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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
fd897522 GM |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1998, 1999 |
4 | @c 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 | |
969fe9b5 | 16 | * Building Emacs:: How to 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 | |
84 | variables) in the file @file{etc/DOC} where they are stored, by calling | |
85 | @code{Snarf-documentation} (@pxref{Accessing Documentation}). | |
86 | ||
a44af9f2 | 87 | @cindex @file{site-init.el} |
a890e1b0 | 88 | You can specify other Lisp expressions to execute just before dumping |
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89 | by putting them in a library named @file{site-init.el}. This file is |
90 | executed after the documentation strings are found. | |
a44af9f2 | 91 | |
2a664e73 RS |
92 | If you want to preload function or variable definitions, there are |
93 | three ways you can do this and make their documentation strings | |
94 | accessible when you subsequently run Emacs: | |
95 | ||
96 | @itemize @bullet | |
97 | @item | |
98 | Arrange to scan these files when producing the @file{etc/DOC} file, | |
99 | and load them with @file{site-load.el}. | |
100 | ||
101 | @item | |
102 | Load the files with @file{site-init.el}, then copy the files into the | |
103 | installation directory for Lisp files when you install Emacs. | |
104 | ||
105 | @item | |
106 | Specify a non-@code{nil} value for | |
8241495d | 107 | @code{byte-compile-dynamic-docstrings} as a local variable in each of these |
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108 | files, and load them with either @file{site-load.el} or |
109 | @file{site-init.el}. (This method has the drawback that the | |
110 | documentation strings take up space in Emacs all the time.) | |
111 | @end itemize | |
112 | ||
113 | It is not advisable to put anything in @file{site-load.el} or | |
114 | @file{site-init.el} that would alter any of the features that users | |
115 | expect in an ordinary unmodified Emacs. If you feel you must override | |
116 | normal features for your site, do it with @file{default.el}, so that | |
8241495d | 117 | users can override your changes if they wish. @xref{Startup Summary}. |
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118 | |
119 | @defun dump-emacs to-file from-file | |
120 | @cindex unexec | |
cb017dde | 121 | This function dumps the current state of Emacs into an executable file |
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122 | @var{to-file}. It takes symbols from @var{from-file} (this is normally |
123 | the executable file @file{temacs}). | |
124 | ||
cb017dde RS |
125 | If you want to use this function in an Emacs that was already dumped, |
126 | you must run Emacs with @samp{-batch}. | |
a44af9f2 RS |
127 | @end defun |
128 | ||
969fe9b5 | 129 | @node Pure Storage |
a44af9f2 RS |
130 | @appendixsec Pure Storage |
131 | @cindex pure storage | |
132 | ||
a890e1b0 RS |
133 | Emacs Lisp uses two kinds of storage for user-created Lisp objects: |
134 | @dfn{normal storage} and @dfn{pure storage}. Normal storage is where | |
8241495d | 135 | all the new data created during an Emacs session are kept; see the |
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136 | following section for information on normal storage. Pure storage is |
137 | used for certain data in the preloaded standard Lisp files---data that | |
138 | should never change during actual use of Emacs. | |
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139 | |
140 | Pure storage is allocated only while @file{temacs} is loading the | |
141 | standard preloaded Lisp libraries. In the file @file{emacs}, it is | |
574efc83 | 142 | marked as read-only (on operating systems that permit this), so that |
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143 | the memory space can be shared by all the Emacs jobs running on the |
144 | machine at once. Pure storage is not expandable; a fixed amount is | |
145 | allocated when Emacs is compiled, and if that is not sufficient for the | |
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146 | preloaded libraries, @file{temacs} crashes. If that happens, you must |
147 | increase the compilation parameter @code{PURESIZE} in the file | |
