 | ||
1106 | @item overlays_before | |
1107 | @itemx overlays_after | |
1108 | These fields hold, respectively, a list of overlays that end at or | |
1109 | before the current overlay center, and a list of overlays that end | |
1110 | after the current overlay center. @xref{Managing Overlays}. | |
1111 | @code{overlays_before} is sorted in order of decreasing end position, | |
1112 | and @code{overlays_after} is sorted in order of increasing beginning | |
1113 | position. | |
b8d4c8d0 | 1114 | |
7d2d7cc0 GM |
1115 | @c FIXME? the following are now all Lisp_Object BUFFER_INTERNAL_FIELD (foo). |
1116 | ||
b8d4c8d0 | 1117 | @item name |
c773345a CY |
1118 | A Lisp string that names the buffer. It is guaranteed to be unique. |
1119 | @xref{Buffer Names}. | |
b8d4c8d0 | 1120 | |
c773345a CY |
1121 | @item save_length |
1122 | The length of the file this buffer is visiting, when last read or | |
1123 | saved. This and other fields concerned with saving are not kept in | |
1124 | the @code{buffer_text} structure because indirect buffers are never | |
1125 | saved. | |
b8d4c8d0 GM |
1126 | |
1127 | @item directory | |
c773345a CY |
1128 | The directory for expanding relative file names. This is the value of |
1129 | the buffer-local variable @code{default-directory} (@pxref{File Name Expansion}). | |
b8d4c8d0 | 1130 | |
c773345a CY |
1131 | @item filename |
1132 | The name of the file visited in this buffer, or @code{nil}. This is | |
1133 | the value of the buffer-local variable @code{buffer-file-name} | |
1134 | (@pxref{Buffer File Name}). | |
b8d4c8d0 | 1135 | |
c773345a CY |
1136 | @item undo_list |
1137 | @itemx backed_up | |
1138 | @itemx auto_save_file_name | |
7d2d7cc0 | 1139 | @itemx auto_save_file_format |
c773345a CY |
1140 | @itemx read_only |
1141 | @itemx file_format | |
1142 | @itemx file_truename | |
1143 | @itemx invisibility_spec | |
1144 | @itemx display_count | |
1145 | @itemx display_time | |
1146 | These fields store the values of Lisp variables that are automatically | |
1147 | buffer-local (@pxref{Buffer-Local Variables}), whose corresponding | |
1148 | variable names have the additional prefix @code{buffer-} and have | |
1149 | underscores replaced with dashes. For instance, @code{undo_list} | |
29157371 | 1150 | stores the value of @code{buffer-undo-list}. |
b8d4c8d0 GM |
1151 | |
1152 | @item mark | |
c773345a CY |
1153 | The mark for the buffer. The mark is a marker, hence it is also |
1154 | included on the list @code{markers}. @xref{The Mark}. | |
b8d4c8d0 GM |
1155 | |
1156 | @item local_var_alist | |
c773345a CY |
1157 | The association list describing the buffer-local variable bindings of |
1158 | this buffer, not including the built-in buffer-local bindings that | |
1159 | have special slots in the buffer object. (Those slots are omitted | |
1160 | from this table.) @xref{Buffer-Local Variables}. | |
b8d4c8d0 GM |
1161 | |
1162 | @item major_mode | |
1163 | Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}. | |
1164 | ||
1165 | @item mode_name | |
c773345a | 1166 | Pretty name of the major mode, e.g., @code{"Lisp"}. |
b8d4c8d0 GM |
1167 | |
1168 | @item keymap | |
c773345a CY |
1169 | @itemx abbrev_table |
1170 | @itemx syntax_table | |
1171 | @itemx category_table | |
1172 | @itemx display_table | |
1173 | These fields store the buffer's local keymap (@pxref{Keymaps}), abbrev | |
1174 | table (@pxref{Abbrev Tables}), syntax table (@pxref{Syntax Tables}), | |
1175 | category table (@pxref{Categories}), and display table (@pxref{Display | |
1176 | Tables}). | |
b8d4c8d0 GM |
1177 | |
1178 | @item downcase_table | |
c773345a CY |
1179 | @itemx upcase_table |
1180 | @itemx case_canon_table | |
1181 | These fields store the conversion tables for converting text to lower | |
1182 | case, upper case, and for canonicalizing text for case-fold search. | |
b8d4c8d0 GM |
1183 | @xref{Case Tables}. |
1184 | ||
b8d4c8d0 GM |
1185 | @item minor_modes |
1186 | An alist of the minor modes of this buffer. | |
1187 | ||
b8d4c8d0 | 1188 | @item pt_marker |
c773345a CY |
