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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 |
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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. | |
20 | @end menu | |
21 | ||
22 | @node Building Emacs | |
520f2425 | 23 | @section Building Emacs |
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24 | @cindex building Emacs |
25 | @pindex temacs | |
26 | ||
27 | This section explains the steps involved in building the Emacs | |
28 | executable. You don't have to know this material to build and install | |
29 | Emacs, since the makefiles do all these things automatically. This | |
d15aac68 | 30 | information is pertinent to Emacs developers. |
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31 | |
32 | Compilation of the C source files in the @file{src} directory | |
33 | produces an executable file called @file{temacs}, also called a | |
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34 | @dfn{bare impure Emacs}. It contains the Emacs Lisp interpreter and |
35 | I/O routines, but not the editing commands. | |
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36 | |
37 | @cindex @file{loadup.el} | |
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38 | The command @w{@command{temacs -l loadup}} would run @file{temacs} |
39 | and direct it to load @file{loadup.el}. The @code{loadup} library | |
40 | loads additional Lisp libraries, which set up the normal Emacs editing | |
41 | environment. After this step, the Emacs executable is no longer | |
42 | @dfn{bare}. | |
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43 | |
44 | @cindex dumping Emacs | |
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45 | Because it takes some time to load the standard Lisp files, the |
46 | @file{temacs} executable usually isn't run directly by users. | |
47 | Instead, as one of the last steps of building Emacs, the command | |
48 | @samp{temacs -batch -l loadup dump} is run. The special @samp{dump} | |
49 | argument causes @command{temacs} to dump out an executable program, | |
50 | called @file{emacs}, which has all the standard Lisp files preloaded. | |
51 | (The @samp{-batch} argument prevents @file{temacs} from trying to | |
52 | initialize any of its data on the terminal, so that the tables of | |
53 | terminal information are empty in the dumped Emacs.) | |
54 | ||
55 | @cindex preloaded Lisp files | |
b578c9cc | 56 | @vindex preloaded-file-list |
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57 | The dumped @file{emacs} executable (also called a @dfn{pure} Emacs) |
58 | is the one which is installed. The variable | |
59 | @code{preloaded-file-list} stores a list of the Lisp files preloaded | |
60 | into the dumped Emacs. If you port Emacs to a new operating system, | |
61 | and are not able to implement dumping, then Emacs must load | |
62 | @file{loadup.el} each time it starts. | |
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63 | |
64 | @cindex @file{site-load.el} | |
b8d4c8d0 | 65 | You can specify additional files to preload by writing a library named |
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66 | @file{site-load.el} that loads them. You may need to rebuild Emacs |
67 | with an added definition | |
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68 | |
69 | @example | |
70 | #define SITELOAD_PURESIZE_EXTRA @var{n} | |
71 | @end example | |
72 | ||
73 | @noindent | |
520f2425 GM |
74 | to make @var{n} added bytes of pure space to hold the additional files; |
75 | see @file{src/puresize.h}. | |
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76 | (Try adding increments of 20000 until it is big enough.) However, the |
77 | advantage of preloading additional files decreases as machines get | |
78 | faster. On modern machines, it is usually not advisable. | |
79 | ||
80 | After @file{loadup.el} reads @file{site-load.el}, it finds the | |
81 | documentation strings for primitive and preloaded functions (and | |
82 | variables) in the file @file{etc/DOC} where they are stored, by | |
83 | calling @code{Snarf-documentation} (@pxref{Definition of | |
84 | Snarf-documentation,, Accessing Documentation}). | |
85 | ||
86 | @cindex @file{site-init.el} | |
87 | @cindex preloading additional functions and variables | |
88 | You can specify other Lisp expressions to execute just before dumping | |
89 | by putting them in a library named @file{site-init.el}. This file is | |
90 | executed after the documentation strings are found. | |
91 | ||
92 | If you want to preload function or variable definitions, there are | |
93 | three ways you can do this and make their documentation strings | |
94 | accessible when you subsequently run Emacs: | |
95 | ||
96 | @itemize @bullet | |
97 | @item | |
98 | Arrange to scan these files when producing the @file{etc/DOC} file, | |
99 | and load them with @file{site-load.el}. | |
100 | ||
101 | @item | |
102 | Load the files with @file{site-init.el}, then copy the files into the | |
103 | installation directory for Lisp files when you install Emacs. | |
104 | ||
105 | @item | |
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106 | Specify a @code{nil} value for @code{byte-compile-dynamic-docstrings} |
107 | as a local variable in each of these files, and load them with either | |
108 | @file{site-load.el} or @file{site-init.el}. (This method has the | |
109 | drawback that the documentation strings take up space in Emacs all the | |
110 | time.) | |
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111 | @end itemize |
112 | ||
113 | It is not advisable to put anything in @file{site-load.el} or | |
114 | @file{site-init.el} that would alter any of the features that users | |
115 | expect in an ordinary unmodified Emacs. If you feel you must override | |
116 | normal features for your site, do it with @file{default.el}, so that | |
117 | users can override your changes if they wish. @xref{Startup Summary}. | |
118 | ||
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119 | In a package that can be preloaded, it is sometimes necessary (or |
120 | useful) to delay certain evaluations until Emacs subsequently starts | |
121 | up. The vast majority of such cases relate to the values of | |
122 | customizable variables. For example, @code{tutorial-directory} is a | |
123 | variable defined in @file{startup.el}, which is preloaded. The default | |
124 | value is set based on @code{data-directory}. The variable needs to | |
125 | access the value of @code{data-directory} when Emacs starts, not when | |
126 | it is dumped, because the Emacs executable has probably been installed | |
127 | in a different location since it was dumped. | |
128 | ||
129 | @defun custom-initialize-delay symbol value | |
130 | This function delays the initialization of @var{symbol} to the next | |
131 | Emacs start. You normally use this function by specifying it as the | |
132 | @code{:initialize} property of a customizable variable. (The argument | |
f003f294 | 133 | @var{value} is unused, and is provided only for compatibility with the |
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134 | form Custom expects.) |
135 | @end defun | |
b8d4c8d0 | 136 | |
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137 | In the unlikely event that you need a more general functionality than |
138 | @code{custom-initialize-delay} provides, you can use | |
139 | @code{before-init-hook} (@pxref{Startup Summary}). | |
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140 | |
141 | @defun dump-emacs to-file from-file | |
142 | @cindex unexec | |
143 | This function dumps the current state of Emacs into an executable file | |
144 | @var{to-file}. It takes symbols from @var{from-file} (this is normally | |
145 | the executable file @file{temacs}). | |
146 | ||
147 | If you want to use this function in an Emacs that was already dumped, | |
148 | you must run Emacs with @samp{-batch}. | |
149 | @end defun | |
150 | ||
151 | @node Pure Storage | |
520f2425 | 152 | @section Pure Storage |
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153 | @cindex pure storage |
154 | ||
155 | Emacs Lisp uses two kinds of storage for user-created Lisp objects: | |
156 | @dfn{normal storage} and @dfn{pure storage}. Normal storage is where | |
