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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
651f374c TTN |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1998, 1999, 2002, 2003, 2004, |
4 | @c 2005 Free Software Foundation, Inc. | |
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5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/internals | |
7 | @node GNU Emacs Internals, Standard Errors, Tips, Top | |
8 | @comment node-name, next, previous, up | |
9 | @appendix GNU Emacs Internals | |
10 | ||
11 | This chapter describes how the runnable Emacs executable is dumped with | |
12 | the preloaded Lisp libraries in it, how storage is allocated, and some | |
13 | internal aspects of GNU Emacs that may be of interest to C programmers. | |
14 | ||
15 | @menu | |
2a233172 | 16 | * Building Emacs:: How the dumped Emacs is made. |
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17 | * Pure Storage:: A kludge to make preloaded Lisp functions sharable. |
18 | * Garbage Collection:: Reclaiming space for Lisp objects no longer used. | |
969fe9b5 | 19 | * Memory Usage:: Info about total size of Lisp objects made so far. |
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20 | * Writing Emacs Primitives:: Writing C code for Emacs. |
21 | * Object Internals:: Data formats of buffers, windows, processes. | |
22 | @end menu | |
23 | ||
969fe9b5 | 24 | @node Building Emacs |
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25 | @appendixsec Building Emacs |
26 | @cindex building Emacs | |
27 | @pindex temacs | |
28 | ||
29 | This section explains the steps involved in building the Emacs | |
30 | executable. You don't have to know this material to build and install | |
31 | Emacs, since the makefiles do all these things automatically. This | |
32 | information is pertinent to Emacs maintenance. | |
33 | ||
34 | Compilation of the C source files in the @file{src} directory | |
35 | produces an executable file called @file{temacs}, also called a | |
36 | @dfn{bare impure Emacs}. It contains the Emacs Lisp interpreter and I/O | |
37 | routines, but not the editing commands. | |
38 | ||
39 | @cindex @file{loadup.el} | |
40 | The command @w{@samp{temacs -l loadup}} uses @file{temacs} to create | |
41 | the real runnable Emacs executable. These arguments direct | |
42 | @file{temacs} to evaluate the Lisp files specified in the file | |
43 | @file{loadup.el}. These files set up the normal Emacs editing | |
574efc83 | 44 | environment, resulting in an Emacs that is still impure but no longer |
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45 | bare. |
46 | ||
47 | It takes a substantial time to load the standard Lisp files. Luckily, | |
48 | you don't have to do this each time you run Emacs; @file{temacs} can | |
574efc83 | 49 | dump out an executable program called @file{emacs} that has these files |
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50 | preloaded. @file{emacs} starts more quickly because it does not need to |
51 | load the files. This is the Emacs executable that is normally | |
52 | installed. | |
53 | ||
54 | To create @file{emacs}, use the command @samp{temacs -batch -l loadup | |
55 | dump}. The purpose of @samp{-batch} here is to prevent @file{temacs} | |
56 | from trying to initialize any of its data on the terminal; this ensures | |
57 | that the tables of terminal information are empty in the dumped Emacs. | |
58 | The argument @samp{dump} tells @file{loadup.el} to dump a new executable | |
59 | named @file{emacs}. | |
60 | ||
61 | Some operating systems don't support dumping. On those systems, you | |
62 | must start Emacs with the @samp{temacs -l loadup} command each time you | |
a890e1b0 RS |
63 | use it. This takes a substantial time, but since you need to start |
64 | Emacs once a day at most---or once a week if you never log out---the | |
65 | extra time is not too severe a problem. | |
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66 | |
67 | @cindex @file{site-load.el} | |
95260b26 | 68 | |
a44af9f2 | 69 | You can specify additional files to preload by writing a library named |
95260b26 GM |
70 | @file{site-load.el} that loads them. You may need to add a definition |
71 | ||
72 | @example | |
73 | #define SITELOAD_PURESIZE_EXTRA @var{n} | |
74 | @end example | |
75 | ||
76 | @noindent | |
77 | to make @var{n} added bytes of pure space to hold the additional files. | |
78 | (Try adding increments of 20000 until it is big enough.) However, the | |
79 | advantage of preloading additional files decreases as machines get | |
80 | faster. On modern machines, it is usually not advisable. | |
a44af9f2 | 81 | |
2a664e73 RS |
82 | After @file{loadup.el} reads @file{site-load.el}, it finds the |
83 | documentation strings for primitive and preloaded functions (and | |
568ffbee LT |
84 | variables) in the file @file{etc/DOC} where they are stored, by |
85 | calling @code{Snarf-documentation} (@pxref{Definition of | |
86 | Snarf-documentation,, Accessing Documentation}). | |
2a664e73 | 87 | |
a44af9f2 | 88 | @cindex @file{site-init.el} |
a890e1b0 | 89 | You can specify other Lisp expressions to execute just before dumping |
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90 | by putting them in a library named @file{site-init.el}. This file is |
91 | executed after the documentation strings are found. | |
a44af9f2 | 92 | |
2a664e73 RS |
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 | |
107 | Specify a non-@code{nil} value for | |
8241495d | 108 | @code{byte-compile-dynamic-docstrings} as a local variable in each of these |
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109 | files, and load them with either @file{site-load.el} or |
110 | @file{site-init.el}. (This method has the drawback that the | |
111 | documentation strings take up space in Emacs all the time.) | |
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 | |
8241495d | 118 | users can override your changes if they wish. @xref{Startup Summary}. |
a44af9f2 | 119 | |
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120 | In a package that can be preloaded, it is sometimes useful to |
121 | specify a computation to be done when Emacs subsequently starts up. | |
122 | For this, use @code{eval-at-startup}: | |
123 | ||
6d1e17be | 124 | @defmac eval-at-startup body@dots{} |
55f77e1c RS |
125 | This evaluates the @var{body} forms, either immediately if running in |
126 | an Emacs that has already started up, or later when Emacs does start | |
127 | up. Since the value of the @var{body} forms is not necessarily | |
128 | available when the @code{eval-at-startup} form is run, that form | |
129 | always returns @code{nil}. | |
6d1e17be | 130 | @end defmac |
55f77e1c | 131 | |
a44af9f2 RS |
132 | @defun dump-emacs to-file from-file |
133 | @cindex unexec | |
cb017dde | 134 | This function dumps the current state of Emacs into an executable file |
a44af9f2 RS |
135 | @var{to-file}. It takes symbols from @var{from-file} (this is normally |
136 | the executable file @file{temacs}). | |
137 | ||
cb017dde RS |
138 | If you want to use this function in an Emacs that was already dumped, |
139 | you must run Emacs with @samp{-batch}. | |
a44af9f2 RS |
140 | @end defun |
141 | ||
969fe9b5 | 142 | @node Pure Storage |
a44af9f2 RS |
143 | @appendixsec Pure Storage |
144 | @cindex pure storage | |
145 | ||
a890e1b0 RS |
146 | Emacs Lisp uses two kinds of storage for user-created Lisp objects: |
147 | @dfn{normal storage} and @dfn{pure storage}. Normal storage is where | |
8241495d | 148 | all the new data created during an Emacs session are kept; see the |
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149 | following section for information on normal storage. Pure storage is |
150 | used for certain data in the preloaded standard Lisp files---data that | |
151 | should never change during actual use of Emacs. | |
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152 | |
153 | Pure storage is allocated only while @file{temacs} is loading the | |
154 | standard preloaded Lisp libraries. In the file @file{emacs}, it is | |
574efc83 | 155 | marked as read-only (on operating systems that permit this), so that |
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156 | the memory space can be shared by all the Emacs jobs running on the |
157 | machine at once. Pure storage is not expandable; a fixed amount is | |
158 | allocated when Emacs is compiled, and if that is not sufficient for the | |
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159 | preloaded libraries, @file{temacs} crashes. If that happens, you must |
160 | increase the compilation parameter @code{PURESIZE} in the file | |
a44af9f2 RS |
161 | @file{src/puresize.h}. This normally won't happen unless you try to |
162 | preload additional libraries or add features to the standard ones. | |
163 | ||
164 | @defun purecopy object | |
8241495d RS |