1189 | @itemx begv_marker |
1190 | @itemx zv_marker | |
1191 | These fields are only used in an indirect buffer, or in a buffer that | |
1192 | is the base of an indirect buffer. Each holds a marker that records | |
1193 | @code{pt}, @code{begv}, and @code{zv} respectively, for this buffer | |
b8d4c8d0 GM |
1194 | when the buffer is not current. |
1195 | ||
c773345a CY |
1196 | @item mode_line_format |
1197 | @itemx header_line_format | |
1198 | @itemx case_fold_search | |
1199 | @itemx tab_width | |
1200 | @itemx fill_column | |
1201 | @itemx left_margin | |
1202 | @itemx auto_fill_function | |
c773345a CY |
1203 | @itemx truncate_lines |
1204 | @itemx word_wrap | |
1205 | @itemx ctl_arrow | |
7d2d7cc0 GM |
1206 | @itemx bidi_display_reordering |
1207 | @itemx bidi_paragraph_direction | |
c773345a CY |
1208 | @itemx selective_display |
1209 | @itemx selective_display_ellipses | |
1210 | @itemx overwrite_mode | |
1211 | @itemx abbrev_mode | |
c773345a CY |
1212 | @itemx mark_active |
1213 | @itemx enable_multibyte_characters | |
1214 | @itemx buffer_file_coding_system | |
c773345a CY |
1215 | @itemx cache_long_line_scans |
1216 | @itemx point_before_scroll | |
1217 | @itemx left_fringe_width | |
1218 | @itemx right_fringe_width | |
1219 | @itemx fringes_outside_margins | |
1220 | @itemx scroll_bar_width | |
1221 | @itemx indicate_empty_lines | |
1222 | @itemx indicate_buffer_boundaries | |
1223 | @itemx fringe_indicator_alist | |
1224 | @itemx fringe_cursor_alist | |
1225 | @itemx scroll_up_aggressively | |
1226 | @itemx scroll_down_aggressively | |
1227 | @itemx cursor_type | |
1228 | @itemx cursor_in_non_selected_windows | |
1229 | These fields store the values of Lisp variables that are automatically | |
1230 | buffer-local (@pxref{Buffer-Local Variables}), whose corresponding | |
1231 | variable names have underscores replaced with dashes. For instance, | |
1232 | @code{mode_line_format} stores the value of @code{mode-line-format}. | |
b8d4c8d0 GM |
1233 | |
1234 | @item last_selected_window | |
1235 | This is the last window that was selected with this buffer in it, or @code{nil} | |
1236 | if that window no longer displays this buffer. | |
b8d4c8d0 GM |
1237 | @end table |
1238 | ||
1239 | @node Window Internals | |
520f2425 | 1240 | @subsection Window Internals |
b8d4c8d0 GM |
1241 | @cindex internals, of window |
1242 | @cindex window internals | |
1243 | ||
7d2d7cc0 GM |
1244 | The fields of a window (for a complete list, see the definition of |
1245 | @code{struct window} in @file{window.h}) include: | |
b8d4c8d0 GM |
1246 | |
1247 | @table @code | |
1248 | @item frame | |
1249 | The frame that this window is on. | |
1250 | ||
1251 | @item mini_p | |
1252 | Non-@code{nil} if this window is a minibuffer window. | |
1253 | ||
1254 | @item parent | |
1255 | Internally, Emacs arranges windows in a tree; each group of siblings has | |
1256 | a parent window whose area includes all the siblings. This field points | |
1257 | to a window's parent. | |
1258 | ||
1259 | Parent windows do not display buffers, and play little role in display | |
1260 | except to shape their child windows. Emacs Lisp programs usually have | |
1261 | no access to the parent windows; they operate on the windows at the | |
1262 | leaves of the tree, which actually display buffers. | |
1263 | ||
b8d4c8d0 | 1264 | @item hchild |
ee2d5b5e CY |
1265 | @itemx vchild |
1266 | These fields contain the window's leftmost child and its topmost child | |
1267 | respectively. @code{hchild} is used if the window is subdivided | |
1268 | horizontally by child windows, and @code{vchild} if it is subdivided | |
7d2d7cc0 | 1269 | vertically. In a live window, only one of @code{hchild}, @code{vchild}, |
1df7defd | 1270 | and @code{buffer} (q.v.@:) is non-@code{nil}. |
b8d4c8d0 GM |
1271 | |
1272 | @item next | |
ee2d5b5e CY |
1273 | @itemx prev |
1274 | The next sibling and previous sibling of this window. @code{next} is | |
520f2425 GM |
1275 | @code{nil} if the window is the right-most or bottom-most in its group; |