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148 | @file{src/puresize.h}. This normally won't happen unless you try to |
149 | preload additional libraries or add features to the standard ones. | |
150 | ||
151 | @defun purecopy object | |
8241495d RS |
152 | This function makes a copy in pure storage of @var{object}, and returns |
153 | it. It copies a string by simply making a new string with the same | |
a44af9f2 | 154 | characters in pure storage. It recursively copies the contents of |
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155 | vectors and cons cells. It does not make copies of other objects such |
156 | as symbols, but just returns them unchanged. It signals an error if | |
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157 | asked to copy markers. |
158 | ||
c2cd5fb7 RS |
159 | This function is a no-op except while Emacs is being built and dumped; |
160 | it is usually called only in the file @file{emacs/lisp/loaddefs.el}, but | |
161 | a few packages call it just in case you decide to preload them. | |
a44af9f2 RS |
162 | @end defun |
163 | ||
164 | @defvar pure-bytes-used | |
a890e1b0 | 165 | The value of this variable is the number of bytes of pure storage |
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166 | allocated so far. Typically, in a dumped Emacs, this number is very |
167 | close to the total amount of pure storage available---if it were not, | |
168 | we would preallocate less. | |
169 | @end defvar | |
170 | ||
171 | @defvar purify-flag | |
a890e1b0 | 172 | This variable determines whether @code{defun} should make a copy of the |
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173 | function definition in pure storage. If it is non-@code{nil}, then the |
174 | function definition is copied into pure storage. | |
175 | ||
a890e1b0 | 176 | This flag is @code{t} while loading all of the basic functions for |
a44af9f2 | 177 | building Emacs initially (allowing those functions to be sharable and |
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178 | non-collectible). Dumping Emacs as an executable always writes |
179 | @code{nil} in this variable, regardless of the value it actually has | |
180 | before and after dumping. | |
a44af9f2 | 181 | |
a890e1b0 | 182 | You should not change this flag in a running Emacs. |
a44af9f2 RS |
183 | @end defvar |
184 | ||
969fe9b5 | 185 | @node Garbage Collection |
a44af9f2 RS |
186 | @appendixsec Garbage Collection |
187 | @cindex garbage collector | |
188 | ||
189 | @cindex memory allocation | |
190 | When a program creates a list or the user defines a new function (such | |
a890e1b0 RS |
191 | as by loading a library), that data is placed in normal storage. If |
192 | normal storage runs low, then Emacs asks the operating system to | |
a44af9f2 | 193 | allocate more memory in blocks of 1k bytes. Each block is used for one |
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194 | type of Lisp object, so symbols, cons cells, markers, etc., are |
195 | segregated in distinct blocks in memory. (Vectors, long strings, | |
196 | buffers and certain other editing types, which are fairly large, are | |
197 | allocated in individual blocks, one per object, while small strings are | |
198 | packed into blocks of 8k bytes.) | |
199 | ||
200 | It is quite common to use some storage for a while, then release it by | |
201 | (for example) killing a buffer or deleting the last pointer to an | |
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202 | object. Emacs provides a @dfn{garbage collector} to reclaim this |
203 | abandoned storage. (This name is traditional, but ``garbage recycler'' | |
204 | might be a more intuitive metaphor for this facility.) | |
205 | ||
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206 | The garbage collector operates by finding and marking all Lisp objects |
207 | that are still accessible to Lisp programs. To begin with, it assumes | |
208 | all the symbols, their values and associated function definitions, and | |
574efc83 | 209 | any data presently on the stack, are accessible. Any objects that can |
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210 | be reached indirectly through other accessible objects are also |
211 | accessible. | |
a44af9f2 | 212 | |
