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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1998, 1999, 2001, 2002, 2003, | |
6ed161e1 | 4 | @c 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/internals |
b8d4c8d0 GM |
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 | |
16 | * Building Emacs:: How the dumped Emacs is made. | |
17 | * Pure Storage:: A kludge to make preloaded Lisp functions sharable. | |
18 | * Garbage Collection:: Reclaiming space for Lisp objects no longer used. | |
19 | * Memory Usage:: Info about total size of Lisp objects made so far. | |
20 | * Writing Emacs Primitives:: Writing C code for Emacs. | |
21 | * Object Internals:: Data formats of buffers, windows, processes. | |
22 | @end menu | |
23 | ||
24 | @node Building Emacs | |
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 | |
44 | environment, resulting in an Emacs that is still impure but no longer | |
45 | bare. | |
46 | ||
47 | @cindex dumping Emacs | |
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 | |
50 | dump out an executable program called @file{emacs} that has these files | |
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 | |
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. | |
67 | ||
68 | @cindex @file{site-load.el} | |
69 | ||
70 | You can specify additional files to preload by writing a library named | |
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. | |
82 | ||
83 | After @file{loadup.el} reads @file{site-load.el}, it finds the | |
84 | documentation strings for primitive and preloaded functions (and | |
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}). | |
88 | ||
89 | @cindex @file{site-init.el} | |
90 | @cindex preloading additional functions and variables | |
91 | You can specify other Lisp expressions to execute just before dumping | |
92 | by putting them in a library named @file{site-init.el}. This file is | |
93 | executed after the documentation strings are found. | |
94 | ||
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 | |
110 | @code{byte-compile-dynamic-docstrings} as a local variable in each of these | |
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 | |
120 | users can override your changes if they wish. @xref{Startup Summary}. | |
121 | ||
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 | ||
126 | @defmac eval-at-startup body@dots{} | |
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}. | |
132 | @end defmac | |
133 | ||
134 | @defun dump-emacs to-file from-file | |
135 | @cindex unexec | |
136 | This function dumps the current state of Emacs into an executable file | |
137 | @var{to-file}. It takes symbols from @var{from-file} (this is normally | |
138 | the executable file @file{temacs}). | |
139 | ||
140 | If you want to use this function in an Emacs that was already dumped, | |
141 | you must run Emacs with @samp{-batch}. | |
142 | @end defun | |
143 | ||
144 | @node Pure Storage | |
145 | @appendixsec Pure Storage | |
146 | @cindex pure storage | |
147 | ||
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 | |
150 | all the new data created during an Emacs session are kept; see the | |
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. | |
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 | |
157 | marked as read-only (on operating systems that permit this), so that | |
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 | |
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 | |
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 | |
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. | |
170 | ||
171 | @defun purecopy object | |
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 | |
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. | |
178 | ||
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. | |
182 | @end defun | |
183 | ||
184 | @defvar pure-bytes-used | |
185 | The value of this variable is the number of bytes of pure storage | |
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 | |
192 | This variable determines whether @code{defun} should make a copy of the | |
193 | function definition in pure storage. If it is non-@code{nil}, then the | |
194 | function definition is copied into pure storage. | |
195 | ||
196 | This flag is @code{t} while loading all of the basic functions for | |
197 | building Emacs initially (allowing those functions to be sharable and | |
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. | |
201 | ||
202 | You should not change this flag in a running Emacs. | |
203 | @end defvar | |
204 | ||
205 | @node Garbage Collection | |
206 | @appendixsec Garbage Collection | |
207 | @cindex garbage collection | |
208 | ||
209 | @cindex memory allocation | |
210 | When a program creates a list or the user defines a new function (such | |
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 | |
213 | allocate more memory in blocks of 1k bytes. Each block is used for one | |
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 | |
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 | ||
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 | |
229 | any data presently on the stack, are accessible. Any objects that can | |
230 | be reached indirectly through other accessible objects are also | |
231 | accessible. | |
232 | ||
233 | When marking is finished, all objects still unmarked are garbage. No | |
234 | matter what the Lisp program or the user does, it is impossible to refer | |
235 | to them, since there is no longer a way to reach them. Their space | |
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. | |
238 | ||
239 | @c ??? Maybe add something describing weak hash tables here? | |
240 | ||
241 | @cindex free list | |
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 | |
245 | other 8k blocks. Vectors, buffers, windows, and other large objects are | |
246 | individually allocated and freed using @code{malloc} and @code{free}. | |
247 | ||
248 | @cindex CL note---allocate more storage | |
249 | @quotation | |
250 | @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not | |
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 | |
264 | This command runs a garbage collection, and returns information on | |
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 | ||
269 | @code{garbage-collect} returns a list containing the following | |
270 | information: | |
271 | ||
272 | @example | |
273 | @group | |
274 | ((@var{used-conses} . @var{free-conses}) | |
275 | (@var{used-syms} . @var{free-syms}) | |
276 | @end group | |
277 | (@var{used-miscs} . @var{free-miscs}) | |
