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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
651f374c | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1998, 1999, 2002, 2003, 2004, |
ceb4c4d3 | 4 | @c 2005, 2006 Free Software Foundation, Inc. |
a44af9f2 RS |
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 | |
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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 |
2a664e73 RS |
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 | |
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158 | allocated when Emacs is compiled, and if that is not sufficient for |
159 | the preloaded libraries, @file{temacs} allocates dynamic memory for | |
160 | the part that didn't fit. If that happens, you should increase the | |
161 | compilation parameter @code{PURESIZE} in the file | |
162 | @file{src/puresize.h} and rebuild Emacs, even though the resulting | |
163 | image will work. Such an overflow normally won't happen unless you | |
164 | try to preload additional libraries or add features to the standard | |
165 | ones. Emacs will display a warning about the overflow when it | |
166 | starts. | |
a44af9f2 RS |
167 | |
168 | @defun purecopy object | |
8241495d RS |
169 | This function makes a copy in pure storage of @var{object}, and returns |
170 | it. It copies a string by simply making a new string with the same | |
568ffbee LT |
171 | characters, but without text properties, in pure storage. It |
172 | recursively copies the contents of vectors and cons cells. It does | |
173 | not make copies of other objects such as symbols, but just returns | |
174 | them unchanged. It signals an error if asked to copy markers. | |
a44af9f2 | 175 | |
c2cd5fb7 RS |
176 | This function is a no-op except while Emacs is being built and dumped; |
177 | it is usually called only in the file @file{emacs/lisp/loaddefs.el}, but | |
178 | a few packages call it just in case you decide to preload them. | |
a44af9f2 RS |
179 | @end defun |
180 | ||
181 | @defvar pure-bytes-used | |
a890e1b0 | 182 | The value of this variable is the number of bytes of pure storage |
a44af9f2 RS |
183 | allocated so far. Typically, in a dumped Emacs, this number is very |
184 | close to the total amount of pure storage available---if it were not, | |
185 | we would preallocate less. | |
186 | @end defvar | |
187 | ||
188 | @defvar purify-flag | |
a890e1b0 | 189 | This variable determines whether @code{defun} should make a copy of the |
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190 | function definition in pure storage. If it is non-@code{nil}, then the |
191 | function definition is copied into pure storage. | |
192 | ||
a890e1b0 | 193 | This flag is @code{t} while loading all of the basic functions for |
a44af9f2 | 194 | building Emacs initially (allowing those functions to be sharable and |
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195 | non-collectible). Dumping Emacs as an executable always writes |
196 | @code{nil} in this variable, regardless of the value it actually has | |
197 | before and after dumping. | |
a44af9f2 | 198 | |
a890e1b0 | 199 | You should not change this flag in a running Emacs. |
a44af9f2 RS |
200 | @end defvar |
201 | ||
969fe9b5 | 202 | @node Garbage Collection |
a44af9f2 RS |
203 | @appendixsec Garbage Collection |
204 | @cindex garbage collector | |
205 | ||
206 | @cindex memory allocation | |
207 | When a program creates a list or the user defines a new function (such | |
a890e1b0 RS |
208 | as by loading a library), that data is placed in normal storage. If |
209 | normal storage runs low, then Emacs asks the operating system to | |
a44af9f2 | 210 | allocate more memory in blocks of 1k bytes. Each block is used for one |
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211 | type of Lisp object, so symbols, cons cells, markers, etc., are |
212 | segregated in distinct blocks in memory. (Vectors, long strings, | |
213 | buffers and certain other editing types, which are fairly large, are | |
214 | allocated in individual blocks, one per object, while small strings are | |
215 | packed into blocks of 8k bytes.) | |
216 | ||
217 | It is quite common to use some storage for a while, then release it by | |
218 | (for example) killing a buffer or deleting the last pointer to an | |
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219 | object. Emacs provides a @dfn{garbage collector} to reclaim this |
220 | abandoned storage. (This name is traditional, but ``garbage recycler'' | |
221 | might be a more intuitive metaphor for this facility.) | |
222 | ||
a890e1b0 RS |
223 | The garbage collector operates by finding and marking all Lisp objects |
224 | that are still accessible to Lisp programs. To begin with, it assumes | |
225 | all the symbols, their values and associated function definitions, and | |
574efc83 | 226 | any data presently on the stack, are accessible. Any objects that can |
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227 | be reached indirectly through other accessible objects are also |
228 | accessible. | |
a44af9f2 | 229 | |
a890e1b0 | 230 | When marking is finished, all objects still unmarked are garbage. No |
a44af9f2 | 231 | matter what the Lisp program or the user does, it is impossible to refer |
a890e1b0 | 232 | to them, since there is no longer a way to reach them. Their space |
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233 | might as well be reused, since no one will miss them. The second |
234 | (``sweep'') phase of the garbage collector arranges to reuse them. | |
a44af9f2 | 235 | |
05aea714 | 236 | @c ??? Maybe add something describing weak hash tables here? |
95260b26 | 237 | |
a44af9f2 | 238 | @cindex free list |
a890e1b0 RS |
239 | The sweep phase puts unused cons cells onto a @dfn{free list} |
240 | for future allocation; likewise for symbols and markers. It compacts | |
241 | the accessible strings so they occupy fewer 8k blocks; then it frees the | |
574efc83 | 242 | other 8k blocks. Vectors, buffers, windows, and other large objects are |
a890e1b0 | 243 | individually allocated and freed using @code{malloc} and @code{free}. |
a44af9f2 RS |
244 | |
245 | @cindex CL note---allocate more storage | |
246 | @quotation | |
574efc83 | 247 | @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not |
a44af9f2 RS |
248 | call the garbage collector when the free list is empty. Instead, it |
249 | simply requests the operating system to allocate more storage, and | |
250 | processing continues until @code{gc-cons-threshold} bytes have been | |
251 | used. | |
252 | ||
253 | This means that you can make sure that the garbage collector will not | |
254 | run during a certain portion of a Lisp program by calling the garbage | |
255 | collector explicitly just before it (provided that portion of the | |
256 | program does not use so much space as to force a second garbage | |
257 | collection). | |
258 | @end quotation | |
259 | ||
260 | @deffn Command garbage-collect | |
a890e1b0 | 261 | This command runs a garbage collection, and returns information on |
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262 | the amount of space in use. (Garbage collection can also occur |
263 | spontaneously if you use more than @code{gc-cons-threshold} bytes of | |
264 | Lisp data since the previous garbage collection.) | |
265 | ||
a890e1b0 | 266 | @code{garbage-collect} returns a list containing the following |
a44af9f2 RS |
267 | information: |
268 | ||
a890e1b0 | 269 | @example |
a44af9f2 RS |
270 | @group |
271 | ((@var{used-conses} . @var{free-conses}) | |
272 | (@var{used-syms} . @var{free-syms}) | |
a890e1b0 | 273 | @end group |
969fe9b5 | 274 | (@var{used-miscs} . @var{free-miscs}) |
40d48fe9 | 275 | @var{used-string-chars} |
a44af9f2 | 276 | @var{used-vector-slots} |
f9f59935 | 277 | (@var{used-floats} . @var{free-floats}) |
40d48fe9 EZ |
278 | (@var{used-intervals} . @var{free-intervals}) |
279 | (@var{used-strings} . @var{free-strings})) | |