165 | This function makes a copy in pure storage of @var{object}, and returns |
166 | it. It copies a string by simply making a new string with the same | |
568ffbee LT |
167 | characters, but without text properties, in pure storage. It |
168 | recursively copies the contents of vectors and cons cells. It does | |
169 | not make copies of other objects such as symbols, but just returns | |
170 | them unchanged. It signals an error if asked to copy markers. | |
a44af9f2 | 171 | |
c2cd5fb7 RS |
172 | This function is a no-op except while Emacs is being built and dumped; |
173 | it is usually called only in the file @file{emacs/lisp/loaddefs.el}, but | |
174 | a few packages call it just in case you decide to preload them. | |
a44af9f2 RS |
175 | @end defun |
176 | ||
177 | @defvar pure-bytes-used | |
a890e1b0 | 178 | The value of this variable is the number of bytes of pure storage |
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179 | allocated so far. Typically, in a dumped Emacs, this number is very |
180 | close to the total amount of pure storage available---if it were not, | |
181 | we would preallocate less. | |
182 | @end defvar | |
183 | ||
184 | @defvar purify-flag | |
a890e1b0 | 185 | This variable determines whether @code{defun} should make a copy of the |
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186 | function definition in pure storage. If it is non-@code{nil}, then the |
187 | function definition is copied into pure storage. | |
188 | ||
a890e1b0 | 189 | This flag is @code{t} while loading all of the basic functions for |
a44af9f2 | 190 | building Emacs initially (allowing those functions to be sharable and |
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191 | non-collectible). Dumping Emacs as an executable always writes |
192 | @code{nil} in this variable, regardless of the value it actually has | |
193 | before and after dumping. | |
a44af9f2 | 194 | |
a890e1b0 | 195 | You should not change this flag in a running Emacs. |
a44af9f2 RS |
196 | @end defvar |
197 | ||
969fe9b5 | 198 | @node Garbage Collection |
a44af9f2 RS |
199 | @appendixsec Garbage Collection |
200 | @cindex garbage collector | |
201 | ||
202 | @cindex memory allocation | |
203 | When a program creates a list or the user defines a new function (such | |
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204 | as by loading a library), that data is placed in normal storage. If |
205 | normal storage runs low, then Emacs asks the operating system to | |
a44af9f2 | 206 | allocate more memory in blocks of 1k bytes. Each block is used for one |
a890e1b0 RS |
207 | type of Lisp object, so symbols, cons cells, markers, etc., are |
208 | segregated in distinct blocks in memory. (Vectors, long strings, | |
209 | buffers and certain other editing types, which are fairly large, are | |
210 | allocated in individual blocks, one per object, while small strings are | |
211 | packed into blocks of 8k bytes.) | |
212 | ||
213 | It is quite common to use some storage for a while, then release it by | |
214 | (for example) killing a buffer or deleting the last pointer to an | |
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215 | object. Emacs provides a @dfn{garbage collector} to reclaim this |
216 | abandoned storage. (This name is traditional, but ``garbage recycler'' | |
217 | might be a more intuitive metaphor for this facility.) | |
218 | ||
a890e1b0 RS |
219 | The garbage collector operates by finding and marking all Lisp objects |
220 | that are still accessible to Lisp programs. To begin with, it assumes | |
221 | all the symbols, their values and associated function definitions, and | |
574efc83 | 222 | any data presently on the stack, are accessible. Any objects that can |
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223 | be reached indirectly through other accessible objects are also |
224 | accessible. | |
a44af9f2 | 225 | |
a890e1b0 | 226 | When marking is finished, all objects still unmarked are garbage. No |
a44af9f2 | 227 | matter what the Lisp program or the user does, it is impossible to refer |
a890e1b0 | 228 | to them, since there is no longer a way to reach them. Their space |
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229 | might as well be reused, since no one will miss them. The second |
230 | (``sweep'') phase of the garbage collector arranges to reuse them. | |
a44af9f2 | 231 | |
05aea714 | 232 | @c ??? Maybe add something describing weak hash tables here? |
95260b26 | 233 | |
a44af9f2 | 234 | @cindex free list |
a890e1b0 RS |
235 | The sweep phase puts unused cons cells onto a @dfn{free list} |
236 | for future allocation; likewise for symbols and markers. It compacts | |
237 | the accessible strings so they occupy fewer 8k blocks; then it frees the | |
574efc83 | 238 | other 8k blocks. Vectors, buffers, windows, and other large objects are |
a890e1b0 | 239 | individually allocated and freed using @code{malloc} and @code{free}. |
a44af9f2 RS |
240 | |
241 | @cindex CL note---allocate more storage | |
242 | @quotation | |
574efc83 | 243 | @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not |
a44af9f2 RS |
244 | call the garbage collector when the free list is empty. Instead, it |
245 | simply requests the operating system to allocate more storage, and | |
246 | processing continues until @code{gc-cons-threshold} bytes have been | |
247 | used. | |
248 | ||
249 | This means that you can make sure that the garbage collector will not | |
250 | run during a certain portion of a Lisp program by calling the garbage | |
251 | collector explicitly just before it (provided that portion of the | |
252 | program does not use so much space as to force a second garbage | |
253 | collection). | |
254 | @end quotation | |
255 | ||
256 | @deffn Command garbage-collect | |
a890e1b0 | 257 | This command runs a garbage collection, and returns information on |
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258 | the amount of space in use. (Garbage collection can also occur |
259 | spontaneously if you use more than @code{gc-cons-threshold} bytes of | |
260 | Lisp data since the previous garbage collection.) | |
261 | ||
a890e1b0 | 262 | @code{garbage-collect} returns a list containing the following |
a44af9f2 RS |
263 | information: |
264 | ||
a890e1b0 | 265 | @example |
a44af9f2 RS |
266 | @group |
267 | ((@var{used-conses} . @var{free-conses}) | |
268 | (@var{used-syms} . @var{free-syms}) | |
a890e1b0 | 269 | @end group |
969fe9b5 | 270 | (@var{used-miscs} . @var{free-miscs}) |
40d48fe9 | 271 | @var{used-string-chars} |
a44af9f2 | 272 | @var{used-vector-slots} |
f9f59935 | 273 | (@var{used-floats} . @var{free-floats}) |
40d48fe9 EZ |
274 | (@var{used-intervals} . @var{free-intervals}) |
275 | (@var{used-strings} . @var{free-strings})) | |
969fe9b5 RS |
276 | @end example |
277 | ||
278 | Here is an example: | |
279 | ||
280 | @example | |
a890e1b0 | 281 | @group |
a44af9f2 | 282 | (garbage-collect) |
f9f59935 RS |
283 | @result{} ((106886 . 13184) (9769 . 0) |
284 | (7731 . 4651) 347543 121628 | |
40d48fe9 EZ |
285 | (31 . 94) (1273 . 168) |
286 | (25474 . 3569)) | |
a44af9f2 | 287 | @end group |
a890e1b0 | 288 | @end example |
a44af9f2 RS |
289 | |
290 | Here is a table explaining each element: | |
291 | ||
292 | @table @var | |
293 | @item used-conses | |
294 | The number of cons cells in use. | |
295 | ||
296 | @item free-conses | |
297 | The number of cons cells for which space has been obtained from the | |
298 | operating system, but that are not currently being used. | |
299 | ||
300 | @item used-syms | |
301 | The number of symbols in use. | |
302 | ||
303 | @item free-syms | |
304 | The number of symbols for which space has been obtained from the | |
305 | operating system, but that are not currently being used. | |
306 | ||
969fe9b5 RS |
307 | @item used-miscs |
308 | The number of miscellaneous objects in use. These include markers and | |
309 | overlays, plus certain objects not visible to users. | |
a44af9f2 | 310 | |
969fe9b5 RS |
311 | @item free-miscs |
312 | The number of miscellaneous objects for which space has been obtained | |
313 | from the operating system, but that are not currently being used. | |
a44af9f2 RS |
314 | |
315 | @item used-string-chars | |
316 | The total size of all strings, in characters. | |
317 | ||
318 | @item used-vector-slots | |
319 | The total number of elements of existing vectors. | |
320 | ||
321 | @item used-floats | |
322 | @c Emacs 19 feature | |
323 | The number of floats in use. | |
324 | ||
325 | @item free-floats | |
326 | @c Emacs 19 feature | |
327 | The number of floats for which space has been obtained from the | |
328 | operating system, but that are not currently being used. | |
a9f0a989 RS |
329 | |
330 | @item used-intervals | |
331 | The number of intervals in use. Intervals are an internal | |
332 | data structure used for representing text properties. | |
333 | ||