a890e1b0 | 213 | When marking is finished, all objects still unmarked are garbage. No |
a44af9f2 | 214 | matter what the Lisp program or the user does, it is impossible to refer |
a890e1b0 | 215 | to them, since there is no longer a way to reach them. Their space |
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216 | might as well be reused, since no one will miss them. The second |
217 | (``sweep'') phase of the garbage collector arranges to reuse them. | |
a44af9f2 | 218 | |
05aea714 | 219 | @c ??? Maybe add something describing weak hash tables here? |
95260b26 | 220 | |
a44af9f2 | 221 | @cindex free list |
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222 | The sweep phase puts unused cons cells onto a @dfn{free list} |
223 | for future allocation; likewise for symbols and markers. It compacts | |
224 | the accessible strings so they occupy fewer 8k blocks; then it frees the | |
574efc83 | 225 | other 8k blocks. Vectors, buffers, windows, and other large objects are |
a890e1b0 | 226 | individually allocated and freed using @code{malloc} and @code{free}. |
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227 | |
228 | @cindex CL note---allocate more storage | |
229 | @quotation | |
574efc83 | 230 | @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not |
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231 | call the garbage collector when the free list is empty. Instead, it |
232 | simply requests the operating system to allocate more storage, and | |
233 | processing continues until @code{gc-cons-threshold} bytes have been | |
234 | used. | |
235 | ||
236 | This means that you can make sure that the garbage collector will not | |
237 | run during a certain portion of a Lisp program by calling the garbage | |
238 | collector explicitly just before it (provided that portion of the | |
239 | program does not use so much space as to force a second garbage | |
240 | collection). | |
241 | @end quotation | |
242 | ||
243 | @deffn Command garbage-collect | |
a890e1b0 | 244 | This command runs a garbage collection, and returns information on |
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245 | the amount of space in use. (Garbage collection can also occur |
246 | spontaneously if you use more than @code{gc-cons-threshold} bytes of | |
247 | Lisp data since the previous garbage collection.) | |
248 | ||
a890e1b0 | 249 | @code{garbage-collect} returns a list containing the following |
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250 | information: |
251 | ||
a890e1b0 | 252 | @example |
a44af9f2 RS |
253 | @group |
254 | ((@var{used-conses} . @var{free-conses}) | |
255 | (@var{used-syms} . @var{free-syms}) | |
a890e1b0 | 256 | @end group |
969fe9b5 | 257 | (@var{used-miscs} . @var{free-miscs}) |
a44af9f2 RS |
258 | @var{used-string-chars} |
259 | @var{used-vector-slots} | |
f9f59935 RS |
260 | (@var{used-floats} . @var{free-floats}) |
261 | (@var{used-intervals} . @var{free-intervals})) | |
969fe9b5 RS |
262 | @end example |
263 | ||
264 | Here is an example: | |
265 | ||
266 | @example | |
a890e1b0 | 267 | @group |
a44af9f2 | 268 | (garbage-collect) |
f9f59935 RS |
269 | @result{} ((106886 . 13184) (9769 . 0) |
270 | (7731 . 4651) 347543 121628 | |
271 | (31 . 94) (1273 . 168)) | |
a44af9f2 | 272 | @end group |
a890e1b0 | 273 | @end example |
a44af9f2 RS |
274 | |
275 | Here is a table explaining each element: | |
276 | ||
277 | @table @var | |
278 | @item used-conses | |
279 | The number of cons cells in use. | |
280 | ||
281 | @item free-conses | |
282 | The number of cons cells for which space has been obtained from the | |
283 | operating system, but that are not currently being used. | |
284 | ||
285 | @item used-syms | |
286 | The number of symbols in use. | |
287 | ||
288 | @item free-syms | |
289 | The number of symbols for which space has been obtained from the | |
290 | operating system, but that are not currently being used. | |
291 | ||
969fe9b5 RS |
292 | @item used-miscs |
293 | The number of miscellaneous objects in use. These include markers and | |
294 | overlays, plus certain objects not visible to users. | |
a44af9f2 | 295 | |
969fe9b5 RS |
296 | @item free-miscs |
297 | The number of miscellaneous objects for which space has been obtained | |