969fe9b5 RS |
280 | @end example |
281 | ||
282 | Here is an example: | |
283 | ||
284 | @example | |
a890e1b0 | 285 | @group |
a44af9f2 | 286 | (garbage-collect) |
f9f59935 RS |
287 | @result{} ((106886 . 13184) (9769 . 0) |
288 | (7731 . 4651) 347543 121628 | |
40d48fe9 EZ |
289 | (31 . 94) (1273 . 168) |
290 | (25474 . 3569)) | |
a44af9f2 | 291 | @end group |
a890e1b0 | 292 | @end example |
a44af9f2 RS |
293 | |
294 | Here is a table explaining each element: | |
295 | ||
296 | @table @var | |
297 | @item used-conses | |
298 | The number of cons cells in use. | |
299 | ||
300 | @item free-conses | |
301 | The number of cons cells for which space has been obtained from the | |
302 | operating system, but that are not currently being used. | |
303 | ||
304 | @item used-syms | |
305 | The number of symbols in use. | |
306 | ||
307 | @item free-syms | |
308 | The number of symbols for which space has been obtained from the | |
309 | operating system, but that are not currently being used. | |
310 | ||
969fe9b5 RS |
311 | @item used-miscs |
312 | The number of miscellaneous objects in use. These include markers and | |
313 | overlays, plus certain objects not visible to users. | |
a44af9f2 | 314 | |
969fe9b5 RS |
315 | @item free-miscs |
316 | The number of miscellaneous objects for which space has been obtained | |
317 | from the operating system, but that are not currently being used. | |
a44af9f2 RS |
318 | |
319 | @item used-string-chars | |
320 | The total size of all strings, in characters. | |
321 | ||
322 | @item used-vector-slots | |
323 | The total number of elements of existing vectors. | |
324 | ||
325 | @item used-floats | |
326 | @c Emacs 19 feature | |
327 | The number of floats in use. | |
328 | ||
329 | @item free-floats | |
330 | @c Emacs 19 feature | |
331 | The number of floats for which space has been obtained from the | |
332 | operating system, but that are not currently being used. | |
a9f0a989 RS |
333 | |
334 | @item used-intervals | |
335 | The number of intervals in use. Intervals are an internal | |
336 | data structure used for representing text properties. | |
337 | ||
338 | @item free-intervals | |
339 | The number of intervals for which space has been obtained | |
340 | from the operating system, but that are not currently being used. | |
40d48fe9 EZ |
341 | |
342 | @item used-strings | |
343 | The number of strings in use. | |
344 | ||
345 | @item free-strings | |
346 | The number of string headers for which the space was obtained from the | |
347 | operating system, but which are currently not in use. (A string | |
348 | object consists of a header and the storage for the string text | |
349 | itself; the latter is only allocated when the string is created.) | |
a44af9f2 RS |
350 | @end table |
351 | @end deffn | |
352 | ||
d64c55d8 RS |
353 | @defopt garbage-collection-messages |
354 | If this variable is non-@code{nil}, Emacs displays a message at the | |
355 | beginning and end of garbage collection. The default value is | |
356 | @code{nil}, meaning there are no such messages. | |
357 | @end defopt | |
358 | ||
e73c3ec4 RS |
359 | @defvar post-gc-hook |
360 | This is a normal hook that is run at the end of garbage collection. | |
361 | Garbage collection is inhibited while the hook functions run, so be | |
362 | careful writing them. | |
363 | @end defvar | |
364 | ||
a44af9f2 | 365 | @defopt gc-cons-threshold |
a890e1b0 | 366 | The value of this variable is the number of bytes of storage that must |
a44af9f2 | 367 | be allocated for Lisp objects after one garbage collection in order to |
a890e1b0 | 368 | trigger another garbage collection. A cons cell counts as eight bytes, |
a44af9f2 | 369 | a string as one byte per character plus a few bytes of overhead, and so |
a890e1b0 RS |
370 | on; space allocated to the contents of buffers does not count. Note |
371 | that the subsequent garbage collection does not happen immediately when | |
372 | the threshold is exhausted, but only the next time the Lisp evaluator is | |
a44af9f2 RS |
373 | called. |
374 | ||
f9f59935 | 375 | The initial threshold value is 400,000. If you specify a larger |
a44af9f2 RS |
376 | value, garbage collection will happen less often. This reduces the |
377 | amount of time spent garbage collecting, but increases total memory use. | |
574efc83 | 378 | You may want to do this when running a program that creates lots of |
a44af9f2 RS |
379 | Lisp data. |
380 | ||
a890e1b0 | 381 | You can make collections more frequent by specifying a smaller value, |
a44af9f2 RS |
382 | down to 10,000. A value less than 10,000 will remain in effect only |
383 | until the subsequent garbage collection, at which time | |
384 | @code{garbage-collect} will set the threshold back to 10,000. | |
0c17e67c SM |
385 | @end defopt |
386 | ||
387 | @defopt gc-cons-percentage | |
6696f2a4 RS |
388 | The value of this variable specifies the amount of consing before a |
389 | garbage collection occurs, as a fraction of the current heap size. | |
390 | This criterion and @code{gc-cons-threshold} apply in parallel, and | |
391 | garbage collection occurs only when both criteria are satisfied. | |
0c17e67c SM |
392 | |
393 | As the heap size increases, the time to perform a garbage collection | |
6696f2a4 RS |
394 | increases. Thus, it can be desirable to do them less frequently in |
395 | proportion. | |
a44af9f2 RS |
396 | @end defopt |
397 | ||
568ffbee | 398 | The value returned by @code{garbage-collect} describes the amount of |
969fe9b5 RS |
399 | memory used by Lisp data, broken down by data type. By contrast, the |
400 | function @code{memory-limit} provides information on the total amount of | |
401 | memory Emacs is currently using. | |
402 | ||
a44af9f2 RS |
403 | @c Emacs 19 feature |
404 | @defun memory-limit | |
405 | This function returns the address of the last byte Emacs has allocated, | |
406 | divided by 1024. We divide the value by 1024 to make sure it fits in a | |
407 | Lisp integer. | |
408 | ||
409 | You can use this to get a general idea of how your actions affect the | |
410 | memory usage. | |
411 | @end defun | |
412 | ||
3c4c00e6 RS |
413 | @defvar memory-full |
414 | This variable is @code{t} if Emacs is close to out of memory for Lisp | |
415 | objects, and @code{nil} otherwise. | |
416 | @end defvar | |
417 | ||
5b2279a3 RS |
418 | @defun memory-use-counts |
419 | This returns a list of numbers that count the number of objects | |
420 | created in this Emacs session. Each of these counters increments for | |
421 | a certain kind of object. See the documentation string for details. | |
422 | @end defun | |
423 | ||
66c0f054 RS |
424 | @defvar gcs-done |
425 | This variable contains the total number of garbage collections | |
426 | done so far in this Emacs session. | |
f0514b34 | 427 | @end defvar |
66c0f054 RS |
428 | |
429 | @defvar gc-elapsed | |
430 | This variable contains the total number of seconds of elapsed time | |
431 | during garbage collection so far in this Emacs session, as a floating | |
432 | point number. | |
f0514b34 | 433 | @end defvar |
66c0f054 | 434 | |
969fe9b5 RS |
435 | @node Memory Usage |
436 | @section Memory Usage | |
437 | ||
438 | These functions and variables give information about the total amount | |
439 | of memory allocation that Emacs has done, broken down by data type. | |
440 | Note the difference between these and the values returned by | |
441 | @code{(garbage-collect)}; those count objects that currently exist, but | |
442 | these count the number or size of all allocations, including those for | |
443 | objects that have since been freed. | |
444 | ||
445 | @defvar cons-cells-consed | |
446 | The total number of cons cells that have been allocated so far | |
447 | in this Emacs session. | |
448 | @end defvar | |
449 | ||
450 | @defvar floats-consed | |
451 | The total number of floats that have been allocated so far | |
452 | in this Emacs session. | |
453 | @end defvar | |
454 | ||
455 | @defvar vector-cells-consed | |