278 | @var{used-string-chars} | |
279 | @var{used-vector-slots} | |
280 | (@var{used-floats} . @var{free-floats}) | |
281 | (@var{used-intervals} . @var{free-intervals}) | |
282 | (@var{used-strings} . @var{free-strings})) | |
283 | @end example | |
284 | ||
285 | Here is an example: | |
286 | ||
287 | @example | |
288 | @group | |
289 | (garbage-collect) | |
290 | @result{} ((106886 . 13184) (9769 . 0) | |
291 | (7731 . 4651) 347543 121628 | |
292 | (31 . 94) (1273 . 168) | |
293 | (25474 . 3569)) | |
294 | @end group | |
295 | @end example | |
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 | ||
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. | |
317 | ||
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. | |
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. | |
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. | |
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.) | |
353 | @end table | |
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. | |
358 | @end deffn | |
359 | ||
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 | ||
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 | ||
372 | @defopt gc-cons-threshold | |
373 | The value of this variable is the number of bytes of storage that must | |
374 | be allocated for Lisp objects after one garbage collection in order to | |
375 | trigger another garbage collection. A cons cell counts as eight bytes, | |
376 | a string as one byte per character plus a few bytes of overhead, and so | |
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 | |
380 | called. | |
381 | ||
382 | The initial threshold value is 400,000. If you specify a larger | |
383 | value, garbage collection will happen less often. This reduces the | |
384 | amount of time spent garbage collecting, but increases total memory use. | |
385 | You may want to do this when running a program that creates lots of | |
386 | Lisp data. | |
387 | ||
388 | You can make collections more frequent by specifying a smaller value, | |
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. | |
392 | @end defopt | |
393 | ||
394 | @defopt gc-cons-percentage | |
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. | |
399 | ||
400 | As the heap size increases, the time to perform a garbage collection | |
401 | increases. Thus, it can be desirable to do them less frequently in | |
402 | proportion. | |
403 | @end defopt | |
404 | ||
405 | The value returned by @code{garbage-collect} describes the amount of | |
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 | ||
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 | ||
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 | ||
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 | ||
431 | @defvar gcs-done | |
432 | This variable contains the total number of garbage collections | |
433 | done so far in this Emacs session. | |
434 | @end defvar | |
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. | |
440 | @end defvar | |
441 | ||
442 | @node Memory Usage | |
443 | @section Memory Usage | |
444 | @cindex memory usage | |
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 | ||
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 | ||
494 | @node Writing Emacs Primitives | |
495 | @appendixsec Writing Emacs Primitives | |
496 | @cindex primitive function internals | |
497 | @cindex writing Emacs primitives | |
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, | |
512 | doc: /* Eval args until one of them yields non-nil, then return that | |
513 | value. The remaining args are not evalled at all. | |
514 | If all args return nil, return nil. | |
515 | @end group | |
516 | @group | |
517 | usage: (or CONDITIONS ...) */) | |
518 | (args) | |
519 | Lisp_Object args; | |
520 | @{ | |
521 | register Lisp_Object val = Qnil; | |
522 | struct gcpro gcpro1; | |
523 | @end group | |
524 | ||
525 | @group | |
526 | GCPRO1 (args); | |
527 | @end group | |
528 | ||
529 | @group | |
530 | while (CONSP (args)) | |
531 | @{ | |
532 | val = Feval (XCAR (args)); | |
533 | if (!NILP (val)) | |
534 | break; | |
535 | args = XCDR (args); | |
536 | @} | |
537 | @end group | |
538 | ||
539 | @group | |
540 | UNGCPRO; | |
541 | return val; | |
542 | @} | |
543 | @end group | |
544 | @end smallexample | |
545 | ||
546 | @cindex @code{DEFUN}, C macro to define Lisp primitives | |
547 | Let's start with a precise explanation of the arguments to the | |
548 | @code{DEFUN} macro. Here is a template for them: | |
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 | |
556 | This is the name of the Lisp symbol to define as the function name; in | |
557 | the example above, it is @code{or}. | |
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 | |
578 | This is the minimum number of arguments that the function requires. The | |
579 | function @code{or} allows a minimum of zero arguments. | |
580 | ||
581 | @item max | |
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 | |
588 | it may not be greater than eight. | |
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 | |
594 | called interactively. A value of @code{""} indicates a function that | |
2c30e468 EZ |
595 | should receive no arguments when called interactively. If the value |
596 | begins with a @samp{(}, the string is evaluated as a Lisp form. | |
b8d4c8d0 GM |
597 | |
598 | @item doc | |
599 | This is the documentation string. It uses C comment syntax rather | |
600 | than C string syntax because comment syntax requires nothing special | |
601 | to include multiple lines. The @samp{doc:} identifies the comment | |
602 | that follows as the documentation string. The @samp{/*} and @samp{*/} | |
603 | delimiters that begin and end the comment are not part of the | |
604 | documentation string. | |
605 | ||
606 | If the last line of the documentation string begins with the keyword | |
607 | @samp{usage:}, the rest of the line is treated as the argument list | |
608 | for documentation purposes. This way, you can use different argument | |
609 | names in the documentation string from the ones used in the C code. | |
610 | @samp{usage:} is required if the function has an unlimited number of | |
611 | arguments. | |
612 | ||
613 | All the usual rules for documentation strings in Lisp code | |
614 | (@pxref{Documentation Tips}) apply to C code documentation strings | |
615 | too. | |
616 | @end table | |
617 | ||
618 | After the call to the @code{DEFUN} macro, you must write the argument | |
619 | name list that every C function must have, followed by ordinary C | |