334 | @item free-intervals | |
335 | The number of intervals for which space has been obtained | |
336 | from the operating system, but that are not currently being used. | |
40d48fe9 EZ |
337 | |
338 | @item used-strings | |
339 | The number of strings in use. | |
340 | ||
341 | @item free-strings | |
342 | The number of string headers for which the space was obtained from the | |
343 | operating system, but which are currently not in use. (A string | |
344 | object consists of a header and the storage for the string text | |
345 | itself; the latter is only allocated when the string is created.) | |
a44af9f2 RS |
346 | @end table |
347 | @end deffn | |
348 | ||
d64c55d8 RS |
349 | @defopt garbage-collection-messages |
350 | If this variable is non-@code{nil}, Emacs displays a message at the | |
351 | beginning and end of garbage collection. The default value is | |
352 | @code{nil}, meaning there are no such messages. | |
353 | @end defopt | |
354 | ||
e73c3ec4 RS |
355 | @defvar post-gc-hook |
356 | This is a normal hook that is run at the end of garbage collection. | |
357 | Garbage collection is inhibited while the hook functions run, so be | |
358 | careful writing them. | |
359 | @end defvar | |
360 | ||
a44af9f2 | 361 | @defopt gc-cons-threshold |
a890e1b0 | 362 | The value of this variable is the number of bytes of storage that must |
a44af9f2 | 363 | be allocated for Lisp objects after one garbage collection in order to |
a890e1b0 | 364 | trigger another garbage collection. A cons cell counts as eight bytes, |
a44af9f2 | 365 | a string as one byte per character plus a few bytes of overhead, and so |
a890e1b0 RS |
366 | on; space allocated to the contents of buffers does not count. Note |
367 | that the subsequent garbage collection does not happen immediately when | |
368 | the threshold is exhausted, but only the next time the Lisp evaluator is | |
a44af9f2 RS |
369 | called. |
370 | ||
f9f59935 | 371 | The initial threshold value is 400,000. If you specify a larger |
a44af9f2 RS |
372 | value, garbage collection will happen less often. This reduces the |
373 | amount of time spent garbage collecting, but increases total memory use. | |
574efc83 | 374 | You may want to do this when running a program that creates lots of |
a44af9f2 RS |
375 | Lisp data. |
376 | ||
a890e1b0 | 377 | You can make collections more frequent by specifying a smaller value, |
a44af9f2 RS |
378 | down to 10,000. A value less than 10,000 will remain in effect only |
379 | until the subsequent garbage collection, at which time | |
380 | @code{garbage-collect} will set the threshold back to 10,000. | |
0c17e67c SM |
381 | @end defopt |
382 | ||
383 | @defopt gc-cons-percentage | |
6696f2a4 RS |
384 | The value of this variable specifies the amount of consing before a |
385 | garbage collection occurs, as a fraction of the current heap size. | |
386 | This criterion and @code{gc-cons-threshold} apply in parallel, and | |
387 | garbage collection occurs only when both criteria are satisfied. | |
0c17e67c SM |
388 | |
389 | As the heap size increases, the time to perform a garbage collection | |
6696f2a4 RS |
390 | increases. Thus, it can be desirable to do them less frequently in |
391 | proportion. | |
a44af9f2 RS |
392 | @end defopt |
393 | ||
568ffbee | 394 | The value returned by @code{garbage-collect} describes the amount of |
969fe9b5 RS |
395 | memory used by Lisp data, broken down by data type. By contrast, the |
396 | function @code{memory-limit} provides information on the total amount of | |
397 | memory Emacs is currently using. | |
398 | ||
a44af9f2 RS |
399 | @c Emacs 19 feature |
400 | @defun memory-limit | |
401 | This function returns the address of the last byte Emacs has allocated, | |
402 | divided by 1024. We divide the value by 1024 to make sure it fits in a | |
403 | Lisp integer. | |
404 | ||
405 | You can use this to get a general idea of how your actions affect the | |
406 | memory usage. | |
407 | @end defun | |
408 | ||
5b2279a3 RS |
409 | @defun memory-use-counts |
410 | This returns a list of numbers that count the number of objects | |
411 | created in this Emacs session. Each of these counters increments for | |
412 | a certain kind of object. See the documentation string for details. | |
413 | @end defun | |
414 | ||
66c0f054 RS |
415 | @defvar gcs-done |
416 | This variable contains the total number of garbage collections | |
417 | done so far in this Emacs session. | |
f0514b34 | 418 | @end defvar |
66c0f054 RS |
419 | |
420 | @defvar gc-elapsed | |
421 | This variable contains the total number of seconds of elapsed time | |
422 | during garbage collection so far in this Emacs session, as a floating | |
423 | point number. | |
f0514b34 | 424 | @end defvar |
66c0f054 | 425 | |
969fe9b5 RS |
426 | @node Memory Usage |
427 | @section Memory Usage | |
428 | ||
429 | These functions and variables give information about the total amount | |
430 | of memory allocation that Emacs has done, broken down by data type. | |
431 | Note the difference between these and the values returned by | |
432 | @code{(garbage-collect)}; those count objects that currently exist, but | |
433 | these count the number or size of all allocations, including those for | |
434 | objects that have since been freed. | |
435 | ||
436 | @defvar cons-cells-consed | |
437 | The total number of cons cells that have been allocated so far | |
438 | in this Emacs session. | |
439 | @end defvar | |
440 | ||
441 | @defvar floats-consed | |
442 | The total number of floats that have been allocated so far | |
443 | in this Emacs session. | |
444 | @end defvar | |
445 | ||
446 | @defvar vector-cells-consed | |
447 | The total number of vector cells that have been allocated so far | |
448 | in this Emacs session. | |
449 | @end defvar | |
450 | ||
451 | @defvar symbols-consed | |
452 | The total number of symbols that have been allocated so far | |
453 | in this Emacs session. | |
454 | @end defvar | |
455 | ||
456 | @defvar string-chars-consed | |
457 | The total number of string characters that have been allocated so far | |
458 | in this Emacs session. | |
459 | @end defvar | |
460 | ||
461 | @defvar misc-objects-consed | |
462 | The total number of miscellaneous objects that have been allocated so | |
463 | far in this Emacs session. These include markers and overlays, plus | |
464 | certain objects not visible to users. | |
465 | @end defvar | |
466 | ||
467 | @defvar intervals-consed | |
468 | The total number of intervals that have been allocated so far | |
469 | in this Emacs session. | |
470 | @end defvar | |
471 | ||
40d48fe9 EZ |
472 | @defvar strings-consed |
473 | The total number of strings that have been allocated so far in this | |
474 | Emacs session. | |
475 | @end defvar | |
476 | ||
969fe9b5 | 477 | @node Writing Emacs Primitives |
a44af9f2 RS |
478 | @appendixsec Writing Emacs Primitives |
479 | @cindex primitive function internals | |
480 | ||
481 | Lisp primitives are Lisp functions implemented in C. The details of | |
482 | interfacing the C function so that Lisp can call it are handled by a few | |
483 | C macros. The only way to really understand how to write new C code is | |
484 | to read the source, but we can explain some things here. | |
485 | ||
486 | An example of a special form is the definition of @code{or}, from | |
487 | @file{eval.c}. (An ordinary function would have the same general | |
488 | appearance.) | |
489 | ||
490 | @cindex garbage collection protection | |
491 | @smallexample | |
492 | @group | |
493 | DEFUN ("or", For, Sor, 0, UNEVALLED, 0, | |
f1842270 RS |
494 | doc: /* Eval args until one of them yields non-nil, then return that value. |
495 | The remaining args are not evalled at all. | |
496 | If all args return nil, return nil. | |
a44af9f2 RS |
497 | @end group |
498 | @group | |
f1842270 | 499 | usage: (or CONDITIONS ...) */) |
a44af9f2 RS |
500 | (args) |
501 | Lisp_Object args; | |
502 | @{ | |
51485df2 | 503 | register Lisp_Object val = Qnil; |
a44af9f2 RS |
504 | struct gcpro gcpro1; |
505 | @end group | |
506 | ||
507 | @group | |
51485df2 | 508 | GCPRO1 (args); |
a44af9f2 RS |
509 | @end group |
510 | ||
511 | @group | |
51485df2 | 512 | while (CONSP (args)) |
a44af9f2 | 513 | @{ |
51485df2 | 514 | val = Feval (XCAR (args)); |
95260b26 | 515 | if (!NILP (val)) |
51485df2 RS |
516 | break; |
517 | args = XCDR (args); | |
a44af9f2 | 518 | @} |
a44af9f2 RS |
519 | @end group |
520 | ||
521 | @group | |
522 | UNGCPRO; | |
523 | return val; | |
524 | @} | |
525 | @end group | |
526 | @end smallexample | |
527 | ||
528 | Let's start with a precise explanation of the arguments to the | |
a890e1b0 | 529 | @code{DEFUN} macro. Here is a template for them: |
a44af9f2 RS |
530 | |
531 | @example | |
532 | DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc}) | |
533 | @end example | |
534 | ||
535 | @table @var | |
536 | @item lname | |
