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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
b3d90e46 GM |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1998, 1999, 2001, 2002, 2003, |
4 | @c 2004, 2005, 2006, 2007 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 | ||
6d95228d | 47 | @cindex dumping Emacs |
a44af9f2 RS |
48 | It takes a substantial time to load the standard Lisp files. Luckily, |
49 | you don't have to do this each time you run Emacs; @file{temacs} can | |
574efc83 | 50 | dump out an executable program called @file{emacs} that has these files |
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51 | preloaded. @file{emacs} starts more quickly because it does not need to |
52 | load the files. This is the Emacs executable that is normally | |
53 | installed. | |
54 | ||
55 | To create @file{emacs}, use the command @samp{temacs -batch -l loadup | |
56 | dump}. The purpose of @samp{-batch} here is to prevent @file{temacs} | |
57 | from trying to initialize any of its data on the terminal; this ensures | |
58 | that the tables of terminal information are empty in the dumped Emacs. | |
59 | The argument @samp{dump} tells @file{loadup.el} to dump a new executable | |
60 | named @file{emacs}. | |
61 | ||
62 | Some operating systems don't support dumping. On those systems, you | |
63 | must start Emacs with the @samp{temacs -l loadup} command each time you | |
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64 | use it. This takes a substantial time, but since you need to start |
65 | Emacs once a day at most---or once a week if you never log out---the | |
66 | extra time is not too severe a problem. | |
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67 | |
68 | @cindex @file{site-load.el} | |
95260b26 | 69 | |
a44af9f2 | 70 | You can specify additional files to preload by writing a library named |
95260b26 GM |
71 | @file{site-load.el} that loads them. You may need to add a definition |
72 | ||
73 | @example | |
74 | #define SITELOAD_PURESIZE_EXTRA @var{n} | |
75 | @end example | |
76 | ||
77 | @noindent | |
78 | to make @var{n} added bytes of pure space to hold the additional files. | |
79 | (Try adding increments of 20000 until it is big enough.) However, the | |
80 | advantage of preloading additional files decreases as machines get | |
81 | faster. On modern machines, it is usually not advisable. | |
a44af9f2 | 82 | |
2a664e73 RS |
83 | After @file{loadup.el} reads @file{site-load.el}, it finds the |
84 | documentation strings for primitive and preloaded functions (and | |
568ffbee LT |
85 | variables) in the file @file{etc/DOC} where they are stored, by |
86 | calling @code{Snarf-documentation} (@pxref{Definition of | |
87 | Snarf-documentation,, Accessing Documentation}). | |
2a664e73 | 88 | |
a44af9f2 | 89 | @cindex @file{site-init.el} |
6d95228d | 90 | @cindex preloading additional functions and variables |
a890e1b0 | 91 | You can specify other Lisp expressions to execute just before dumping |
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92 | by putting them in a library named @file{site-init.el}. This file is |
93 | executed after the documentation strings are found. | |
a44af9f2 | 94 | |
2a664e73 RS |
95 | If you want to preload function or variable definitions, there are |
96 | three ways you can do this and make their documentation strings | |
97 | accessible when you subsequently run Emacs: | |
98 | ||
99 | @itemize @bullet | |
100 | @item | |
101 | Arrange to scan these files when producing the @file{etc/DOC} file, | |
102 | and load them with @file{site-load.el}. | |
103 | ||
104 | @item | |
105 | Load the files with @file{site-init.el}, then copy the files into the | |
106 | installation directory for Lisp files when you install Emacs. | |
107 | ||
108 | @item | |
109 | Specify a non-@code{nil} value for | |
8241495d | 110 | @code{byte-compile-dynamic-docstrings} as a local variable in each of these |
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111 | files, and load them with either @file{site-load.el} or |
112 | @file{site-init.el}. (This method has the drawback that the | |
113 | documentation strings take up space in Emacs all the time.) | |
114 | @end itemize | |
115 | ||
116 | It is not advisable to put anything in @file{site-load.el} or | |
117 | @file{site-init.el} that would alter any of the features that users | |
118 | expect in an ordinary unmodified Emacs. If you feel you must override | |
119 | normal features for your site, do it with @file{default.el}, so that | |
8241495d | 120 | users can override your changes if they wish. @xref{Startup Summary}. |
a44af9f2 | 121 | |
55f77e1c RS |
122 | In a package that can be preloaded, it is sometimes useful to |
123 | specify a computation to be done when Emacs subsequently starts up. | |
124 | For this, use @code{eval-at-startup}: | |
125 | ||
6d1e17be | 126 | @defmac eval-at-startup body@dots{} |
55f77e1c RS |
127 | This evaluates the @var{body} forms, either immediately if running in |
128 | an Emacs that has already started up, or later when Emacs does start | |
129 | up. Since the value of the @var{body} forms is not necessarily | |
130 | available when the @code{eval-at-startup} form is run, that form | |
131 | always returns @code{nil}. | |
6d1e17be | 132 | @end defmac |
55f77e1c | 133 | |
a44af9f2 RS |
134 | @defun dump-emacs to-file from-file |
135 | @cindex unexec | |
cb017dde | 136 | This function dumps the current state of Emacs into an executable file |
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137 | @var{to-file}. It takes symbols from @var{from-file} (this is normally |
138 | the executable file @file{temacs}). | |
139 | ||
cb017dde RS |
140 | If you want to use this function in an Emacs that was already dumped, |
141 | you must run Emacs with @samp{-batch}. | |
a44af9f2 RS |
142 | @end defun |
143 | ||
969fe9b5 | 144 | @node Pure Storage |
a44af9f2 RS |
145 | @appendixsec Pure Storage |
146 | @cindex pure storage | |
147 | ||
a890e1b0 RS |
148 | Emacs Lisp uses two kinds of storage for user-created Lisp objects: |
149 | @dfn{normal storage} and @dfn{pure storage}. Normal storage is where | |
8241495d | 150 | all the new data created during an Emacs session are kept; see the |
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151 | following section for information on normal storage. Pure storage is |
152 | used for certain data in the preloaded standard Lisp files---data that | |
153 | should never change during actual use of Emacs. | |
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154 | |
155 | Pure storage is allocated only while @file{temacs} is loading the | |
156 | standard preloaded Lisp libraries. In the file @file{emacs}, it is | |
574efc83 | 157 | marked as read-only (on operating systems that permit this), so that |
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158 | the memory space can be shared by all the Emacs jobs running on the |
159 | machine at once. Pure storage is not expandable; a fixed amount is | |
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160 | allocated when Emacs is compiled, and if that is not sufficient for |
161 | the preloaded libraries, @file{temacs} allocates dynamic memory for | |
162 | the part that didn't fit. If that happens, you should increase the | |
163 | compilation parameter @code{PURESIZE} in the file | |
164 | @file{src/puresize.h} and rebuild Emacs, even though the resulting | |
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165 | image will work: garbage collection is disabled in this situation, |
166 | causing a memory leak. Such an overflow normally won't happen unless you | |
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167 | try to preload additional libraries or add features to the standard |
168 | ones. Emacs will display a warning about the overflow when it | |
169 | starts. | |
a44af9f2 RS |
170 | |
171 | @defun purecopy object | |
8241495d RS |
172 | This function makes a copy in pure storage of @var{object}, and returns |
173 | it. It copies a string by simply making a new string with the same | |
568ffbee LT |
174 | characters, but without text properties, in pure storage. It |
175 | recursively copies the contents of vectors and cons cells. It does | |
176 | not make copies of other objects such as symbols, but just returns | |
177 | them unchanged. It signals an error if asked to copy markers. | |
a44af9f2 | 178 | |
c2cd5fb7 RS |
179 | This function is a no-op except while Emacs is being built and dumped; |
180 | it is usually called only in the file @file{emacs/lisp/loaddefs.el}, but | |
181 | a few packages call it just in case you decide to preload them. | |
a44af9f2 RS |
182 | @end defun |
183 | ||
184 | @defvar pure-bytes-used | |
a890e1b0 | 185 | The value of this variable is the number of bytes of pure storage |
a44af9f2 RS |
186 | allocated so far. Typically, in a dumped Emacs, this number is very |