456 | The total number of vector cells that have been allocated so far | |
457 | in this Emacs session. | |
458 | @end defvar | |
459 | ||
460 | @defvar symbols-consed | |
461 | The total number of symbols that have been allocated so far | |
462 | in this Emacs session. | |
463 | @end defvar | |
464 | ||
465 | @defvar string-chars-consed | |
466 | The total number of string characters that have been allocated so far | |
467 | in this Emacs session. | |
468 | @end defvar | |
469 | ||
470 | @defvar misc-objects-consed | |
471 | The total number of miscellaneous objects that have been allocated so | |
472 | far in this Emacs session. These include markers and overlays, plus | |
473 | certain objects not visible to users. | |
474 | @end defvar | |
475 | ||
476 | @defvar intervals-consed | |
477 | The total number of intervals that have been allocated so far | |
478 | in this Emacs session. | |
479 | @end defvar | |
480 | ||
40d48fe9 EZ |
481 | @defvar strings-consed |
482 | The total number of strings that have been allocated so far in this | |
483 | Emacs session. | |
484 | @end defvar | |
485 | ||
969fe9b5 | 486 | @node Writing Emacs Primitives |
a44af9f2 RS |
487 | @appendixsec Writing Emacs Primitives |
488 | @cindex primitive function internals | |
489 | ||
490 | Lisp primitives are Lisp functions implemented in C. The details of | |
491 | interfacing the C function so that Lisp can call it are handled by a few | |
492 | C macros. The only way to really understand how to write new C code is | |
493 | to read the source, but we can explain some things here. | |
494 | ||
495 | An example of a special form is the definition of @code{or}, from | |
496 | @file{eval.c}. (An ordinary function would have the same general | |
497 | appearance.) | |
498 | ||
499 | @cindex garbage collection protection | |
500 | @smallexample | |
501 | @group | |
502 | DEFUN ("or", For, Sor, 0, UNEVALLED, 0, | |
f1842270 RS |
503 | doc: /* Eval args until one of them yields non-nil, then return that value. |
504 | The remaining args are not evalled at all. | |
505 | If all args return nil, return nil. | |
a44af9f2 RS |
506 | @end group |
507 | @group | |
f1842270 | 508 | usage: (or CONDITIONS ...) */) |
a44af9f2 RS |
509 | (args) |
510 | Lisp_Object args; | |
511 | @{ | |
51485df2 | 512 | register Lisp_Object val = Qnil; |
a44af9f2 RS |
513 | struct gcpro gcpro1; |
514 | @end group | |
515 | ||
516 | @group | |
51485df2 | 517 | GCPRO1 (args); |
a44af9f2 RS |
518 | @end group |
519 | ||
520 | @group | |
51485df2 | 521 | while (CONSP (args)) |
a44af9f2 | 522 | @{ |
51485df2 | 523 | val = Feval (XCAR (args)); |
95260b26 | 524 | if (!NILP (val)) |
51485df2 RS |
525 | break; |
526 | args = XCDR (args); | |
a44af9f2 | 527 | @} |
a44af9f2 RS |
528 | @end group |
529 | ||
530 | @group | |
531 | UNGCPRO; | |
532 | return val; | |
533 | @} | |
534 | @end group | |
535 | @end smallexample | |
536 | ||
537 | Let's start with a precise explanation of the arguments to the | |
a890e1b0 | 538 | @code{DEFUN} macro. Here is a template for them: |
a44af9f2 RS |
539 | |
540 | @example | |
541 | DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc}) | |
542 | @end example | |
543 | ||
544 | @table @var | |
545 | @item lname | |
a890e1b0 RS |
546 | This is the name of the Lisp symbol to define as the function name; in |
547 | the example above, it is @code{or}. | |
a44af9f2 RS |
548 | |
549 | @item fname | |
550 | This is the C function name for this function. This is | |
551 | the name that is used in C code for calling the function. The name is, | |
552 | by convention, @samp{F} prepended to the Lisp name, with all dashes | |
553 | (@samp{-}) in the Lisp name changed to underscores. Thus, to call this | |
554 | function from C code, call @code{For}. Remember that the arguments must | |
555 | be of type @code{Lisp_Object}; various macros and functions for creating | |
556 | values of type @code{Lisp_Object} are declared in the file | |
557 | @file{lisp.h}. | |
558 | ||
559 | @item sname | |
560 | This is a C variable name to use for a structure that holds the data for | |
561 | the subr object that represents the function in Lisp. This structure | |
562 | conveys the Lisp symbol name to the initialization routine that will | |
563 | create the symbol and store the subr object as its definition. By | |
564 | convention, this name is always @var{fname} with @samp{F} replaced with | |
565 | @samp{S}. | |
566 | ||
567 | @item min | |
a890e1b0 RS |
568 | This is the minimum number of arguments that the function requires. The |
569 | function @code{or} allows a minimum of zero arguments. | |
a44af9f2 RS |
570 | |
571 | @item max | |
a890e1b0 RS |
572 | This is the maximum number of arguments that the function accepts, if |
573 | there is a fixed maximum. Alternatively, it can be @code{UNEVALLED}, | |
574 | indicating a special form that receives unevaluated arguments, or | |
575 | @code{MANY}, indicating an unlimited number of evaluated arguments (the | |
576 | equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are | |
577 | macros. If @var{max} is a number, it may not be less than @var{min} and | |
51485df2 | 578 | it may not be greater than eight. |
a44af9f2 RS |
579 | |
580 | @item interactive | |
581 | This is an interactive specification, a string such as might be used as | |
582 | the argument of @code{interactive} in a Lisp function. In the case of | |
583 | @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be | |
a890e1b0 RS |
584 | called interactively. A value of @code{""} indicates a function that |
585 | should receive no arguments when called interactively. | |
a44af9f2 RS |
586 | |
587 | @item doc | |
f1842270 RS |
588 | This is the documentation string. It uses C comment syntax rather |
589 | than C string syntax because comment syntax requires nothing special | |
590 | to include multiple lines. The @samp{doc:} identifies the comment | |
591 | that follows as the documentation string. The @samp{/*} and @samp{*/} | |
592 | delimiters that begin and end the comment are not part of the | |
593 | documentation string. | |
594 | ||
595 | If the last line of the documentation string begins with the keyword | |
596 | @samp{usage:}, the rest of the line is treated as the argument list | |
597 | for documentation purposes. This way, you can use different argument | |
598 | names in the documentation string from the ones used in the C code. | |
0a692803 DL |
599 | @samp{usage:} is required if the function has an unlimited number of |
600 | arguments. | |
f1842270 RS |
601 | |
602 | All the usual rules for documentation strings in Lisp code | |
603 | (@pxref{Documentation Tips}) apply to C code documentation strings | |
604 | too. | |
a44af9f2 RS |
605 | @end table |
606 | ||
a890e1b0 RS |
607 | After the call to the @code{DEFUN} macro, you must write the argument |
608 | name list that every C function must have, followed by ordinary C | |
609 | declarations for the arguments. For a function with a fixed maximum | |
610 | number of arguments, declare a C argument for each Lisp argument, and | |
574efc83 RS |
611 | give them all type @code{Lisp_Object}. When a Lisp function has no |
612 | upper limit on the number of arguments, its implementation in C actually | |
613 | receives exactly two arguments: the first is the number of Lisp | |
614 | arguments, and the second is the address of a block containing their | |
615 | values. They have types @code{int} and @w{@code{Lisp_Object *}}. | |
a44af9f2 RS |
616 | |
617 | Within the function @code{For} itself, note the use of the macros | |
e4c068c0 RS |
618 | @code{GCPRO1} and @code{UNGCPRO}. @code{GCPRO1} is used to |
619 | ``protect'' a variable from garbage collection---to inform the garbage | |
620 | collector that it must look in that variable and regard its contents | |
621 | as an accessible object. GC protection is necessary whenever you call | |
622 | @code{Feval} or anything that can directly or indirectly call | |