1276 | @code{prev} is @code{nil} if it is the left-most or top-most in its | |
ee2d5b5e CY |
1277 | group. |
1278 | ||
1279 | @item left_col | |
1280 | The left-hand edge of the window, measured in columns, relative to the | |
1281 | leftmost column in the frame (column 0). | |
1282 | ||
1283 | @item top_line | |
1284 | The top edge of the window, measured in lines, relative to the topmost | |
1285 | line in the frame (line 0). | |
1286 | ||
1287 | @item total_cols | |
1288 | @itemx total_lines | |
1289 | The width and height of the window, measured in columns and lines | |
1290 | respectively. The width includes the scroll bar and fringes, and/or | |
1291 | the separator line on the right of the window (if any). | |
b8d4c8d0 GM |
1292 | |
1293 | @item buffer | |
ee2d5b5e | 1294 | The buffer that the window is displaying. |
b8d4c8d0 GM |
1295 | |
1296 | @item start | |
ee2d5b5e CY |
1297 | A marker pointing to the position in the buffer that is the first |
1298 | character displayed in the window. | |
b8d4c8d0 GM |
1299 | |
1300 | @item pointm | |
1301 | @cindex window point internals | |
1302 | This is the value of point in the current buffer when this window is | |
1303 | selected; when it is not selected, it retains its previous value. | |
1304 | ||
1305 | @item force_start | |
1306 | If this flag is non-@code{nil}, it says that the window has been | |
1307 | scrolled explicitly by the Lisp program. This affects what the next | |
1308 | redisplay does if point is off the screen: instead of scrolling the | |
1309 | window to show the text around point, it moves point to a location that | |
1310 | is on the screen. | |
1311 | ||
1312 | @item frozen_window_start_p | |
1313 | This field is set temporarily to 1 to indicate to redisplay that | |
1314 | @code{start} of this window should not be changed, even if point | |
1315 | gets invisible. | |
1316 | ||
1317 | @item start_at_line_beg | |
1318 | Non-@code{nil} means current value of @code{start} was the beginning of a line | |
1319 | when it was chosen. | |
1320 | ||
b8d4c8d0 GM |
1321 | @item use_time |
1322 | This is the last time that the window was selected. The function | |
1323 | @code{get-lru-window} uses this field. | |
1324 | ||
1325 | @item sequence_number | |
1326 | A unique number assigned to this window when it was created. | |
1327 | ||
1328 | @item last_modified | |
1329 | The @code{modiff} field of the window's buffer, as of the last time | |
1330 | a redisplay completed in this window. | |
1331 | ||
1332 | @item last_overlay_modified | |
1333 | The @code{overlay_modiff} field of the window's buffer, as of the last | |
1334 | time a redisplay completed in this window. | |
1335 | ||
1336 | @item last_point | |
1337 | The buffer's value of point, as of the last time a redisplay completed | |
1338 | in this window. | |
1339 | ||
1340 | @item last_had_star | |
1341 | A non-@code{nil} value means the window's buffer was ``modified'' when the | |
1342 | window was last updated. | |
1343 | ||
1344 | @item vertical_scroll_bar | |
1345 | This window's vertical scroll bar. | |
1346 | ||
7d2d7cc0 GM |
1347 | @item left_margin_cols |
1348 | @itemx right_margin_cols | |
ee2d5b5e | 1349 | The widths of the left and right margins in this window. A value of |
7d2d7cc0 GM |
1350 | @code{nil} means no margin. |
1351 | ||
1352 | @item left_fringe_width | |
1353 | @itemx right_fringe_width | |
1354 | The widths of the left and right fringes in this window. A value of | |
1355 | @code{nil} or @code{t} means use the values of the frame. | |
1356 | ||
1357 | @item fringes_outside_margins | |
1358 | A non-@code{nil} value means the fringes outside the display margins; | |
1359 | othersize they are between the margin and the text. | |
b8d4c8d0 GM |
1360 | |
1361 | @item window_end_pos | |
1362 | This is computed as @code{z} minus the buffer position of the last glyph | |
1363 | in the current matrix of the window. The value is only valid if | |
1364 | @code{window_end_valid} is not @code{nil}. | |
1365 | ||
1366 | @item window_end_bytepos | |