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157 | all the new data created during an Emacs session are kept |
158 | (@pxref{Garbage Collection}). Pure storage is used for certain data | |
159 | in the preloaded standard Lisp files---data that should never change | |
160 | during actual use of Emacs. | |
b8d4c8d0 | 161 | |
d15aac68 | 162 | Pure storage is allocated only while @command{temacs} is loading the |
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163 | standard preloaded Lisp libraries. In the file @file{emacs}, it is |
164 | marked as read-only (on operating systems that permit this), so that | |
165 | the memory space can be shared by all the Emacs jobs running on the | |
166 | machine at once. Pure storage is not expandable; a fixed amount is | |
167 | allocated when Emacs is compiled, and if that is not sufficient for | |
168 | the preloaded libraries, @file{temacs} allocates dynamic memory for | |
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169 | the part that didn't fit. The resulting image will work, but garbage |
170 | collection (@pxref{Garbage Collection}) is disabled in this situation, | |
171 | causing a memory leak. Such an overflow normally won't happen unless | |
172 | you try to preload additional libraries or add features to the | |
173 | standard ones. Emacs will display a warning about the overflow when | |
174 | it starts. If this happens, you should increase the compilation | |
175 | parameter @code{SYSTEM_PURESIZE_EXTRA} in the file | |
176 | @file{src/puresize.h} and rebuild Emacs. | |
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177 | |
178 | @defun purecopy object | |
179 | This function makes a copy in pure storage of @var{object}, and returns | |
180 | it. It copies a string by simply making a new string with the same | |
181 | characters, but without text properties, in pure storage. It | |
182 | recursively copies the contents of vectors and cons cells. It does | |
183 | not make copies of other objects such as symbols, but just returns | |
184 | them unchanged. It signals an error if asked to copy markers. | |
185 | ||
186 | This function is a no-op except while Emacs is being built and dumped; | |
999dd333 | 187 | it is usually called only in preloaded Lisp files. |
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188 | @end defun |
189 | ||
190 | @defvar pure-bytes-used | |
191 | The value of this variable is the number of bytes of pure storage | |
192 | allocated so far. Typically, in a dumped Emacs, this number is very | |
193 | close to the total amount of pure storage available---if it were not, | |
194 | we would preallocate less. | |
195 | @end defvar | |
196 | ||
197 | @defvar purify-flag | |
198 | This variable determines whether @code{defun} should make a copy of the | |
199 | function definition in pure storage. If it is non-@code{nil}, then the | |
200 | function definition is copied into pure storage. | |
201 | ||
202 | This flag is @code{t} while loading all of the basic functions for | |
333f9019 | 203 | building Emacs initially (allowing those functions to be shareable and |
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204 | non-collectible). Dumping Emacs as an executable always writes |
205 | @code{nil} in this variable, regardless of the value it actually has | |
206 | before and after dumping. | |
207 | ||
208 | You should not change this flag in a running Emacs. | |
209 | @end defvar | |
210 | ||
211 | @node Garbage Collection | |
520f2425 | 212 | @section Garbage Collection |
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213 | |
214 | @cindex memory allocation | |
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215 | When a program creates a list or the user defines a new function |
216 | (such as by loading a library), that data is placed in normal storage. | |
217 | If normal storage runs low, then Emacs asks the operating system to | |
218 | allocate more memory. Different types of Lisp objects, such as | |
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219 | symbols, cons cells, small vectors, markers, etc., are segregated in |
220 | distinct blocks in memory. (Large vectors, long strings, buffers and | |
221 | certain other editing types, which are fairly large, are allocated in | |
222 | individual blocks, one per object; small strings are packed into blocks | |
223 | of 8k bytes, and small vectors are packed into blocks of 4k bytes). | |
224 | ||
225 | @cindex vector-like objects, storage | |
226 | @cindex storage of vector-like Lisp objects | |
227 | Beyond the basic vector, a lot of objects like window, buffer, and | |
228 | frame are managed as if they were vectors. The corresponding C data | |
229 | structures include the @code{struct vectorlike_header} field whose | |
230 | @code{next} field points to the next object in the chain: | |
231 | @code{header.next.buffer} points to the next buffer (which could be | |
232 | a killed buffer), and @code{header.next.vector} points to the next | |
233 | vector in a free list. If a vector is small (smaller than or equal to | |
dbab98c7 | 234 | @code{VBLOCK_BYTES_MAX} bytes, see @file{alloc.c}), then |
f3372c87 | 235 | @code{header.next.nbytes} contains the vector size in bytes. |
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 | ||
288 | @code{garbage-collect} returns a list containing the following | |
289 | information: | |
290 | ||
291 | @example | |
292 | @group | |
293 | ((@var{used-conses} . @var{free-conses}) | |
294 | (@var{used-syms} . @var{free-syms}) | |
295 | @end group | |
296 | (@var{used-miscs} . @var{free-miscs}) | |
297 | @var{used-string-chars} | |
298 | @var{used-vector-slots} | |
299 | (@var{used-floats} . @var{free-floats}) | |
300 | (@var{used-intervals} . @var{free-intervals}) | |
301 | (@var{used-strings} . @var{free-strings})) | |
302 | @end example | |
303 | ||
304 | Here is an example: | |
305 | ||
306 | @example | |
307 | @group | |
308 | (garbage-collect) | |
309 | @result{} ((106886 . 13184) (9769 . 0) | |
310 | (7731 . 4651) 347543 121628 | |
311 | (31 . 94) (1273 . 168) | |
312 | (25474 . 3569)) | |
313 | @end group | |
314 | @end example | |
315 | ||
316 | Here is a table explaining each element: | |
317 | ||
318 | @table @var | |
319 | @item used-conses | |
320 | The number of cons cells in use. | |
321 | ||
322 | @item free-conses | |
323 | The number of cons cells for which space has been obtained from the | |
324 | operating system, but that are not currently being used. | |
325 | ||
326 | @item used-syms | |
327 | The number of symbols in use. | |
328 | ||
329 | @item free-syms | |
330 | The number of symbols for which space has been obtained from the | |
331 | operating system, but that are not currently being used. | |
332 | ||
333 | @item used-miscs | |
334 | The number of miscellaneous objects in use. These include markers and | |
335 | overlays, plus certain objects not visible to users. | |
336 | ||
337 | @item free-miscs | |
338 | The number of miscellaneous objects for which space has been obtained | |
339 | from the operating system, but that are not currently being used. | |
340 | ||
341 | @item used-string-chars | |
342 | The total size of all strings, in characters. | |
343 | ||
344 | @item used-vector-slots | |
345 | The total number of elements of existing vectors. | |
346 | ||
347 | @item used-floats | |
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348 | The number of floats in use. |
349 | ||
350 | @item free-floats | |
b8d4c8d0 GM |
351 | The number of floats for which space has been obtained from the |
352 | operating system, but that are not currently being used. | |
353 | ||
354 | @item used-intervals | |
355 | The number of intervals in use. Intervals are an internal | |
356 | data structure used for representing text properties. | |
357 | ||
358 | @item free-intervals | |
359 | The number of intervals for which space has been obtained | |
360 | from the operating system, but that are not currently being used. | |
361 | ||
362 | @item used-strings | |
363 | The number of strings in use. | |
364 | ||
365 | @item free-strings | |
366 | The number of string headers for which the space was obtained from the | |