623 | @code{Feval}. At such a time, any Lisp object that this function may | |
624 | refer to again must be protected somehow. | |
a44af9f2 | 625 | |
70bb4402 | 626 | It suffices to ensure that at least one pointer to each object is |
e4c068c0 RS |
627 | GC-protected; that way, the object cannot be recycled, so all pointers |
628 | to it remain valid. Thus, a particular local variable can do without | |
629 | protection if it is certain that the object it points to will be | |
630 | preserved by some other pointer (such as another local variable which | |
631 | has a @code{GCPRO})@footnote{Formerly, strings were a special | |
632 | exception; in older Emacs versions, every local variable that might | |
633 | point to a string needed a @code{GCPRO}.}. Otherwise, the local | |
634 | variable needs a @code{GCPRO}. | |
70bb4402 RS |
635 | |
636 | The macro @code{GCPRO1} protects just one local variable. If you | |
e4c068c0 RS |
637 | want to protect two variables, use @code{GCPRO2} instead; repeating |
638 | @code{GCPRO1} will not work. Macros @code{GCPRO3}, @code{GCPRO4}, | |
639 | @code{GCPRO5}, and @code{GCPRO6} also exist. All these macros | |
640 | implicitly use local variables such as @code{gcpro1}; you must declare | |
641 | these explicitly, with type @code{struct gcpro}. Thus, if you use | |
70bb4402 | 642 | @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}. |
a890e1b0 RS |
643 | Alas, we can't explain all the tricky details here. |
644 | ||
e4c068c0 RS |
645 | @code{UNGCPRO} cancels the protection of the variables that are |
646 | protected in the current function. It is necessary to do this | |
647 | explicitly. | |
648 | ||
70bb4402 RS |
649 | Built-in functions that take a variable number of arguments actually |
650 | accept two arguments at the C level: the number of Lisp arguments, and | |
651 | a @code{Lisp_Object *} pointer to a C vector containing those Lisp | |
652 | arguments. This C vector may be part of a Lisp vector, but it need | |
568ffbee | 653 | not be. The responsibility for using @code{GCPRO} to protect the Lisp |
236a1914 RS |
654 | arguments from GC if necessary rests with the caller in this case, |
655 | since the caller allocated or found the storage for them. | |
70bb4402 | 656 | |
e610024b | 657 | You must not use C initializers for static or global variables unless |
05aea714 | 658 | the variables are never written once Emacs is dumped. These variables |
8241495d RS |
659 | with initializers are allocated in an area of memory that becomes |
660 | read-only (on certain operating systems) as a result of dumping Emacs. | |
661 | @xref{Pure Storage}. | |
e610024b RS |
662 | |
663 | Do not use static variables within functions---place all static | |
664 | variables at top level in the file. This is necessary because Emacs on | |
665 | some operating systems defines the keyword @code{static} as a null | |
666 | macro. (This definition is used because those systems put all variables | |
667 | declared static in a place that becomes read-only after dumping, whether | |
668 | they have initializers or not.) | |
77223f05 | 669 | |
a890e1b0 RS |
670 | Defining the C function is not enough to make a Lisp primitive |
671 | available; you must also create the Lisp symbol for the primitive and | |
672 | store a suitable subr object in its function cell. The code looks like | |
673 | this: | |
a44af9f2 RS |
674 | |
675 | @example | |
676 | defsubr (&@var{subr-structure-name}); | |
677 | @end example | |
678 | ||
679 | @noindent | |
a890e1b0 RS |
680 | Here @var{subr-structure-name} is the name you used as the third |
681 | argument to @code{DEFUN}. | |
682 | ||
683 | If you add a new primitive to a file that already has Lisp primitives | |
684 | defined in it, find the function (near the end of the file) named | |
685 | @code{syms_of_@var{something}}, and add the call to @code{defsubr} | |
686 | there. If the file doesn't have this function, or if you create a new | |
687 | file, add to it a @code{syms_of_@var{filename}} (e.g., | |
688 | @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all | |
689 | of these functions are called, and add a call to | |
690 | @code{syms_of_@var{filename}} there. | |
a44af9f2 | 691 | |
568ffbee | 692 | @anchor{Defining Lisp variables in C} |
8241495d | 693 | @vindex byte-boolean-vars |
574efc83 RS |
694 | The function @code{syms_of_@var{filename}} is also the place to define |
695 | any C variables that are to be visible as Lisp variables. | |
a890e1b0 RS |
696 | @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible |
697 | in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int} | |
698 | visible in Lisp with a value that is always an integer. | |
699 | @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp | |
8241495d RS |
700 | with a value that is either @code{t} or @code{nil}. Note that variables |
701 | defined with @code{DEFVAR_BOOL} are automatically added to the list | |
702 | @code{byte-boolean-vars} used by the byte compiler. | |
a44af9f2 | 703 | |
969fe9b5 | 704 | If you define a file-scope C variable of type @code{Lisp_Object}, |
8241495d | 705 | you must protect it from garbage-collection by calling @code{staticpro} |
969fe9b5 RS |
706 | in @code{syms_of_@var{filename}}, like this: |
707 | ||
708 | @example | |
709 | staticpro (&@var{variable}); | |
710 | @end example | |
711 | ||
a890e1b0 | 712 | Here is another example function, with more complicated arguments. |
969fe9b5 RS |
713 | This comes from the code in @file{window.c}, and it demonstrates the use |
714 | of macros and functions to manipulate Lisp objects. | |
a44af9f2 RS |
715 | |
716 | @smallexample | |
717 | @group | |
718 | DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p, | |
719 | Scoordinates_in_window_p, 2, 2, | |
720 | "xSpecify coordinate pair: \nXExpression which evals to window: ", | |
88510b17 | 721 | "Return non-nil if COORDINATES is in WINDOW.\n\ |
969fe9b5 RS |
722 | COORDINATES is a cons of the form (X . Y), X and Y being distances\n\ |
723 | ... | |
a44af9f2 RS |
724 | @end group |
725 | @group | |
969fe9b5 RS |
726 | If they are on the border between WINDOW and its right sibling,\n\ |
727 | `vertical-line' is returned.") | |
728 | (coordinates, window) | |
729 | register Lisp_Object coordinates, window; | |
a44af9f2 | 730 | @{ |
969fe9b5 | 731 | int x, y; |
a44af9f2 RS |
732 | @end group |
733 | ||
734 | @group | |
969fe9b5 RS |
735 | CHECK_LIVE_WINDOW (window, 0); |
736 | CHECK_CONS (coordinates, 1); | |
737 | x = XINT (Fcar (coordinates)); | |
738 | y = XINT (Fcdr (coordinates)); | |
a44af9f2 | 739 | @end group |
969fe9b5 | 740 | |
a44af9f2 | 741 | @group |
969fe9b5 RS |
742 | switch (coordinates_in_window (XWINDOW (window), &x, &y)) |
743 | @{ | |
744 | case 0: /* NOT in window at all. */ | |
745 | return Qnil; | |
a44af9f2 | 746 | @end group |
969fe9b5 | 747 | |
a44af9f2 | 748 | @group |
969fe9b5 RS |
749 | case 1: /* In text part of window. */ |
750 | return Fcons (make_number (x), make_number (y)); | |
a44af9f2 | 751 | @end group |
969fe9b5 | 752 | |
a44af9f2 | 753 | @group |
969fe9b5 RS |
754 | case 2: /* In mode line of window. */ |
755 | return Qmode_line; | |
a44af9f2 | 756 | @end group |
969fe9b5 | 757 | |
a44af9f2 | 758 | @group |
969fe9b5 RS |
759 | case 3: /* On right border of window. */ |
760 | return Qvertical_line; | |
761 | @end group | |
762 | ||
763 | @group | |
764 | default: | |
765 | abort (); | |
766 | @} | |
a44af9f2 RS |
767 | @} |
768 | @end group | |
769 | @end smallexample | |
770 | ||
a890e1b0 RS |
771 | Note that C code cannot call functions by name unless they are defined |
772 | in C. The way to call a function written in Lisp is to use | |
773 | @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since | |
774 | the Lisp function @code{funcall} accepts an unlimited number of | |
775 | arguments, in C it takes two: the number of Lisp-level arguments, and a | |
776 | one-dimensional array containing their values. The first Lisp-level | |
777 | argument is the Lisp function to call, and the rest are the arguments to | |