298 | from the operating system, but that are not currently being used. | |
a44af9f2 RS |
299 | |
300 | @item used-string-chars | |
301 | The total size of all strings, in characters. | |
302 | ||
303 | @item used-vector-slots | |
304 | The total number of elements of existing vectors. | |
305 | ||
306 | @item used-floats | |
307 | @c Emacs 19 feature | |
308 | The number of floats in use. | |
309 | ||
310 | @item free-floats | |
311 | @c Emacs 19 feature | |
312 | The number of floats for which space has been obtained from the | |
313 | operating system, but that are not currently being used. | |
a9f0a989 RS |
314 | |
315 | @item used-intervals | |
316 | The number of intervals in use. Intervals are an internal | |
317 | data structure used for representing text properties. | |
318 | ||
319 | @item free-intervals | |
320 | The number of intervals for which space has been obtained | |
321 | from the operating system, but that are not currently being used. | |
a44af9f2 RS |
322 | @end table |
323 | @end deffn | |
324 | ||
d64c55d8 RS |
325 | @defopt garbage-collection-messages |
326 | If this variable is non-@code{nil}, Emacs displays a message at the | |
327 | beginning and end of garbage collection. The default value is | |
328 | @code{nil}, meaning there are no such messages. | |
329 | @end defopt | |
330 | ||
a44af9f2 | 331 | @defopt gc-cons-threshold |
a890e1b0 | 332 | The value of this variable is the number of bytes of storage that must |
a44af9f2 | 333 | be allocated for Lisp objects after one garbage collection in order to |
a890e1b0 | 334 | trigger another garbage collection. A cons cell counts as eight bytes, |
a44af9f2 | 335 | a string as one byte per character plus a few bytes of overhead, and so |
a890e1b0 RS |
336 | on; space allocated to the contents of buffers does not count. Note |
337 | that the subsequent garbage collection does not happen immediately when | |
338 | the threshold is exhausted, but only the next time the Lisp evaluator is | |
a44af9f2 RS |
339 | called. |
340 | ||
f9f59935 | 341 | The initial threshold value is 400,000. If you specify a larger |
a44af9f2 RS |
342 | value, garbage collection will happen less often. This reduces the |
343 | amount of time spent garbage collecting, but increases total memory use. | |
574efc83 | 344 | You may want to do this when running a program that creates lots of |
a44af9f2 RS |
345 | Lisp data. |
346 | ||
a890e1b0 | 347 | You can make collections more frequent by specifying a smaller value, |
a44af9f2 RS |
348 | down to 10,000. A value less than 10,000 will remain in effect only |
349 | until the subsequent garbage collection, at which time | |
350 | @code{garbage-collect} will set the threshold back to 10,000. | |
351 | @end defopt | |
352 | ||
969fe9b5 RS |
353 | The value return by @code{garbage-collect} describes the amount of |
354 | memory used by Lisp data, broken down by data type. By contrast, the | |
355 | function @code{memory-limit} provides information on the total amount of | |
356 | memory Emacs is currently using. | |
357 | ||
a44af9f2 RS |
358 | @c Emacs 19 feature |
359 | @defun memory-limit | |
360 | This function returns the address of the last byte Emacs has allocated, | |
361 | divided by 1024. We divide the value by 1024 to make sure it fits in a | |
362 | Lisp integer. | |
363 | ||
364 | You can use this to get a general idea of how your actions affect the | |
365 | memory usage. | |
366 | @end defun | |
367 | ||
969fe9b5 RS |
368 | @node Memory Usage |
369 | @section Memory Usage | |
370 | ||
371 | These functions and variables give information about the total amount | |
372 | of memory allocation that Emacs has done, broken down by data type. | |
373 | Note the difference between these and the values returned by | |
374 | @code{(garbage-collect)}; those count objects that currently exist, but | |
375 | these count the number or size of all allocations, including those for | |
376 | objects that have since been freed. | |
377 | ||
378 | @defvar cons-cells-consed | |
379 | The total number of cons cells that have been allocated so far | |
380 | in this Emacs session. | |
381 | @end defvar | |
382 | ||
383 | @defvar floats-consed | |
384 | The total number of floats that have been allocated so far | |
385 | in this Emacs session. | |