367 | operating system, but which are currently not in use. (A string | |
368 | object consists of a header and the storage for the string text | |
369 | itself; the latter is only allocated when the string is created.) | |
370 | @end table | |
371 | ||
999dd333 | 372 | If there was overflow in pure space (@pxref{Pure Storage}), |
b8d4c8d0 | 373 | @code{garbage-collect} returns @code{nil}, because a real garbage |
9658dc2a | 374 | collection cannot be done. |
b8d4c8d0 GM |
375 | @end deffn |
376 | ||
377 | @defopt garbage-collection-messages | |
378 | If this variable is non-@code{nil}, Emacs displays a message at the | |
379 | beginning and end of garbage collection. The default value is | |
999dd333 | 380 | @code{nil}. |
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381 | @end defopt |
382 | ||
383 | @defvar post-gc-hook | |
384 | This is a normal hook that is run at the end of garbage collection. | |
385 | Garbage collection is inhibited while the hook functions run, so be | |
386 | careful writing them. | |
387 | @end defvar | |
388 | ||
389 | @defopt gc-cons-threshold | |
390 | The value of this variable is the number of bytes of storage that must | |
391 | be allocated for Lisp objects after one garbage collection in order to | |
392 | trigger another garbage collection. A cons cell counts as eight bytes, | |
393 | a string as one byte per character plus a few bytes of overhead, and so | |
394 | on; space allocated to the contents of buffers does not count. Note | |
395 | that the subsequent garbage collection does not happen immediately when | |
396 | the threshold is exhausted, but only the next time the Lisp evaluator is | |
397 | called. | |
398 | ||
999dd333 | 399 | The initial threshold value is 800,000. If you specify a larger |
b8d4c8d0 GM |
400 | value, garbage collection will happen less often. This reduces the |
401 | amount of time spent garbage collecting, but increases total memory use. | |
402 | You may want to do this when running a program that creates lots of | |
403 | Lisp data. | |
404 | ||
405 | You can make collections more frequent by specifying a smaller value, | |
406 | down to 10,000. A value less than 10,000 will remain in effect only | |
407 | until the subsequent garbage collection, at which time | |
408 | @code{garbage-collect} will set the threshold back to 10,000. | |
409 | @end defopt | |
410 | ||
411 | @defopt gc-cons-percentage | |
412 | The value of this variable specifies the amount of consing before a | |
413 | garbage collection occurs, as a fraction of the current heap size. | |
414 | This criterion and @code{gc-cons-threshold} apply in parallel, and | |
415 | garbage collection occurs only when both criteria are satisfied. | |
416 | ||
417 | As the heap size increases, the time to perform a garbage collection | |
418 | increases. Thus, it can be desirable to do them less frequently in | |
419 | proportion. | |
420 | @end defopt | |
421 | ||
422 | The value returned by @code{garbage-collect} describes the amount of | |
423 | memory used by Lisp data, broken down by data type. By contrast, the | |
424 | function @code{memory-limit} provides information on the total amount of | |
425 | memory Emacs is currently using. | |
426 | ||
b8d4c8d0 GM |
427 | @defun memory-limit |
428 | This function returns the address of the last byte Emacs has allocated, | |
429 | divided by 1024. We divide the value by 1024 to make sure it fits in a | |
430 | Lisp integer. | |
431 | ||
432 | You can use this to get a general idea of how your actions affect the | |
433 | memory usage. | |
434 | @end defun | |
435 | ||
436 | @defvar memory-full | |
d15aac68 | 437 | This variable is @code{t} if Emacs is nearly out of memory for Lisp |
b8d4c8d0 GM |
438 | objects, and @code{nil} otherwise. |
439 | @end defvar | |
440 | ||
441 | @defun memory-use-counts | |
442 | This returns a list of numbers that count the number of objects | |
443 | created in this Emacs session. Each of these counters increments for | |
444 | a certain kind of object. See the documentation string for details. | |
445 | @end defun | |
446 | ||
447 | @defvar gcs-done | |
448 | This variable contains the total number of garbage collections | |
449 | done so far in this Emacs session. | |
450 | @end defvar | |
451 | ||
452 | @defvar gc-elapsed | |
453 | This variable contains the total number of seconds of elapsed time | |
454 | during garbage collection so far in this Emacs session, as a floating | |
455 | point number. | |
456 | @end defvar | |
457 | ||
458 | @node Memory Usage | |
459 | @section Memory Usage | |
460 | @cindex memory usage | |
461 | ||
462 | These functions and variables give information about the total amount | |
463 | of memory allocation that Emacs has done, broken down by data type. | |
464 | Note the difference between these and the values returned by | |
01a6dcc8 | 465 | @code{garbage-collect}; those count objects that currently exist, but |
b8d4c8d0 GM |
466 | these count the number or size of all allocations, including those for |
467 | objects that have since been freed. | |
468 | ||
469 | @defvar cons-cells-consed | |
470 | The total number of cons cells that have been allocated so far | |
471 | in this Emacs session. | |
472 | @end defvar | |
473 | ||
474 | @defvar floats-consed | |
475 | The total number of floats that have been allocated so far | |
476 | in this Emacs session. | |
477 | @end defvar | |
478 | ||
479 | @defvar vector-cells-consed | |
480 | The total number of vector cells that have been allocated so far | |
481 | in this Emacs session. | |
482 | @end defvar | |
483 | ||
484 | @defvar symbols-consed | |
485 | The total number of symbols that have been allocated so far | |
486 | in this Emacs session. | |
487 | @end defvar | |
488 | ||
489 | @defvar string-chars-consed | |
490 | The total number of string characters that have been allocated so far | |
9658dc2a | 491 | in this session. |
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492 | @end defvar |
493 | ||
494 | @defvar misc-objects-consed | |
495 | The total number of miscellaneous objects that have been allocated so | |
9658dc2a | 496 | far in this session. These include markers and overlays, plus |
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497 | certain objects not visible to users. |
498 | @end defvar | |
499 | ||
500 | @defvar intervals-consed | |
501 | The total number of intervals that have been allocated so far | |
502 | in this Emacs session. | |
503 | @end defvar | |
504 | ||
505 | @defvar strings-consed | |
506 | The total number of strings that have been allocated so far in this | |
507 | Emacs session. | |
508 | @end defvar | |
509 | ||
510 | @node Writing Emacs Primitives | |
520f2425 | 511 | @section Writing Emacs Primitives |
b8d4c8d0 GM |
512 | @cindex primitive function internals |
513 | @cindex writing Emacs primitives | |
514 | ||
1df7defd | 515 | Lisp primitives are Lisp functions implemented in C@. The details of |
b8d4c8d0 GM |
516 | interfacing the C function so that Lisp can call it are handled by a few |
517 | C macros. The only way to really understand how to write new C code is | |
518 | to read the source, but we can explain some things here. | |
519 | ||
520 | An example of a special form is the definition of @code{or}, from | |
521 | @file{eval.c}. (An ordinary function would have the same general | |
522 | appearance.) | |
523 | ||
524 | @cindex garbage collection protection | |
525 | @smallexample | |
526 | @group | |
527 | DEFUN ("or", For, Sor, 0, UNEVALLED, 0, | |
d15aac68 CY |
528 | doc: /* Eval args until one of them yields non-nil, then return |
529 | that value. | |
530 | The remaining args are not evalled at all. | |
b8d4c8d0 GM |
531 | If all args return nil, return nil. |
532 | @end group | |
533 | @group | |
534 | usage: (or CONDITIONS ...) */) | |
b88746ba | 535 | (Lisp_Object args) |
b8d4c8d0 GM |
536 | @{ |
537 | register Lisp_Object val = Qnil; | |
538 | struct gcpro gcpro1; | |
539 | @end group | |
540 | ||
541 | @group | |
542 | GCPRO1 (args); | |
543 | @end group | |
544 | ||
545 | @group | |
546 | while (CONSP (args)) | |
547 | @{ | |
7d2d7cc0 | 548 | val = eval_sub (XCAR (args)); |
b8d4c8d0 GM |
549 | if (!NILP (val)) |
550 | break; | |
551 | args = XCDR (args); | |