1367 | The byte position corresponding to @code{window_end_pos}. | |
1368 | ||
1369 | @item window_end_vpos | |
1370 | The window-relative vertical position of the line containing | |
1371 | @code{window_end_pos}. | |
1372 | ||
1373 | @item window_end_valid | |
1374 | This field is set to a non-@code{nil} value if @code{window_end_pos} is truly | |
7d2d7cc0 | 1375 | valid. This is @code{nil} if nontrivial redisplay is pre-empted, since in that |
b8d4c8d0 GM |
1376 | case the display that @code{window_end_pos} was computed for did not get |
1377 | onto the screen. | |
1378 | ||
b8d4c8d0 GM |
1379 | @item cursor |
1380 | A structure describing where the cursor is in this window. | |
1381 | ||
1382 | @item last_cursor | |
1383 | The value of @code{cursor} as of the last redisplay that finished. | |
1384 | ||
1385 | @item phys_cursor | |
1386 | A structure describing where the cursor of this window physically is. | |
1387 | ||
1388 | @item phys_cursor_type | |
7d2d7cc0 GM |
1389 | @c FIXME What is this? |
1390 | @c itemx phys_cursor_ascent | |
1391 | @itemx phys_cursor_height | |
1392 | @itemx phys_cursor_width | |
1393 | The type, height, and width of the cursor that was last displayed on | |
1394 | this window. | |
b8d4c8d0 GM |
1395 | |
1396 | @item phys_cursor_on_p | |
1397 | This field is non-zero if the cursor is physically on. | |
1398 | ||
1399 | @item cursor_off_p | |
7d2d7cc0 GM |
1400 | Non-zero means the cursor in this window is logically off. This is |
1401 | used for blinking the cursor. | |
b8d4c8d0 GM |
1402 | |
1403 | @item last_cursor_off_p | |
1404 | This field contains the value of @code{cursor_off_p} as of the time of | |
1405 | the last redisplay. | |
1406 | ||
1407 | @item must_be_updated_p | |
1408 | This is set to 1 during redisplay when this window must be updated. | |
1409 | ||
1410 | @item hscroll | |
1411 | This is the number of columns that the display in the window is scrolled | |
1412 | horizontally to the left. Normally, this is 0. | |
1413 | ||
1414 | @item vscroll | |
1415 | Vertical scroll amount, in pixels. Normally, this is 0. | |
1416 | ||
1417 | @item dedicated | |
1418 | Non-@code{nil} if this window is dedicated to its buffer. | |
1419 | ||
1420 | @item display_table | |
1421 | The window's display table, or @code{nil} if none is specified for it. | |
1422 | ||
1423 | @item update_mode_line | |
1424 | Non-@code{nil} means this window's mode line needs to be updated. | |
1425 | ||
1426 | @item base_line_number | |
1427 | The line number of a certain position in the buffer, or @code{nil}. | |
1428 | This is used for displaying the line number of point in the mode line. | |
1429 | ||
1430 | @item base_line_pos | |
1431 | The position in the buffer for which the line number is known, or | |
7d2d7cc0 GM |
1432 | @code{nil} meaning none is known. If it is a buffer, don't display |
1433 | the line number as long as the window shows that buffer. | |
b8d4c8d0 GM |
1434 | |
1435 | @item region_showing | |
1436 | If the region (or part of it) is highlighted in this window, this field | |
1437 | holds the mark position that made one end of that region. Otherwise, | |
1438 | this field is @code{nil}. | |
1439 | ||
1440 | @item column_number_displayed | |
1441 | The column number currently displayed in this window's mode line, or @code{nil} | |
1442 | if column numbers are not being displayed. | |
1443 | ||
1444 | @item current_matrix | |
7d2d7cc0 GM |
1445 | @itemx desired_matrix |
1446 | Glyph matrices describing the current and desired display of this window. | |
b8d4c8d0 GM |
1447 | @end table |
1448 | ||
1449 | @node Process Internals | |
520f2425 | 1450 | @subsection Process Internals |
b8d4c8d0 GM |
1451 | @cindex internals, of process |
1452 | @cindex process internals | |
1453 | ||
7d2d7cc0 GM |
1454 | The fields of a process (for a complete list, see the definition of |
1455 | @code{struct Lisp_Process} in @file{process.h}) include: | |
b8d4c8d0 GM |
1456 | |
1457 | @table @code | |
1458 | @item name | |
1459 | A string, the name of the process. | |
1460 | ||