778 | pass to it. Since @code{Ffuncall} can call the evaluator, you must | |
779 | protect pointers from garbage collection around the call to | |
780 | @code{Ffuncall}. | |
781 | ||
782 | The C functions @code{call0}, @code{call1}, @code{call2}, and so on, | |
783 | provide handy ways to call a Lisp function conveniently with a fixed | |
784 | number of arguments. They work by calling @code{Ffuncall}. | |
a44af9f2 RS |
785 | |
786 | @file{eval.c} is a very good file to look through for examples; | |
787 | @file{lisp.h} contains the definitions for some important macros and | |
788 | functions. | |
789 | ||
0a692803 DL |
790 | If you define a function which is side-effect free, update the code |
791 | in @file{byte-opt.el} which binds @code{side-effect-free-fns} and | |
792 | @code{side-effect-and-error-free-fns} so that the compiler optimizer | |
793 | knows about it. | |
8241495d | 794 | |
969fe9b5 | 795 | @node Object Internals |
a44af9f2 RS |
796 | @appendixsec Object Internals |
797 | @cindex object internals | |
798 | ||
799 | GNU Emacs Lisp manipulates many different types of data. The actual | |
f9f59935 RS |
800 | data are stored in a heap and the only access that programs have to it |
801 | is through pointers. Pointers are thirty-two bits wide in most | |
a44af9f2 | 802 | implementations. Depending on the operating system and type of machine |
568ffbee LT |
803 | for which you compile Emacs, twenty-nine bits are used to address the |
804 | object, and the remaining three bits are used for the tag that | |
805 | identifies the object's type. | |
a44af9f2 | 806 | |
a890e1b0 RS |
807 | Because Lisp objects are represented as tagged pointers, it is always |
808 | possible to determine the Lisp data type of any object. The C data type | |
809 | @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary | |
810 | variables have type @code{Lisp_Object}, which means they can hold any | |
811 | type of Lisp value; you can determine the actual data type only at run | |
812 | time. The same is true for function arguments; if you want a function | |
813 | to accept only a certain type of argument, you must check the type | |
814 | explicitly using a suitable predicate (@pxref{Type Predicates}). | |
a44af9f2 RS |
815 | @cindex type checking internals |
816 | ||
817 | @menu | |
818 | * Buffer Internals:: Components of a buffer structure. | |
819 | * Window Internals:: Components of a window structure. | |
820 | * Process Internals:: Components of a process structure. | |
821 | @end menu | |
822 | ||
969fe9b5 | 823 | @node Buffer Internals |
a44af9f2 RS |
824 | @appendixsubsec Buffer Internals |
825 | @cindex internals, of buffer | |
826 | @cindex buffer internals | |
827 | ||
828 | Buffers contain fields not directly accessible by the Lisp programmer. | |
829 | We describe them here, naming them by the names used in the C code. | |
830 | Many are accessible indirectly in Lisp programs via Lisp primitives. | |
831 | ||
95260b26 GM |
832 | Two structures are used to represent buffers in C. The |
833 | @code{buffer_text} structure contains fields describing the text of a | |
834 | buffer; the @code{buffer} structure holds other fields. In the case | |
835 | of indirect buffers, two or more @code{buffer} structures reference | |
836 | the same @code{buffer_text} structure. | |
837 | ||
838 | Here is a list of the @code{struct buffer_text} fields: | |
839 | ||
a44af9f2 | 840 | @table @code |
95260b26 | 841 | @item beg |
05aea714 | 842 | This field contains the actual address of the buffer contents. |
95260b26 | 843 | |
d7255d62 | 844 | @item gpt |
95260b26 | 845 | This holds the character position of the gap in the buffer. |
88510b17 | 846 | @xref{Buffer Gap}. |
95260b26 GM |
847 | |
848 | @item z | |
849 | This field contains the character position of the end of the buffer | |
850 | text. | |
851 | ||
852 | @item gpt_byte | |
853 | Contains the byte position of the gap. | |
854 | ||
855 | @item z_byte | |
856 | Holds the byte position of the end of the buffer text. | |
857 | ||
858 | @item gap_size | |
88510b17 | 859 | Contains the size of buffer's gap. @xref{Buffer Gap}. |
95260b26 GM |
860 | |
861 | @item modiff | |
862 | This field counts buffer-modification events for this buffer. It is | |
863 | incremented for each such event, and never otherwise changed. | |
864 | ||
865 | @item save_modiff | |
866 | Contains the previous value of @code{modiff}, as of the last time a | |
867 | buffer was visited or saved in a file. | |
88510b17 | 868 | |
95260b26 GM |
869 | @item overlay_modiff |
870 | Counts modifications to overlays analogous to @code{modiff}. | |
88510b17 | 871 | |
95260b26 GM |
872 | @item beg_unchanged |
873 | Holds the number of characters at the start of the text that are known | |
874 | to be unchanged since the last redisplay that finished. | |
88510b17 | 875 | |
95260b26 GM |
876 | @item end_unchanged |
877 | Holds the number of characters at the end of the text that are known to | |
878 | be unchanged since the last redisplay that finished. | |
88510b17 | 879 | |
95260b26 GM |
880 | @item unchanged_modified |
881 | Contains the value of @code{modiff} at the time of the last redisplay | |
882 | that finished. If this value matches @code{modiff}, | |
883 | @code{beg_unchanged} and @code{end_unchanged} contain no useful | |
884 | information. | |
88510b17 | 885 | |
95260b26 GM |
886 | @item overlay_unchanged_modified |
887 | Contains the value of @code{overlay_modiff} at the time of the last | |
888 | redisplay that finished. If this value matches @code{overlay_modiff}, | |
889 | @code{beg_unchanged} and @code{end_unchanged} contain no useful | |
890 | information. | |
88510b17 | 891 | |
95260b26 GM |
892 | @item markers |
893 | The markers that refer to this buffer. This is actually a single | |
894 | marker, and successive elements in its marker @code{chain} are the other | |
895 | markers referring to this buffer text. | |
a44af9f2 | 896 | |
95260b26 GM |
897 | @item intervals |
898 | Contains the interval tree which records the text properties of this | |
899 | buffer. | |
900 | @end table | |
901 | ||
902 | The fields of @code{struct buffer} are: | |
903 | ||
904 | @table @code | |
905 | @item next | |
906 | Points to the next buffer, in the chain of all buffers including killed | |
907 | buffers. This chain is used only for garbage collection, in order to | |
908 | collect killed buffers properly. Note that vectors, and most kinds of | |
909 | objects allocated as vectors, are all on one chain, but buffers are on a | |
910 | separate chain of their own. | |
911 | ||
912 | @item own_text | |
913 | This is a @code{struct buffer_text} structure. In an ordinary buffer, | |
914 | it holds the buffer contents. In indirect buffers, this field is not | |
915 | used. | |
916 | ||
917 | @item text | |
918 | This points to the @code{buffer_text} structure that is used for this | |
919 | buffer. In an ordinary buffer, this is the @code{own_text} field above. | |
920 | In an indirect buffer, this is the @code{own_text} field of the base | |
921 | buffer. | |
922 | ||
923 | @item pt | |
924 | Contains the character position of point in a buffer. | |
925 | ||
926 | @item pt_byte | |
927 | Contains the byte position of point in a buffer. | |
928 | ||
929 | @item begv | |
88510b17 | 930 | This field contains the character position of the beginning of the |
95260b26 GM |
931 | accessible range of text in the buffer. |
932 | ||
933 | @item begv_byte | |
88510b17 | 934 | This field contains the byte position of the beginning of the |
95260b26 GM |
935 | accessible range of text in the buffer. |
936 | ||
937 | @item zv | |
88510b17 | 938 | This field contains the character position of the end of the |
95260b26 GM |
939 | accessible range of text in the buffer. |
940 | ||
941 | @item zv_byte | |
88510b17 | 942 | This field contains the byte position of the end of the |
95260b26 GM |
943 | accessible range of text in the buffer. |
944 | ||
945 | @item base_buffer | |