386 | @end defvar | |
387 | ||
388 | @defvar vector-cells-consed | |
389 | The total number of vector cells that have been allocated so far | |
390 | in this Emacs session. | |
391 | @end defvar | |
392 | ||
393 | @defvar symbols-consed | |
394 | The total number of symbols that have been allocated so far | |
395 | in this Emacs session. | |
396 | @end defvar | |
397 | ||
398 | @defvar string-chars-consed | |
399 | The total number of string characters that have been allocated so far | |
400 | in this Emacs session. | |
401 | @end defvar | |
402 | ||
403 | @defvar misc-objects-consed | |
404 | The total number of miscellaneous objects that have been allocated so | |
405 | far in this Emacs session. These include markers and overlays, plus | |
406 | certain objects not visible to users. | |
407 | @end defvar | |
408 | ||
409 | @defvar intervals-consed | |
410 | The total number of intervals that have been allocated so far | |
411 | in this Emacs session. | |
412 | @end defvar | |
413 | ||
414 | @node Writing Emacs Primitives | |
a44af9f2 RS |
415 | @appendixsec Writing Emacs Primitives |
416 | @cindex primitive function internals | |
417 | ||
418 | Lisp primitives are Lisp functions implemented in C. The details of | |
419 | interfacing the C function so that Lisp can call it are handled by a few | |
420 | C macros. The only way to really understand how to write new C code is | |
421 | to read the source, but we can explain some things here. | |
422 | ||
423 | An example of a special form is the definition of @code{or}, from | |
424 | @file{eval.c}. (An ordinary function would have the same general | |
425 | appearance.) | |
426 | ||
427 | @cindex garbage collection protection | |
428 | @smallexample | |
429 | @group | |
430 | DEFUN ("or", For, Sor, 0, UNEVALLED, 0, | |
9e2b495b | 431 | "Eval args until one of them yields non-nil; return that value.\n\ |
a44af9f2 RS |
432 | The remaining args are not evalled at all.\n\ |
433 | @end group | |
434 | @group | |
a890e1b0 | 435 | If all args return nil, return nil.") |
a44af9f2 RS |
436 | (args) |
437 | Lisp_Object args; | |
438 | @{ | |
439 | register Lisp_Object val; | |
440 | Lisp_Object args_left; | |
441 | struct gcpro gcpro1; | |
442 | @end group | |
443 | ||
444 | @group | |
95260b26 | 445 | if (NILP (args)) |
a44af9f2 RS |
446 | return Qnil; |
447 | ||
448 | args_left = args; | |
449 | GCPRO1 (args_left); | |
450 | @end group | |
451 | ||
452 | @group | |
453 | do | |
454 | @{ | |
455 | val = Feval (Fcar (args_left)); | |
95260b26 | 456 | if (!NILP (val)) |
a44af9f2 RS |
457 | break; |
458 | args_left = Fcdr (args_left); | |
459 | @} | |
95260b26 | 460 | while (!NILP (args_left)); |
a44af9f2 RS |
461 | @end group |
462 | ||
463 | @group | |
464 | UNGCPRO; | |
465 | return val; | |
466 | @} | |
467 | @end group | |
468 | @end smallexample | |
469 | ||
470 | Let's start with a precise explanation of the arguments to the | |
a890e1b0 | 471 | @code{DEFUN} macro. Here is a template for them: |
a44af9f2 RS |
472 | |
473 | @example | |
474 | DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc}) | |
475 | @end example | |
476 | ||
477 | @table @var | |
478 | @item lname | |
a890e1b0 RS |
479 | This is the name of the Lisp symbol to define as the function name; in |
480 | the example above, it is @code{or}. | |
a44af9f2 RS |
481 | |
482 | @item fname | |
483 | This is the C function name for this function. This is | |
484 | the name that is used in C code for calling the function. The name is, | |
485 | by convention, @samp{F} prepended to the Lisp name, with all dashes | |
486 | (@samp{-}) in the Lisp name changed to underscores. Thus, to call this | |
487 | function from C code, call @code{For}. Remember that the arguments must | |
488 | be of type @code{Lisp_Object}; various macros and functions for creating | |
489 | values of type @code{Lisp_Object} are declared in the file | |
490 | @file{lisp.h}. | |
491 | ||
492 | @item sname | |
493 | This is a C variable name to use for a structure that holds the data for | |
494 | the subr object that represents the function in Lisp. This structure | |
495 | conveys the Lisp symbol name to the initialization routine that will | |
496 | create the symbol and store the subr object as its definition. By | |