1461 | @item command | |
1462 | A list containing the command arguments that were used to start this | |
c73e02fa GM |
1463 | process. For a network or serial process, it is @code{nil} if the |
1464 | process is running or @code{t} if the process is stopped. | |
b8d4c8d0 GM |
1465 | |
1466 | @item filter | |
7d2d7cc0 GM |
1467 | If non-@code{nil}, a function used to accept output from the process |
1468 | instead of a buffer. | |
b8d4c8d0 GM |
1469 | |
1470 | @item sentinel | |
7d2d7cc0 GM |
1471 | If non-@code{nil}, a function called whenever the state of the process |
1472 | changes. | |
b8d4c8d0 GM |
1473 | |
1474 | @item buffer | |
1475 | The associated buffer of the process. | |
1476 | ||
1477 | @item pid | |
1478 | An integer, the operating system's process @acronym{ID}. | |
7d2d7cc0 | 1479 | Pseudo-processes such as network or serial connections use a value of 0. |
b8d4c8d0 GM |
1480 | |
1481 | @item childp | |
7d2d7cc0 GM |
1482 | A flag, @code{t} if this is really a child process. For a network or |
1483 | serial connection, it is a plist based on the arguments to | |
1484 | @code{make-network-process} or @code{make-serial-process}. | |
b8d4c8d0 GM |
1485 | |
1486 | @item mark | |
1487 | A marker indicating the position of the end of the last output from this | |
1488 | process inserted into the buffer. This is often but not always the end | |
1489 | of the buffer. | |
1490 | ||
1491 | @item kill_without_query | |
ee2d5b5e CY |
1492 | If this is non-zero, killing Emacs while this process is still running |
1493 | does not ask for confirmation about killing the process. | |
b8d4c8d0 | 1494 | |
7d2d7cc0 GM |
1495 | @item raw_status |
1496 | The raw process status, as returned by the @code{wait} system call. | |
b8d4c8d0 GM |
1497 | |
1498 | @item status | |
1499 | The process status, as @code{process-status} should return it. | |
1500 | ||
1501 | @item tick | |
1502 | @itemx update_tick | |
1503 | If these two fields are not equal, a change in the status of the process | |
1504 | needs to be reported, either by running the sentinel or by inserting a | |
1505 | message in the process buffer. | |
1506 | ||
1507 | @item pty_flag | |
a2eb421b | 1508 | Non-@code{nil} if communication with the subprocess uses a pty; |
b8d4c8d0 GM |
1509 | @code{nil} if it uses a pipe. |
1510 | ||
1511 | @item infd | |
1512 | The file descriptor for input from the process. | |
1513 | ||
1514 | @item outfd | |
1515 | The file descriptor for output to the process. | |
1516 | ||
b8d4c8d0 GM |
1517 | @item tty_name |
1518 | The name of the terminal that the subprocess is using, | |
1519 | or @code{nil} if it is using pipes. | |
1520 | ||
1521 | @item decode_coding_system | |
1522 | Coding-system for decoding the input from this process. | |
1523 | ||
1524 | @item decoding_buf | |
1525 | A working buffer for decoding. | |
1526 | ||
1527 | @item decoding_carryover | |
1528 | Size of carryover in decoding. | |
1529 | ||
1530 | @item encode_coding_system | |
1531 | Coding-system for encoding the output to this process. | |
1532 | ||
1533 | @item encoding_buf | |
1534 | A working buffer for encoding. | |
1535 | ||
b8d4c8d0 GM |
1536 | @item inherit_coding_system_flag |
1537 | Flag to set @code{coding-system} of the process buffer from the | |
1538 | coding system used to decode process output. | |
c73e02fa GM |
1539 | |
1540 | @item type | |
1541 | Symbol indicating the type of process: @code{real}, @code{network}, | |
7d2d7cc0 | 1542 | @code{serial}. |
c73e02fa | 1543 | |
b8d4c8d0 | 1544 | @end table |
7d2d7cc0 | 1545 | |
d92d9c95 PE |
1546 | @node C Integer Types |
1547 | @section C Integer Types | |
1548 | @cindex integer types (C programming language) | |
1549 | ||
1550 | Here are some guidelines for use of integer types in the Emacs C | |
1551 | source code. These guidelines sometimes give competing advice; common | |
1552 | sense is advised. | |
1553 | ||
1554 | @itemize @bullet | |
1555 | @item | |
1556 | Avoid arbitrary limits. For example, avoid @code{int len = strlen | |
1557 | (s);} unless the length of @code{s} is required for other reasons to | |