946 | In an indirect buffer, this points to the base buffer. In an ordinary | |
947 | buffer, it is null. | |
948 | ||
949 | @item local_var_flags | |
950 | This field contains flags indicating that certain variables are local in | |
951 | this buffer. Such variables are declared in the C code using | |
952 | @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored in | |
953 | fields in the buffer structure itself. (Some of these fields are | |
954 | described in this table.) | |
a44af9f2 RS |
955 | |
956 | @item modtime | |
957 | This field contains the modification time of the visited file. It is | |
8241495d RS |
958 | set when the file is written or read. Before writing the buffer into a |
959 | file, this field is compared to the modification time of the file to see | |
960 | if the file has changed on disk. @xref{Buffer Modification}. | |
a44af9f2 RS |
961 | |
962 | @item auto_save_modified | |
963 | This field contains the time when the buffer was last auto-saved. | |
964 | ||
95260b26 GM |
965 | @item auto_save_failure_time |
966 | The time at which we detected a failure to auto-save, or -1 if we didn't | |
967 | have a failure. | |
968 | ||
a44af9f2 RS |
969 | @item last_window_start |
970 | This field contains the @code{window-start} position in the buffer as of | |
971 | the last time the buffer was displayed in a window. | |
972 | ||
95260b26 GM |
973 | @item clip_changed |
974 | This flag is set when narrowing changes in a buffer. | |
975 | ||
976 | @item prevent_redisplay_optimizations_p | |
88510b17 | 977 | this flag indicates that redisplay optimizations should not be used |
95260b26 GM |
978 | to display this buffer. |
979 | ||
a890e1b0 RS |
980 | @item undo_list |
981 | This field points to the buffer's undo list. @xref{Undo}. | |
a44af9f2 | 982 | |
95260b26 GM |
983 | @item name |
984 | The buffer name is a string that names the buffer. It is guaranteed to | |
985 | be unique. @xref{Buffer Names}. | |
986 | ||
987 | @item filename | |
988 | The name of the file visited in this buffer, or @code{nil}. | |
88510b17 | 989 | |
95260b26 GM |
990 | @item directory |
991 | The directory for expanding relative file names. | |
992 | ||
993 | @item save_length | |
994 | Length of the file this buffer is visiting, when last read or saved. | |
995 | This and other fields concerned with saving are not kept in the | |
996 | @code{buffer_text} structure because indirect buffers are never saved. | |
997 | ||
998 | @item auto_save_file_name | |
88510b17 | 999 | File name used for auto-saving this buffer. This is not in the |
95260b26 GM |
1000 | @code{buffer_text} because it's not used in indirect buffers at all. |
1001 | ||
1002 | @item read_only | |
1003 | Non-@code{nil} means this buffer is read-only. | |
1004 | ||
1005 | @item mark | |
1006 | This field contains the mark for the buffer. The mark is a marker, | |
1007 | hence it is also included on the list @code{markers}. @xref{The Mark}. | |
1008 | ||
1009 | @item local_var_alist | |
1010 | This field contains the association list describing the buffer-local | |
1011 | variable bindings of this buffer, not including the built-in | |
1012 | buffer-local bindings that have special slots in the buffer object. | |
1013 | (Those slots are omitted from this table.) @xref{Buffer-Local | |
1014 | Variables}. | |
1015 | ||
1016 | @item major_mode | |
1017 | Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}. | |
1018 | ||
1019 | @item mode_name | |
1020 | Pretty name of major mode, e.g., @code{"Lisp"}. | |
1021 | ||
1022 | @item mode_line_format | |
1023 | Mode line element that controls the format of the mode line. If this | |
1024 | is @code{nil}, no mode line will be displayed. | |
1025 | ||
1026 | @item header_line_format | |
5a36d834 | 1027 | This field is analogous to @code{mode_line_format} for the mode |
95260b26 GM |
1028 | line displayed at the top of windows. |
1029 | ||
1030 | @item keymap | |
1031 | This field holds the buffer's local keymap. @xref{Keymaps}. | |
1032 | ||
1033 | @item abbrev_table | |
1034 | This buffer's local abbrevs. | |
1035 | ||
1036 | @item syntax_table | |
a44af9f2 RS |
1037 | This field contains the syntax table for the buffer. @xref{Syntax Tables}. |
1038 | ||
95260b26 GM |
1039 | @item category_table |
1040 | This field contains the category table for the buffer. | |
1041 | ||
1042 | @item case_fold_search | |
1043 | The value of @code{case-fold-search} in this buffer. | |
1044 | ||
1045 | @item tab_width | |
1046 | The value of @code{tab-width} in this buffer. | |
1047 | ||
1048 | @item fill_column | |
1049 | The value of @code{fill-column} in this buffer. | |
1050 | ||
1051 | @item left_margin | |
1052 | The value of @code{left-margin} in this buffer. | |
1053 | ||
1054 | @item auto_fill_function | |
1055 | The value of @code{auto-fill-function} in this buffer. | |
1056 | ||
a44af9f2 RS |
1057 | @item downcase_table |
1058 | This field contains the conversion table for converting text to lower case. | |
969fe9b5 | 1059 | @xref{Case Tables}. |
a44af9f2 RS |
1060 | |
1061 | @item upcase_table | |
1062 | This field contains the conversion table for converting text to upper case. | |
969fe9b5 | 1063 | @xref{Case Tables}. |
a44af9f2 RS |
1064 | |
1065 | @item case_canon_table | |
1066 | This field contains the conversion table for canonicalizing text for | |
969fe9b5 | 1067 | case-folding search. @xref{Case Tables}. |
a44af9f2 RS |
1068 | |
1069 | @item case_eqv_table | |
1070 | This field contains the equivalence table for case-folding search. | |
969fe9b5 | 1071 | @xref{Case Tables}. |
a44af9f2 | 1072 | |
95260b26 GM |
1073 | @item truncate_lines |
1074 | The value of @code{truncate-lines} in this buffer. | |
a44af9f2 | 1075 | |
95260b26 GM |
1076 | @item ctl_arrow |
1077 | The value of @code{ctl-arrow} in this buffer. | |
a44af9f2 | 1078 | |
95260b26 GM |
1079 | @item selective_display |
1080 | The value of @code{selective-display} in this buffer. | |
a44af9f2 | 1081 | |
95260b26 GM |
1082 | @item selective_display_ellipsis |
1083 | The value of @code{selective-display-ellipsis} in this buffer. | |
a44af9f2 | 1084 | |
95260b26 GM |
1085 | @item minor_modes |
1086 | An alist of the minor modes of this buffer. | |
a890e1b0 | 1087 | |
95260b26 GM |
1088 | @item overwrite_mode |
1089 | The value of @code{overwrite_mode} in this buffer. | |
a890e1b0 | 1090 | |
95260b26 GM |
1091 | @item abbrev_mode |
1092 | The value of @code{abbrev-mode} in this buffer. | |
bfe721d1 | 1093 | |
95260b26 GM |
1094 | @item display_table |
1095 | This field contains the buffer's display table, or @code{nil} if it doesn't | |
1096 | have one. @xref{Display Tables}. | |
a890e1b0 | 1097 | |
95260b26 GM |
1098 | @item save_modified |
1099 | This field contains the time when the buffer was last saved, as an integer. | |
1100 | @xref{Buffer Modification}. | |
1101 | ||
1102 | @item mark_active | |
1103 | This field is non-@code{nil} if the buffer's mark is active. | |
a890e1b0 RS |
1104 | |
1105 | @item overlays_before | |
1106 | This field holds a list of the overlays in this buffer that end at or | |
1107 | before the current overlay center position. They are sorted in order of | |
1108 | decreasing end position. | |
1109 | ||
1110 | @item overlays_after | |
1111 | This field holds a list of the overlays in this buffer that end after | |
1112 | the current overlay center position. They are sorted in order of | |
1113 | increasing beginning position. | |
969fe9b5 | 1114 | |
95260b26 GM |
1115 | @item overlay_center |
1116 | This field holds the current overlay center position. @xref{Overlays}. | |
1117 | ||
969fe9b5 RS |
1118 | @item enable_multibyte_characters |
1119 | This field holds the buffer's local value of | |
1120 | @code{enable-multibyte-characters}---either @code{t} or @code{nil}. | |
95260b26 GM |
1121 | |
1122 | @item buffer_file_coding_system | |
1123 | The value of @code{buffer-file-coding-system} in this buffer. | |
1124 | ||
1125 | @item file_format | |