187 | close to the total amount of pure storage available---if it were not, | |
188 | we would preallocate less. | |
189 | @end defvar | |
190 | ||
191 | @defvar purify-flag | |
a890e1b0 | 192 | This variable determines whether @code{defun} should make a copy of the |
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193 | function definition in pure storage. If it is non-@code{nil}, then the |
194 | function definition is copied into pure storage. | |
195 | ||
a890e1b0 | 196 | This flag is @code{t} while loading all of the basic functions for |
a44af9f2 | 197 | building Emacs initially (allowing those functions to be sharable and |
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198 | non-collectible). Dumping Emacs as an executable always writes |
199 | @code{nil} in this variable, regardless of the value it actually has | |
200 | before and after dumping. | |
a44af9f2 | 201 | |
a890e1b0 | 202 | You should not change this flag in a running Emacs. |
a44af9f2 RS |
203 | @end defvar |
204 | ||
969fe9b5 | 205 | @node Garbage Collection |
a44af9f2 | 206 | @appendixsec Garbage Collection |
c9b965bd | 207 | @cindex garbage collection |
a44af9f2 RS |
208 | |
209 | @cindex memory allocation | |
210 | When a program creates a list or the user defines a new function (such | |
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211 | as by loading a library), that data is placed in normal storage. If |
212 | normal storage runs low, then Emacs asks the operating system to | |
a44af9f2 | 213 | allocate more memory in blocks of 1k bytes. Each block is used for one |
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214 | type of Lisp object, so symbols, cons cells, markers, etc., are |
215 | segregated in distinct blocks in memory. (Vectors, long strings, | |
216 | buffers and certain other editing types, which are fairly large, are | |
217 | allocated in individual blocks, one per object, while small strings are | |
218 | packed into blocks of 8k bytes.) | |
219 | ||
220 | It is quite common to use some storage for a while, then release it by | |
221 | (for example) killing a buffer or deleting the last pointer to an | |
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222 | object. Emacs provides a @dfn{garbage collector} to reclaim this |
223 | abandoned storage. (This name is traditional, but ``garbage recycler'' | |
224 | might be a more intuitive metaphor for this facility.) | |
225 | ||
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226 | The garbage collector operates by finding and marking all Lisp objects |
227 | that are still accessible to Lisp programs. To begin with, it assumes | |
228 | all the symbols, their values and associated function definitions, and | |
574efc83 | 229 | any data presently on the stack, are accessible. Any objects that can |
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230 | be reached indirectly through other accessible objects are also |
231 | accessible. | |
a44af9f2 | 232 | |
a890e1b0 | 233 | When marking is finished, all objects still unmarked are garbage. No |
a44af9f2 | 234 | matter what the Lisp program or the user does, it is impossible to refer |
a890e1b0 | 235 | to them, since there is no longer a way to reach them. Their space |
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236 | might as well be reused, since no one will miss them. The second |
237 | (``sweep'') phase of the garbage collector arranges to reuse them. | |
a44af9f2 | 238 | |
05aea714 | 239 | @c ??? Maybe add something describing weak hash tables here? |
95260b26 | 240 | |
a44af9f2 | 241 | @cindex free list |
a890e1b0 RS |
242 | The sweep phase puts unused cons cells onto a @dfn{free list} |
243 | for future allocation; likewise for symbols and markers. It compacts | |
244 | the accessible strings so they occupy fewer 8k blocks; then it frees the | |
574efc83 | 245 | other 8k blocks. Vectors, buffers, windows, and other large objects are |
a890e1b0 | 246 | individually allocated and freed using @code{malloc} and @code{free}. |
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247 | |
248 | @cindex CL note---allocate more storage | |
249 | @quotation | |
574efc83 | 250 | @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not |
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251 | call the garbage collector when the free list is empty. Instead, it |
252 | simply requests the operating system to allocate more storage, and | |
253 | processing continues until @code{gc-cons-threshold} bytes have been | |
254 | used. | |
255 | ||
256 | This means that you can make sure that the garbage collector will not | |
257 | run during a certain portion of a Lisp program by calling the garbage | |
258 | collector explicitly just before it (provided that portion of the | |
259 | program does not use so much space as to force a second garbage | |
260 | collection). | |
261 | @end quotation | |
262 | ||
263 | @deffn Command garbage-collect | |
a890e1b0 | 264 | This command runs a garbage collection, and returns information on |
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265 | the amount of space in use. (Garbage collection can also occur |
266 | spontaneously if you use more than @code{gc-cons-threshold} bytes of | |
267 | Lisp data since the previous garbage collection.) | |
268 | ||
a890e1b0 | 269 | @code{garbage-collect} returns a list containing the following |
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270 | information: |
271 | ||
a890e1b0 | 272 | @example |
a44af9f2 RS |
273 | @group |
274 | ((@var{used-conses} . @var{free-conses}) | |
275 | (@var{used-syms} . @var{free-syms}) | |
a890e1b0 | 276 | @end group |
969fe9b5 | 277 | (@var{used-miscs} . @var{free-miscs}) |
40d48fe9 | 278 | @var{used-string-chars} |
a44af9f2 | 279 | @var{used-vector-slots} |
f9f59935 | 280 | (@var{used-floats} . @var{free-floats}) |
40d48fe9 EZ |
281 | (@var{used-intervals} . @var{free-intervals}) |
282 | (@var{used-strings} . @var{free-strings})) | |
969fe9b5 RS |
283 | @end example |
284 | ||
285 | Here is an example: | |
286 | ||
287 | @example | |
a890e1b0 | 288 | @group |
a44af9f2 | 289 | (garbage-collect) |
f9f59935 RS |
290 | @result{} ((106886 . 13184) (9769 . 0) |
291 | (7731 . 4651) 347543 121628 | |
40d48fe9 EZ |
292 | (31 . 94) (1273 . 168) |
293 | (25474 . 3569)) | |
a44af9f2 | 294 | @end group |
a890e1b0 | 295 | @end example |
a44af9f2 RS |
296 | |
297 | Here is a table explaining each element: | |
298 | ||
299 | @table @var | |
300 | @item used-conses | |
301 | The number of cons cells in use. | |
302 | ||
303 | @item free-conses | |
304 | The number of cons cells for which space has been obtained from the | |
305 | operating system, but that are not currently being used. | |
306 | ||
307 | @item used-syms | |
308 | The number of symbols in use. | |
309 | ||
310 | @item free-syms | |
311 | The number of symbols for which space has been obtained from the | |
312 | operating system, but that are not currently being used. | |
313 | ||
969fe9b5 RS |
314 | @item used-miscs |
315 | The number of miscellaneous objects in use. These include markers and | |
316 | overlays, plus certain objects not visible to users. | |
a44af9f2 | 317 | |
969fe9b5 RS |
318 | @item free-miscs |
319 | The number of miscellaneous objects for which space has been obtained | |
320 | from the operating system, but that are not currently being used. | |
a44af9f2 RS |
321 | |
322 | @item used-string-chars | |
323 | The total size of all strings, in characters. | |
324 | ||
325 | @item used-vector-slots | |
326 | The total number of elements of existing vectors. | |
327 | ||
328 | @item used-floats | |
329 | @c Emacs 19 feature | |
330 | The number of floats in use. | |
331 | ||
332 | @item free-floats | |
333 | @c Emacs 19 feature | |
334 | The number of floats for which space has been obtained from the | |
335 | operating system, but that are not currently being used. | |
a9f0a989 RS |
336 | |
337 | @item used-intervals | |
338 | The number of intervals in use. Intervals are an internal | |
339 | data structure used for representing text properties. | |
340 | ||
341 | @item free-intervals | |
342 | The number of intervals for which space has been obtained | |
343 | from the operating system, but that are not currently being used. | |
40d48fe9 EZ |
344 | |
345 | @item used-strings | |
346 | The number of strings in use. | |
347 | ||
348 | @item free-strings | |
349 | The number of string headers for which the space was obtained from the | |
350 | operating system, but which are currently not in use. (A string | |
351 | object consists of a header and the storage for the string text | |
352 | itself; the latter is only allocated when the string is created.) | |
a44af9f2 | 353 | @end table |
361ed4fd LT |
354 | |
355 | If there was overflow in pure space (see the previous section), | |
356 | @code{garbage-collect} returns @code{nil}, because a real garbage | |
357 | collection can not be done in this situation. | |