552 | @} | |
553 | @end group | |
554 | ||
555 | @group | |
556 | UNGCPRO; | |
557 | return val; | |
558 | @} | |
559 | @end group | |
560 | @end smallexample | |
561 | ||
562 | @cindex @code{DEFUN}, C macro to define Lisp primitives | |
563 | Let's start with a precise explanation of the arguments to the | |
564 | @code{DEFUN} macro. Here is a template for them: | |
565 | ||
566 | @example | |
567 | DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc}) | |
568 | @end example | |
569 | ||
570 | @table @var | |
571 | @item lname | |
572 | This is the name of the Lisp symbol to define as the function name; in | |
573 | the example above, it is @code{or}. | |
574 | ||
575 | @item fname | |
d15aac68 CY |
576 | This is the C function name for this function. This is the name that |
577 | is used in C code for calling the function. The name is, by | |
578 | convention, @samp{F} prepended to the Lisp name, with all dashes | |
579 | (@samp{-}) in the Lisp name changed to underscores. Thus, to call | |
580 | this function from C code, call @code{For}. | |
b8d4c8d0 GM |
581 | |
582 | @item sname | |
583 | This is a C variable name to use for a structure that holds the data for | |
584 | the subr object that represents the function in Lisp. This structure | |
585 | conveys the Lisp symbol name to the initialization routine that will | |
586 | create the symbol and store the subr object as its definition. By | |
587 | convention, this name is always @var{fname} with @samp{F} replaced with | |
588 | @samp{S}. | |
589 | ||
590 | @item min | |
591 | This is the minimum number of arguments that the function requires. The | |
592 | function @code{or} allows a minimum of zero arguments. | |
593 | ||
594 | @item max | |
595 | This is the maximum number of arguments that the function accepts, if | |
596 | there is a fixed maximum. Alternatively, it can be @code{UNEVALLED}, | |
597 | indicating a special form that receives unevaluated arguments, or | |
598 | @code{MANY}, indicating an unlimited number of evaluated arguments (the | |
599 | equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are | |
9658dc2a GM |
600 | macros. If @var{max} is a number, it must be more than @var{min} but |
601 | less than 8. | |
b8d4c8d0 GM |
602 | |
603 | @item interactive | |
604 | This is an interactive specification, a string such as might be used as | |
605 | the argument of @code{interactive} in a Lisp function. In the case of | |
606 | @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be | |
607 | called interactively. A value of @code{""} indicates a function that | |
2c30e468 EZ |
608 | should receive no arguments when called interactively. If the value |
609 | begins with a @samp{(}, the string is evaluated as a Lisp form. | |
7d2d7cc0 GM |
610 | For examples of the last two forms, see @code{widen} and |
611 | @code{narrow-to-region} in @file{editfns.c}. | |
b8d4c8d0 GM |
612 | |
613 | @item doc | |
614 | This is the documentation string. It uses C comment syntax rather | |
615 | than C string syntax because comment syntax requires nothing special | |
616 | to include multiple lines. The @samp{doc:} identifies the comment | |
617 | that follows as the documentation string. The @samp{/*} and @samp{*/} | |
618 | delimiters that begin and end the comment are not part of the | |
619 | documentation string. | |
620 | ||
621 | If the last line of the documentation string begins with the keyword | |
622 | @samp{usage:}, the rest of the line is treated as the argument list | |
623 | for documentation purposes. This way, you can use different argument | |
624 | names in the documentation string from the ones used in the C code. | |
625 | @samp{usage:} is required if the function has an unlimited number of | |
626 | arguments. | |
627 | ||
628 | All the usual rules for documentation strings in Lisp code | |
629 | (@pxref{Documentation Tips}) apply to C code documentation strings | |
630 | too. | |
631 | @end table | |
632 | ||
b88746ba | 633 | After the call to the @code{DEFUN} macro, you must write the |
d15aac68 CY |
634 | argument list for the C function, including the types for the |
635 | arguments. If the primitive accepts a fixed maximum number of Lisp | |
636 | arguments, there must be one C argument for each Lisp argument, and | |
637 | each argument must be of type @code{Lisp_Object}. (Various macros and | |
638 | functions for creating values of type @code{Lisp_Object} are declared | |
639 | in the file @file{lisp.h}.) If the primitive has no upper limit on | |
640 | the number of Lisp arguments, it must have exactly two C arguments: | |
641 | the first is the number of Lisp arguments, and the second is the | |
642 | address of a block containing their values. These have types | |
643 | @code{int} and @w{@code{Lisp_Object *}} respectively. | |
b8d4c8d0 GM |
644 | |
645 | @cindex @code{GCPRO} and @code{UNGCPRO} | |
646 | @cindex protect C variables from garbage collection | |
647 | Within the function @code{For} itself, note the use of the macros | |
d15aac68 CY |
648 | @code{GCPRO1} and @code{UNGCPRO}. These macros are defined for the |
649 | sake of the few platforms which do not use Emacs' default | |
650 | stack-marking garbage collector. The @code{GCPRO1} macro ``protects'' | |
651 | a variable from garbage collection, explicitly informing the garbage | |
652 | collector that that variable and all its contents must be as | |
653 | accessible. GC protection is necessary in any function which can | |
654 | perform Lisp evaluation by calling @code{eval_sub} or @code{Feval} as | |
655 | a subroutine, either directly or indirectly. | |
b8d4c8d0 GM |
656 | |
657 | It suffices to ensure that at least one pointer to each object is | |
d15aac68 | 658 | GC-protected. Thus, a particular local variable can do without |
b8d4c8d0 | 659 | protection if it is certain that the object it points to will be |
7d2d7cc0 | 660 | preserved by some other pointer (such as another local variable that |
d15aac68 CY |
661 | has a @code{GCPRO}). Otherwise, the local variable needs a |
662 | @code{GCPRO}. | |
b8d4c8d0 GM |
663 | |
664 | The macro @code{GCPRO1} protects just one local variable. If you | |
665 | want to protect two variables, use @code{GCPRO2} instead; repeating | |
666 | @code{GCPRO1} will not work. Macros @code{GCPRO3}, @code{GCPRO4}, | |
667 | @code{GCPRO5}, and @code{GCPRO6} also exist. All these macros | |
668 | implicitly use local variables such as @code{gcpro1}; you must declare | |
669 | these explicitly, with type @code{struct gcpro}. Thus, if you use | |
670 | @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}. | |
b8d4c8d0 GM |
671 | |
672 | @code{UNGCPRO} cancels the protection of the variables that are | |
673 | protected in the current function. It is necessary to do this | |
674 | explicitly. | |
675 | ||
b8d4c8d0 GM |
676 | You must not use C initializers for static or global variables unless |
677 | the variables are never written once Emacs is dumped. These variables | |
678 | with initializers are allocated in an area of memory that becomes | |
679 | read-only (on certain operating systems) as a result of dumping Emacs. | |
680 | @xref{Pure Storage}. | |
681 | ||
b8d4c8d0 GM |
682 | @cindex @code{defsubr}, Lisp symbol for a primitive |
683 | Defining the C function is not enough to make a Lisp primitive | |
684 | available; you must also create the Lisp symbol for the primitive and | |
685 | store a suitable subr object in its function cell. The code looks like | |
686 | this: | |
687 | ||
688 | @example | |
7d2d7cc0 | 689 | defsubr (&@var{sname}); |
b8d4c8d0 GM |
690 | @end example |
691 | ||
692 | @noindent | |
7d2d7cc0 | 693 | Here @var{sname} is the name you used as the third argument to @code{DEFUN}. |
b8d4c8d0 GM |
694 | |
695 | If you add a new primitive to a file that already has Lisp primitives | |
696 | defined in it, find the function (near the end of the file) named | |
697 | @code{syms_of_@var{something}}, and add the call to @code{defsubr} | |
698 | there. If the file doesn't have this function, or if you create a new | |
699 | file, add to it a @code{syms_of_@var{filename}} (e.g., | |
700 | @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all | |
701 | of these functions are called, and add a call to | |