620 | declarations for the arguments. For a function with a fixed maximum | |
621 | number of arguments, declare a C argument for each Lisp argument, and | |
622 | give them all type @code{Lisp_Object}. When a Lisp function has no | |
623 | upper limit on the number of arguments, its implementation in C actually | |
624 | receives exactly two arguments: the first is the number of Lisp | |
625 | arguments, and the second is the address of a block containing their | |
626 | values. They have types @code{int} and @w{@code{Lisp_Object *}}. | |
627 | ||
628 | @cindex @code{GCPRO} and @code{UNGCPRO} | |
629 | @cindex protect C variables from garbage collection | |
630 | Within the function @code{For} itself, note the use of the macros | |
631 | @code{GCPRO1} and @code{UNGCPRO}. @code{GCPRO1} is used to | |
632 | ``protect'' a variable from garbage collection---to inform the garbage | |
633 | collector that it must look in that variable and regard its contents | |
634 | as an accessible object. GC protection is necessary whenever you call | |
635 | @code{Feval} or anything that can directly or indirectly call | |
636 | @code{Feval}. At such a time, any Lisp object that this function may | |
637 | refer to again must be protected somehow. | |
638 | ||
639 | It suffices to ensure that at least one pointer to each object is | |
640 | GC-protected; that way, the object cannot be recycled, so all pointers | |
641 | to it remain valid. Thus, a particular local variable can do without | |
642 | protection if it is certain that the object it points to will be | |
643 | preserved by some other pointer (such as another local variable which | |
644 | has a @code{GCPRO})@footnote{Formerly, strings were a special | |
645 | exception; in older Emacs versions, every local variable that might | |
646 | point to a string needed a @code{GCPRO}.}. Otherwise, the local | |
647 | variable needs a @code{GCPRO}. | |
648 | ||
649 | The macro @code{GCPRO1} protects just one local variable. If you | |
650 | want to protect two variables, use @code{GCPRO2} instead; repeating | |
651 | @code{GCPRO1} will not work. Macros @code{GCPRO3}, @code{GCPRO4}, | |
652 | @code{GCPRO5}, and @code{GCPRO6} also exist. All these macros | |
653 | implicitly use local variables such as @code{gcpro1}; you must declare | |
654 | these explicitly, with type @code{struct gcpro}. Thus, if you use | |
655 | @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}. | |
656 | Alas, we can't explain all the tricky details here. | |
657 | ||
658 | @code{UNGCPRO} cancels the protection of the variables that are | |
659 | protected in the current function. It is necessary to do this | |
660 | explicitly. | |
661 | ||
662 | Built-in functions that take a variable number of arguments actually | |
663 | accept two arguments at the C level: the number of Lisp arguments, and | |
664 | a @code{Lisp_Object *} pointer to a C vector containing those Lisp | |
665 | arguments. This C vector may be part of a Lisp vector, but it need | |
666 | not be. The responsibility for using @code{GCPRO} to protect the Lisp | |
667 | arguments from GC if necessary rests with the caller in this case, | |
668 | since the caller allocated or found the storage for them. | |
669 | ||
670 | You must not use C initializers for static or global variables unless | |
671 | the variables are never written once Emacs is dumped. These variables | |
672 | with initializers are allocated in an area of memory that becomes | |
673 | read-only (on certain operating systems) as a result of dumping Emacs. | |
674 | @xref{Pure Storage}. | |
675 | ||
676 | Do not use static variables within functions---place all static | |
677 | variables at top level in the file. This is necessary because Emacs on | |
678 | some operating systems defines the keyword @code{static} as a null | |
679 | macro. (This definition is used because those systems put all variables | |
680 | declared static in a place that becomes read-only after dumping, whether | |
681 | they have initializers or not.) | |
682 | ||
683 | @cindex @code{defsubr}, Lisp symbol for a primitive | |
684 | Defining the C function is not enough to make a Lisp primitive | |
685 | available; you must also create the Lisp symbol for the primitive and | |
686 | store a suitable subr object in its function cell. The code looks like | |
687 | this: | |
688 | ||
689 | @example | |
690 | defsubr (&@var{subr-structure-name}); | |
691 | @end example | |
692 | ||
693 | @noindent | |
694 | Here @var{subr-structure-name} is the name you used as the third | |
695 | argument to @code{DEFUN}. | |
696 | ||
697 | If you add a new primitive to a file that already has Lisp primitives | |
698 | defined in it, find the function (near the end of the file) named | |
699 | @code{syms_of_@var{something}}, and add the call to @code{defsubr} | |
700 | there. If the file doesn't have this function, or if you create a new | |
701 | file, add to it a @code{syms_of_@var{filename}} (e.g., | |
702 | @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all | |
703 | of these functions are called, and add a call to | |
704 | @code{syms_of_@var{filename}} there. | |
705 | ||
706 | @anchor{Defining Lisp variables in C} | |
707 | @vindex byte-boolean-vars | |
708 | @cindex defining Lisp variables in C | |
709 | @cindex @code{DEFVAR_INT}, @code{DEFVAR_LISP}, @code{DEFVAR_BOOL} | |
710 | The function @code{syms_of_@var{filename}} is also the place to define | |
711 | any C variables that are to be visible as Lisp variables. | |
712 | @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible | |
713 | in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int} | |
714 | visible in Lisp with a value that is always an integer. | |
715 | @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp | |
716 | with a value that is either @code{t} or @code{nil}. Note that variables | |
717 | defined with @code{DEFVAR_BOOL} are automatically added to the list | |
718 | @code{byte-boolean-vars} used by the byte compiler. | |
719 | ||
720 | @cindex @code{staticpro}, protection from GC | |
721 | If you define a file-scope C variable of type @code{Lisp_Object}, | |
722 | you must protect it from garbage-collection by calling @code{staticpro} | |
723 | in @code{syms_of_@var{filename}}, like this: | |
724 | ||
725 | @example | |
726 | staticpro (&@var{variable}); | |
727 | @end example | |
728 | ||
729 | Here is another example function, with more complicated arguments. | |
730 | This comes from the code in @file{window.c}, and it demonstrates the use | |