a44af9f2 RS |
358 | @end deffn |
359 | ||
d64c55d8 RS |
360 | @defopt garbage-collection-messages |
361 | If this variable is non-@code{nil}, Emacs displays a message at the | |
362 | beginning and end of garbage collection. The default value is | |
363 | @code{nil}, meaning there are no such messages. | |
364 | @end defopt | |
365 | ||
e73c3ec4 RS |
366 | @defvar post-gc-hook |
367 | This is a normal hook that is run at the end of garbage collection. | |
368 | Garbage collection is inhibited while the hook functions run, so be | |
369 | careful writing them. | |
370 | @end defvar | |
371 | ||
a44af9f2 | 372 | @defopt gc-cons-threshold |
a890e1b0 | 373 | The value of this variable is the number of bytes of storage that must |
a44af9f2 | 374 | be allocated for Lisp objects after one garbage collection in order to |
a890e1b0 | 375 | trigger another garbage collection. A cons cell counts as eight bytes, |
a44af9f2 | 376 | a string as one byte per character plus a few bytes of overhead, and so |
a890e1b0 RS |
377 | on; space allocated to the contents of buffers does not count. Note |
378 | that the subsequent garbage collection does not happen immediately when | |
379 | the threshold is exhausted, but only the next time the Lisp evaluator is | |
a44af9f2 RS |
380 | called. |
381 | ||
f9f59935 | 382 | The initial threshold value is 400,000. If you specify a larger |
a44af9f2 RS |
383 | value, garbage collection will happen less often. This reduces the |
384 | amount of time spent garbage collecting, but increases total memory use. | |
574efc83 | 385 | You may want to do this when running a program that creates lots of |
a44af9f2 RS |
386 | Lisp data. |
387 | ||
a890e1b0 | 388 | You can make collections more frequent by specifying a smaller value, |
a44af9f2 RS |
389 | down to 10,000. A value less than 10,000 will remain in effect only |
390 | until the subsequent garbage collection, at which time | |
391 | @code{garbage-collect} will set the threshold back to 10,000. | |
0c17e67c SM |
392 | @end defopt |
393 | ||
394 | @defopt gc-cons-percentage | |
6696f2a4 RS |
395 | The value of this variable specifies the amount of consing before a |
396 | garbage collection occurs, as a fraction of the current heap size. | |
397 | This criterion and @code{gc-cons-threshold} apply in parallel, and | |
398 | garbage collection occurs only when both criteria are satisfied. | |
0c17e67c SM |
399 | |
400 | As the heap size increases, the time to perform a garbage collection | |
6696f2a4 RS |
401 | increases. Thus, it can be desirable to do them less frequently in |
402 | proportion. | |
a44af9f2 RS |
403 | @end defopt |
404 | ||
568ffbee | 405 | The value returned by @code{garbage-collect} describes the amount of |
969fe9b5 RS |
406 | memory used by Lisp data, broken down by data type. By contrast, the |
407 | function @code{memory-limit} provides information on the total amount of | |
408 | memory Emacs is currently using. | |
409 | ||
a44af9f2 RS |
410 | @c Emacs 19 feature |
411 | @defun memory-limit | |
412 | This function returns the address of the last byte Emacs has allocated, | |
413 | divided by 1024. We divide the value by 1024 to make sure it fits in a | |
414 | Lisp integer. | |
415 | ||
416 | You can use this to get a general idea of how your actions affect the | |
417 | memory usage. | |
418 | @end defun | |
419 | ||
3c4c00e6 RS |
420 | @defvar memory-full |
421 | This variable is @code{t} if Emacs is close to out of memory for Lisp | |
422 | objects, and @code{nil} otherwise. | |
423 | @end defvar | |
424 | ||
5b2279a3 RS |
425 | @defun memory-use-counts |
426 | This returns a list of numbers that count the number of objects | |
427 | created in this Emacs session. Each of these counters increments for | |
428 | a certain kind of object. See the documentation string for details. | |
429 | @end defun | |
430 | ||
66c0f054 RS |
431 | @defvar gcs-done |
432 | This variable contains the total number of garbage collections | |
433 | done so far in this Emacs session. | |
f0514b34 | 434 | @end defvar |
66c0f054 RS |
435 | |
436 | @defvar gc-elapsed | |
437 | This variable contains the total number of seconds of elapsed time | |
438 | during garbage collection so far in this Emacs session, as a floating | |
439 | point number. | |
f0514b34 | 440 | @end defvar |
66c0f054 | 441 | |
969fe9b5 RS |
442 | @node Memory Usage |
443 | @section Memory Usage | |
ad8d30b3 | 444 | @cindex memory usage |
969fe9b5 RS |
445 | |
446 | These functions and variables give information about the total amount | |
447 | of memory allocation that Emacs has done, broken down by data type. | |
448 | Note the difference between these and the values returned by | |
449 | @code{(garbage-collect)}; those count objects that currently exist, but | |
450 | these count the number or size of all allocations, including those for | |
451 | objects that have since been freed. | |
452 | ||
453 | @defvar cons-cells-consed | |
454 | The total number of cons cells that have been allocated so far | |
455 | in this Emacs session. | |
456 | @end defvar | |
457 | ||
458 | @defvar floats-consed | |
459 | The total number of floats that have been allocated so far | |
460 | in this Emacs session. | |
461 | @end defvar | |
462 | ||
463 | @defvar vector-cells-consed | |
464 | The total number of vector cells that have been allocated so far | |
465 | in this Emacs session. | |
466 | @end defvar | |
467 | ||
468 | @defvar symbols-consed | |
469 | The total number of symbols that have been allocated so far | |
470 | in this Emacs session. | |
471 | @end defvar | |
472 | ||
473 | @defvar string-chars-consed | |
474 | The total number of string characters that have been allocated so far | |
475 | in this Emacs session. | |
476 | @end defvar | |
477 | ||
478 | @defvar misc-objects-consed | |
479 | The total number of miscellaneous objects that have been allocated so | |
480 | far in this Emacs session. These include markers and overlays, plus | |
481 | certain objects not visible to users. | |
482 | @end defvar | |
483 | ||
484 | @defvar intervals-consed | |
485 | The total number of intervals that have been allocated so far | |
486 | in this Emacs session. | |
487 | @end defvar | |
488 | ||
40d48fe9 EZ |
489 | @defvar strings-consed |
490 | The total number of strings that have been allocated so far in this | |
491 | Emacs session. | |
492 | @end defvar | |
493 | ||
969fe9b5 | 494 | @node Writing Emacs Primitives |
a44af9f2 RS |
495 | @appendixsec Writing Emacs Primitives |
496 | @cindex primitive function internals | |
6d95228d | 497 | @cindex writing Emacs primitives |
a44af9f2 RS |
498 | |
499 | Lisp primitives are Lisp functions implemented in C. The details of | |
500 | interfacing the C function so that Lisp can call it are handled by a few | |
501 | C macros. The only way to really understand how to write new C code is | |
502 | to read the source, but we can explain some things here. | |
503 | ||
504 | An example of a special form is the definition of @code{or}, from | |
505 | @file{eval.c}. (An ordinary function would have the same general | |
506 | appearance.) | |
507 | ||
508 | @cindex garbage collection protection | |
509 | @smallexample | |
510 | @group | |
511 | DEFUN ("or", For, Sor, 0, UNEVALLED, 0, | |
42b50684 KB |
512 | doc: /* Eval args until one of them yields non-nil, then return that |
513 | value. The remaining args are not evalled at all. | |
f1842270 | 514 | If all args return nil, return nil. |
a44af9f2 RS |
515 | @end group |
516 | @group | |
f1842270 | 517 | usage: (or CONDITIONS ...) */) |
a44af9f2 RS |
518 | (args) |
519 | Lisp_Object args; | |
520 | @{ | |
51485df2 | 521 | register Lisp_Object val = Qnil; |
a44af9f2 RS |
522 | struct gcpro gcpro1; |
523 | @end group | |
524 | ||
525 | @group | |
51485df2 | 526 | GCPRO1 (args); |
a44af9f2 RS |
527 | @end group |
528 | ||
529 | @group | |
51485df2 | 530 | while (CONSP (args)) |
a44af9f2 | 531 | @{ |
51485df2 | 532 | val = Feval (XCAR (args)); |
95260b26 | 533 | if (!NILP (val)) |
539775c0 | 534 | break; |
51485df2 | 535 | args = XCDR (args); |
a44af9f2 | 536 | @} |
a44af9f2 RS |
537 | @end group |
538 | ||
539 | @group | |
540 | UNGCPRO; | |
541 | return val; | |
542 | @} | |
543 | @end group | |
544 | @end smallexample | |
545 | ||
6d95228d | 546 | @cindex @code{DEFUN}, C macro to define Lisp primitives |
a44af9f2 | 547 | Let's start with a precise explanation of the arguments to the |
a890e1b0 | 548 | @code{DEFUN} macro. Here is a template for them: |
a44af9f2 RS |
549 | |
550 | @example | |
551 | DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc}) | |
552 | @end example | |
553 | ||
554 | @table @var | |
555 | @item lname | |
a890e1b0 RS |
556 | This is the name of the Lisp symbol to define as the function name; in |
557 | the example above, it is @code{or}. | |
a44af9f2 RS |
558 | |
559 | @item fname | |
560 | This is the C function name for this function. This is | |