702 | @code{syms_of_@var{filename}} there. | |
703 | ||
704 | @anchor{Defining Lisp variables in C} | |
705 | @vindex byte-boolean-vars | |
706 | @cindex defining Lisp variables in C | |
707 | @cindex @code{DEFVAR_INT}, @code{DEFVAR_LISP}, @code{DEFVAR_BOOL} | |
708 | The function @code{syms_of_@var{filename}} is also the place to define | |
709 | any C variables that are to be visible as Lisp variables. | |
710 | @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible | |
711 | in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int} | |
712 | visible in Lisp with a value that is always an integer. | |
713 | @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp | |
714 | with a value that is either @code{t} or @code{nil}. Note that variables | |
715 | defined with @code{DEFVAR_BOOL} are automatically added to the list | |
716 | @code{byte-boolean-vars} used by the byte compiler. | |
717 | ||
7d2d7cc0 GM |
718 | @cindex defining customization variables in C |
719 | If you want to make a Lisp variables that is defined in C behave | |
720 | like one declared with @code{defcustom}, add an appropriate entry to | |
721 | @file{cus-start.el}. | |
722 | ||
b8d4c8d0 GM |
723 | @cindex @code{staticpro}, protection from GC |
724 | If you define a file-scope C variable of type @code{Lisp_Object}, | |
725 | you must protect it from garbage-collection by calling @code{staticpro} | |
726 | in @code{syms_of_@var{filename}}, like this: | |
727 | ||
728 | @example | |
729 | staticpro (&@var{variable}); | |
730 | @end example | |
731 | ||
732 | Here is another example function, with more complicated arguments. | |
733 | This comes from the code in @file{window.c}, and it demonstrates the use | |
734 | of macros and functions to manipulate Lisp objects. | |
735 | ||
736 | @smallexample | |
737 | @group | |
738 | DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p, | |
7d2d7cc0 GM |
739 | Scoordinates_in_window_p, 2, 2, 0, |
740 | doc: /* Return non-nil if COORDINATES are in WINDOW. | |
741 | ... | |
b8d4c8d0 GM |
742 | @end group |
743 | @group | |
7d2d7cc0 GM |
744 | or `right-margin' is returned. */) |
745 | (register Lisp_Object coordinates, Lisp_Object window) | |
b8d4c8d0 | 746 | @{ |
7d2d7cc0 GM |
747 | struct window *w; |
748 | struct frame *f; | |
b8d4c8d0 | 749 | int x, y; |
7d2d7cc0 | 750 | Lisp_Object lx, ly; |
b8d4c8d0 GM |
751 | @end group |
752 | ||
753 | @group | |
7d2d7cc0 GM |
754 | CHECK_LIVE_WINDOW (window); |
755 | w = XWINDOW (window); | |
756 | f = XFRAME (w->frame); | |
757 | CHECK_CONS (coordinates); | |
758 | lx = Fcar (coordinates); | |
759 | ly = Fcdr (coordinates); | |
760 | CHECK_NUMBER_OR_FLOAT (lx); | |
761 | CHECK_NUMBER_OR_FLOAT (ly); | |
762 | x = FRAME_PIXEL_X_FROM_CANON_X (f, lx) + FRAME_INTERNAL_BORDER_WIDTH(f); | |
763 | y = FRAME_PIXEL_Y_FROM_CANON_Y (f, ly) + FRAME_INTERNAL_BORDER_WIDTH(f); | |
b8d4c8d0 GM |
764 | @end group |
765 | ||
766 | @group | |
7d2d7cc0 | 767 | switch (coordinates_in_window (w, x, y)) |
b8d4c8d0 | 768 | @{ |
7d2d7cc0 | 769 | case ON_NOTHING: /* NOT in window at all. */ |
b8d4c8d0 GM |
770 | return Qnil; |
771 | @end group | |
772 | ||
7d2d7cc0 | 773 | ... |
b8d4c8d0 GM |
774 | |
775 | @group | |
7d2d7cc0 | 776 | case ON_MODE_LINE: /* In mode line of window. */ |
b8d4c8d0 GM |
777 | return Qmode_line; |
778 | @end group | |
779 | ||
7d2d7cc0 GM |
780 | ... |
781 | ||
b8d4c8d0 | 782 | @group |
7d2d7cc0 GM |
783 | case ON_SCROLL_BAR: /* On scroll-bar of window. */ |
784 | /* Historically we are supposed to return nil in this case. */ | |
785 | return Qnil; | |
b8d4c8d0 GM |
786 | @end group |
787 | ||
788 | @group | |
789 | default: | |
790 | abort (); | |
791 | @} | |
792 | @} | |
793 | @end group | |
794 | @end smallexample | |
795 | ||
796 | Note that C code cannot call functions by name unless they are defined | |
1df7defd | 797 | in C@. The way to call a function written in Lisp is to use |
b8d4c8d0 GM |
798 | @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since |
799 | the Lisp function @code{funcall} accepts an unlimited number of | |
800 | arguments, in C it takes two: the number of Lisp-level arguments, and a | |
801 | one-dimensional array containing their values. The first Lisp-level | |
802 | argument is the Lisp function to call, and the rest are the arguments to | |
803 | pass to it. Since @code{Ffuncall} can call the evaluator, you must | |
804 | protect pointers from garbage collection around the call to | |
805 | @code{Ffuncall}. | |
806 | ||
807 | The C functions @code{call0}, @code{call1}, @code{call2}, and so on, | |
808 | provide handy ways to call a Lisp function conveniently with a fixed | |
809 | number of arguments. They work by calling @code{Ffuncall}. | |
810 | ||
811 | @file{eval.c} is a very good file to look through for examples; | |
812 | @file{lisp.h} contains the definitions for some important macros and | |
813 | functions. | |
814 | ||
815 | If you define a function which is side-effect free, update the code | |
7d2d7cc0 | 816 | in @file{byte-opt.el} that binds @code{side-effect-free-fns} and |
b8d4c8d0 GM |
817 | @code{side-effect-and-error-free-fns} so that the compiler optimizer |
818 | knows about it. | |
819 | ||
820 | @node Object Internals | |
520f2425 | 821 | @section Object Internals |
b8d4c8d0 GM |
822 | @cindex object internals |
823 | ||
7d2d7cc0 | 824 | @c FIXME Is this still true? Does --with-wide-int affect anything? |
b8d4c8d0 GM |
825 | GNU Emacs Lisp manipulates many different types of data. The actual |
826 | data are stored in a heap and the only access that programs have to it | |
c773345a CY |
827 | is through pointers. Each pointer is 32 bits wide on 32-bit machines, |
828 | and 64 bits wide on 64-bit machines; three of these bits are used for | |
829 | the tag that identifies the object's type, and the remainder are used | |
830 | to address the object. | |
b8d4c8d0 GM |
831 | |
832 | Because Lisp objects are represented as tagged pointers, it is always | |
833 | possible to determine the Lisp data type of any object. The C data type | |
834 | @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary | |
835 | variables have type @code{Lisp_Object}, which means they can hold any | |
836 | type of Lisp value; you can determine the actual data type only at run | |
837 | time. The same is true for function arguments; if you want a function | |
838 | to accept only a certain type of argument, you must check the type | |
839 | explicitly using a suitable predicate (@pxref{Type Predicates}). | |
840 | @cindex type checking internals | |
841 | ||
842 | @menu | |
843 | * Buffer Internals:: Components of a buffer structure. | |
844 | * Window Internals:: Components of a window structure. | |
845 | * Process Internals:: Components of a process structure. | |
846 | @end menu | |
847 | ||
848 | @node Buffer Internals | |
520f2425 | 849 | @subsection Buffer Internals |
b8d4c8d0 GM |
850 | @cindex internals, of buffer |
851 | @cindex buffer internals | |
852 | ||
7d2d7cc0 | 853 | Two structures (see @file{buffer.h}) are used to represent buffers |
1df7defd | 854 | in C@. The @code{buffer_text} structure contains fields describing the |
7d2d7cc0 GM |
855 | text of a buffer; the @code{buffer} structure holds other fields. In |
856 | the case of indirect buffers, two or more @code{buffer} structures | |
857 | reference the same @code{buffer_text} structure. | |
b8d4c8d0 | 858 | |
c773345a | 859 | Here are some of the fields in @code{struct buffer_text}: |
b8d4c8d0 GM |
860 | |
861 | @table @code | |
862 | @item beg | |
c773345a | 863 | The address of the buffer contents. |
b8d4c8d0 GM |
864 | |
865 | @item gpt | |
c773345a CY |
866 | @itemx gpt_byte |
867 | The character and byte positions of the buffer gap. @xref{Buffer | |
868 | Gap}. | |
b8d4c8d0 GM |
869 | |
870 | @item z | |
c773345a CY |
871 | @itemx z_byte |
872 | The character and byte positions of the end of the buffer text. | |
b8d4c8d0 GM |
873 | |
874 | @item gap_size | |
c773345a | 875 | The size of buffer's gap. @xref{Buffer Gap}. |
b8d4c8d0 GM |
876 | |
877 | @item modiff | |
c773345a CY |
878 | @itemx save_modiff |
879 | @itemx chars_modiff | |
880 | @itemx overlay_modiff | |
881 | These fields count the number of buffer-modification events performed | |