1126 | The value of @code{buffer-file-format} in this buffer. | |
1127 | ||
980aaec7 LT |
1128 | @item auto_save_file_format |
1129 | The value of @code{buffer-auto-save-file-format} in this buffer. | |
1130 | ||
95260b26 GM |
1131 | @item pt_marker |
1132 | In an indirect buffer, or a buffer that is the base of an indirect | |
1133 | buffer, this holds a marker that records point for this buffer when the | |
1134 | buffer is not current. | |
1135 | ||
1136 | @item begv_marker | |
1137 | In an indirect buffer, or a buffer that is the base of an indirect | |
1138 | buffer, this holds a marker that records @code{begv} for this buffer | |
1139 | when the buffer is not current. | |
88510b17 | 1140 | |
95260b26 GM |
1141 | @item zv_marker |
1142 | In an indirect buffer, or a buffer that is the base of an indirect | |
1143 | buffer, this holds a marker that records @code{zv} for this buffer when | |
1144 | the buffer is not current. | |
1145 | ||
1146 | @item file_truename | |
1147 | The truename of the visited file, or @code{nil}. | |
1148 | ||
1149 | @item invisibility_spec | |
1150 | The value of @code{buffer-invisibility-spec} in this buffer. | |
1151 | ||
1152 | @item last_selected_window | |
1153 | This is the last window that was selected with this buffer in it, or @code{nil} | |
1154 | if that window no longer displays this buffer. | |
1155 | ||
1156 | @item display_count | |
1157 | This field is incremented each time the buffer is displayed in a window. | |
1158 | ||
1159 | @item left_margin_width | |
1160 | The value of @code{left-margin-width} in this buffer. | |
1161 | ||
1162 | @item right_margin_width | |
1163 | The value of @code{right-margin-width} in this buffer. | |
1164 | ||
1165 | @item indicate_empty_lines | |
1166 | Non-@code{nil} means indicate empty lines (lines with no text) with a | |
1167 | small bitmap in the fringe, when using a window system that can do it. | |
1168 | ||
1169 | @item display_time | |
1170 | This holds a time stamp that is updated each time this buffer is | |
1171 | displayed in a window. | |
1172 | ||
1173 | @item scroll_up_aggressively | |
1174 | The value of @code{scroll-up-aggressively} in this buffer. | |
88510b17 | 1175 | |
95260b26 GM |
1176 | @item scroll_down_aggressively |
1177 | The value of @code{scroll-down-aggressively} in this buffer. | |
a44af9f2 RS |
1178 | @end table |
1179 | ||
969fe9b5 | 1180 | @node Window Internals |
a44af9f2 RS |
1181 | @appendixsubsec Window Internals |
1182 | @cindex internals, of window | |
1183 | @cindex window internals | |
1184 | ||
1185 | Windows have the following accessible fields: | |
1186 | ||
1187 | @table @code | |
1188 | @item frame | |
a890e1b0 | 1189 | The frame that this window is on. |
a44af9f2 RS |
1190 | |
1191 | @item mini_p | |
a890e1b0 | 1192 | Non-@code{nil} if this window is a minibuffer window. |
a44af9f2 | 1193 | |
95260b26 GM |
1194 | @item parent |
1195 | Internally, Emacs arranges windows in a tree; each group of siblings has | |
1196 | a parent window whose area includes all the siblings. This field points | |
1197 | to a window's parent. | |
1198 | ||
1199 | Parent windows do not display buffers, and play little role in display | |
1200 | except to shape their child windows. Emacs Lisp programs usually have | |
1201 | no access to the parent windows; they operate on the windows at the | |
1202 | leaves of the tree, which actually display buffers. | |
1203 | ||
1204 | The following four fields also describe the window tree structure. | |
1205 | ||
1206 | @item hchild | |
1207 | In a window subdivided horizontally by child windows, the leftmost child. | |
1208 | Otherwise, @code{nil}. | |
1209 | ||
1210 | @item vchild | |
1211 | In a window subdivided vertically by child windows, the topmost child. | |
1212 | Otherwise, @code{nil}. | |
1213 | ||
1214 | @item next | |
1215 | The next sibling of this window. It is @code{nil} in a window that is | |
1216 | the rightmost or bottommost of a group of siblings. | |
1217 | ||
1218 | @item prev | |
1219 | The previous sibling of this window. It is @code{nil} in a window that | |
1220 | is the leftmost or topmost of a group of siblings. | |
1221 | ||
1222 | @item left | |
1223 | This is the left-hand edge of the window, measured in columns. (The | |
1224 | leftmost column on the screen is @w{column 0}.) | |
1225 | ||
1226 | @item top | |
1227 | This is the top edge of the window, measured in lines. (The top line on | |
1228 | the screen is @w{line 0}.) | |
1229 | ||
1230 | @item height | |
1231 | The height of the window, measured in lines. | |
1232 | ||
1233 | @item width | |
1234 | The width of the window, measured in columns. This width includes the | |
1235 | scroll bar and fringes, and/or the separator line on the right of the | |
1236 | window (if any). | |
1237 | ||
a44af9f2 | 1238 | @item buffer |
574efc83 | 1239 | The buffer that the window is displaying. This may change often during |
a44af9f2 RS |
1240 | the life of the window. |
1241 | ||
95260b26 GM |
1242 | @item start |
1243 | The position in the buffer that is the first character to be displayed | |
1244 | in the window. | |
a44af9f2 RS |
1245 | |
1246 | @item pointm | |
1247 | @cindex window point internals | |
a890e1b0 | 1248 | This is the value of point in the current buffer when this window is |
a44af9f2 RS |
1249 | selected; when it is not selected, it retains its previous value. |
1250 | ||
a890e1b0 RS |
1251 | @item force_start |
1252 | If this flag is non-@code{nil}, it says that the window has been | |
1253 | scrolled explicitly by the Lisp program. This affects what the next | |
1254 | redisplay does if point is off the screen: instead of scrolling the | |
1255 | window to show the text around point, it moves point to a location that | |
1256 | is on the screen. | |
1257 | ||
95260b26 | 1258 | @item frozen_window_start_p |
88510b17 | 1259 | This field is set temporarily to 1 to indicate to redisplay that |
95260b26 GM |
1260 | @code{start} of this window should not be changed, even if point |
1261 | gets invisible. | |
1262 | ||
1263 | @item start_at_line_beg | |
1264 | Non-@code{nil} means current value of @code{start} was the beginning of a line | |
1265 | when it was chosen. | |
1266 | ||
1267 | @item too_small_ok | |
1268 | Non-@code{nil} means don't delete this window for becoming ``too small''. | |
1269 | ||
1270 | @item height_fixed_p | |
1271 | This field is temporarily set to 1 to fix the height of the selected | |
1272 | window when the echo area is resized. | |
1273 | ||
1274 | @item use_time | |
1275 | This is the last time that the window was selected. The function | |
1276 | @code{get-lru-window} uses this field. | |
1277 | ||
1278 | @item sequence_number | |
1279 | A unique number assigned to this window when it was created. | |
1280 | ||
a890e1b0 | 1281 | @item last_modified |
95260b26 | 1282 | The @code{modiff} field of the window's buffer, as of the last time |
a890e1b0 RS |
1283 | a redisplay completed in this window. |
1284 | ||
95260b26 GM |
1285 | @item last_overlay_modified |
1286 | The @code{overlay_modiff} field of the window's buffer, as of the last | |
1287 | time a redisplay completed in this window. | |
1288 | ||
a890e1b0 | 1289 | @item last_point |
95260b26 GM |
1290 | The buffer's value of point, as of the last time a redisplay completed |
1291 | in this window. | |
a890e1b0 | 1292 | |
95260b26 GM |
1293 | @item last_had_star |
1294 | A non-@code{nil} value means the window's buffer was ``modified'' when the | |
1295 | window was last updated. | |
a44af9f2 | 1296 | |
95260b26 GM |
1297 | @item vertical_scroll_bar |
1298 | This window's vertical scroll bar. | |
a44af9f2 | 1299 | |
95260b26 GM |
1300 | @item left_margin_width |
1301 | The width of the left margin in this window, or @code{nil} not to | |
1302 | specify it (in which case the buffer's value of @code{left-margin-width} | |
1303 | is used. | |
a890e1b0 | 1304 | |
95260b26 GM |
1305 | @item right_margin_width |
1306 | Likewise for the right margin. | |
a890e1b0 | 1307 | |