561 | the name that is used in C code for calling the function. The name is, | |
562 | by convention, @samp{F} prepended to the Lisp name, with all dashes | |
563 | (@samp{-}) in the Lisp name changed to underscores. Thus, to call this | |
564 | function from C code, call @code{For}. Remember that the arguments must | |
565 | be of type @code{Lisp_Object}; various macros and functions for creating | |
566 | values of type @code{Lisp_Object} are declared in the file | |
567 | @file{lisp.h}. | |
568 | ||
569 | @item sname | |
570 | This is a C variable name to use for a structure that holds the data for | |
571 | the subr object that represents the function in Lisp. This structure | |
572 | conveys the Lisp symbol name to the initialization routine that will | |
573 | create the symbol and store the subr object as its definition. By | |
574 | convention, this name is always @var{fname} with @samp{F} replaced with | |
575 | @samp{S}. | |
576 | ||
577 | @item min | |
a890e1b0 RS |
578 | This is the minimum number of arguments that the function requires. The |
579 | function @code{or} allows a minimum of zero arguments. | |
a44af9f2 RS |
580 | |
581 | @item max | |
a890e1b0 RS |
582 | This is the maximum number of arguments that the function accepts, if |
583 | there is a fixed maximum. Alternatively, it can be @code{UNEVALLED}, | |
584 | indicating a special form that receives unevaluated arguments, or | |
585 | @code{MANY}, indicating an unlimited number of evaluated arguments (the | |
586 | equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are | |
587 | macros. If @var{max} is a number, it may not be less than @var{min} and | |
51485df2 | 588 | it may not be greater than eight. |
a44af9f2 RS |
589 | |
590 | @item interactive | |
591 | This is an interactive specification, a string such as might be used as | |
592 | the argument of @code{interactive} in a Lisp function. In the case of | |
593 | @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be | |
a890e1b0 RS |
594 | called interactively. A value of @code{""} indicates a function that |
595 | should receive no arguments when called interactively. | |
a44af9f2 RS |
596 | |
597 | @item doc | |
f1842270 RS |
598 | This is the documentation string. It uses C comment syntax rather |
599 | than C string syntax because comment syntax requires nothing special | |
600 | to include multiple lines. The @samp{doc:} identifies the comment | |
601 | that follows as the documentation string. The @samp{/*} and @samp{*/} | |
602 | delimiters that begin and end the comment are not part of the | |
603 | documentation string. | |
604 | ||
605 | If the last line of the documentation string begins with the keyword | |
606 | @samp{usage:}, the rest of the line is treated as the argument list | |
607 | for documentation purposes. This way, you can use different argument | |
608 | names in the documentation string from the ones used in the C code. | |
0a692803 DL |
609 | @samp{usage:} is required if the function has an unlimited number of |
610 | arguments. | |
f1842270 RS |
611 | |
612 | All the usual rules for documentation strings in Lisp code | |
613 | (@pxref{Documentation Tips}) apply to C code documentation strings | |
614 | too. | |
a44af9f2 RS |
615 | @end table |
616 | ||
a890e1b0 RS |
617 | After the call to the @code{DEFUN} macro, you must write the argument |
618 | name list that every C function must have, followed by ordinary C | |
619 | declarations for the arguments. For a function with a fixed maximum | |
620 | number of arguments, declare a C argument for each Lisp argument, and | |
574efc83 RS |
621 | give them all type @code{Lisp_Object}. When a Lisp function has no |
622 | upper limit on the number of arguments, its implementation in C actually | |
623 | receives exactly two arguments: the first is the number of Lisp | |
624 | arguments, and the second is the address of a block containing their | |
625 | values. They have types @code{int} and @w{@code{Lisp_Object *}}. | |
a44af9f2 | 626 | |
6d95228d EZ |
627 | @cindex @code{GCPRO} and @code{UNGCPRO} |
628 | @cindex protect C variables from garbage collection | |
a44af9f2 | 629 | Within the function @code{For} itself, note the use of the macros |
e4c068c0 RS |
630 | @code{GCPRO1} and @code{UNGCPRO}. @code{GCPRO1} is used to |
631 | ``protect'' a variable from garbage collection---to inform the garbage | |
632 | collector that it must look in that variable and regard its contents | |
633 | as an accessible object. GC protection is necessary whenever you call | |
634 | @code{Feval} or anything that can directly or indirectly call | |
635 | @code{Feval}. At such a time, any Lisp object that this function may | |
636 | refer to again must be protected somehow. | |
a44af9f2 | 637 | |
70bb4402 | 638 | It suffices to ensure that at least one pointer to each object is |
e4c068c0 RS |
639 | GC-protected; that way, the object cannot be recycled, so all pointers |
640 | to it remain valid. Thus, a particular local variable can do without | |
641 | protection if it is certain that the object it points to will be | |
642 | preserved by some other pointer (such as another local variable which | |
643 | has a @code{GCPRO})@footnote{Formerly, strings were a special | |
644 | exception; in older Emacs versions, every local variable that might | |
645 | point to a string needed a @code{GCPRO}.}. Otherwise, the local | |
646 | variable needs a @code{GCPRO}. | |
70bb4402 RS |
647 | |
648 | The macro @code{GCPRO1} protects just one local variable. If you | |
e4c068c0 RS |
649 | want to protect two variables, use @code{GCPRO2} instead; repeating |
650 | @code{GCPRO1} will not work. Macros @code{GCPRO3}, @code{GCPRO4}, | |
651 | @code{GCPRO5}, and @code{GCPRO6} also exist. All these macros | |
652 | implicitly use local variables such as @code{gcpro1}; you must declare | |
653 | these explicitly, with type @code{struct gcpro}. Thus, if you use | |
70bb4402 | 654 | @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}. |
a890e1b0 RS |
655 | Alas, we can't explain all the tricky details here. |
656 | ||
e4c068c0 RS |
657 | @code{UNGCPRO} cancels the protection of the variables that are |
658 | protected in the current function. It is necessary to do this | |
659 | explicitly. | |
660 | ||
70bb4402 RS |
661 | Built-in functions that take a variable number of arguments actually |
662 | accept two arguments at the C level: the number of Lisp arguments, and | |
663 | a @code{Lisp_Object *} pointer to a C vector containing those Lisp | |
664 | arguments. This C vector may be part of a Lisp vector, but it need | |
568ffbee | 665 | not be. The responsibility for using @code{GCPRO} to protect the Lisp |
236a1914 RS |
666 | arguments from GC if necessary rests with the caller in this case, |
667 | since the caller allocated or found the storage for them. | |
70bb4402 | 668 | |
e610024b | 669 | You must not use C initializers for static or global variables unless |
05aea714 | 670 | the variables are never written once Emacs is dumped. These variables |
8241495d RS |
671 | with initializers are allocated in an area of memory that becomes |
672 | read-only (on certain operating systems) as a result of dumping Emacs. | |
673 | @xref{Pure Storage}. | |
e610024b RS |
674 | |
675 | Do not use static variables within functions---place all static | |
676 | variables at top level in the file. This is necessary because Emacs on | |
677 | some operating systems defines the keyword @code{static} as a null | |
678 | macro. (This definition is used because those systems put all variables | |
679 | declared static in a place that becomes read-only after dumping, whether | |
680 | they have initializers or not.) | |
77223f05 | 681 | |
6d95228d | 682 | @cindex @code{defsubr}, Lisp symbol for a primitive |
a890e1b0 RS |
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: | |
a44af9f2 RS |
687 | |
688 | @example | |
689 | defsubr (&@var{subr-structure-name}); | |
690 | @end example | |
691 | ||
692 | @noindent | |
a890e1b0 RS |
693 | Here @var{subr-structure-name} is the name you used as the third |
694 | argument to @code{DEFUN}. | |
695 | ||
696 | If you add a new primitive to a file that already has Lisp primitives | |
697 | defined in it, find the function (near the end of the file) named | |
698 | @code{syms_of_@var{something}}, and add the call to @code{defsubr} | |
699 | there. If the file doesn't have this function, or if you create a new | |
700 | file, add to it a @code{syms_of_@var{filename}} (e.g., | |
701 | @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all | |
702 | of these functions are called, and add a call to | |
703 | @code{syms_of_@var{filename}} there. | |
a44af9f2 | 704 | |
568ffbee | 705 | @anchor{Defining Lisp variables in C} |
8241495d | 706 | @vindex byte-boolean-vars |
6d95228d EZ |
707 | @cindex defining Lisp variables in C |
708 | @cindex @code{DEFVAR_INT}, @code{DEFVAR_LISP}, @code{DEFVAR_BOOL} | |
574efc83 RS |