731 | of macros and functions to manipulate Lisp objects. | |
732 | ||
733 | @smallexample | |
734 | @group | |
735 | DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p, | |
736 | Scoordinates_in_window_p, 2, 2, | |
737 | "xSpecify coordinate pair: \nXExpression which evals to window: ", | |
738 | "Return non-nil if COORDINATES is in WINDOW.\n\ | |
739 | COORDINATES is a cons of the form (X . Y), X and Y being distances\n\ | |
740 | ... | |
741 | @end group | |
742 | @group | |
743 | If they are on the border between WINDOW and its right sibling,\n\ | |
744 | `vertical-line' is returned.") | |
745 | (coordinates, window) | |
746 | register Lisp_Object coordinates, window; | |
747 | @{ | |
748 | int x, y; | |
749 | @end group | |
750 | ||
751 | @group | |
752 | CHECK_LIVE_WINDOW (window, 0); | |
753 | CHECK_CONS (coordinates, 1); | |
754 | x = XINT (Fcar (coordinates)); | |
755 | y = XINT (Fcdr (coordinates)); | |
756 | @end group | |
757 | ||
758 | @group | |
759 | switch (coordinates_in_window (XWINDOW (window), &x, &y)) | |
760 | @{ | |
761 | case 0: /* NOT in window at all. */ | |
762 | return Qnil; | |
763 | @end group | |
764 | ||
765 | @group | |
766 | case 1: /* In text part of window. */ | |
767 | return Fcons (make_number (x), make_number (y)); | |
768 | @end group | |
769 | ||
770 | @group | |
771 | case 2: /* In mode line of window. */ | |
772 | return Qmode_line; | |
773 | @end group | |
774 | ||
775 | @group | |
776 | case 3: /* On right border of window. */ | |
777 | return Qvertical_line; | |
778 | @end group | |
779 | ||
780 | @group | |
781 | default: | |
782 | abort (); | |
783 | @} | |
784 | @} | |
785 | @end group | |
786 | @end smallexample | |
787 | ||
788 | Note that C code cannot call functions by name unless they are defined | |
789 | in C. The way to call a function written in Lisp is to use | |
790 | @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since | |
791 | the Lisp function @code{funcall} accepts an unlimited number of | |
792 | arguments, in C it takes two: the number of Lisp-level arguments, and a | |
793 | one-dimensional array containing their values. The first Lisp-level | |
794 | argument is the Lisp function to call, and the rest are the arguments to | |
795 | pass to it. Since @code{Ffuncall} can call the evaluator, you must | |
796 | protect pointers from garbage collection around the call to | |
797 | @code{Ffuncall}. | |
798 | ||
799 | The C functions @code{call0}, @code{call1}, @code{call2}, and so on, | |
800 | provide handy ways to call a Lisp function conveniently with a fixed | |
801 | number of arguments. They work by calling @code{Ffuncall}. | |
802 | ||
803 | @file{eval.c} is a very good file to look through for examples; | |
804 | @file{lisp.h} contains the definitions for some important macros and | |
805 | functions. | |
806 | ||
807 | If you define a function which is side-effect free, update the code | |
808 | in @file{byte-opt.el} which binds @code{side-effect-free-fns} and | |
809 | @code{side-effect-and-error-free-fns} so that the compiler optimizer | |
810 | knows about it. | |
811 | ||
812 | @node Object Internals | |
813 | @appendixsec Object Internals | |
814 | @cindex object internals | |
815 | ||
816 | GNU Emacs Lisp manipulates many different types of data. The actual | |
817 | data are stored in a heap and the only access that programs have to it | |
818 | is through pointers. Pointers are thirty-two bits wide in most | |
819 | implementations. Depending on the operating system and type of machine | |
820 | for which you compile Emacs, twenty-nine bits are used to address the | |
821 | object, and the remaining three bits are used for the tag that | |
822 | identifies the object's type. | |
823 | ||
824 | Because Lisp objects are represented as tagged pointers, it is always | |
825 | possible to determine the Lisp data type of any object. The C data type | |
826 | @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary | |
827 | variables have type @code{Lisp_Object}, which means they can hold any | |
828 | type of Lisp value; you can determine the actual data type only at run | |
829 | time. The same is true for function arguments; if you want a function | |
830 | to accept only a certain type of argument, you must check the type | |
831 | explicitly using a suitable predicate (@pxref{Type Predicates}). | |
832 | @cindex type checking internals | |
833 | ||
834 | @menu | |
835 | * Buffer Internals:: Components of a buffer structure. | |
836 | * Window Internals:: Components of a window structure. | |
837 | * Process Internals:: Components of a process structure. | |
838 | @end menu | |
839 | ||
840 | @node Buffer Internals | |
841 | @appendixsubsec Buffer Internals | |
842 | @cindex internals, of buffer | |
843 | @cindex buffer internals | |
844 | ||
845 | Buffers contain fields not directly accessible by the Lisp programmer. | |
846 | We describe them here, naming them by the names used in the C code. | |
847 | Many are accessible indirectly in Lisp programs via Lisp primitives. | |
848 | ||
849 | Two structures are used to represent buffers in C. The | |
850 | @code{buffer_text} structure contains fields describing the text of a | |
851 | buffer; the @code{buffer} structure holds other fields. In the case | |
852 | of indirect buffers, two or more @code{buffer} structures reference | |
853 | the same @code{buffer_text} structure. | |
854 | ||
855 | Here is a list of the @code{struct buffer_text} fields: | |
856 | ||
857 | @table @code | |
858 | @item beg | |
859 | This field contains the actual address of the buffer contents. | |
860 | ||
861 | @item gpt | |
862 | This holds the character position of the gap in the buffer. | |
863 | @xref{Buffer Gap}. | |
864 | ||
865 | @item z | |
866 | This field contains the character position of the end of the buffer | |
867 | text. | |
868 | ||
869 | @item gpt_byte | |
870 | Contains the byte position of the gap. | |
871 | ||
872 | @item z_byte | |
873 | Holds the byte position of the end of the buffer text. | |
874 | ||
875 | @item gap_size | |
876 | Contains the size of buffer's gap. @xref{Buffer Gap}. | |
877 | ||
878 | @item modiff | |
879 | This field counts buffer-modification events for this buffer. It is | |
880 | incremented for each such event, and never otherwise changed. | |
881 | ||
882 | @item save_modiff | |
883 | Contains the previous value of @code{modiff}, as of the last time a | |
884 | buffer was visited or saved in a file. | |
885 | ||
886 | @item overlay_modiff | |