a890e1b0 RS |
537 | This is the name of the Lisp symbol to define as the function name; in |
538 | the example above, it is @code{or}. | |
a44af9f2 RS |
539 | |
540 | @item fname | |
541 | This is the C function name for this function. This is | |
542 | the name that is used in C code for calling the function. The name is, | |
543 | by convention, @samp{F} prepended to the Lisp name, with all dashes | |
544 | (@samp{-}) in the Lisp name changed to underscores. Thus, to call this | |
545 | function from C code, call @code{For}. Remember that the arguments must | |
546 | be of type @code{Lisp_Object}; various macros and functions for creating | |
547 | values of type @code{Lisp_Object} are declared in the file | |
548 | @file{lisp.h}. | |
549 | ||
550 | @item sname | |
551 | This is a C variable name to use for a structure that holds the data for | |
552 | the subr object that represents the function in Lisp. This structure | |
553 | conveys the Lisp symbol name to the initialization routine that will | |
554 | create the symbol and store the subr object as its definition. By | |
555 | convention, this name is always @var{fname} with @samp{F} replaced with | |
556 | @samp{S}. | |
557 | ||
558 | @item min | |
a890e1b0 RS |
559 | This is the minimum number of arguments that the function requires. The |
560 | function @code{or} allows a minimum of zero arguments. | |
a44af9f2 RS |
561 | |
562 | @item max | |
a890e1b0 RS |
563 | This is the maximum number of arguments that the function accepts, if |
564 | there is a fixed maximum. Alternatively, it can be @code{UNEVALLED}, | |
565 | indicating a special form that receives unevaluated arguments, or | |
566 | @code{MANY}, indicating an unlimited number of evaluated arguments (the | |
567 | equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are | |
568 | macros. If @var{max} is a number, it may not be less than @var{min} and | |
51485df2 | 569 | it may not be greater than eight. |
a44af9f2 RS |
570 | |
571 | @item interactive | |
572 | This is an interactive specification, a string such as might be used as | |
573 | the argument of @code{interactive} in a Lisp function. In the case of | |
574 | @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be | |
a890e1b0 RS |
575 | called interactively. A value of @code{""} indicates a function that |
576 | should receive no arguments when called interactively. | |
a44af9f2 RS |
577 | |
578 | @item doc | |
f1842270 RS |
579 | This is the documentation string. It uses C comment syntax rather |
580 | than C string syntax because comment syntax requires nothing special | |
581 | to include multiple lines. The @samp{doc:} identifies the comment | |
582 | that follows as the documentation string. The @samp{/*} and @samp{*/} | |
583 | delimiters that begin and end the comment are not part of the | |
584 | documentation string. | |
585 | ||
586 | If the last line of the documentation string begins with the keyword | |
587 | @samp{usage:}, the rest of the line is treated as the argument list | |
588 | for documentation purposes. This way, you can use different argument | |
589 | names in the documentation string from the ones used in the C code. | |
0a692803 DL |
590 | @samp{usage:} is required if the function has an unlimited number of |
591 | arguments. | |
f1842270 RS |
592 | |
593 | All the usual rules for documentation strings in Lisp code | |
594 | (@pxref{Documentation Tips}) apply to C code documentation strings | |
595 | too. | |
a44af9f2 RS |
596 | @end table |
597 | ||
a890e1b0 RS |
598 | After the call to the @code{DEFUN} macro, you must write the argument |
599 | name list that every C function must have, followed by ordinary C | |
600 | declarations for the arguments. For a function with a fixed maximum | |
601 | number of arguments, declare a C argument for each Lisp argument, and | |
574efc83 RS |
602 | give them all type @code{Lisp_Object}. When a Lisp function has no |
603 | upper limit on the number of arguments, its implementation in C actually | |
604 | receives exactly two arguments: the first is the number of Lisp | |
605 | arguments, and the second is the address of a block containing their | |
606 | values. They have types @code{int} and @w{@code{Lisp_Object *}}. | |
a44af9f2 RS |
607 | |
608 | Within the function @code{For} itself, note the use of the macros | |
609 | @code{GCPRO1} and @code{UNGCPRO}. @code{GCPRO1} is used to ``protect'' | |
610 | a variable from garbage collection---to inform the garbage collector that | |
611 | it must look in that variable and regard its contents as an accessible | |
612 | object. This is necessary whenever you call @code{Feval} or anything | |
613 | that can directly or indirectly call @code{Feval}. At such a time, any | |
614 | Lisp object that you intend to refer to again must be protected somehow. | |
615 | @code{UNGCPRO} cancels the protection of the variables that are | |
616 | protected in the current function. It is necessary to do this explicitly. | |
617 | ||
70bb4402 RS |
618 | It suffices to ensure that at least one pointer to each object is |
619 | GC-protected; as long as the object is not recycled, all pointers to | |
620 | it remain valid. So if you are sure that a local variable points to | |
621 | an object that will be preserved by some other pointer, that local | |
568ffbee LT |
622 | variable does not need a @code{GCPRO}. (Formerly, strings were an |
623 | exception to this rule; in older Emacs versions, every pointer to a | |
624 | string needed to be marked by GC.) | |
70bb4402 RS |
625 | |
626 | The macro @code{GCPRO1} protects just one local variable. If you | |
627 | want to protect two, use @code{GCPRO2} instead; repeating | |
628 | @code{GCPRO1} will not work. Macros, @code{GCPRO3}, @code{GCPRO4}, | |
629 | @code{GCPRO5}, and @code{GCPRO6} also exist. These macros implicitly | |
630 | use local variables such as @code{gcpro1}; you must declare these | |
631 | explicitly, with type @code{struct gcpro}. Thus, if you use | |
632 | @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}. | |
a890e1b0 RS |
633 | Alas, we can't explain all the tricky details here. |
634 | ||
70bb4402 RS |
635 | Built-in functions that take a variable number of arguments actually |
636 | accept two arguments at the C level: the number of Lisp arguments, and | |
637 | a @code{Lisp_Object *} pointer to a C vector containing those Lisp | |
638 | arguments. This C vector may be part of a Lisp vector, but it need | |
568ffbee | 639 | not be. The responsibility for using @code{GCPRO} to protect the Lisp |
236a1914 RS |
640 | arguments from GC if necessary rests with the caller in this case, |
641 | since the caller allocated or found the storage for them. | |
70bb4402 | 642 | |
e610024b | 643 | You must not use C initializers for static or global variables unless |
05aea714 | 644 | the variables are never written once Emacs is dumped. These variables |
8241495d RS |
645 | with initializers are allocated in an area of memory that becomes |
646 | read-only (on certain operating systems) as a result of dumping Emacs. | |
647 | @xref{Pure Storage}. | |
e610024b RS |
648 | |
649 | Do not use static variables within functions---place all static | |
650 | variables at top level in the file. This is necessary because Emacs on | |
651 | some operating systems defines the keyword @code{static} as a null | |
652 | macro. (This definition is used because those systems put all variables | |
653 | declared static in a place that becomes read-only after dumping, whether | |
654 | they have initializers or not.) | |
77223f05 | 655 | |
a890e1b0 RS |
656 | Defining the C function is not enough to make a Lisp primitive |
657 | available; you must also create the Lisp symbol for the primitive and | |
658 | store a suitable subr object in its function cell. The code looks like | |
659 | this: | |
a44af9f2 RS |
660 | |
661 | @example | |
662 | defsubr (&@var{subr-structure-name}); | |
663 | @end example | |
664 | ||
665 | @noindent | |
a890e1b0 RS |
666 | Here @var{subr-structure-name} is the name you used as the third |
667 | argument to @code{DEFUN}. | |
668 | ||
669 | If you add a new primitive to a file that already has Lisp primitives | |
670 | defined in it, find the function (near the end of the file) named | |
671 | @code{syms_of_@var{something}}, and add the call to @code{defsubr} | |
672 | there. If the file doesn't have this function, or if you create a new | |
673 | file, add to it a @code{syms_of_@var{filename}} (e.g., | |
674 | @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all | |
675 | of these functions are called, and add a call to | |
676 | @code{syms_of_@var{filename}} there. | |
a44af9f2 | 677 | |
568ffbee | 678 | @anchor{Defining Lisp variables in C} |
8241495d | 679 | @vindex byte-boolean-vars |
574efc83 RS |
680 | The function @code{syms_of_@var{filename}} is also the place to define |