882 | in this buffer. @code{modiff} is incremented after each | |
883 | buffer-modification event, and is never otherwise changed; | |
884 | @code{save_modiff} contains the value of @code{modiff} the last time | |
885 | the buffer was visited or saved; @code{chars_modiff} counts only | |
886 | modifications to the characters in the buffer, ignoring all other | |
887 | kinds of changes; and @code{overlay_modiff} counts only modifications | |
888 | to the overlays. | |
b8d4c8d0 GM |
889 | |
890 | @item beg_unchanged | |
c773345a CY |
891 | @itemx end_unchanged |
892 | The number of characters at the start and end of the text that are | |
893 | known to be unchanged since the last complete redisplay. | |
b8d4c8d0 GM |
894 | |
895 | @item unchanged_modified | |
c773345a CY |
896 | @itemx overlay_unchanged_modified |
897 | The values of @code{modiff} and @code{overlay_modiff}, respectively, | |
da6062e6 | 898 | after the last complete redisplay. If their current values match |
c773345a | 899 | @code{modiff} or @code{overlay_modiff}, that means |
b8d4c8d0 GM |
900 | @code{beg_unchanged} and @code{end_unchanged} contain no useful |
901 | information. | |
902 | ||
903 | @item markers | |
904 | The markers that refer to this buffer. This is actually a single | |
905 | marker, and successive elements in its marker @code{chain} are the other | |
906 | markers referring to this buffer text. | |
907 | ||
908 | @item intervals | |
c773345a | 909 | The interval tree which records the text properties of this buffer. |
b8d4c8d0 GM |
910 | @end table |
911 | ||
c773345a | 912 | Some of the fields of @code{struct buffer} are: |
b8d4c8d0 GM |
913 | |
914 | @table @code | |
7d2d7cc0 GM |
915 | @item header |
916 | A @code{struct vectorlike_header} structure where @code{header.next} | |
917 | points to the next buffer, in the chain of all buffers (including | |
c773345a CY |
918 | killed buffers). This chain is used only for garbage collection, in |
919 | order to collect killed buffers properly. Note that vectors, and most | |
920 | kinds of objects allocated as vectors, are all on one chain, but | |
921 | buffers are on a separate chain of their own. | |
b8d4c8d0 GM |
922 | |
923 | @item own_text | |
c773345a CY |
924 | A @code{struct buffer_text} structure that ordinarily holds the buffer |
925 | contents. In indirect buffers, this field is not used. | |
b8d4c8d0 GM |
926 | |
927 | @item text | |
c773345a CY |
928 | A pointer to the @code{buffer_text} structure for this buffer. In an |
929 | ordinary buffer, this is the @code{own_text} field above. In an | |
930 | indirect buffer, this is the @code{own_text} field of the base buffer. | |
b8d4c8d0 GM |
931 | |
932 | @item pt | |
c773345a CY |
933 | @itemx pt_byte |
934 | The character and byte positions of point in a buffer. | |
b8d4c8d0 GM |
935 | |
936 | @item begv | |
c773345a CY |
937 | @itemx begv_byte |
938 | The character and byte positions of the beginning of the accessible | |
939 | range of text in the buffer. | |
b8d4c8d0 GM |
940 | |
941 | @item zv | |
c773345a CY |
942 | @itemx zv_byte |
943 | The character and byte positions of the end of the accessible range of | |
944 | text in the buffer. | |
b8d4c8d0 GM |
945 | |
946 | @item base_buffer | |
947 | In an indirect buffer, this points to the base buffer. In an ordinary | |
948 | buffer, it is null. | |
949 | ||
c773345a CY |
950 | @item local_flags |
951 | This field contains flags indicating that certain variables are local | |
952 | in this buffer. Such variables are declared in the C code using | |
953 | @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored | |
954 | in fields in the buffer structure itself. (Some of these fields are | |
b8d4c8d0 GM |
955 | described in this table.) |
956 | ||
957 | @item modtime | |
c773345a CY |
958 | The modification time of the visited file. It is set when the file is |
959 | written or read. Before writing the buffer into a file, this field is | |
960 | compared to the modification time of the file to see if the file has | |
961 | changed on disk. @xref{Buffer Modification}. | |
b8d4c8d0 GM |
962 | |
963 | @item auto_save_modified | |
c773345a | 964 | The time when the buffer was last auto-saved. |
b8d4c8d0 GM |
965 | |
966 | @item last_window_start | |
c773345a CY |
967 | The @code{window-start} position in the buffer as of the last time the |
968 | buffer was displayed in a window. | |
b8d4c8d0 GM |
969 | |
970 | @item clip_changed | |
c773345a CY |
971 | This flag indicates that narrowing has changed in the buffer. |
972 | @xref{Narrowing}. | |
b8d4c8d0 GM |
973 | |
974 | @item prevent_redisplay_optimizations_p | |
c773345a CY |
975 | This flag indicates that redisplay optimizations should not be used to |
976 | display this buffer. | |
b8d4c8d0 | 977 | |
c773345a CY |
978 | @item overlay_center |
979 | This field holds the current overlay center position. @xref{Managing | |
980 | Overlays}. | |
981 | ||
982 | @item overlays_before | |
983 | @itemx overlays_after | |
984 | These fields hold, respectively, a list of overlays that end at or | |
985 | before the current overlay center, and a list of overlays that end | |
986 | after the current overlay center. @xref{Managing Overlays}. | |
987 | @code{overlays_before} is sorted in order of decreasing end position, | |
988 | and @code{overlays_after} is sorted in order of increasing beginning | |
989 | position. | |
b8d4c8d0 | 990 | |
7d2d7cc0 GM |
991 | @c FIXME? the following are now all Lisp_Object BUFFER_INTERNAL_FIELD (foo). |
992 | ||
b8d4c8d0 | 993 | @item name |
c773345a CY |
994 | A Lisp string that names the buffer. It is guaranteed to be unique. |
995 | @xref{Buffer Names}. | |
b8d4c8d0 | 996 | |
c773345a CY |
997 | @item save_length |
998 | The length of the file this buffer is visiting, when last read or | |
999 | saved. This and other fields concerned with saving are not kept in | |
1000 | the @code{buffer_text} structure because indirect buffers are never | |
1001 | saved. | |
b8d4c8d0 GM |
1002 | |
1003 | @item directory | |
c773345a CY |
1004 | The directory for expanding relative file names. This is the value of |
1005 | the buffer-local variable @code{default-directory} (@pxref{File Name Expansion}). | |
b8d4c8d0 | 1006 | |
c773345a CY |
1007 | @item filename |
1008 | The name of the file visited in this buffer, or @code{nil}. This is | |
1009 | the value of the buffer-local variable @code{buffer-file-name} | |
1010 | (@pxref{Buffer File Name}). | |
b8d4c8d0 | 1011 | |
c773345a CY |
1012 | @item undo_list |
1013 | @itemx backed_up | |
1014 | @itemx auto_save_file_name | |
7d2d7cc0 | 1015 | @itemx auto_save_file_format |
c773345a CY |
1016 | @itemx read_only |
1017 | @itemx file_format | |
1018 | @itemx file_truename | |
1019 | @itemx invisibility_spec | |
1020 | @itemx display_count | |
1021 | @itemx display_time | |
1022 | These fields store the values of Lisp variables that are automatically | |
1023 | buffer-local (@pxref{Buffer-Local Variables}), whose corresponding | |
1024 | variable names have the additional prefix @code{buffer-} and have | |
1025 | underscores replaced with dashes. For instance, @code{undo_list} | |
29157371 | 1026 | stores the value of @code{buffer-undo-list}. |
b8d4c8d0 GM |
1027 | |
1028 | @item mark | |
c773345a CY |
1029 | The mark for the buffer. The mark is a marker, hence it is also |
1030 | included on the list @code{markers}. @xref{The Mark}. | |
b8d4c8d0 GM |
1031 | |
1032 | @item local_var_alist | |
c773345a CY |
1033 | The association list describing the buffer-local variable bindings of |
1034 | this buffer, not including the built-in buffer-local bindings that | |
1035 | have special slots in the buffer object. (Those slots are omitted | |
1036 | from this table.) @xref{Buffer-Local Variables}. | |
b8d4c8d0 GM |
1037 | |
1038 | @item major_mode | |
1039 | Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}. | |
1040 | ||
1041 | @item mode_name | |
c773345a | 1042 | Pretty name of the major mode, e.g., @code{"Lisp"}. |
b8d4c8d0 GM |
1043 | |
1044 | @item keymap | |
c773345a CY |
1045 | @itemx abbrev_table |
1046 | @itemx syntax_table | |
1047 | @itemx category_table | |
1048 | @itemx display_table | |
1049 | These fields store the buffer's local keymap (@pxref{Keymaps}), abbrev | |