887 | Counts modifications to overlays analogous to @code{modiff}. | |
888 | ||
889 | @item beg_unchanged | |
890 | Holds the number of characters at the start of the text that are known | |
891 | to be unchanged since the last redisplay that finished. | |
892 | ||
893 | @item end_unchanged | |
894 | Holds the number of characters at the end of the text that are known to | |
895 | be unchanged since the last redisplay that finished. | |
896 | ||
897 | @item unchanged_modified | |
898 | Contains the value of @code{modiff} at the time of the last redisplay | |
899 | that finished. If this value matches @code{modiff}, | |
900 | @code{beg_unchanged} and @code{end_unchanged} contain no useful | |
901 | information. | |
902 | ||
903 | @item overlay_unchanged_modified | |
904 | Contains the value of @code{overlay_modiff} at the time of the last | |
905 | redisplay that finished. If this value matches @code{overlay_modiff}, | |
906 | @code{beg_unchanged} and @code{end_unchanged} contain no useful | |
907 | information. | |
908 | ||
909 | @item markers | |
910 | The markers that refer to this buffer. This is actually a single | |
911 | marker, and successive elements in its marker @code{chain} are the other | |
912 | markers referring to this buffer text. | |
913 | ||
914 | @item intervals | |
915 | Contains the interval tree which records the text properties of this | |
916 | buffer. | |
917 | @end table | |
918 | ||
919 | The fields of @code{struct buffer} are: | |
920 | ||
921 | @table @code | |
922 | @item next | |
923 | Points to the next buffer, in the chain of all buffers including killed | |
924 | buffers. This chain is used only for garbage collection, in order to | |
925 | collect killed buffers properly. Note that vectors, and most kinds of | |
926 | objects allocated as vectors, are all on one chain, but buffers are on a | |
927 | separate chain of their own. | |
928 | ||
929 | @item own_text | |
930 | This is a @code{struct buffer_text} structure. In an ordinary buffer, | |
931 | it holds the buffer contents. In indirect buffers, this field is not | |
932 | used. | |
933 | ||
934 | @item text | |
935 | This points to the @code{buffer_text} structure that is used for this | |
936 | buffer. In an ordinary buffer, this is the @code{own_text} field above. | |
937 | In an indirect buffer, this is the @code{own_text} field of the base | |
938 | buffer. | |
939 | ||
940 | @item pt | |
941 | Contains the character position of point in a buffer. | |
942 | ||
943 | @item pt_byte | |
944 | Contains the byte position of point in a buffer. | |
945 | ||
946 | @item begv | |
947 | This field contains the character position of the beginning of the | |
948 | accessible range of text in the buffer. | |
949 | ||
950 | @item begv_byte | |
951 | This field contains the byte position of the beginning of the | |
952 | accessible range of text in the buffer. | |
953 | ||
954 | @item zv | |
955 | This field contains the character position of the end of the | |
956 | accessible range of text in the buffer. | |
957 | ||
958 | @item zv_byte | |
959 | This field contains the byte position of the end of the | |
960 | accessible range of text in the buffer. | |
961 | ||
962 | @item base_buffer | |
963 | In an indirect buffer, this points to the base buffer. In an ordinary | |
964 | buffer, it is null. | |
965 | ||
966 | @item local_var_flags | |
967 | This field contains flags indicating that certain variables are local in | |
968 | this buffer. Such variables are declared in the C code using | |
969 | @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored in | |
970 | fields in the buffer structure itself. (Some of these fields are | |
971 | described in this table.) | |
972 | ||
973 | @item modtime | |
974 | This field contains the modification time of the visited file. It is | |
975 | set when the file is written or read. Before writing the buffer into a | |
976 | file, this field is compared to the modification time of the file to see | |
977 | if the file has changed on disk. @xref{Buffer Modification}. | |
978 | ||
979 | @item auto_save_modified | |
980 | This field contains the time when the buffer was last auto-saved. | |
981 | ||
982 | @item auto_save_failure_time | |
983 | The time at which we detected a failure to auto-save, or -1 if we didn't | |
984 | have a failure. | |
985 | ||
986 | @item last_window_start | |
987 | This field contains the @code{window-start} position in the buffer as of | |
988 | the last time the buffer was displayed in a window. | |
989 | ||
990 | @item clip_changed | |
991 | This flag is set when narrowing changes in a buffer. | |
992 | ||
993 | @item prevent_redisplay_optimizations_p | |
994 | this flag indicates that redisplay optimizations should not be used | |
995 | to display this buffer. | |
996 | ||
997 | @item undo_list | |
998 | This field points to the buffer's undo list. @xref{Undo}. | |
999 | ||
1000 | @item name | |
1001 | The buffer name is a string that names the buffer. It is guaranteed to | |
1002 | be unique. @xref{Buffer Names}. | |
1003 | ||
1004 | @item filename | |
1005 | The name of the file visited in this buffer, or @code{nil}. | |
1006 | ||
1007 | @item directory | |
1008 | The directory for expanding relative file names. | |
1009 | ||
1010 | @item save_length | |
1011 | Length of the file this buffer is visiting, when last read or saved. | |
1012 | This and other fields concerned with saving are not kept in the | |
1013 | @code{buffer_text} structure because indirect buffers are never saved. | |
1014 | ||
1015 | @item auto_save_file_name | |
1016 | File name used for auto-saving this buffer. This is not in the | |
1017 | @code{buffer_text} because it's not used in indirect buffers at all. | |
1018 | ||
1019 | @item read_only | |
1020 | Non-@code{nil} means this buffer is read-only. | |
1021 | ||
1022 | @item mark | |
1023 | This field contains the mark for the buffer. The mark is a marker, | |
1024 | hence it is also included on the list @code{markers}. @xref{The Mark}. | |
1025 | ||
1026 | @item local_var_alist | |
1027 | This field contains the association list describing the buffer-local | |
1028 | variable bindings of this buffer, not including the built-in | |
1029 | buffer-local bindings that have special slots in the buffer object. | |
1030 | (Those slots are omitted from this table.) @xref{Buffer-Local | |
1031 | Variables}. | |
1032 | ||
1033 | @item major_mode | |
1034 | Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}. | |
1035 | ||
1036 | @item mode_name | |
1037 | Pretty name of major mode, e.g., @code{"Lisp"}. | |