681 | any C variables that are to be visible as Lisp variables. | |
a890e1b0 RS |
682 | @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible |
683 | in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int} | |
684 | visible in Lisp with a value that is always an integer. | |
685 | @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp | |
8241495d RS |
686 | with a value that is either @code{t} or @code{nil}. Note that variables |
687 | defined with @code{DEFVAR_BOOL} are automatically added to the list | |
688 | @code{byte-boolean-vars} used by the byte compiler. | |
a44af9f2 | 689 | |
969fe9b5 | 690 | If you define a file-scope C variable of type @code{Lisp_Object}, |
8241495d | 691 | you must protect it from garbage-collection by calling @code{staticpro} |
969fe9b5 RS |
692 | in @code{syms_of_@var{filename}}, like this: |
693 | ||
694 | @example | |
695 | staticpro (&@var{variable}); | |
696 | @end example | |
697 | ||
a890e1b0 | 698 | Here is another example function, with more complicated arguments. |
969fe9b5 RS |
699 | This comes from the code in @file{window.c}, and it demonstrates the use |
700 | of macros and functions to manipulate Lisp objects. | |
a44af9f2 RS |
701 | |
702 | @smallexample | |
703 | @group | |
704 | DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p, | |
705 | Scoordinates_in_window_p, 2, 2, | |
706 | "xSpecify coordinate pair: \nXExpression which evals to window: ", | |
88510b17 | 707 | "Return non-nil if COORDINATES is in WINDOW.\n\ |
969fe9b5 RS |
708 | COORDINATES is a cons of the form (X . Y), X and Y being distances\n\ |
709 | ... | |
a44af9f2 RS |
710 | @end group |
711 | @group | |
969fe9b5 RS |
712 | If they are on the border between WINDOW and its right sibling,\n\ |
713 | `vertical-line' is returned.") | |
714 | (coordinates, window) | |
715 | register Lisp_Object coordinates, window; | |
a44af9f2 | 716 | @{ |
969fe9b5 | 717 | int x, y; |
a44af9f2 RS |
718 | @end group |
719 | ||
720 | @group | |
969fe9b5 RS |
721 | CHECK_LIVE_WINDOW (window, 0); |
722 | CHECK_CONS (coordinates, 1); | |
723 | x = XINT (Fcar (coordinates)); | |
724 | y = XINT (Fcdr (coordinates)); | |
a44af9f2 | 725 | @end group |
969fe9b5 | 726 | |
a44af9f2 | 727 | @group |
969fe9b5 RS |
728 | switch (coordinates_in_window (XWINDOW (window), &x, &y)) |
729 | @{ | |
730 | case 0: /* NOT in window at all. */ | |
731 | return Qnil; | |
a44af9f2 | 732 | @end group |
969fe9b5 | 733 | |
a44af9f2 | 734 | @group |
969fe9b5 RS |
735 | case 1: /* In text part of window. */ |
736 | return Fcons (make_number (x), make_number (y)); | |
a44af9f2 | 737 | @end group |
969fe9b5 | 738 | |
a44af9f2 | 739 | @group |
969fe9b5 RS |
740 | case 2: /* In mode line of window. */ |
741 | return Qmode_line; | |
a44af9f2 | 742 | @end group |
969fe9b5 | 743 | |
a44af9f2 | 744 | @group |
969fe9b5 RS |
745 | case 3: /* On right border of window. */ |
746 | return Qvertical_line; | |
747 | @end group | |
748 | ||
749 | @group | |
750 | default: | |
751 | abort (); | |
752 | @} | |
a44af9f2 RS |
753 | @} |
754 | @end group | |
755 | @end smallexample | |
756 | ||
a890e1b0 RS |
757 | Note that C code cannot call functions by name unless they are defined |
758 | in C. The way to call a function written in Lisp is to use | |
759 | @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since | |
760 | the Lisp function @code{funcall} accepts an unlimited number of | |
761 | arguments, in C it takes two: the number of Lisp-level arguments, and a | |
762 | one-dimensional array containing their values. The first Lisp-level | |
763 | argument is the Lisp function to call, and the rest are the arguments to | |
764 | pass to it. Since @code{Ffuncall} can call the evaluator, you must | |
765 | protect pointers from garbage collection around the call to | |
766 | @code{Ffuncall}. | |
767 | ||
768 | The C functions @code{call0}, @code{call1}, @code{call2}, and so on, | |
769 | provide handy ways to call a Lisp function conveniently with a fixed | |
770 | number of arguments. They work by calling @code{Ffuncall}. | |
a44af9f2 RS |
771 | |
772 | @file{eval.c} is a very good file to look through for examples; | |
773 | @file{lisp.h} contains the definitions for some important macros and | |
774 | functions. | |
775 | ||
0a692803 DL |
776 | If you define a function which is side-effect free, update the code |
777 | in @file{byte-opt.el} which binds @code{side-effect-free-fns} and | |
778 | @code{side-effect-and-error-free-fns} so that the compiler optimizer | |
779 | knows about it. | |
8241495d | 780 | |
969fe9b5 | 781 | @node Object Internals |
a44af9f2 RS |
782 | @appendixsec Object Internals |
783 | @cindex object internals | |
784 | ||
785 | GNU Emacs Lisp manipulates many different types of data. The actual | |
f9f59935 RS |
786 | data are stored in a heap and the only access that programs have to it |
787 | is through pointers. Pointers are thirty-two bits wide in most | |
a44af9f2 | 788 | implementations. Depending on the operating system and type of machine |
568ffbee LT |
789 | for which you compile Emacs, twenty-nine bits are used to address the |
790 | object, and the remaining three bits are used for the tag that | |
791 | identifies the object's type. | |
a44af9f2 | 792 | |
a890e1b0 RS |
793 | Because Lisp objects are represented as tagged pointers, it is always |
794 | possible to determine the Lisp data type of any object. The C data type | |
795 | @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary | |
796 | variables have type @code{Lisp_Object}, which means they can hold any | |
797 | type of Lisp value; you can determine the actual data type only at run | |
798 | time. The same is true for function arguments; if you want a function | |
799 | to accept only a certain type of argument, you must check the type | |
800 | explicitly using a suitable predicate (@pxref{Type Predicates}). | |
a44af9f2 RS |
801 | @cindex type checking internals |
802 | ||
803 | @menu | |
804 | * Buffer Internals:: Components of a buffer structure. | |
805 | * Window Internals:: Components of a window structure. | |
806 | * Process Internals:: Components of a process structure. | |
807 | @end menu | |
808 | ||
969fe9b5 | 809 | @node Buffer Internals |
a44af9f2 RS |
810 | @appendixsubsec Buffer Internals |
811 | @cindex internals, of buffer | |
812 | @cindex buffer internals | |
813 | ||
814 | Buffers contain fields not directly accessible by the Lisp programmer. | |
815 | We describe them here, naming them by the names used in the C code. | |
816 | Many are accessible indirectly in Lisp programs via Lisp primitives. | |
817 | ||
95260b26 GM |
818 | Two structures are used to represent buffers in C. The |
819 | @code{buffer_text} structure contains fields describing the text of a | |
820 | buffer; the @code{buffer} structure holds other fields. In the case | |
821 | of indirect buffers, two or more @code{buffer} structures reference | |
822 | the same @code{buffer_text} structure. | |
823 | ||
824 | Here is a list of the @code{struct buffer_text} fields: | |
825 | ||
a44af9f2 | 826 | @table @code |
95260b26 | 827 | @item beg |
05aea714 | 828 | This field contains the actual address of the buffer contents. |
95260b26 | 829 | |
d7255d62 | 830 | @item gpt |
95260b26 | 831 | This holds the character position of the gap in the buffer. |
88510b17 | 832 | @xref{Buffer Gap}. |
95260b26 GM |
833 | |
834 | @item z | |
835 | This field contains the character position of the end of the buffer | |
836 | text. | |
837 | ||
838 | @item gpt_byte | |
839 | Contains the byte position of the gap. | |
840 | ||
841 | @item z_byte | |
842 | Holds the byte position of the end of the buffer text. | |
843 | ||
844 | @item gap_size | |
88510b17 | 845 | Contains the size of buffer's gap. @xref{Buffer Gap}. |
95260b26 GM |
846 | |
847 | @item modiff | |
848 | This field counts buffer-modification events for this buffer. It is | |
849 | incremented for each such event, and never otherwise changed. | |
850 | ||
851 | @item save_modiff | |
852 | Contains the previous value of @code{modiff}, as of the last time a | |
853 | buffer was visited or saved in a file. | |
88510b17 | 854 | |
95260b26 GM |
855 | @item overlay_modiff |
856 | Counts modifications to overlays analogous to @code{modiff}. | |
88510b17 | 857 | |
95260b26 GM |
858 | @item beg_unchanged |
859 | Holds the number of characters at the start of the text that are known | |
860 | to be unchanged since the last redisplay that finished. | |
88510b17 | 861 | |
95260b26 GM |
862 | @item end_unchanged |
863 | Holds the number of characters at the end of the text that are known to | |
864 | be unchanged since the last redisplay that finished. | |
88510b17 | 865 | |
95260b26 GM |
866 | @item unchanged_modified |
867 | Contains the value of @code{modiff} at the time of the last redisplay | |
868 | that finished. If this value matches @code{modiff}, | |