497 | convention, this name is always @var{fname} with @samp{F} replaced with | |
498 | @samp{S}. | |
499 | ||
500 | @item min | |
a890e1b0 RS |
501 | This is the minimum number of arguments that the function requires. The |
502 | function @code{or} allows a minimum of zero arguments. | |
a44af9f2 RS |
503 | |
504 | @item max | |
a890e1b0 RS |
505 | This is the maximum number of arguments that the function accepts, if |
506 | there is a fixed maximum. Alternatively, it can be @code{UNEVALLED}, | |
507 | indicating a special form that receives unevaluated arguments, or | |
508 | @code{MANY}, indicating an unlimited number of evaluated arguments (the | |
509 | equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are | |
510 | macros. If @var{max} is a number, it may not be less than @var{min} and | |
511 | it may not be greater than seven. | |
a44af9f2 RS |
512 | |
513 | @item interactive | |
514 | This is an interactive specification, a string such as might be used as | |
515 | the argument of @code{interactive} in a Lisp function. In the case of | |
516 | @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be | |
a890e1b0 RS |
517 | called interactively. A value of @code{""} indicates a function that |
518 | should receive no arguments when called interactively. | |
a44af9f2 RS |
519 | |
520 | @item doc | |
521 | This is the documentation string. It is written just like a | |
522 | documentation string for a function defined in Lisp, except you must | |
523 | write @samp{\n\} at the end of each line. In particular, the first line | |
524 | should be a single sentence. | |
525 | @end table | |
526 | ||
a890e1b0 RS |
527 | After the call to the @code{DEFUN} macro, you must write the argument |
528 | name list that every C function must have, followed by ordinary C | |
529 | declarations for the arguments. For a function with a fixed maximum | |
530 | number of arguments, declare a C argument for each Lisp argument, and | |
574efc83 RS |
531 | give them all type @code{Lisp_Object}. When a Lisp function has no |
532 | upper limit on the number of arguments, its implementation in C actually | |
533 | receives exactly two arguments: the first is the number of Lisp | |
534 | arguments, and the second is the address of a block containing their | |
535 | values. They have types @code{int} and @w{@code{Lisp_Object *}}. | |
a44af9f2 RS |
536 | |
537 | Within the function @code{For} itself, note the use of the macros | |
538 | @code{GCPRO1} and @code{UNGCPRO}. @code{GCPRO1} is used to ``protect'' | |
539 | a variable from garbage collection---to inform the garbage collector that | |
540 | it must look in that variable and regard its contents as an accessible | |
541 | object. This is necessary whenever you call @code{Feval} or anything | |
542 | that can directly or indirectly call @code{Feval}. At such a time, any | |
543 | Lisp object that you intend to refer to again must be protected somehow. | |
544 | @code{UNGCPRO} cancels the protection of the variables that are | |
545 | protected in the current function. It is necessary to do this explicitly. | |
546 | ||
a890e1b0 RS |
547 | For most data types, it suffices to protect at least one pointer to |
548 | the object; as long as the object is not recycled, all pointers to it | |
549 | remain valid. This is not so for strings, because the garbage collector | |
550 | can move them. When the garbage collector moves a string, it relocates | |
551 | all the pointers it knows about; any other pointers become invalid. | |
552 | Therefore, you must protect all pointers to strings across any point | |
553 | where garbage collection may be possible. | |
554 | ||
555 | The macro @code{GCPRO1} protects just one local variable. If you want | |
556 | to protect two, use @code{GCPRO2} instead; repeating @code{GCPRO1} will | |
557 | not work. Macros @code{GCPRO3} and @code{GCPRO4} also exist. | |
558 | ||
559 | These macros implicitly use local variables such as @code{gcpro1}; you | |
560 | must declare these explicitly, with type @code{struct gcpro}. Thus, if | |
561 | you use @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}. | |
562 | Alas, we can't explain all the tricky details here. | |
563 | ||
e610024b | 564 | You must not use C initializers for static or global variables unless |