1038 | ||
1039 | @item mode_line_format | |
1040 | Mode line element that controls the format of the mode line. If this | |
1041 | is @code{nil}, no mode line will be displayed. | |
1042 | ||
1043 | @item header_line_format | |
1044 | This field is analogous to @code{mode_line_format} for the mode | |
1045 | line displayed at the top of windows. | |
1046 | ||
1047 | @item keymap | |
1048 | This field holds the buffer's local keymap. @xref{Keymaps}. | |
1049 | ||
1050 | @item abbrev_table | |
1051 | This buffer's local abbrevs. | |
1052 | ||
1053 | @item syntax_table | |
1054 | This field contains the syntax table for the buffer. @xref{Syntax Tables}. | |
1055 | ||
1056 | @item category_table | |
1057 | This field contains the category table for the buffer. | |
1058 | ||
1059 | @item case_fold_search | |
1060 | The value of @code{case-fold-search} in this buffer. | |
1061 | ||
1062 | @item tab_width | |
1063 | The value of @code{tab-width} in this buffer. | |
1064 | ||
1065 | @item fill_column | |
1066 | The value of @code{fill-column} in this buffer. | |
1067 | ||
1068 | @item left_margin | |
1069 | The value of @code{left-margin} in this buffer. | |
1070 | ||
1071 | @item auto_fill_function | |
1072 | The value of @code{auto-fill-function} in this buffer. | |
1073 | ||
1074 | @item downcase_table | |
1075 | This field contains the conversion table for converting text to lower case. | |
1076 | @xref{Case Tables}. | |
1077 | ||
1078 | @item upcase_table | |
1079 | This field contains the conversion table for converting text to upper case. | |
1080 | @xref{Case Tables}. | |
1081 | ||
1082 | @item case_canon_table | |
1083 | This field contains the conversion table for canonicalizing text for | |
1084 | case-folding search. @xref{Case Tables}. | |
1085 | ||
1086 | @item case_eqv_table | |
1087 | This field contains the equivalence table for case-folding search. | |
1088 | @xref{Case Tables}. | |
1089 | ||
1090 | @item truncate_lines | |
1091 | The value of @code{truncate-lines} in this buffer. | |
1092 | ||
1093 | @item ctl_arrow | |
1094 | The value of @code{ctl-arrow} in this buffer. | |
1095 | ||
1096 | @item selective_display | |
1097 | The value of @code{selective-display} in this buffer. | |
1098 | ||
1099 | @item selective_display_ellipsis | |
1100 | The value of @code{selective-display-ellipsis} in this buffer. | |
1101 | ||
1102 | @item minor_modes | |
1103 | An alist of the minor modes of this buffer. | |
1104 | ||
1105 | @item overwrite_mode | |
1106 | The value of @code{overwrite_mode} in this buffer. | |
1107 | ||
1108 | @item abbrev_mode | |
1109 | The value of @code{abbrev-mode} in this buffer. | |
1110 | ||
1111 | @item display_table | |
1112 | This field contains the buffer's display table, or @code{nil} if it doesn't | |
1113 | have one. @xref{Display Tables}. | |
1114 | ||
1115 | @item save_modified | |
1116 | This field contains the time when the buffer was last saved, as an integer. | |
1117 | @xref{Buffer Modification}. | |
1118 | ||
1119 | @item mark_active | |
1120 | This field is non-@code{nil} if the buffer's mark is active. | |
1121 | ||
1122 | @item overlays_before | |
1123 | This field holds a list of the overlays in this buffer that end at or | |
1124 | before the current overlay center position. They are sorted in order of | |
1125 | decreasing end position. | |
1126 | ||
1127 | @item overlays_after | |
1128 | This field holds a list of the overlays in this buffer that end after | |
1129 | the current overlay center position. They are sorted in order of | |
1130 | increasing beginning position. | |
1131 | ||
1132 | @item overlay_center | |
1133 | This field holds the current overlay center position. @xref{Overlays}. | |
1134 | ||
1135 | @item enable_multibyte_characters | |
1136 | This field holds the buffer's local value of | |
1137 | @code{enable-multibyte-characters}---either @code{t} or @code{nil}. | |
1138 | ||
1139 | @item buffer_file_coding_system | |
1140 | The value of @code{buffer-file-coding-system} in this buffer. | |
1141 | ||
1142 | @item file_format | |
1143 | The value of @code{buffer-file-format} in this buffer. | |
1144 | ||
1145 | @item auto_save_file_format | |
1146 | The value of @code{buffer-auto-save-file-format} in this buffer. | |
1147 | ||
1148 | @item pt_marker | |
1149 | In an indirect buffer, or a buffer that is the base of an indirect | |
1150 | buffer, this holds a marker that records point for this buffer when the | |
1151 | buffer is not current. | |
1152 | ||
1153 | @item begv_marker | |
1154 | In an indirect buffer, or a buffer that is the base of an indirect | |
1155 | buffer, this holds a marker that records @code{begv} for this buffer | |
1156 | when the buffer is not current. | |
1157 | ||
1158 | @item zv_marker | |
1159 | In an indirect buffer, or a buffer that is the base of an indirect | |
1160 | buffer, this holds a marker that records @code{zv} for this buffer when | |
1161 | the buffer is not current. | |
1162 | ||
1163 | @item file_truename | |
1164 | The truename of the visited file, or @code{nil}. | |
1165 | ||
1166 | @item invisibility_spec | |
1167 | The value of @code{buffer-invisibility-spec} in this buffer. | |
1168 | ||
1169 | @item last_selected_window | |
1170 | This is the last window that was selected with this buffer in it, or @code{nil} | |
1171 | if that window no longer displays this buffer. | |
1172 | ||
1173 | @item display_count | |
1174 | This field is incremented each time the buffer is displayed in a window. | |
1175 | ||
1176 | @item left_margin_width | |
1177 | The value of @code{left-margin-width} in this buffer. | |
1178 | ||
1179 | @item right_margin_width | |
1180 | The value of @code{right-margin-width} in this buffer. | |
1181 | ||
1182 | @item indicate_empty_lines | |
1183 | Non-@code{nil} means indicate empty lines (lines with no text) with a | |
1184 | small bitmap in the fringe, when using a window system that can do it. | |
1185 | ||
1186 | @item display_time | |
1187 | This holds a time stamp that is updated each time this buffer is | |
1188 | displayed in a window. | |
1189 | ||
1190 | @item scroll_up_aggressively | |
1191 | The value of @code{scroll-up-aggressively} in this buffer. | |
1192 | ||
1193 | @item scroll_down_aggressively | |
1194 | The value of @code{scroll-down-aggressively} in this buffer. | |
1195 | @end table | |
1196 | ||
1197 | @node Window Internals | |
1198 | @appendixsubsec Window Internals | |
1199 | @cindex internals, of window | |
1200 | @cindex window internals | |
1201 | ||