869 | @code{beg_unchanged} and @code{end_unchanged} contain no useful | |
870 | information. | |
88510b17 | 871 | |
95260b26 GM |
872 | @item overlay_unchanged_modified |
873 | Contains the value of @code{overlay_modiff} at the time of the last | |
874 | redisplay that finished. If this value matches @code{overlay_modiff}, | |
875 | @code{beg_unchanged} and @code{end_unchanged} contain no useful | |
876 | information. | |
88510b17 | 877 | |
95260b26 GM |
878 | @item markers |
879 | The markers that refer to this buffer. This is actually a single | |
880 | marker, and successive elements in its marker @code{chain} are the other | |
881 | markers referring to this buffer text. | |
a44af9f2 | 882 | |
95260b26 GM |
883 | @item intervals |
884 | Contains the interval tree which records the text properties of this | |
885 | buffer. | |
886 | @end table | |
887 | ||
888 | The fields of @code{struct buffer} are: | |
889 | ||
890 | @table @code | |
891 | @item next | |
892 | Points to the next buffer, in the chain of all buffers including killed | |
893 | buffers. This chain is used only for garbage collection, in order to | |
894 | collect killed buffers properly. Note that vectors, and most kinds of | |
895 | objects allocated as vectors, are all on one chain, but buffers are on a | |
896 | separate chain of their own. | |
897 | ||
898 | @item own_text | |
899 | This is a @code{struct buffer_text} structure. In an ordinary buffer, | |
900 | it holds the buffer contents. In indirect buffers, this field is not | |
901 | used. | |
902 | ||
903 | @item text | |
904 | This points to the @code{buffer_text} structure that is used for this | |
905 | buffer. In an ordinary buffer, this is the @code{own_text} field above. | |
906 | In an indirect buffer, this is the @code{own_text} field of the base | |
907 | buffer. | |
908 | ||
909 | @item pt | |
910 | Contains the character position of point in a buffer. | |
911 | ||
912 | @item pt_byte | |
913 | Contains the byte position of point in a buffer. | |
914 | ||
915 | @item begv | |
88510b17 | 916 | This field contains the character position of the beginning of the |
95260b26 GM |
917 | accessible range of text in the buffer. |
918 | ||
919 | @item begv_byte | |
88510b17 | 920 | This field contains the byte position of the beginning of the |
95260b26 GM |
921 | accessible range of text in the buffer. |
922 | ||
923 | @item zv | |
88510b17 | 924 | This field contains the character position of the end of the |
95260b26 GM |
925 | accessible range of text in the buffer. |
926 | ||
927 | @item zv_byte | |
88510b17 | 928 | This field contains the byte position of the end of the |
95260b26 GM |
929 | accessible range of text in the buffer. |
930 | ||
931 | @item base_buffer | |
932 | In an indirect buffer, this points to the base buffer. In an ordinary | |
933 | buffer, it is null. | |
934 | ||
935 | @item local_var_flags | |
936 | This field contains flags indicating that certain variables are local in | |
937 | this buffer. Such variables are declared in the C code using | |
938 | @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored in | |
939 | fields in the buffer structure itself. (Some of these fields are | |
940 | described in this table.) | |
a44af9f2 RS |
941 | |
942 | @item modtime | |
943 | This field contains the modification time of the visited file. It is | |
8241495d RS |
944 | set when the file is written or read. Before writing the buffer into a |
945 | file, this field is compared to the modification time of the file to see | |
946 | if the file has changed on disk. @xref{Buffer Modification}. | |
a44af9f2 RS |
947 | |
948 | @item auto_save_modified | |
949 | This field contains the time when the buffer was last auto-saved. | |
950 | ||
95260b26 GM |
951 | @item auto_save_failure_time |
952 | The time at which we detected a failure to auto-save, or -1 if we didn't | |
953 | have a failure. | |
954 | ||
a44af9f2 RS |
955 | @item last_window_start |
956 | This field contains the @code{window-start} position in the buffer as of | |
957 | the last time the buffer was displayed in a window. | |
958 | ||
95260b26 GM |
959 | @item clip_changed |
960 | This flag is set when narrowing changes in a buffer. | |
961 | ||
962 | @item prevent_redisplay_optimizations_p | |
88510b17 | 963 | this flag indicates that redisplay optimizations should not be used |
95260b26 GM |
964 | to display this buffer. |
965 | ||
a890e1b0 RS |
966 | @item undo_list |
967 | This field points to the buffer's undo list. @xref{Undo}. | |
a44af9f2 | 968 | |
95260b26 GM |
969 | @item name |
970 | The buffer name is a string that names the buffer. It is guaranteed to | |
971 | be unique. @xref{Buffer Names}. | |
972 | ||
973 | @item filename | |
974 | The name of the file visited in this buffer, or @code{nil}. | |
88510b17 | 975 | |
95260b26 GM |
976 | @item directory |
977 | The directory for expanding relative file names. | |
978 | ||
979 | @item save_length | |
980 | Length of the file this buffer is visiting, when last read or saved. | |
981 | This and other fields concerned with saving are not kept in the | |
982 | @code{buffer_text} structure because indirect buffers are never saved. | |
983 | ||
984 | @item auto_save_file_name | |
88510b17 | 985 | File name used for auto-saving this buffer. This is not in the |
95260b26 GM |
986 | @code{buffer_text} because it's not used in indirect buffers at all. |
987 | ||
988 | @item read_only | |
989 | Non-@code{nil} means this buffer is read-only. | |
990 | ||
991 | @item mark | |
992 | This field contains the mark for the buffer. The mark is a marker, | |
993 | hence it is also included on the list @code{markers}. @xref{The Mark}. | |
994 | ||
995 | @item local_var_alist | |
996 | This field contains the association list describing the buffer-local | |
997 | variable bindings of this buffer, not including the built-in | |
998 | buffer-local bindings that have special slots in the buffer object. | |
999 | (Those slots are omitted from this table.) @xref{Buffer-Local | |
1000 | Variables}. | |
1001 | ||
1002 | @item major_mode | |
1003 | Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}. | |
1004 | ||
1005 | @item mode_name | |
1006 | Pretty name of major mode, e.g., @code{"Lisp"}. | |
1007 | ||
1008 | @item mode_line_format | |
1009 | Mode line element that controls the format of the mode line. If this | |
1010 | is @code{nil}, no mode line will be displayed. | |
1011 | ||
1012 | @item header_line_format | |
88510b17 | 1013 | This field is analoguous to @code{mode_line_format} for the mode |
95260b26 GM |
1014 | line displayed at the top of windows. |
1015 | ||
1016 | @item keymap | |
1017 | This field holds the buffer's local keymap. @xref{Keymaps}. | |
1018 | ||
1019 | @item abbrev_table | |
1020 | This buffer's local abbrevs. | |
1021 | ||
1022 | @item syntax_table | |
a44af9f2 RS |
1023 | This field contains the syntax table for the buffer. @xref{Syntax Tables}. |
1024 | ||
95260b26 GM |
1025 | @item category_table |
1026 | This field contains the category table for the buffer. | |
1027 | ||
1028 | @item case_fold_search | |
1029 | The value of @code{case-fold-search} in this buffer. | |
1030 | ||
1031 | @item tab_width | |
1032 | The value of @code{tab-width} in this buffer. | |
1033 | ||
1034 | @item fill_column | |
1035 | The value of @code{fill-column} in this buffer. | |
1036 | ||
1037 | @item left_margin | |
1038 | The value of @code{left-margin} in this buffer. | |
1039 | ||
1040 | @item auto_fill_function | |
1041 | The value of @code{auto-fill-function} in this buffer. | |
1042 | ||
a44af9f2 RS |
1043 | @item downcase_table |
1044 | This field contains the conversion table for converting text to lower case. | |
969fe9b5 | 1045 | @xref{Case Tables}. |
a44af9f2 RS |
1046 | |
1047 | @item upcase_table | |
1048 | This field contains the conversion table for converting text to upper case. | |
969fe9b5 | 1049 | @xref{Case Tables}. |
a44af9f2 RS |
1050 | |
1051 | @item case_canon_table | |
1052 | This field contains the conversion table for canonicalizing text for | |
969fe9b5 | 1053 | case-folding search. @xref{Case Tables}. |
a44af9f2 RS |
1054 | |
1055 | @item case_eqv_table | |
1056 | This field contains the equivalence table for case-folding search. | |
969fe9b5 | 1057 | @xref{Case Tables}. |
a44af9f2 | 1058 | |
95260b26 GM |
1059 | @item truncate_lines |
1060 | The value of @code{truncate-lines} in this buffer. | |
a44af9f2 | 1061 | |
95260b26 GM |
1062 | @item ctl_arrow |
1063 | The value of @code{ctl-arrow} in this buffer. | |
a44af9f2 | 1064 | |
95260b26 GM |
1065 | @item selective_display |
1066 | The value of @code{selective-display} in this buffer. | |
a44af9f2 | 1067 | |
95260b26 GM |
1068 | @item selective_display_ellipsis |
1069 | The value of @code{selective-display-ellipsis} in this buffer. | |
a44af9f2 | 1070 | |
95260b26 GM |
1071 | @item minor_modes |
1072 | An alist of the minor modes of this buffer. | |