1050 | table (@pxref{Abbrev Tables}), syntax table (@pxref{Syntax Tables}), | |
1051 | category table (@pxref{Categories}), and display table (@pxref{Display | |
1052 | Tables}). | |
b8d4c8d0 GM |
1053 | |
1054 | @item downcase_table | |
c773345a CY |
1055 | @itemx upcase_table |
1056 | @itemx case_canon_table | |
1057 | These fields store the conversion tables for converting text to lower | |
1058 | case, upper case, and for canonicalizing text for case-fold search. | |
b8d4c8d0 GM |
1059 | @xref{Case Tables}. |
1060 | ||
b8d4c8d0 GM |
1061 | @item minor_modes |
1062 | An alist of the minor modes of this buffer. | |
1063 | ||
b8d4c8d0 | 1064 | @item pt_marker |
c773345a CY |
1065 | @itemx begv_marker |
1066 | @itemx zv_marker | |
1067 | These fields are only used in an indirect buffer, or in a buffer that | |
1068 | is the base of an indirect buffer. Each holds a marker that records | |
1069 | @code{pt}, @code{begv}, and @code{zv} respectively, for this buffer | |
b8d4c8d0 GM |
1070 | when the buffer is not current. |
1071 | ||
c773345a CY |
1072 | @item mode_line_format |
1073 | @itemx header_line_format | |
1074 | @itemx case_fold_search | |
1075 | @itemx tab_width | |
1076 | @itemx fill_column | |
1077 | @itemx left_margin | |
1078 | @itemx auto_fill_function | |
c773345a CY |
1079 | @itemx truncate_lines |
1080 | @itemx word_wrap | |
1081 | @itemx ctl_arrow | |
7d2d7cc0 GM |
1082 | @itemx bidi_display_reordering |
1083 | @itemx bidi_paragraph_direction | |
c773345a CY |
1084 | @itemx selective_display |
1085 | @itemx selective_display_ellipses | |
1086 | @itemx overwrite_mode | |
1087 | @itemx abbrev_mode | |
c773345a CY |
1088 | @itemx mark_active |
1089 | @itemx enable_multibyte_characters | |
1090 | @itemx buffer_file_coding_system | |
c773345a CY |
1091 | @itemx cache_long_line_scans |
1092 | @itemx point_before_scroll | |
1093 | @itemx left_fringe_width | |
1094 | @itemx right_fringe_width | |
1095 | @itemx fringes_outside_margins | |
1096 | @itemx scroll_bar_width | |
1097 | @itemx indicate_empty_lines | |
1098 | @itemx indicate_buffer_boundaries | |
1099 | @itemx fringe_indicator_alist | |
1100 | @itemx fringe_cursor_alist | |
1101 | @itemx scroll_up_aggressively | |
1102 | @itemx scroll_down_aggressively | |
1103 | @itemx cursor_type | |
1104 | @itemx cursor_in_non_selected_windows | |
1105 | These fields store the values of Lisp variables that are automatically | |
1106 | buffer-local (@pxref{Buffer-Local Variables}), whose corresponding | |
1107 | variable names have underscores replaced with dashes. For instance, | |
1108 | @code{mode_line_format} stores the value of @code{mode-line-format}. | |
b8d4c8d0 GM |
1109 | |
1110 | @item last_selected_window | |
1111 | This is the last window that was selected with this buffer in it, or @code{nil} | |
1112 | if that window no longer displays this buffer. | |
b8d4c8d0 GM |
1113 | @end table |
1114 | ||
1115 | @node Window Internals | |
520f2425 | 1116 | @subsection Window Internals |
b8d4c8d0 GM |
1117 | @cindex internals, of window |
1118 | @cindex window internals | |
1119 | ||
7d2d7cc0 GM |
1120 | The fields of a window (for a complete list, see the definition of |
1121 | @code{struct window} in @file{window.h}) include: | |
b8d4c8d0 GM |
1122 | |
1123 | @table @code | |
1124 | @item frame | |
1125 | The frame that this window is on. | |
1126 | ||
1127 | @item mini_p | |
1128 | Non-@code{nil} if this window is a minibuffer window. | |
1129 | ||
1130 | @item parent | |
1131 | Internally, Emacs arranges windows in a tree; each group of siblings has | |
1132 | a parent window whose area includes all the siblings. This field points | |
1133 | to a window's parent. | |
1134 | ||
1135 | Parent windows do not display buffers, and play little role in display | |
1136 | except to shape their child windows. Emacs Lisp programs usually have | |
1137 | no access to the parent windows; they operate on the windows at the | |
1138 | leaves of the tree, which actually display buffers. | |
1139 | ||
b8d4c8d0 | 1140 | @item hchild |
ee2d5b5e CY |
1141 | @itemx vchild |
1142 | These fields contain the window's leftmost child and its topmost child | |
1143 | respectively. @code{hchild} is used if the window is subdivided | |
1144 | horizontally by child windows, and @code{vchild} if it is subdivided | |
7d2d7cc0 | 1145 | vertically. In a live window, only one of @code{hchild}, @code{vchild}, |
1df7defd | 1146 | and @code{buffer} (q.v.@:) is non-@code{nil}. |
b8d4c8d0 GM |
1147 | |
1148 | @item next | |
ee2d5b5e CY |
1149 | @itemx prev |
1150 | The next sibling and previous sibling of this window. @code{next} is | |
520f2425 GM |
1151 | @code{nil} if the window is the right-most or bottom-most in its group; |
1152 | @code{prev} is @code{nil} if it is the left-most or top-most in its | |
ee2d5b5e CY |
1153 | group. |
1154 | ||
1155 | @item left_col | |
1156 | The left-hand edge of the window, measured in columns, relative to the | |
1157 | leftmost column in the frame (column 0). | |
1158 | ||
1159 | @item top_line | |
1160 | The top edge of the window, measured in lines, relative to the topmost | |
1161 | line in the frame (line 0). | |
1162 | ||
1163 | @item total_cols | |
1164 | @itemx total_lines | |
1165 | The width and height of the window, measured in columns and lines | |
1166 | respectively. The width includes the scroll bar and fringes, and/or | |
1167 | the separator line on the right of the window (if any). | |
b8d4c8d0 GM |
1168 | |
1169 | @item buffer | |
ee2d5b5e | 1170 | The buffer that the window is displaying. |
b8d4c8d0 GM |
1171 | |
1172 | @item start | |
ee2d5b5e CY |
1173 | A marker pointing to the position in the buffer that is the first |
1174 | character displayed in the window. | |
b8d4c8d0 GM |
1175 | |
1176 | @item pointm | |
1177 | @cindex window point internals | |
1178 | This is the value of point in the current buffer when this window is | |
1179 | selected; when it is not selected, it retains its previous value. | |
1180 | ||
1181 | @item force_start | |
1182 | If this flag is non-@code{nil}, it says that the window has been | |
1183 | scrolled explicitly by the Lisp program. This affects what the next | |
1184 | redisplay does if point is off the screen: instead of scrolling the | |
1185 | window to show the text around point, it moves point to a location that | |
1186 | is on the screen. | |
1187 | ||
1188 | @item frozen_window_start_p | |
1189 | This field is set temporarily to 1 to indicate to redisplay that | |
1190 | @code{start} of this window should not be changed, even if point | |
1191 | gets invisible. | |
1192 | ||
1193 | @item start_at_line_beg | |
1194 | Non-@code{nil} means current value of @code{start} was the beginning of a line | |
1195 | when it was chosen. | |
1196 | ||
b8d4c8d0 GM |
1197 | @item use_time |
1198 | This is the last time that the window was selected. The function | |
1199 | @code{get-lru-window} uses this field. | |
1200 | ||
1201 | @item sequence_number | |
1202 | A unique number assigned to this window when it was created. | |
1203 | ||
1204 | @item last_modified | |
1205 | The @code{modiff} field of the window's buffer, as of the last time | |
1206 | a redisplay completed in this window. | |
1207 | ||
1208 | @item last_overlay_modified | |
1209 | The @code{overlay_modiff} field of the window's buffer, as of the last | |
1210 | time a redisplay completed in this window. | |
1211 | ||
1212 | @item last_point | |
1213 | The buffer's value of point, as of the last time a redisplay completed | |
1214 | in this window. | |
1215 | ||
1216 | @item last_had_star | |
1217 | A non-@code{nil} value means the window's buffer was ``modified'' when the | |
1218 | window was last updated. | |
1219 | ||
1220 | @item vertical_scroll_bar | |
1221 | This window's vertical scroll bar. | |
1222 | ||
7d2d7cc0 GM |
1223 | @item left_margin_cols |
1224 | @itemx right_margin_cols | |
ee2d5b5e | 1225 | The widths of the left and right margins in this window. A value of |
7d2d7cc0 GM |
1226 | @code{nil} means no margin. |
1227 | ||
1228 | @item left_fringe_width | |
1229 | @itemx right_fringe_width | |
1230 | The widths of the left and right fringes in this window. A value of | |