1202 | Windows have the following accessible fields: | |
1203 | ||
1204 | @table @code | |
1205 | @item frame | |
1206 | The frame that this window is on. | |
1207 | ||
1208 | @item mini_p | |
1209 | Non-@code{nil} if this window is a minibuffer window. | |
1210 | ||
1211 | @item parent | |
1212 | Internally, Emacs arranges windows in a tree; each group of siblings has | |
1213 | a parent window whose area includes all the siblings. This field points | |
1214 | to a window's parent. | |
1215 | ||
1216 | Parent windows do not display buffers, and play little role in display | |
1217 | except to shape their child windows. Emacs Lisp programs usually have | |
1218 | no access to the parent windows; they operate on the windows at the | |
1219 | leaves of the tree, which actually display buffers. | |
1220 | ||
1221 | The following four fields also describe the window tree structure. | |
1222 | ||
1223 | @item hchild | |
1224 | In a window subdivided horizontally by child windows, the leftmost child. | |
1225 | Otherwise, @code{nil}. | |
1226 | ||
1227 | @item vchild | |
1228 | In a window subdivided vertically by child windows, the topmost child. | |
1229 | Otherwise, @code{nil}. | |
1230 | ||
1231 | @item next | |
1232 | The next sibling of this window. It is @code{nil} in a window that is | |
1233 | the rightmost or bottommost of a group of siblings. | |
1234 | ||
1235 | @item prev | |
1236 | The previous sibling of this window. It is @code{nil} in a window that | |
1237 | is the leftmost or topmost of a group of siblings. | |
1238 | ||
1239 | @item left | |
1240 | This is the left-hand edge of the window, measured in columns. (The | |
1241 | leftmost column on the screen is @w{column 0}.) | |
1242 | ||
1243 | @item top | |
1244 | This is the top edge of the window, measured in lines. (The top line on | |
1245 | the screen is @w{line 0}.) | |
1246 | ||
1247 | @item height | |
1248 | The height of the window, measured in lines. | |
1249 | ||
1250 | @item width | |
1251 | The width of the window, measured in columns. This width includes the | |
1252 | scroll bar and fringes, and/or the separator line on the right of the | |
1253 | window (if any). | |
1254 | ||
1255 | @item buffer | |
1256 | The buffer that the window is displaying. This may change often during | |
1257 | the life of the window. | |
1258 | ||
1259 | @item start | |
1260 | The position in the buffer that is the first character to be displayed | |
1261 | in the window. | |
1262 | ||
1263 | @item pointm | |
1264 | @cindex window point internals | |
1265 | This is the value of point in the current buffer when this window is | |
1266 | selected; when it is not selected, it retains its previous value. | |
1267 | ||
1268 | @item force_start | |
1269 | If this flag is non-@code{nil}, it says that the window has been | |
1270 | scrolled explicitly by the Lisp program. This affects what the next | |
1271 | redisplay does if point is off the screen: instead of scrolling the | |
1272 | window to show the text around point, it moves point to a location that | |
1273 | is on the screen. | |
1274 | ||
1275 | @item frozen_window_start_p | |
1276 | This field is set temporarily to 1 to indicate to redisplay that | |
1277 | @code{start} of this window should not be changed, even if point | |
1278 | gets invisible. | |
1279 | ||
1280 | @item start_at_line_beg | |
1281 | Non-@code{nil} means current value of @code{start} was the beginning of a line | |
1282 | when it was chosen. | |
1283 | ||
1284 | @item too_small_ok | |
1285 | Non-@code{nil} means don't delete this window for becoming ``too small.'' | |
1286 | ||
1287 | @item height_fixed_p | |
1288 | This field is temporarily set to 1 to fix the height of the selected | |
1289 | window when the echo area is resized. | |
1290 | ||
1291 | @item use_time | |
1292 | This is the last time that the window was selected. The function | |
1293 | @code{get-lru-window} uses this field. | |
1294 | ||
1295 | @item sequence_number | |
1296 | A unique number assigned to this window when it was created. | |
1297 | ||
1298 | @item last_modified | |
1299 | The @code{modiff} field of the window's buffer, as of the last time | |
1300 | a redisplay completed in this window. | |
1301 | ||
1302 | @item last_overlay_modified | |
1303 | The @code{overlay_modiff} field of the window's buffer, as of the last | |
1304 | time a redisplay completed in this window. | |
1305 | ||
1306 | @item last_point | |
1307 | The buffer's value of point, as of the last time a redisplay completed | |
1308 | in this window. | |
1309 | ||
1310 | @item last_had_star | |
1311 | A non-@code{nil} value means the window's buffer was ``modified'' when the | |
1312 | window was last updated. | |
1313 | ||
1314 | @item vertical_scroll_bar | |
1315 | This window's vertical scroll bar. | |
1316 | ||
1317 | @item left_margin_width | |
1318 | The width of the left margin in this window, or @code{nil} not to | |
1319 | specify it (in which case the buffer's value of @code{left-margin-width} | |
1320 | is used. | |
1321 | ||
1322 | @item right_margin_width | |
1323 | Likewise for the right margin. | |
1324 | ||
1325 | @ignore | |
1326 | @item last_mark_x | |
1327 | @item last_mark_y | |
1328 | ???Not used. | |
1329 | @end ignore | |
1330 | ||
1331 | @item window_end_pos | |
1332 | This is computed as @code{z} minus the buffer position of the last glyph | |
1333 | in the current matrix of the window. The value is only valid if | |
1334 | @code{window_end_valid} is not @code{nil}. | |
1335 | ||
1336 | @item window_end_bytepos | |
1337 | The byte position corresponding to @code{window_end_pos}. | |
1338 | ||
1339 | @item window_end_vpos | |
1340 | The window-relative vertical position of the line containing | |
1341 | @code{window_end_pos}. | |
1342 | ||
1343 | @item window_end_valid | |
1344 | This field is set to a non-@code{nil} value if @code{window_end_pos} is truly | |
1345 | valid. This is @code{nil} if nontrivial redisplay is preempted since in that | |
1346 | case the display that @code{window_end_pos} was computed for did not get | |
1347 | onto the screen. | |
1348 | ||
1349 | @item redisplay_end_trigger | |
1350 | If redisplay in this window goes beyond this buffer position, it runs | |
1351 | the @code{redisplay-end-trigger-hook}. | |
1352 | ||
1353 | @ignore | |
1354 | @item orig_height | |
1355 | @item orig_top | |
1356 | ??? Are temporary storage areas. | |
1357 | @end ignore | |
1358 | ||
1359 | @item cursor | |
1360 | A structure describing where the cursor is in this window. | |
1361 | ||