a890e1b0 | 1073 | |
95260b26 GM |
1074 | @item overwrite_mode |
1075 | The value of @code{overwrite_mode} in this buffer. | |
a890e1b0 | 1076 | |
95260b26 GM |
1077 | @item abbrev_mode |
1078 | The value of @code{abbrev-mode} in this buffer. | |
bfe721d1 | 1079 | |
95260b26 GM |
1080 | @item display_table |
1081 | This field contains the buffer's display table, or @code{nil} if it doesn't | |
1082 | have one. @xref{Display Tables}. | |
a890e1b0 | 1083 | |
95260b26 GM |
1084 | @item save_modified |
1085 | This field contains the time when the buffer was last saved, as an integer. | |
1086 | @xref{Buffer Modification}. | |
1087 | ||
1088 | @item mark_active | |
1089 | This field is non-@code{nil} if the buffer's mark is active. | |
a890e1b0 RS |
1090 | |
1091 | @item overlays_before | |
1092 | This field holds a list of the overlays in this buffer that end at or | |
1093 | before the current overlay center position. They are sorted in order of | |
1094 | decreasing end position. | |
1095 | ||
1096 | @item overlays_after | |
1097 | This field holds a list of the overlays in this buffer that end after | |
1098 | the current overlay center position. They are sorted in order of | |
1099 | increasing beginning position. | |
969fe9b5 | 1100 | |
95260b26 GM |
1101 | @item overlay_center |
1102 | This field holds the current overlay center position. @xref{Overlays}. | |
1103 | ||
969fe9b5 RS |
1104 | @item enable_multibyte_characters |
1105 | This field holds the buffer's local value of | |
1106 | @code{enable-multibyte-characters}---either @code{t} or @code{nil}. | |
95260b26 GM |
1107 | |
1108 | @item buffer_file_coding_system | |
1109 | The value of @code{buffer-file-coding-system} in this buffer. | |
1110 | ||
1111 | @item file_format | |
1112 | The value of @code{buffer-file-format} in this buffer. | |
1113 | ||
980aaec7 LT |
1114 | @item auto_save_file_format |
1115 | The value of @code{buffer-auto-save-file-format} in this buffer. | |
1116 | ||
95260b26 GM |
1117 | @item pt_marker |
1118 | In an indirect buffer, or a buffer that is the base of an indirect | |
1119 | buffer, this holds a marker that records point for this buffer when the | |
1120 | buffer is not current. | |
1121 | ||
1122 | @item begv_marker | |
1123 | In an indirect buffer, or a buffer that is the base of an indirect | |
1124 | buffer, this holds a marker that records @code{begv} for this buffer | |
1125 | when the buffer is not current. | |
88510b17 | 1126 | |
95260b26 GM |
1127 | @item zv_marker |
1128 | In an indirect buffer, or a buffer that is the base of an indirect | |
1129 | buffer, this holds a marker that records @code{zv} for this buffer when | |
1130 | the buffer is not current. | |
1131 | ||
1132 | @item file_truename | |
1133 | The truename of the visited file, or @code{nil}. | |
1134 | ||
1135 | @item invisibility_spec | |
1136 | The value of @code{buffer-invisibility-spec} in this buffer. | |
1137 | ||
1138 | @item last_selected_window | |
1139 | This is the last window that was selected with this buffer in it, or @code{nil} | |
1140 | if that window no longer displays this buffer. | |
1141 | ||
1142 | @item display_count | |
1143 | This field is incremented each time the buffer is displayed in a window. | |
1144 | ||
1145 | @item left_margin_width | |
1146 | The value of @code{left-margin-width} in this buffer. | |
1147 | ||
1148 | @item right_margin_width | |
1149 | The value of @code{right-margin-width} in this buffer. | |
1150 | ||
1151 | @item indicate_empty_lines | |
1152 | Non-@code{nil} means indicate empty lines (lines with no text) with a | |
1153 | small bitmap in the fringe, when using a window system that can do it. | |
1154 | ||
1155 | @item display_time | |
1156 | This holds a time stamp that is updated each time this buffer is | |
1157 | displayed in a window. | |
1158 | ||
1159 | @item scroll_up_aggressively | |
1160 | The value of @code{scroll-up-aggressively} in this buffer. | |
88510b17 | 1161 | |
95260b26 GM |
1162 | @item scroll_down_aggressively |
1163 | The value of @code{scroll-down-aggressively} in this buffer. | |
a44af9f2 RS |
1164 | @end table |
1165 | ||
969fe9b5 | 1166 | @node Window Internals |
a44af9f2 RS |
1167 | @appendixsubsec Window Internals |
1168 | @cindex internals, of window | |
1169 | @cindex window internals | |
1170 | ||
1171 | Windows have the following accessible fields: | |
1172 | ||
1173 | @table @code | |
1174 | @item frame | |
a890e1b0 | 1175 | The frame that this window is on. |
a44af9f2 RS |
1176 | |
1177 | @item mini_p | |
a890e1b0 | 1178 | Non-@code{nil} if this window is a minibuffer window. |
a44af9f2 | 1179 | |
95260b26 GM |
1180 | @item parent |
1181 | Internally, Emacs arranges windows in a tree; each group of siblings has | |
1182 | a parent window whose area includes all the siblings. This field points | |
1183 | to a window's parent. | |
1184 | ||
1185 | Parent windows do not display buffers, and play little role in display | |
1186 | except to shape their child windows. Emacs Lisp programs usually have | |
1187 | no access to the parent windows; they operate on the windows at the | |
1188 | leaves of the tree, which actually display buffers. | |
1189 | ||
1190 | The following four fields also describe the window tree structure. | |
1191 | ||
1192 | @item hchild | |
1193 | In a window subdivided horizontally by child windows, the leftmost child. | |
1194 | Otherwise, @code{nil}. | |
1195 | ||
1196 | @item vchild | |
1197 | In a window subdivided vertically by child windows, the topmost child. | |
1198 | Otherwise, @code{nil}. | |
1199 | ||
1200 | @item next | |
1201 | The next sibling of this window. It is @code{nil} in a window that is | |
1202 | the rightmost or bottommost of a group of siblings. | |
1203 | ||
1204 | @item prev | |
1205 | The previous sibling of this window. It is @code{nil} in a window that | |
1206 | is the leftmost or topmost of a group of siblings. | |
1207 | ||
1208 | @item left | |
1209 | This is the left-hand edge of the window, measured in columns. (The | |
1210 | leftmost column on the screen is @w{column 0}.) | |
1211 | ||
1212 | @item top | |
1213 | This is the top edge of the window, measured in lines. (The top line on | |
1214 | the screen is @w{line 0}.) | |
1215 | ||
1216 | @item height | |
1217 | The height of the window, measured in lines. | |
1218 | ||
1219 | @item width | |
1220 | The width of the window, measured in columns. This width includes the | |
1221 | scroll bar and fringes, and/or the separator line on the right of the | |
1222 | window (if any). | |
1223 | ||
a44af9f2 | 1224 | @item buffer |
574efc83 | 1225 | The buffer that the window is displaying. This may change often during |
a44af9f2 RS |
1226 | the life of the window. |
1227 | ||
95260b26 GM |
1228 | @item start |
1229 | The position in the buffer that is the first character to be displayed | |
1230 | in the window. | |
a44af9f2 RS |
1231 | |
1232 | @item pointm | |
1233 | @cindex window point internals | |
a890e1b0 | 1234 | This is the value of point in the current buffer when this window is |
a44af9f2 RS |
1235 | selected; when it is not selected, it retains its previous value. |
1236 | ||
a890e1b0 RS |
1237 | @item force_start |
1238 | If this flag is non-@code{nil}, it says that the window has been | |
1239 | scrolled explicitly by the Lisp program. This affects what the next | |
1240 | redisplay does if point is off the screen: instead of scrolling the | |
1241 | window to show the text around point, it moves point to a location that | |
1242 | is on the screen. | |
1243 | ||
95260b26 | 1244 | @item frozen_window_start_p |
88510b17 | 1245 | This field is set temporarily to 1 to indicate to redisplay that |
95260b26 GM |
1246 | @code{start} of this window should not be changed, even if point |
1247 | gets invisible. | |
1248 | ||
1249 | @item start_at_line_beg | |
1250 | Non-@code{nil} means current value of @code{start} was the beginning of a line | |
1251 | when it was chosen. | |
1252 | ||
1253 | @item too_small_ok | |
1254 | Non-@code{nil} means don't delete this window for becoming ``too small''. | |
1255 | ||
1256 | @item height_fixed_p | |
1257 | This field is temporarily set to 1 to fix the height of the selected | |
1258 | window when the echo area is resized. | |
1259 | ||
1260 | @item use_time | |
1261 | This is the last time that the window was selected. The function | |
1262 | @code{get-lru-window} uses this field. | |
1263 | ||
1264 | @item sequence_number | |
1265 | A unique number assigned to this window when it was created. | |
1266 | ||
a890e1b0 | 1267 | @item last_modified |
95260b26 | 1268 | The @code{modiff} field of the window's buffer, as of the last time |
a890e1b0 RS |
1269 | a redisplay completed in this window. |
1270 | ||
95260b26 GM |
1271 | @item last_overlay_modified |
1272 | The @code{overlay_modiff} field of the window's buffer, as of the last | |