1231 | @code{nil} or @code{t} means use the values of the frame. | |
1232 | ||
1233 | @item fringes_outside_margins | |
1234 | A non-@code{nil} value means the fringes outside the display margins; | |
1235 | othersize they are between the margin and the text. | |
b8d4c8d0 GM |
1236 | |
1237 | @item window_end_pos | |
1238 | This is computed as @code{z} minus the buffer position of the last glyph | |
1239 | in the current matrix of the window. The value is only valid if | |
1240 | @code{window_end_valid} is not @code{nil}. | |
1241 | ||
1242 | @item window_end_bytepos | |
1243 | The byte position corresponding to @code{window_end_pos}. | |
1244 | ||
1245 | @item window_end_vpos | |
1246 | The window-relative vertical position of the line containing | |
1247 | @code{window_end_pos}. | |
1248 | ||
1249 | @item window_end_valid | |
1250 | This field is set to a non-@code{nil} value if @code{window_end_pos} is truly | |
7d2d7cc0 | 1251 | valid. This is @code{nil} if nontrivial redisplay is pre-empted, since in that |
b8d4c8d0 GM |
1252 | case the display that @code{window_end_pos} was computed for did not get |
1253 | onto the screen. | |
1254 | ||
b8d4c8d0 GM |
1255 | @item cursor |
1256 | A structure describing where the cursor is in this window. | |
1257 | ||
1258 | @item last_cursor | |
1259 | The value of @code{cursor} as of the last redisplay that finished. | |
1260 | ||
1261 | @item phys_cursor | |
1262 | A structure describing where the cursor of this window physically is. | |
1263 | ||
1264 | @item phys_cursor_type | |
7d2d7cc0 GM |
1265 | @c FIXME What is this? |
1266 | @c itemx phys_cursor_ascent | |
1267 | @itemx phys_cursor_height | |
1268 | @itemx phys_cursor_width | |
1269 | The type, height, and width of the cursor that was last displayed on | |
1270 | this window. | |
b8d4c8d0 GM |
1271 | |
1272 | @item phys_cursor_on_p | |
1273 | This field is non-zero if the cursor is physically on. | |
1274 | ||
1275 | @item cursor_off_p | |
7d2d7cc0 GM |
1276 | Non-zero means the cursor in this window is logically off. This is |
1277 | used for blinking the cursor. | |
b8d4c8d0 GM |
1278 | |
1279 | @item last_cursor_off_p | |
1280 | This field contains the value of @code{cursor_off_p} as of the time of | |
1281 | the last redisplay. | |
1282 | ||
1283 | @item must_be_updated_p | |
1284 | This is set to 1 during redisplay when this window must be updated. | |
1285 | ||
1286 | @item hscroll | |
1287 | This is the number of columns that the display in the window is scrolled | |
1288 | horizontally to the left. Normally, this is 0. | |
1289 | ||
1290 | @item vscroll | |
1291 | Vertical scroll amount, in pixels. Normally, this is 0. | |
1292 | ||
1293 | @item dedicated | |
1294 | Non-@code{nil} if this window is dedicated to its buffer. | |
1295 | ||
1296 | @item display_table | |
1297 | The window's display table, or @code{nil} if none is specified for it. | |
1298 | ||
1299 | @item update_mode_line | |
1300 | Non-@code{nil} means this window's mode line needs to be updated. | |
1301 | ||
1302 | @item base_line_number | |
1303 | The line number of a certain position in the buffer, or @code{nil}. | |
1304 | This is used for displaying the line number of point in the mode line. | |
1305 | ||
1306 | @item base_line_pos | |
1307 | The position in the buffer for which the line number is known, or | |
7d2d7cc0 GM |
1308 | @code{nil} meaning none is known. If it is a buffer, don't display |
1309 | the line number as long as the window shows that buffer. | |
b8d4c8d0 GM |
1310 | |
1311 | @item region_showing | |
1312 | If the region (or part of it) is highlighted in this window, this field | |
1313 | holds the mark position that made one end of that region. Otherwise, | |
1314 | this field is @code{nil}. | |
1315 | ||
1316 | @item column_number_displayed | |
1317 | The column number currently displayed in this window's mode line, or @code{nil} | |
1318 | if column numbers are not being displayed. | |
1319 | ||
1320 | @item current_matrix | |
7d2d7cc0 GM |
1321 | @itemx desired_matrix |
1322 | Glyph matrices describing the current and desired display of this window. | |
b8d4c8d0 GM |
1323 | @end table |
1324 | ||
1325 | @node Process Internals | |
520f2425 | 1326 | @subsection Process Internals |
b8d4c8d0 GM |
1327 | @cindex internals, of process |
1328 | @cindex process internals | |
1329 | ||
7d2d7cc0 GM |
1330 | The fields of a process (for a complete list, see the definition of |
1331 | @code{struct Lisp_Process} in @file{process.h}) include: | |
b8d4c8d0 GM |
1332 | |
1333 | @table @code | |
1334 | @item name | |
1335 | A string, the name of the process. | |
1336 | ||
1337 | @item command | |
1338 | A list containing the command arguments that were used to start this | |
c73e02fa GM |
1339 | process. For a network or serial process, it is @code{nil} if the |
1340 | process is running or @code{t} if the process is stopped. | |
b8d4c8d0 GM |
1341 | |
1342 | @item filter | |
7d2d7cc0 GM |
1343 | If non-@code{nil}, a function used to accept output from the process |
1344 | instead of a buffer. | |
b8d4c8d0 GM |
1345 | |
1346 | @item sentinel | |
7d2d7cc0 GM |
1347 | If non-@code{nil}, a function called whenever the state of the process |
1348 | changes. | |
b8d4c8d0 GM |
1349 | |
1350 | @item buffer | |
1351 | The associated buffer of the process. | |
1352 | ||
1353 | @item pid | |
1354 | An integer, the operating system's process @acronym{ID}. | |
7d2d7cc0 | 1355 | Pseudo-processes such as network or serial connections use a value of 0. |
b8d4c8d0 GM |
1356 | |
1357 | @item childp | |
7d2d7cc0 GM |
1358 | A flag, @code{t} if this is really a child process. For a network or |
1359 | serial connection, it is a plist based on the arguments to | |
1360 | @code{make-network-process} or @code{make-serial-process}. | |
b8d4c8d0 GM |
1361 | |
1362 | @item mark | |
1363 | A marker indicating the position of the end of the last output from this | |
1364 | process inserted into the buffer. This is often but not always the end | |
1365 | of the buffer. | |
1366 | ||
1367 | @item kill_without_query | |
ee2d5b5e CY |
1368 | If this is non-zero, killing Emacs while this process is still running |
1369 | does not ask for confirmation about killing the process. | |
b8d4c8d0 | 1370 | |
7d2d7cc0 GM |
1371 | @item raw_status |
1372 | The raw process status, as returned by the @code{wait} system call. | |
b8d4c8d0 GM |
1373 | |
1374 | @item status | |
1375 | The process status, as @code{process-status} should return it. | |
1376 | ||
1377 | @item tick | |
1378 | @itemx update_tick | |
1379 | If these two fields are not equal, a change in the status of the process | |
1380 | needs to be reported, either by running the sentinel or by inserting a | |
1381 | message in the process buffer. | |
1382 | ||
1383 | @item pty_flag | |
a2eb421b | 1384 | Non-@code{nil} if communication with the subprocess uses a pty; |
b8d4c8d0 GM |
1385 | @code{nil} if it uses a pipe. |
1386 | ||
1387 | @item infd | |
1388 | The file descriptor for input from the process. | |
1389 | ||
1390 | @item outfd | |
1391 | The file descriptor for output to the process. | |
1392 | ||
b8d4c8d0 GM |
1393 | @item tty_name |
1394 | The name of the terminal that the subprocess is using, | |
1395 | or @code{nil} if it is using pipes. | |
1396 | ||
1397 | @item decode_coding_system | |
1398 | Coding-system for decoding the input from this process. | |
1399 | ||
1400 | @item decoding_buf | |
1401 | A working buffer for decoding. | |
1402 | ||
1403 | @item decoding_carryover | |
1404 | Size of carryover in decoding. | |
1405 | ||
1406 | @item encode_coding_system | |
1407 | Coding-system for encoding the output to this process. | |
1408 | ||
1409 | @item encoding_buf | |
1410 | A working buffer for encoding. | |
1411 | ||
b8d4c8d0 GM |
1412 | @item inherit_coding_system_flag |
1413 | Flag to set @code{coding-system} of the process buffer from the | |
1414 | coding system used to decode process output. | |
c73e02fa GM |
1415 | |
1416 | @item type | |
1417 | Symbol indicating the type of process: @code{real}, @code{network}, | |
7d2d7cc0 | 1418 | @code{serial}. |
c73e02fa | 1419 | |
b8d4c8d0 | 1420 | @end table |
7d2d7cc0 GM |
1421 | |
1422 | @c FIXME Mention src/globals.h somewhere in this file? |