1558 | fit in @code{int} range. | |
1559 | ||
1560 | @item | |
1561 | Do not assume that signed integer arithmetic wraps around on overflow. | |
1562 | This is no longer true of Emacs porting targets: signed integer | |
1563 | overflow has undefined behavior in practice, and can dump core or | |
1564 | even cause earlier or later code to behave ``illogically''. Unsigned | |
1565 | overflow does wrap around reliably, modulo a power of two. | |
1566 | ||
1567 | @item | |
1568 | Prefer signed types to unsigned, as code gets confusing when signed | |
1569 | and unsigned types are combined. Many other guidelines assume that | |
1570 | types are signed; in the rarer cases where unsigned types are needed, | |
1571 | similar advice may apply to the unsigned counterparts (e.g., | |
1572 | @code{size_t} instead of @code{ptrdiff_t}, or @code{uintptr_t} instead | |
1573 | of @code{intptr_t}). | |
1574 | ||
1575 | @item | |
1576 | Prefer @code{int} for Emacs character codes, in the range 0 ..@: 0x3FFFFF. | |
1577 | ||
1578 | @item | |
1579 | Prefer @code{ptrdiff_t} for sizes, i.e., for integers bounded by the | |
1580 | maximum size of any individual C object or by the maximum number of | |
1581 | elements in any C array. This is part of Emacs's general preference | |
1582 | for signed types. Using @code{ptrdiff_t} limits objects to | |
1583 | @code{PTRDIFF_MAX} bytes, but larger objects would cause trouble | |
1584 | anyway since they would break pointer subtraction, so this does not | |
1585 | impose an arbitrary limit. | |
1586 | ||
1587 | @item | |
1588 | Prefer @code{intptr_t} for internal representations of pointers, or | |
1589 | for integers bounded only by the number of objects that can exist at | |
1590 | any given time or by the total number of bytes that can be allocated. | |
1591 | Currently Emacs sometimes uses other types when @code{intptr_t} would | |
1592 | be better; fixing this is lower priority, as the code works as-is on | |
1593 | Emacs's current porting targets. | |
1594 | ||
1595 | @item | |
1596 | Prefer the Emacs-defined type @code{EMACS_INT} for representing values | |
1597 | converted to or from Emacs Lisp fixnums, as fixnum arithmetic is based | |
1598 | on @code{EMACS_INT}. | |
1599 | ||
1600 | @item | |
1601 | When representing a system value (such as a file size or a count of | |
1602 | seconds since the Epoch), prefer the corresponding system type (e.g., | |
1603 | @code{off_t}, @code{time_t}). Do not assume that a system type is | |
1604 | signed, unless this assumption is known to be safe. For example, | |
1605 | although @code{off_t} is always signed, @code{time_t} need not be. | |
1606 | ||
1607 | @item | |
1608 | Prefer the Emacs-defined type @code{printmax_t} for representing | |
1609 | values that might be any signed integer value that can be printed, | |
1610 | using a @code{printf}-family function. | |
1611 | ||
1612 | @item | |
1613 | Prefer @code{intmax_t} for representing values that might be any | |
1614 | signed integer value. | |
1615 | ||
1616 | @item | |
1617 | In bitfields, prefer @code{unsigned int} or @code{signed int} to | |
1618 | @code{int}, as @code{int} is less portable: it might be signed, and | |
1619 | might not be. Single-bit bit fields are invariably @code{unsigned | |
1620 | int} so that their values are 0 and 1. | |
1621 | ||
1622 | @item | |
1623 | In C, Emacs commonly uses @code{bool}, 1, and 0 for boolean values. | |
1624 | Using @code{bool} for booleans can make programs easier to read and a | |
1625 | bit faster than using @code{int}. Although it is also OK to use | |
1626 | @code{int}, this older style is gradually being phased out. When | |
1627 | using @code{bool}, respect the limitations of the replacement | |
1628 | implementation of @code{bool}, as documented in the source file | |
1629 | @file{lib/stdbool.in.h}, so that Emacs remains portable to pre-C99 | |
1630 | platforms. | |
1631 | @end itemize | |
1632 | ||
7d2d7cc0 | 1633 | @c FIXME Mention src/globals.h somewhere in this file? |