1273 | time a redisplay completed in this window. | |
1274 | ||
a890e1b0 | 1275 | @item last_point |
95260b26 GM |
1276 | The buffer's value of point, as of the last time a redisplay completed |
1277 | in this window. | |
a890e1b0 | 1278 | |
95260b26 GM |
1279 | @item last_had_star |
1280 | A non-@code{nil} value means the window's buffer was ``modified'' when the | |
1281 | window was last updated. | |
a44af9f2 | 1282 | |
95260b26 GM |
1283 | @item vertical_scroll_bar |
1284 | This window's vertical scroll bar. | |
a44af9f2 | 1285 | |
95260b26 GM |
1286 | @item left_margin_width |
1287 | The width of the left margin in this window, or @code{nil} not to | |
1288 | specify it (in which case the buffer's value of @code{left-margin-width} | |
1289 | is used. | |
a890e1b0 | 1290 | |
95260b26 GM |
1291 | @item right_margin_width |
1292 | Likewise for the right margin. | |
a890e1b0 | 1293 | |
13ede7fc | 1294 | @ignore |
95260b26 GM |
1295 | @item last_mark_x |
1296 | @item last_mark_y | |
1297 | ???Not used. | |
1298 | @end ignore | |
a44af9f2 | 1299 | |
95260b26 GM |
1300 | @item window_end_pos |
1301 | This is computed as @code{z} minus the buffer position of the last glyph | |
1302 | in the current matrix of the window. The value is only valid if | |
1303 | @code{window_end_valid} is not @code{nil}. | |
a44af9f2 | 1304 | |
95260b26 GM |
1305 | @item window_end_bytepos |
1306 | The byte position corresponding to @code{window_end_pos}. | |
a890e1b0 | 1307 | |
95260b26 GM |
1308 | @item window_end_vpos |
1309 | The window-relative vertical position of the line containing | |
1310 | @code{window_end_pos}. | |
a44af9f2 | 1311 | |
95260b26 GM |
1312 | @item window_end_valid |
1313 | This field is set to a non-@code{nil} value if @code{window_end_pos} is truly | |
1314 | valid. This is @code{nil} if nontrivial redisplay is preempted since in that | |
1315 | case the display that @code{window_end_pos} was computed for did not get | |
1316 | onto the screen. | |
1317 | ||
1318 | @item redisplay_end_trigger | |
1319 | If redisplay in this window goes beyond this buffer position, it runs | |
2a233172 | 1320 | the @code{redisplay-end-trigger-hook}. |
95260b26 | 1321 | |
13ede7fc | 1322 | @ignore |
95260b26 GM |
1323 | @item orig_height |
1324 | @item orig_top | |
1325 | ??? Are temporary storage areas. | |
1326 | @end ignore | |
1327 | ||
1328 | @item cursor | |
1329 | A structure describing where the cursor is in this window. | |
1330 | ||
1331 | @item last_cursor | |
1332 | The value of @code{cursor} as of the last redisplay that finished. | |
1333 | ||
1334 | @item phys_cursor | |
1335 | A structure describing where the cursor of this window physically is. | |
1336 | ||
1337 | @item phys_cursor_type | |
1338 | The type of cursor that was last displayed on this window. | |
1339 | ||
1340 | @item phys_cursor_on_p | |
1341 | This field is non-zero if the cursor is physically on. | |
1342 | ||
1343 | @item cursor_off_p | |
1344 | Non-zero means the cursor in this window is logically on. | |
1345 | ||
1346 | @item last_cursor_off_p | |
1347 | This field contains the value of @code{cursor_off_p} as of the time of | |
1348 | the last redisplay. | |
1349 | ||
1350 | @item must_be_updated_p | |
1351 | This is set to 1 during redisplay when this window must be updated. | |
1352 | ||
a44af9f2 | 1353 | @item hscroll |
a890e1b0 | 1354 | This is the number of columns that the display in the window is scrolled |
a44af9f2 RS |
1355 | horizontally to the left. Normally, this is 0. |
1356 | ||
95260b26 GM |
1357 | @item vscroll |
1358 | Vertical scroll amount, in pixels. Normally, this is 0. | |
1359 | ||
1360 | @item dedicated | |
1361 | Non-@code{nil} if this window is dedicated to its buffer. | |
a44af9f2 RS |
1362 | |
1363 | @item display_table | |
a890e1b0 RS |
1364 | The window's display table, or @code{nil} if none is specified for it. |
1365 | ||
1366 | @item update_mode_line | |
1367 | Non-@code{nil} means this window's mode line needs to be updated. | |
1368 | ||
1369 | @item base_line_number | |
1370 | The line number of a certain position in the buffer, or @code{nil}. | |
1371 | This is used for displaying the line number of point in the mode line. | |
1372 | ||
1373 | @item base_line_pos | |
1374 | The position in the buffer for which the line number is known, or | |
1375 | @code{nil} meaning none is known. | |
1376 | ||
1377 | @item region_showing | |
1378 | If the region (or part of it) is highlighted in this window, this field | |
1379 | holds the mark position that made one end of that region. Otherwise, | |
1380 | this field is @code{nil}. | |
95260b26 GM |
1381 | |
1382 | @item column_number_displayed | |
1383 | The column number currently displayed in this window's mode line, or @code{nil} | |
1384 | if column numbers are not being displayed. | |
1385 | ||
1386 | @item current_matrix | |
1387 | A glyph matrix describing the current display of this window. | |
1388 | ||
1389 | @item desired_matrix | |
1390 | A glyph matrix describing the desired display of this window. | |
a44af9f2 RS |
1391 | @end table |
1392 | ||
969fe9b5 | 1393 | @node Process Internals |
a44af9f2 RS |
1394 | @appendixsubsec Process Internals |
1395 | @cindex internals, of process | |
1396 | @cindex process internals | |
1397 | ||
1398 | The fields of a process are: | |
1399 | ||
1400 | @table @code | |
1401 | @item name | |
1402 | A string, the name of the process. | |
1403 | ||
1404 | @item command | |
1405 | A list containing the command arguments that were used to start this | |
1406 | process. | |
1407 | ||
1408 | @item filter | |
1409 | A function used to accept output from the process instead of a buffer, | |
1410 | or @code{nil}. | |
1411 | ||
1412 | @item sentinel | |
1413 | A function called whenever the process receives a signal, or @code{nil}. | |
1414 | ||
1415 | @item buffer | |
1416 | The associated buffer of the process. | |
1417 | ||
1418 | @item pid | |
2a233172 | 1419 | An integer, the operating system's process @acronym{ID}. |
a44af9f2 RS |
1420 | |
1421 | @item childp | |
1422 | A flag, non-@code{nil} if this is really a child process. | |
1423 | It is @code{nil} for a network connection. | |
1424 | ||
a44af9f2 | 1425 | @item mark |
574efc83 RS |
1426 | A marker indicating the position of the end of the last output from this |
1427 | process inserted into the buffer. This is often but not always the end | |
1428 | of the buffer. | |
a44af9f2 RS |
1429 | |
1430 | @item kill_without_query | |
a890e1b0 RS |
1431 | If this is non-@code{nil}, killing Emacs while this process is still |
1432 | running does not ask for confirmation about killing the process. | |
1433 | ||
1434 | @item raw_status_low | |
1435 | @itemx raw_status_high | |
1436 | These two fields record 16 bits each of the process status returned by | |
1437 | the @code{wait} system call. | |
1438 | ||
1439 | @item status | |
1440 | The process status, as @code{process-status} should return it. | |
1441 | ||
1442 | @item tick | |
1443 | @itemx update_tick | |
1444 | If these two fields are not equal, a change in the status of the process | |
1445 | needs to be reported, either by running the sentinel or by inserting a | |
1446 | message in the process buffer. | |
1447 | ||
1448 | @item pty_flag | |
ad800164 | 1449 | Non-@code{nil} if communication with the subprocess uses a @acronym{PTY}; |
a890e1b0 RS |
1450 | @code{nil} if it uses a pipe. |
1451 | ||
1452 | @item infd | |
1453 | The file descriptor for input from the process. | |
1454 | ||
1455 | @item outfd | |
1456 | The file descriptor for output to the process. | |
1457 | ||
1458 | @item subtty | |
1459 | The file descriptor for the terminal that the subprocess is using. (On | |
1460 | some systems, there is no need to record this, so the value is | |
1461 | @code{nil}.) | |
bfe721d1 KH |
1462 | |
1463 | @item tty_name | |
1464 | The name of the terminal that the subprocess is using, | |
1465 | or @code{nil} if it is using pipes. | |
95260b26 GM |
1466 | |
1467 | @item decode_coding_system | |
1468 | Coding-system for decoding the input from this process. | |
1469 | ||
1470 | @item decoding_buf | |
1471 | A working buffer for decoding. | |
1472 | ||
1473 | @item decoding_carryover | |
1474 | Size of carryover in decoding. | |
1475 | ||
1476 | @item encode_coding_system | |
1477 | Coding-system for encoding the output to this process. | |
1478 | ||
1479 | @item encoding_buf | |
a39c2e0d | 1480 | A working buffer for encoding. |
95260b26 GM |
1481 | |
1482 | @item encoding_carryover | |
1483 | Size of carryover in encoding. | |
1484 | ||
1485 | @item inherit_coding_system_flag | |
1486 | Flag to set @code{coding-system} of the process buffer from the | |
1487 | coding system used to decode process output. | |
a44af9f2 | 1488 | @end table |
ab5796a9 MB |
1489 | |
1490 | @ignore | |
1491 | arch-tag: 4b2c33bc-d7e4-43f5-bc20-27c0db52a53e | |
1492 | @end ignore |