709 | The function @code{syms_of_@var{filename}} is also the place to define |
710 | any C variables that are to be visible as Lisp variables. | |
a890e1b0 RS |
711 | @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible |
712 | in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int} | |
713 | visible in Lisp with a value that is always an integer. | |
714 | @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp | |
8241495d RS |
715 | with a value that is either @code{t} or @code{nil}. Note that variables |
716 | defined with @code{DEFVAR_BOOL} are automatically added to the list | |
717 | @code{byte-boolean-vars} used by the byte compiler. | |
a44af9f2 | 718 | |
c9b965bd | 719 | @cindex @code{staticpro}, protection from GC |
969fe9b5 | 720 | If you define a file-scope C variable of type @code{Lisp_Object}, |
8241495d | 721 | you must protect it from garbage-collection by calling @code{staticpro} |
969fe9b5 RS |
722 | in @code{syms_of_@var{filename}}, like this: |
723 | ||
724 | @example | |
725 | staticpro (&@var{variable}); | |
726 | @end example | |
727 | ||
a890e1b0 | 728 | Here is another example function, with more complicated arguments. |
969fe9b5 RS |
729 | This comes from the code in @file{window.c}, and it demonstrates the use |
730 | of macros and functions to manipulate Lisp objects. | |
a44af9f2 RS |
731 | |
732 | @smallexample | |
733 | @group | |
734 | DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p, | |
735 | Scoordinates_in_window_p, 2, 2, | |
736 | "xSpecify coordinate pair: \nXExpression which evals to window: ", | |
88510b17 | 737 | "Return non-nil if COORDINATES is in WINDOW.\n\ |
969fe9b5 RS |
738 | COORDINATES is a cons of the form (X . Y), X and Y being distances\n\ |
739 | ... | |
a44af9f2 RS |
740 | @end group |
741 | @group | |
969fe9b5 RS |
742 | If they are on the border between WINDOW and its right sibling,\n\ |
743 | `vertical-line' is returned.") | |
744 | (coordinates, window) | |
745 | register Lisp_Object coordinates, window; | |
a44af9f2 | 746 | @{ |
969fe9b5 | 747 | int x, y; |
a44af9f2 RS |
748 | @end group |
749 | ||
750 | @group | |
969fe9b5 RS |
751 | CHECK_LIVE_WINDOW (window, 0); |
752 | CHECK_CONS (coordinates, 1); | |
753 | x = XINT (Fcar (coordinates)); | |
754 | y = XINT (Fcdr (coordinates)); | |
a44af9f2 | 755 | @end group |
969fe9b5 | 756 | |
a44af9f2 | 757 | @group |
969fe9b5 RS |
758 | switch (coordinates_in_window (XWINDOW (window), &x, &y)) |
759 | @{ | |
760 | case 0: /* NOT in window at all. */ | |
761 | return Qnil; | |
a44af9f2 | 762 | @end group |
969fe9b5 | 763 | |
a44af9f2 | 764 | @group |
969fe9b5 RS |
765 | case 1: /* In text part of window. */ |
766 | return Fcons (make_number (x), make_number (y)); | |
a44af9f2 | 767 | @end group |
969fe9b5 | 768 | |
a44af9f2 | 769 | @group |
969fe9b5 RS |
770 | case 2: /* In mode line of window. */ |
771 | return Qmode_line; | |
a44af9f2 | 772 | @end group |
969fe9b5 | 773 | |
a44af9f2 | 774 | @group |
969fe9b5 RS |
775 | case 3: /* On right border of window. */ |
776 | return Qvertical_line; | |
777 | @end group | |
778 | ||
779 | @group | |
780 | default: | |
781 | abort (); | |
782 | @} | |
a44af9f2 RS |
783 | @} |
784 | @end group | |
785 | @end smallexample | |
786 | ||
a890e1b0 RS |
787 | Note that C code cannot call functions by name unless they are defined |
788 | in C. The way to call a function written in Lisp is to use | |
789 | @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since | |
790 | the Lisp function @code{funcall} accepts an unlimited number of | |
791 | arguments, in C it takes two: the number of Lisp-level arguments, and a | |
792 | one-dimensional array containing their values. The first Lisp-level | |
793 | argument is the Lisp function to call, and the rest are the arguments to | |
794 | pass to it. Since @code{Ffuncall} can call the evaluator, you must | |
795 | protect pointers from garbage collection around the call to | |
796 | @code{Ffuncall}. | |
797 | ||
798 | The C functions @code{call0}, @code{call1}, @code{call2}, and so on, | |
799 | provide handy ways to call a Lisp function conveniently with a fixed | |
800 | number of arguments. They work by calling @code{Ffuncall}. | |
a44af9f2 RS |
801 | |
802 | @file{eval.c} is a very good file to look through for examples; | |
803 | @file{lisp.h} contains the definitions for some important macros and | |
804 | functions. | |
805 | ||
0a692803 DL |
806 | If you define a function which is side-effect free, update the code |
807 | in @file{byte-opt.el} which binds @code{side-effect-free-fns} and | |
808 | @code{side-effect-and-error-free-fns} so that the compiler optimizer | |
809 | knows about it. | |
8241495d | 810 | |
969fe9b5 | 811 | @node Object Internals |
a44af9f2 RS |
812 | @appendixsec Object Internals |
813 | @cindex object internals | |
814 | ||
815 | GNU Emacs Lisp manipulates many different types of data. The actual | |
f9f59935 RS |
816 | data are stored in a heap and the only access that programs have to it |
817 | is through pointers. Pointers are thirty-two bits wide in most | |
a44af9f2 | 818 | implementations. Depending on the operating system and type of machine |
568ffbee LT |
819 | for which you compile Emacs, twenty-nine bits are used to address the |
820 | object, and the remaining three bits are used for the tag that | |
821 | identifies the object's type. | |
a44af9f2 | 822 | |
a890e1b0 RS |
823 | Because Lisp objects are represented as tagged pointers, it is always |
824 | possible to determine the Lisp data type of any object. The C data type | |
825 | @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary | |
826 | variables have type @code{Lisp_Object}, which means they can hold any | |
827 | type of Lisp value; you can determine the actual data type only at run | |
828 | time. The same is true for function arguments; if you want a function | |
829 | to accept only a certain type of argument, you must check the type | |
830 | explicitly using a suitable predicate (@pxref{Type Predicates}). | |
a44af9f2 RS |
831 | @cindex type checking internals |
832 | ||
833 | @menu | |
834 | * Buffer Internals:: Components of a buffer structure. | |
835 | * Window Internals:: Components of a window structure. | |
836 | * Process Internals:: Components of a process structure. | |
837 | @end menu | |
838 | ||
969fe9b5 | 839 | @node Buffer Internals |
a44af9f2 RS |
840 | @appendixsubsec Buffer Internals |
841 | @cindex internals, of buffer | |
842 | @cindex buffer internals | |
843 | ||
844 | Buffers contain fields not directly accessible by the Lisp programmer. | |
845 | We describe them here, naming them by the names used in the C code. | |
846 | Many are accessible indirectly in Lisp programs via Lisp primitives. | |
847 | ||
95260b26 GM |
848 | Two structures are used to represent buffers in C. The |
849 | @code{buffer_text} structure contains fields describing the text of a | |
850 | buffer; the @code{buffer} structure holds other fields. In the case | |
851 | of indirect buffers, two or more @code{buffer} structures reference | |
852 | the same @code{buffer_text} structure. | |
853 | ||
854 | Here is a list of the @code{struct buffer_text} fields: | |
855 | ||
a44af9f2 | 856 | @table @code |
95260b26 | 857 | @item beg |
05aea714 | 858 | This field contains the actual address of the buffer contents. |
95260b26 | 859 | |
d7255d62 | 860 | @item gpt |
95260b26 | 861 | This holds the character position of the gap in the buffer. |
88510b17 | 862 | @xref{Buffer Gap}. |
95260b26 GM |
863 | |
864 | @item z | |
865 | This field contains the character position of the end of the buffer | |
866 | text. | |
867 | ||
868 | @item gpt_byte | |
869 | Contains the byte position of the gap. | |
870 | ||
871 | @item z_byte | |
872 | Holds the byte position of the end of the buffer text. | |
873 | ||
874 | @item gap_size | |
88510b17 | 875 | Contains the size of buffer's gap. @xref{Buffer Gap}. |
95260b26 GM |
876 | |
877 | @item modiff | |
878 | This field counts buffer-modification events for this buffer. It is | |
879 | incremented for each such event, and never otherwise changed. | |
880 | ||
881 | @item save_modiff | |
882 | Contains the previous value of @code{modiff}, as of the last time a | |
883 | buffer was visited or saved in a file. | |
88510b17 | 884 | |
95260b26 GM |
885 | @item overlay_modiff |
886 | Counts modifications to overlays analogous to @code{modiff}. | |
88510b17 | 887 | |
95260b26 GM |
888 | @item beg_unchanged |
889 | Holds the number of characters at the start of the text that are known | |
890 | to be unchanged since the last redisplay that finished. | |
88510b17 | 891 | |
95260b26 GM |
892 | @item end_unchanged |
893 | Holds the number of characters at the end of the text that are known to | |
894 | be unchanged since the last redisplay that finished. | |
88510b17 | 895 | |
95260b26 GM |
896 | @item unchanged_modified |
897 | Contains the value of @code{modiff} at the time of the last redisplay | |