1362 | @item last_cursor | |
1363 | The value of @code{cursor} as of the last redisplay that finished. | |
1364 | ||
1365 | @item phys_cursor | |
1366 | A structure describing where the cursor of this window physically is. | |
1367 | ||
1368 | @item phys_cursor_type | |
1369 | The type of cursor that was last displayed on this window. | |
1370 | ||
1371 | @item phys_cursor_on_p | |
1372 | This field is non-zero if the cursor is physically on. | |
1373 | ||
1374 | @item cursor_off_p | |
1375 | Non-zero means the cursor in this window is logically on. | |
1376 | ||
1377 | @item last_cursor_off_p | |
1378 | This field contains the value of @code{cursor_off_p} as of the time of | |
1379 | the last redisplay. | |
1380 | ||
1381 | @item must_be_updated_p | |
1382 | This is set to 1 during redisplay when this window must be updated. | |
1383 | ||
1384 | @item hscroll | |
1385 | This is the number of columns that the display in the window is scrolled | |
1386 | horizontally to the left. Normally, this is 0. | |
1387 | ||
1388 | @item vscroll | |
1389 | Vertical scroll amount, in pixels. Normally, this is 0. | |
1390 | ||
1391 | @item dedicated | |
1392 | Non-@code{nil} if this window is dedicated to its buffer. | |
1393 | ||
1394 | @item display_table | |
1395 | The window's display table, or @code{nil} if none is specified for it. | |
1396 | ||
1397 | @item update_mode_line | |
1398 | Non-@code{nil} means this window's mode line needs to be updated. | |
1399 | ||
1400 | @item base_line_number | |
1401 | The line number of a certain position in the buffer, or @code{nil}. | |
1402 | This is used for displaying the line number of point in the mode line. | |
1403 | ||
1404 | @item base_line_pos | |
1405 | The position in the buffer for which the line number is known, or | |
1406 | @code{nil} meaning none is known. | |
1407 | ||
1408 | @item region_showing | |
1409 | If the region (or part of it) is highlighted in this window, this field | |
1410 | holds the mark position that made one end of that region. Otherwise, | |
1411 | this field is @code{nil}. | |
1412 | ||
1413 | @item column_number_displayed | |
1414 | The column number currently displayed in this window's mode line, or @code{nil} | |
1415 | if column numbers are not being displayed. | |
1416 | ||
1417 | @item current_matrix | |
1418 | A glyph matrix describing the current display of this window. | |
1419 | ||
1420 | @item desired_matrix | |
1421 | A glyph matrix describing the desired display of this window. | |
1422 | @end table | |
1423 | ||
1424 | @node Process Internals | |
1425 | @appendixsubsec Process Internals | |
1426 | @cindex internals, of process | |
1427 | @cindex process internals | |
1428 | ||
1429 | The fields of a process are: | |
1430 | ||
1431 | @table @code | |
1432 | @item name | |
1433 | A string, the name of the process. | |
1434 | ||
1435 | @item command | |
1436 | A list containing the command arguments that were used to start this | |
c73e02fa GM |
1437 | process. For a network or serial process, it is @code{nil} if the |
1438 | process is running or @code{t} if the process is stopped. | |
b8d4c8d0 GM |
1439 | |
1440 | @item filter | |
1441 | A function used to accept output from the process instead of a buffer, | |
1442 | or @code{nil}. | |
1443 | ||
1444 | @item sentinel | |
1445 | A function called whenever the process receives a signal, or @code{nil}. | |
1446 | ||
1447 | @item buffer | |
1448 | The associated buffer of the process. | |
1449 | ||
1450 | @item pid | |
1451 | An integer, the operating system's process @acronym{ID}. | |
1452 | ||
1453 | @item childp | |
c73e02fa | 1454 | |
b8d4c8d0 | 1455 | A flag, non-@code{nil} if this is really a child process. |
c73e02fa | 1456 | It is @code{nil} for a network or serial connection. |
b8d4c8d0 GM |
1457 | |
1458 | @item mark | |
1459 | A marker indicating the position of the end of the last output from this | |
1460 | process inserted into the buffer. This is often but not always the end | |
1461 | of the buffer. | |
1462 | ||
1463 | @item kill_without_query | |
1464 | If this is non-@code{nil}, killing Emacs while this process is still | |
1465 | running does not ask for confirmation about killing the process. | |
1466 | ||
1467 | @item raw_status_low | |
1468 | @itemx raw_status_high | |
1469 | These two fields record 16 bits each of the process status returned by | |
1470 | the @code{wait} system call. | |
1471 | ||
1472 | @item status | |
1473 | The process status, as @code{process-status} should return it. | |
1474 | ||
1475 | @item tick | |
1476 | @itemx update_tick | |
1477 | If these two fields are not equal, a change in the status of the process | |
1478 | needs to be reported, either by running the sentinel or by inserting a | |
1479 | message in the process buffer. | |
1480 | ||
1481 | @item pty_flag | |
1482 | Non-@code{nil} if communication with the subprocess uses a @acronym{PTY}; | |
1483 | @code{nil} if it uses a pipe. | |
1484 | ||
1485 | @item infd | |
1486 | The file descriptor for input from the process. | |
1487 | ||
1488 | @item outfd | |
1489 | The file descriptor for output to the process. | |
1490 | ||
1491 | @item subtty | |
1492 | The file descriptor for the terminal that the subprocess is using. (On | |
1493 | some systems, there is no need to record this, so the value is | |
1494 | @code{nil}.) | |
1495 | ||
1496 | @item tty_name | |
1497 | The name of the terminal that the subprocess is using, | |
1498 | or @code{nil} if it is using pipes. | |
1499 | ||
1500 | @item decode_coding_system | |
1501 | Coding-system for decoding the input from this process. | |
1502 | ||
1503 | @item decoding_buf | |
1504 | A working buffer for decoding. | |
1505 | ||
1506 | @item decoding_carryover | |
1507 | Size of carryover in decoding. | |
1508 | ||
1509 | @item encode_coding_system | |
1510 | Coding-system for encoding the output to this process. | |
1511 | ||
1512 | @item encoding_buf | |
1513 | A working buffer for encoding. | |
1514 | ||
1515 | @item encoding_carryover | |
1516 | Size of carryover in encoding. | |
1517 | ||
1518 | @item inherit_coding_system_flag | |
1519 | Flag to set @code{coding-system} of the process buffer from the | |
1520 | coding system used to decode process output. | |
c73e02fa GM |
1521 | |
1522 | @item type | |
1523 | Symbol indicating the type of process: @code{real}, @code{network}, | |
1524 | @code{serial} | |
1525 | ||
b8d4c8d0 GM |
1526 | @end table |
1527 | ||
1528 | @ignore | |
1529 | arch-tag: 4b2c33bc-d7e4-43f5-bc20-27c0db52a53e | |
1530 | @end ignore |