13ede7fc | 1308 | @ignore |
95260b26 GM |
1309 | @item last_mark_x |
1310 | @item last_mark_y | |
1311 | ???Not used. | |
1312 | @end ignore | |
a44af9f2 | 1313 | |
95260b26 GM |
1314 | @item window_end_pos |
1315 | This is computed as @code{z} minus the buffer position of the last glyph | |
1316 | in the current matrix of the window. The value is only valid if | |
1317 | @code{window_end_valid} is not @code{nil}. | |
a44af9f2 | 1318 | |
95260b26 GM |
1319 | @item window_end_bytepos |
1320 | The byte position corresponding to @code{window_end_pos}. | |
a890e1b0 | 1321 | |
95260b26 GM |
1322 | @item window_end_vpos |
1323 | The window-relative vertical position of the line containing | |
1324 | @code{window_end_pos}. | |
a44af9f2 | 1325 | |
95260b26 GM |
1326 | @item window_end_valid |
1327 | This field is set to a non-@code{nil} value if @code{window_end_pos} is truly | |
1328 | valid. This is @code{nil} if nontrivial redisplay is preempted since in that | |
1329 | case the display that @code{window_end_pos} was computed for did not get | |
1330 | onto the screen. | |
1331 | ||
1332 | @item redisplay_end_trigger | |
1333 | If redisplay in this window goes beyond this buffer position, it runs | |
2a233172 | 1334 | the @code{redisplay-end-trigger-hook}. |
95260b26 | 1335 | |
13ede7fc | 1336 | @ignore |
95260b26 GM |
1337 | @item orig_height |
1338 | @item orig_top | |
1339 | ??? Are temporary storage areas. | |
1340 | @end ignore | |
1341 | ||
1342 | @item cursor | |
1343 | A structure describing where the cursor is in this window. | |
1344 | ||
1345 | @item last_cursor | |
1346 | The value of @code{cursor} as of the last redisplay that finished. | |
1347 | ||
1348 | @item phys_cursor | |
1349 | A structure describing where the cursor of this window physically is. | |
1350 | ||
1351 | @item phys_cursor_type | |
1352 | The type of cursor that was last displayed on this window. | |
1353 | ||
1354 | @item phys_cursor_on_p | |
1355 | This field is non-zero if the cursor is physically on. | |
1356 | ||
1357 | @item cursor_off_p | |
1358 | Non-zero means the cursor in this window is logically on. | |
1359 | ||
1360 | @item last_cursor_off_p | |
1361 | This field contains the value of @code{cursor_off_p} as of the time of | |
1362 | the last redisplay. | |
1363 | ||
1364 | @item must_be_updated_p | |
1365 | This is set to 1 during redisplay when this window must be updated. | |
1366 | ||
a44af9f2 | 1367 | @item hscroll |
a890e1b0 | 1368 | This is the number of columns that the display in the window is scrolled |
a44af9f2 RS |
1369 | horizontally to the left. Normally, this is 0. |
1370 | ||
95260b26 GM |
1371 | @item vscroll |
1372 | Vertical scroll amount, in pixels. Normally, this is 0. | |
1373 | ||
1374 | @item dedicated | |
1375 | Non-@code{nil} if this window is dedicated to its buffer. | |
a44af9f2 RS |
1376 | |
1377 | @item display_table | |
a890e1b0 RS |
1378 | The window's display table, or @code{nil} if none is specified for it. |
1379 | ||
1380 | @item update_mode_line | |
1381 | Non-@code{nil} means this window's mode line needs to be updated. | |
1382 | ||
1383 | @item base_line_number | |
1384 | The line number of a certain position in the buffer, or @code{nil}. | |
1385 | This is used for displaying the line number of point in the mode line. | |
1386 | ||
1387 | @item base_line_pos | |
1388 | The position in the buffer for which the line number is known, or | |
1389 | @code{nil} meaning none is known. | |
1390 | ||
1391 | @item region_showing | |
1392 | If the region (or part of it) is highlighted in this window, this field | |
1393 | holds the mark position that made one end of that region. Otherwise, | |
1394 | this field is @code{nil}. | |
95260b26 GM |
1395 | |
1396 | @item column_number_displayed | |
1397 | The column number currently displayed in this window's mode line, or @code{nil} | |
1398 | if column numbers are not being displayed. | |
1399 | ||
1400 | @item current_matrix | |
1401 | A glyph matrix describing the current display of this window. | |
1402 | ||
1403 | @item desired_matrix | |
1404 | A glyph matrix describing the desired display of this window. | |
a44af9f2 RS |
1405 | @end table |
1406 | ||
969fe9b5 | 1407 | @node Process Internals |
a44af9f2 RS |
1408 | @appendixsubsec Process Internals |
1409 | @cindex internals, of process | |
1410 | @cindex process internals | |
1411 | ||
1412 | The fields of a process are: | |
1413 | ||
1414 | @table @code | |
1415 | @item name | |
1416 | A string, the name of the process. | |
1417 | ||
1418 | @item command | |
1419 | A list containing the command arguments that were used to start this | |
1420 | process. | |
1421 | ||
1422 | @item filter | |
1423 | A function used to accept output from the process instead of a buffer, | |
1424 | or @code{nil}. | |
1425 | ||
1426 | @item sentinel | |
1427 | A function called whenever the process receives a signal, or @code{nil}. | |
1428 | ||
1429 | @item buffer | |
1430 | The associated buffer of the process. | |
1431 | ||
1432 | @item pid | |
2a233172 | 1433 | An integer, the operating system's process @acronym{ID}. |
a44af9f2 RS |
1434 | |
1435 | @item childp | |
1436 | A flag, non-@code{nil} if this is really a child process. | |
1437 | It is @code{nil} for a network connection. | |
1438 | ||
a44af9f2 | 1439 | @item mark |
574efc83 RS |
1440 | A marker indicating the position of the end of the last output from this |
1441 | process inserted into the buffer. This is often but not always the end | |
1442 | of the buffer. | |
a44af9f2 RS |
1443 | |
1444 | @item kill_without_query | |
a890e1b0 RS |
1445 | If this is non-@code{nil}, killing Emacs while this process is still |
1446 | running does not ask for confirmation about killing the process. | |
1447 | ||
1448 | @item raw_status_low | |
1449 | @itemx raw_status_high | |
1450 | These two fields record 16 bits each of the process status returned by | |
1451 | the @code{wait} system call. | |
1452 | ||
1453 | @item status | |
1454 | The process status, as @code{process-status} should return it. | |
1455 | ||
1456 | @item tick | |
1457 | @itemx update_tick | |
1458 | If these two fields are not equal, a change in the status of the process | |
1459 | needs to be reported, either by running the sentinel or by inserting a | |
1460 | message in the process buffer. | |
1461 | ||
1462 | @item pty_flag | |
ad800164 | 1463 | Non-@code{nil} if communication with the subprocess uses a @acronym{PTY}; |
a890e1b0 RS |
1464 | @code{nil} if it uses a pipe. |
1465 | ||
1466 | @item infd | |
1467 | The file descriptor for input from the process. | |
1468 | ||
1469 | @item outfd | |
1470 | The file descriptor for output to the process. | |
1471 | ||
1472 | @item subtty | |
1473 | The file descriptor for the terminal that the subprocess is using. (On | |
1474 | some systems, there is no need to record this, so the value is | |
1475 | @code{nil}.) | |
bfe721d1 KH |
1476 | |
1477 | @item tty_name | |
1478 | The name of the terminal that the subprocess is using, | |
1479 | or @code{nil} if it is using pipes. | |
95260b26 GM |
1480 | |
1481 | @item decode_coding_system | |
1482 | Coding-system for decoding the input from this process. | |
1483 | ||
1484 | @item decoding_buf | |
1485 | A working buffer for decoding. | |
1486 | ||
1487 | @item decoding_carryover | |
1488 | Size of carryover in decoding. | |
1489 | ||
1490 | @item encode_coding_system | |
1491 | Coding-system for encoding the output to this process. | |
1492 | ||
1493 | @item encoding_buf | |
a39c2e0d | 1494 | A working buffer for encoding. |
95260b26 GM |
1495 | |
1496 | @item encoding_carryover | |
1497 | Size of carryover in encoding. | |
1498 | ||
1499 | @item inherit_coding_system_flag | |
1500 | Flag to set @code{coding-system} of the process buffer from the | |
1501 | coding system used to decode process output. | |
a44af9f2 | 1502 | @end table |
ab5796a9 MB |
1503 | |
1504 | @ignore | |
1505 | arch-tag: 4b2c33bc-d7e4-43f5-bc20-27c0db52a53e | |
1506 | @end ignore |