898 | that finished. If this value matches @code{modiff}, | |
899 | @code{beg_unchanged} and @code{end_unchanged} contain no useful | |
900 | information. | |
88510b17 | 901 | |
95260b26 GM |
902 | @item overlay_unchanged_modified |
903 | Contains the value of @code{overlay_modiff} at the time of the last | |
904 | redisplay that finished. If this value matches @code{overlay_modiff}, | |
905 | @code{beg_unchanged} and @code{end_unchanged} contain no useful | |
906 | information. | |
88510b17 | 907 | |
95260b26 GM |
908 | @item markers |
909 | The markers that refer to this buffer. This is actually a single | |
910 | marker, and successive elements in its marker @code{chain} are the other | |
911 | markers referring to this buffer text. | |
a44af9f2 | 912 | |
95260b26 GM |
913 | @item intervals |
914 | Contains the interval tree which records the text properties of this | |
915 | buffer. | |
916 | @end table | |
917 | ||
918 | The fields of @code{struct buffer} are: | |
919 | ||
920 | @table @code | |
921 | @item next | |
922 | Points to the next buffer, in the chain of all buffers including killed | |
923 | buffers. This chain is used only for garbage collection, in order to | |
924 | collect killed buffers properly. Note that vectors, and most kinds of | |
925 | objects allocated as vectors, are all on one chain, but buffers are on a | |
926 | separate chain of their own. | |
927 | ||
928 | @item own_text | |
929 | This is a @code{struct buffer_text} structure. In an ordinary buffer, | |
930 | it holds the buffer contents. In indirect buffers, this field is not | |
931 | used. | |
932 | ||
933 | @item text | |
934 | This points to the @code{buffer_text} structure that is used for this | |
935 | buffer. In an ordinary buffer, this is the @code{own_text} field above. | |
936 | In an indirect buffer, this is the @code{own_text} field of the base | |
937 | buffer. | |
938 | ||
939 | @item pt | |
940 | Contains the character position of point in a buffer. | |
941 | ||
942 | @item pt_byte | |
943 | Contains the byte position of point in a buffer. | |
944 | ||
945 | @item begv | |
88510b17 | 946 | This field contains the character position of the beginning of the |
95260b26 GM |
947 | accessible range of text in the buffer. |
948 | ||
949 | @item begv_byte | |
88510b17 | 950 | This field contains the byte position of the beginning of the |
95260b26 GM |
951 | accessible range of text in the buffer. |
952 | ||
953 | @item zv | |
88510b17 | 954 | This field contains the character position of the end of the |
95260b26 GM |
955 | accessible range of text in the buffer. |
956 | ||
957 | @item zv_byte | |
88510b17 | 958 | This field contains the byte position of the end of the |
95260b26 GM |
959 | accessible range of text in the buffer. |
960 | ||
961 | @item base_buffer | |
962 | In an indirect buffer, this points to the base buffer. In an ordinary | |
963 | buffer, it is null. | |
964 | ||
965 | @item local_var_flags | |
966 | This field contains flags indicating that certain variables are local in | |
967 | this buffer. Such variables are declared in the C code using | |
968 | @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored in | |
969 | fields in the buffer structure itself. (Some of these fields are | |
970 | described in this table.) | |
a44af9f2 RS |
971 | |
972 | @item modtime | |
973 | This field contains the modification time of the visited file. It is | |
8241495d RS |
974 | set when the file is written or read. Before writing the buffer into a |
975 | file, this field is compared to the modification time of the file to see | |
976 | if the file has changed on disk. @xref{Buffer Modification}. | |
a44af9f2 RS |
977 | |
978 | @item auto_save_modified | |
979 | This field contains the time when the buffer was last auto-saved. | |
980 | ||
95260b26 GM |
981 | @item auto_save_failure_time |
982 | The time at which we detected a failure to auto-save, or -1 if we didn't | |
983 | have a failure. | |
984 | ||
a44af9f2 RS |
985 | @item last_window_start |
986 | This field contains the @code{window-start} position in the buffer as of | |
987 | the last time the buffer was displayed in a window. | |
988 | ||
95260b26 GM |
989 | @item clip_changed |
990 | This flag is set when narrowing changes in a buffer. | |
991 | ||
992 | @item prevent_redisplay_optimizations_p | |
88510b17 | 993 | this flag indicates that redisplay optimizations should not be used |
95260b26 GM |
994 | to display this buffer. |
995 | ||
a890e1b0 RS |
996 | @item undo_list |
997 | This field points to the buffer's undo list. @xref{Undo}. | |
a44af9f2 | 998 | |
95260b26 GM |
999 | @item name |
1000 | The buffer name is a string that names the buffer. It is guaranteed to | |
1001 | be unique. @xref{Buffer Names}. | |
1002 | ||
1003 | @item filename | |
1004 | The name of the file visited in this buffer, or @code{nil}. | |
88510b17 | 1005 | |
95260b26 GM |
1006 | @item directory |
1007 | The directory for expanding relative file names. | |
1008 | ||
1009 | @item save_length | |
1010 | Length of the file this buffer is visiting, when last read or saved. | |
1011 | This and other fields concerned with saving are not kept in the | |
1012 | @code{buffer_text} structure because indirect buffers are never saved. | |
1013 | ||
1014 | @item auto_save_file_name | |
88510b17 | 1015 | File name used for auto-saving this buffer. This is not in the |
95260b26 GM |
1016 | @code{buffer_text} because it's not used in indirect buffers at all. |
1017 | ||
1018 | @item read_only | |
1019 | Non-@code{nil} means this buffer is read-only. | |
1020 | ||
1021 | @item mark | |
1022 | This field contains the mark for the buffer. The mark is a marker, | |
1023 | hence it is also included on the list @code{markers}. @xref{The Mark}. | |
1024 | ||
1025 | @item local_var_alist | |
1026 | This field contains the association list describing the buffer-local | |
1027 | variable bindings of this buffer, not including the built-in | |
1028 | buffer-local bindings that have special slots in the buffer object. | |
1029 | (Those slots are omitted from this table.) @xref{Buffer-Local | |
1030 | Variables}. | |
1031 | ||
1032 | @item major_mode | |
1033 | Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}. | |
1034 | ||
1035 | @item mode_name | |
1036 | Pretty name of major mode, e.g., @code{"Lisp"}. | |
1037 | ||
1038 | @item mode_line_format | |
1039 | Mode line element that controls the format of the mode line. If this | |
1040 | is @code{nil}, no mode line will be displayed. | |
1041 | ||
1042 | @item header_line_format | |
5a36d834 | 1043 | This field is analogous to @code{mode_line_format} for the mode |
95260b26 GM |
1044 | line displayed at the top of windows. |
1045 | ||
1046 | @item keymap | |
1047 | This field holds the buffer's local keymap. @xref{Keymaps}. | |
1048 | ||
1049 | @item abbrev_table | |
1050 | This buffer's local abbrevs. | |
1051 | ||
1052 | @item syntax_table | |
a44af9f2 RS |
1053 | This field contains the syntax table for the buffer. @xref{Syntax Tables}. |
1054 | ||
95260b26 GM |
1055 | @item category_table |
1056 | This field contains the category table for the buffer. | |
1057 | ||
1058 | @item case_fold_search | |
1059 | The value of @code{case-fold-search} in this buffer. | |
1060 | ||
1061 | @item tab_width | |
1062 | The value of @code{tab-width} in this buffer. | |
1063 | ||
1064 | @item fill_column | |
1065 | The value of @code{fill-column} in this buffer. | |
1066 | ||
1067 | @item left_margin | |
1068 | The value of @code{left-margin} in this buffer. | |
1069 | ||
1070 | @item auto_fill_function | |
1071 | The value of @code{auto-fill-function} in this buffer. | |
1072 | ||
a44af9f2 RS |
1073 | @item downcase_table |
1074 | This field contains the conversion table for converting text to lower case. | |
969fe9b5 | 1075 | @xref{Case Tables}. |
a44af9f2 RS |
1076 | |
1077 | @item upcase_table | |
1078 | This field contains the conversion table for converting text to upper case. | |
969fe9b5 | 1079 | @xref{Case Tables}. |
a44af9f2 RS |
1080 | |
1081 | @item case_canon_table | |
1082 | This field contains the conversion table for canonicalizing text for | |
969fe9b5 | 1083 | case-folding search. @xref{Case Tables}. |
a44af9f2 RS |
1084 | |
1085 | @item case_eqv_table | |
1086 | This field contains the equivalence table for case-folding search. | |
969fe9b5 | 1087 | @xref{Case Tables}. |
a44af9f2 | 1088 | |
95260b26 GM |
1089 | @item truncate_lines |
1090 | The value of @code{truncate-lines} in this buffer. | |
a44af9f2 | 1091 | |
95260b26 GM |
1092 | @item ctl_arrow |
1093 | The value of @code{ctl-arrow} in this buffer. | |
a44af9f2 | 1094 | |
95260b26 GM |
1095 | @item selective_display |
1096 | The value of @code{selective-display} in this buffer. | |
a44af9f2 | 1097 | |
95260b26 GM |
1098 | @item selective_display_ellipsis |
1099 | The value of @code{selective-display-ellipsis} in this buffer. | |
a44af9f2 | 1100 | |
95260b26 GM |
1101 | @item minor_modes |
1102 | An alist of the minor modes of this buffer. | |
a890e1b0 | 1103 | |
95260b26 GM |
1104 | @item overwrite_mode |
1105 | The value of @code{overwrite_mode} in this buffer. | |
a890e1b0 | 1106 | |
95260b26 GM |
1107 | @item abbrev_mode |
1108 | The value of @code{abbrev-mode} in this buffer. | |
bfe721d1 | 1109 | |
95260b26 GM |
1110 | @item display_table |
1111 | This field contains the buffer's display table, or @code{nil} if it doesn't | |
1112 | have one. @xref{Display Tables}. | |
a890e1b0 | 1113 | |
95260b26 GM |
1114 | @item save_modified |
1115 | This field contains the time when the buffer was last saved, as an integer. | |
1116 | @xref{Buffer Modification}. | |
1117 | ||
1118 | @item mark_active | |
1119 | This field is non-@code{nil} if the buffer's mark is active. | |
a890e1b0 RS |
1120 | |
1121 | @item overlays_before | |
1122 | This field holds a list of the overlays in this buffer that end at or | |
1123 | before the current overlay center position. They are sorted in order of | |
1124 | decreasing end position. | |
1125 | ||
1126 | @item overlays_after | |
1127 | This field holds a list of the overlays in this buffer that end after | |
1128 | the current overlay center position. They are sorted in order of | |
1129 | increasing beginning position. | |
969fe9b5 | 1130 | |
95260b26 GM |
1131 | @item overlay_center |
1132 | This field holds the current overlay center position. @xref{Overlays}. | |
1133 | ||
969fe9b5 RS |
1134 | @item enable_multibyte_characters |
1135 | This field holds the buffer's local value of | |
1136 | @code{enable-multibyte-characters}---either @code{t} or @code{nil}. | |
95260b26 GM |
1137 | |
1138 | @item buffer_file_coding_system | |
1139 | The value of @code{buffer-file-coding-system} in this buffer. | |
1140 | ||
1141 | @item file_format | |
1142 | The value of @code{buffer-file-format} in this buffer. | |
1143 | ||
980aaec7 LT |
1144 | @item auto_save_file_format |
1145 | The value of @code{buffer-auto-save-file-format} in this buffer. | |
1146 | ||
95260b26 GM |
1147 | @item pt_marker |
1148 | In an indirect buffer, or a buffer that is the base of an indirect | |
1149 | buffer, this holds a marker that records point for this buffer when the | |
1150 | buffer is not current. | |
1151 | ||
1152 | @item begv_marker | |
1153 | In an indirect buffer, or a buffer that is the base of an indirect | |
1154 | buffer, this holds a marker that records @code{begv} for this buffer | |
1155 | when the buffer is not current. | |
88510b17 | 1156 | |
95260b26 GM |
1157 | @item zv_marker |
1158 | In an indirect buffer, or a buffer that is the base of an indirect | |
1159 | buffer, this holds a marker that records @code{zv} for this buffer when | |
1160 | the buffer is not current. | |
1161 | ||
1162 | @item file_truename | |
1163 | The truename of the visited file, or @code{nil}. | |
1164 | ||
1165 | @item invisibility_spec | |
1166 | The value of @code{buffer-invisibility-spec} in this buffer. | |
1167 | ||
1168 | @item last_selected_window | |
1169 | This is the last window that was selected with this buffer in it, or @code{nil} | |
1170 | if that window no longer displays this buffer. | |
1171 | ||
1172 | @item display_count | |
1173 | This field is incremented each time the buffer is displayed in a window. | |
1174 | ||
1175 | @item left_margin_width | |
1176 | The value of @code{left-margin-width} in this buffer. | |
1177 | ||
1178 | @item right_margin_width | |
1179 | The value of @code{right-margin-width} in this buffer. | |
1180 | ||
1181 | @item indicate_empty_lines | |
1182 | Non-@code{nil} means indicate empty lines (lines with no text) with a | |
1183 | small bitmap in the fringe, when using a window system that can do it. | |
1184 | ||
1185 | @item display_time | |
1186 | This holds a time stamp that is updated each time this buffer is | |
1187 | displayed in a window. | |
1188 | ||
1189 | @item scroll_up_aggressively | |
1190 | The value of @code{scroll-up-aggressively} in this buffer. | |
88510b17 | 1191 | |
95260b26 GM |
1192 | @item scroll_down_aggressively |
1193 | The value of @code{scroll-down-aggressively} in this buffer. | |
a44af9f2 RS |
1194 | @end table |
1195 | ||
969fe9b5 | 1196 | @node Window Internals |
a44af9f2 RS |
1197 | @appendixsubsec Window Internals |
1198 | @cindex internals, of window | |
1199 | @cindex window internals | |
1200 | ||
1201 | Windows have the following accessible fields: | |
1202 | ||
1203 | @table @code | |
1204 | @item frame | |
a890e1b0 | 1205 | The frame that this window is on. |
a44af9f2 RS |
1206 | |
1207 | @item mini_p | |
a890e1b0 | 1208 | Non-@code{nil} if this window is a minibuffer window. |
a44af9f2 | 1209 | |
95260b26 GM |
1210 | @item parent |
1211 | Internally, Emacs arranges windows in a tree; each group of siblings has | |
1212 | a parent window whose area includes all the siblings. This field points | |
1213 | to a window's parent. | |
1214 | ||
1215 | Parent windows do not display buffers, and play little role in display | |
1216 | except to shape their child windows. Emacs Lisp programs usually have | |
1217 | no access to the parent windows; they operate on the windows at the | |
1218 | leaves of the tree, which actually display buffers. | |
1219 | ||
1220 | The following four fields also describe the window tree structure. | |
1221 | ||
1222 | @item hchild | |
1223 | In a window subdivided horizontally by child windows, the leftmost child. | |
1224 | Otherwise, @code{nil}. | |
1225 | ||
1226 | @item vchild | |
1227 | In a window subdivided vertically by child windows, the topmost child. | |
1228 | Otherwise, @code{nil}. | |
1229 | ||
1230 | @item next | |
1231 | The next sibling of this window. It is @code{nil} in a window that is | |
1232 | the rightmost or bottommost of a group of siblings. | |
1233 | ||
1234 | @item prev | |
1235 | The previous sibling of this window. It is @code{nil} in a window that | |
1236 | is the leftmost or topmost of a group of siblings. | |
1237 | ||
1238 | @item left | |
1239 | This is the left-hand edge of the window, measured in columns. (The | |
1240 | leftmost column on the screen is @w{column 0}.) | |
1241 | ||
1242 | @item top | |
1243 | This is the top edge of the window, measured in lines. (The top line on | |
1244 | the screen is @w{line 0}.) | |
1245 | ||
1246 | @item height | |
1247 | The height of the window, measured in lines. | |
1248 | ||
1249 | @item width | |
1250 | The width of the window, measured in columns. This width includes the | |
1251 | scroll bar and fringes, and/or the separator line on the right of the | |
1252 | window (if any). | |
1253 | ||
a44af9f2 | 1254 | @item buffer |
574efc83 | 1255 | The buffer that the window is displaying. This may change often during |
a44af9f2 RS |
1256 | the life of the window. |
1257 | ||
95260b26 GM |
1258 | @item start |
1259 | The position in the buffer that is the first character to be displayed | |
1260 | in the window. | |
a44af9f2 RS |
1261 | |
1262 | @item pointm | |
1263 | @cindex window point internals | |
a890e1b0 | 1264 | This is the value of point in the current buffer when this window is |
a44af9f2 RS |
1265 | selected; when it is not selected, it retains its previous value. |
1266 | ||
a890e1b0 RS |
1267 | @item force_start |
1268 | If this flag is non-@code{nil}, it says that the window has been | |
1269 | scrolled explicitly by the Lisp program. This affects what the next | |
1270 | redisplay does if point is off the screen: instead of scrolling the | |
1271 | window to show the text around point, it moves point to a location that | |
1272 | is on the screen. | |
1273 | ||
95260b26 | 1274 | @item frozen_window_start_p |
88510b17 | 1275 | This field is set temporarily to 1 to indicate to redisplay that |
95260b26 GM |
1276 | @code{start} of this window should not be changed, even if point |
1277 | gets invisible. | |
1278 | ||
1279 | @item start_at_line_beg | |
1280 | Non-@code{nil} means current value of @code{start} was the beginning of a line | |
1281 | when it was chosen. | |
1282 | ||
1283 | @item too_small_ok | |
827b7ee7 | 1284 | Non-@code{nil} means don't delete this window for becoming ``too small.'' |
95260b26 GM |
1285 | |
1286 | @item height_fixed_p | |
1287 | This field is temporarily set to 1 to fix the height of the selected | |
1288 | window when the echo area is resized. | |
1289 | ||
1290 | @item use_time | |
1291 | This is the last time that the window was selected. The function | |
1292 | @code{get-lru-window} uses this field. | |
1293 | ||
1294 | @item sequence_number | |
1295 | A unique number assigned to this window when it was created. | |
1296 | ||
a890e1b0 | 1297 | @item last_modified |
95260b26 | 1298 | The @code{modiff} field of the window's buffer, as of the last time |
a890e1b0 RS |
1299 | a redisplay completed in this window. |
1300 | ||
95260b26 GM |
1301 | @item last_overlay_modified |
1302 | The @code{overlay_modiff} field of the window's buffer, as of the last | |
1303 | time a redisplay completed in this window. | |
1304 | ||
a890e1b0 | 1305 | @item last_point |
95260b26 GM |
1306 | The buffer's value of point, as of the last time a redisplay completed |
1307 | in this window. | |
a890e1b0 | 1308 | |
95260b26 GM |
1309 | @item last_had_star |
1310 | A non-@code{nil} value means the window's buffer was ``modified'' when the | |
1311 | window was last updated. | |
a44af9f2 | 1312 | |
95260b26 GM |
1313 | @item vertical_scroll_bar |
1314 | This window's vertical scroll bar. | |
a44af9f2 | 1315 | |
95260b26 GM |
1316 | @item left_margin_width |
1317 | The width of the left margin in this window, or @code{nil} not to | |
1318 | specify it (in which case the buffer's value of @code{left-margin-width} | |
1319 | is used. | |
a890e1b0 | 1320 | |
95260b26 GM |
1321 | @item right_margin_width |
1322 | Likewise for the right margin. | |
a890e1b0 | 1323 | |
13ede7fc | 1324 | @ignore |
95260b26 GM |
1325 | @item last_mark_x |
1326 | @item last_mark_y | |
1327 | ???Not used. | |
1328 | @end ignore | |
a44af9f2 | 1329 | |
95260b26 GM |
1330 | @item window_end_pos |
1331 | This is computed as @code{z} minus the buffer position of the last glyph | |
1332 | in the current matrix of the window. The value is only valid if | |
1333 | @code{window_end_valid} is not @code{nil}. | |
a44af9f2 | 1334 | |
95260b26 GM |
1335 | @item window_end_bytepos |
1336 | The byte position corresponding to @code{window_end_pos}. | |
a890e1b0 | 1337 | |
95260b26 GM |
1338 | @item window_end_vpos |
1339 | The window-relative vertical position of the line containing | |
1340 | @code{window_end_pos}. | |
a44af9f2 | 1341 | |
95260b26 GM |
1342 | @item window_end_valid |
1343 | This field is set to a non-@code{nil} value if @code{window_end_pos} is truly | |
1344 | valid. This is @code{nil} if nontrivial redisplay is preempted since in that | |
1345 | case the display that @code{window_end_pos} was computed for did not get | |
1346 | onto the screen. | |
1347 | ||
1348 | @item redisplay_end_trigger | |
1349 | If redisplay in this window goes beyond this buffer position, it runs | |
2a233172 | 1350 | the @code{redisplay-end-trigger-hook}. |
95260b26 | 1351 | |
13ede7fc | 1352 | @ignore |
95260b26 GM |
1353 | @item orig_height |
1354 | @item orig_top | |
1355 | ??? Are temporary storage areas. | |
1356 | @end ignore | |
1357 | ||
1358 | @item cursor | |
1359 | A structure describing where the cursor is in this window. | |
1360 | ||
1361 | @item last_cursor | |
1362 | The value of @code{cursor} as of the last redisplay that finished. | |
1363 | ||
1364 | @item phys_cursor | |
1365 | A structure describing where the cursor of this window physically is. | |
1366 | ||
1367 | @item phys_cursor_type | |
1368 | The type of cursor that was last displayed on this window. | |
1369 | ||
1370 | @item phys_cursor_on_p | |
1371 | This field is non-zero if the cursor is physically on. | |
1372 | ||
1373 | @item cursor_off_p | |
1374 | Non-zero means the cursor in this window is logically on. | |
1375 | ||
1376 | @item last_cursor_off_p | |
1377 | This field contains the value of @code{cursor_off_p} as of the time of | |
1378 | the last redisplay. | |
1379 | ||
1380 | @item must_be_updated_p | |
1381 | This is set to 1 during redisplay when this window must be updated. | |
1382 | ||
a44af9f2 | 1383 | @item hscroll |
a890e1b0 | 1384 | This is the number of columns that the display in the window is scrolled |
a44af9f2 RS |
1385 | horizontally to the left. Normally, this is 0. |
1386 | ||
95260b26 GM |
1387 | @item vscroll |
1388 | Vertical scroll amount, in pixels. Normally, this is 0. | |
1389 | ||
1390 | @item dedicated | |
1391 | Non-@code{nil} if this window is dedicated to its buffer. | |
a44af9f2 RS |
1392 | |
1393 | @item display_table | |
a890e1b0 RS |
1394 | The window's display table, or @code{nil} if none is specified for it. |
1395 | ||
1396 | @item update_mode_line | |
1397 | Non-@code{nil} means this window's mode line needs to be updated. | |
1398 | ||
1399 | @item base_line_number | |
1400 | The line number of a certain position in the buffer, or @code{nil}. | |
1401 | This is used for displaying the line number of point in the mode line. | |
1402 | ||
1403 | @item base_line_pos | |
1404 | The position in the buffer for which the line number is known, or | |
1405 | @code{nil} meaning none is known. | |
1406 | ||
1407 | @item region_showing | |
1408 | If the region (or part of it) is highlighted in this window, this field | |
1409 | holds the mark position that made one end of that region. Otherwise, | |
1410 | this field is @code{nil}. | |
95260b26 GM |
1411 | |
1412 | @item column_number_displayed | |
1413 | The column number currently displayed in this window's mode line, or @code{nil} | |
1414 | if column numbers are not being displayed. | |
1415 | ||
1416 | @item current_matrix | |
1417 | A glyph matrix describing the current display of this window. | |
1418 | ||
1419 | @item desired_matrix | |
1420 | A glyph matrix describing the desired display of this window. | |
a44af9f2 RS |
1421 | @end table |
1422 | ||
969fe9b5 | 1423 | @node Process Internals |
a44af9f2 RS |
1424 | @appendixsubsec Process Internals |
1425 | @cindex internals, of process | |
1426 | @cindex process internals | |
1427 | ||
1428 | The fields of a process are: | |
1429 | ||
1430 | @table @code | |
1431 | @item name | |
1432 | A string, the name of the process. | |
1433 | ||
1434 | @item command | |
1435 | A list containing the command arguments that were used to start this | |
1436 | process. | |
1437 | ||
1438 | @item filter | |
1439 | A function used to accept output from the process instead of a buffer, | |
1440 | or @code{nil}. | |
1441 | ||
1442 | @item sentinel | |
1443 | A function called whenever the process receives a signal, or @code{nil}. | |
1444 | ||
1445 | @item buffer | |
1446 | The associated buffer of the process. | |
1447 | ||
1448 | @item pid | |
2a233172 | 1449 | An integer, the operating system's process @acronym{ID}. |
a44af9f2 RS |
1450 | |
1451 | @item childp | |
1452 | A flag, non-@code{nil} if this is really a child process. | |
1453 | It is @code{nil} for a network connection. | |
1454 | ||
a44af9f2 | 1455 | @item mark |
574efc83 RS |
1456 | A marker indicating the position of the end of the last output from this |
1457 | process inserted into the buffer. This is often but not always the end | |
1458 | of the buffer. | |
a44af9f2 RS |
1459 | |
1460 | @item kill_without_query | |
a890e1b0 RS |
1461 | If this is non-@code{nil}, killing Emacs while this process is still |
1462 | running does not ask for confirmation about killing the process. | |
1463 | ||
1464 | @item raw_status_low | |
1465 | @itemx raw_status_high | |
1466 | These two fields record 16 bits each of the process status returned by | |
1467 | the @code{wait} system call. | |
1468 | ||
1469 | @item status | |
1470 | The process status, as @code{process-status} should return it. | |
1471 | ||
1472 | @item tick | |
1473 | @itemx update_tick | |
1474 | If these two fields are not equal, a change in the status of the process | |
1475 | needs to be reported, either by running the sentinel or by inserting a | |
1476 | message in the process buffer. | |
1477 | ||
1478 | @item pty_flag | |
ad800164 | 1479 | Non-@code{nil} if communication with the subprocess uses a @acronym{PTY}; |
a890e1b0 RS |
1480 | @code{nil} if it uses a pipe. |
1481 | ||
1482 | @item infd | |
1483 | The file descriptor for input from the process. | |
1484 | ||
1485 | @item outfd | |
1486 | The file descriptor for output to the process. | |
1487 | ||
1488 | @item subtty | |
1489 | The file descriptor for the terminal that the subprocess is using. (On | |
1490 | some systems, there is no need to record this, so the value is | |
1491 | @code{nil}.) | |
bfe721d1 KH |
1492 | |
1493 | @item tty_name | |
1494 | The name of the terminal that the subprocess is using, | |
1495 | or @code{nil} if it is using pipes. | |
95260b26 GM |
1496 | |
1497 | @item decode_coding_system | |
1498 | Coding-system for decoding the input from this process. | |
1499 | ||
1500 | @item decoding_buf | |
1501 | A working buffer for decoding. | |
1502 | ||
1503 | @item decoding_carryover | |
1504 | Size of carryover in decoding. | |
1505 | ||
1506 | @item encode_coding_system | |
1507 | Coding-system for encoding the output to this process. | |
1508 | ||
1509 | @item encoding_buf | |
a39c2e0d | 1510 | A working buffer for encoding. |
95260b26 GM |
1511 | |
1512 | @item encoding_carryover | |
1513 | Size of carryover in encoding. | |
1514 | ||
1515 | @item inherit_coding_system_flag | |
1516 | Flag to set @code{coding-system} of the process buffer from the | |
1517 | coding system used to decode process output. | |
a44af9f2 | 1518 | @end table |
ab5796a9 MB |
1519 | |
1520 | @ignore | |
1521 | arch-tag: 4b2c33bc-d7e4-43f5-bc20-27c0db52a53e | |
1522 | @end ignore |