05aea714 | 565 | the variables are never written once Emacs is dumped. These variables |
8241495d RS |
566 | with initializers are allocated in an area of memory that becomes |
567 | read-only (on certain operating systems) as a result of dumping Emacs. | |
568 | @xref{Pure Storage}. | |
e610024b RS |
569 | |
570 | Do not use static variables within functions---place all static | |
571 | variables at top level in the file. This is necessary because Emacs on | |
572 | some operating systems defines the keyword @code{static} as a null | |
573 | macro. (This definition is used because those systems put all variables | |
574 | declared static in a place that becomes read-only after dumping, whether | |
575 | they have initializers or not.) | |
77223f05 | 576 | |
a890e1b0 RS |
577 | Defining the C function is not enough to make a Lisp primitive |
578 | available; you must also create the Lisp symbol for the primitive and | |
579 | store a suitable subr object in its function cell. The code looks like | |
580 | this: | |
a44af9f2 RS |
581 | |
582 | @example | |
583 | defsubr (&@var{subr-structure-name}); | |
584 | @end example | |
585 | ||
586 | @noindent | |
a890e1b0 RS |
587 | Here @var{subr-structure-name} is the name you used as the third |
588 | argument to @code{DEFUN}. | |
589 | ||
590 | If you add a new primitive to a file that already has Lisp primitives | |
591 | defined in it, find the function (near the end of the file) named | |
592 | @code{syms_of_@var{something}}, and add the call to @code{defsubr} | |
593 | there. If the file doesn't have this function, or if you create a new | |
594 | file, add to it a @code{syms_of_@var{filename}} (e.g., | |
595 | @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all | |
596 | of these functions are called, and add a call to | |
597 | @code{syms_of_@var{filename}} there. | |
a44af9f2 | 598 | |
8241495d | 599 | @vindex byte-boolean-vars |
574efc83 RS |
600 | The function @code{syms_of_@var{filename}} is also the place to define |
601 | any C variables that are to be visible as Lisp variables. | |
a890e1b0 RS |
602 | @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible |
603 | in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int} | |
604 | visible in Lisp with a value that is always an integer. | |
605 | @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp | |
8241495d RS |
606 | with a value that is either @code{t} or @code{nil}. Note that variables |
607 | defined with @code{DEFVAR_BOOL} are automatically added to the list | |
608 | @code{byte-boolean-vars} used by the byte compiler. | |
a44af9f2 | 609 | |
969fe9b5 | 610 | If you define a file-scope C variable of type @code{Lisp_Object}, |
8241495d | 611 | you must protect it from garbage-collection by calling @code{staticpro} |
969fe9b5 RS |
612 | in @code{syms_of_@var{filename}}, like this: |
613 | ||
614 | @example | |
615 | staticpro (&@var{variable}); | |
616 | @end example | |
617 | ||
a890e1b0 | 618 | Here is another example function, with more complicated arguments. |
969fe9b5 RS |
619 | This comes from the code in @file{window.c}, and it demonstrates the use |
620 | of macros and functions to manipulate Lisp objects. | |
a44af9f2 RS |
621 | |
622 | @smallexample | |
623 | @group | |
624 | DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p, | |
625 | Scoordinates_in_window_p, 2, 2, | |
626 | "xSpecify coordinate pair: \nXExpression which evals to window: ", | |
969fe9b5 RS |
627 | "Return non-nil if COORDINATES is in WINDOW.\n\ |
628 | COORDINATES is a cons of the form (X . Y), X and Y being distances\n\ | |
629 | ... | |
a44af9f2 RS |
630 | @end group |
631 | @group | |
969fe9b5 RS |
632 | If they are on the border between WINDOW and its right sibling,\n\ |
633 | `vertical-line' is returned.") | |
634 | (coordinates, window) | |
635 | register Lisp_Object coordinates, window; | |
a44af9f2 | 636 | @{ |
969fe9b5 | 637 | int x, y; |
a44af9f2 RS |
638 | @end group |
639 | ||
640 | @group | |
969fe9b5 RS |
641 | CHECK_LIVE_WINDOW (window, 0); |
642 | CHECK_CONS (coordinates, 1); | |
643 | x = XINT (Fcar (coordinates)); | |
644 | y = XINT (Fcdr (coordinates)); | |
a44af9f2 | 645 | @end group |
969fe9b5 | 646 | |
a44af9f2 | 647 | @group |
969fe9b5 RS |
648 | switch (coordinates_in_window (XWINDOW (window), &x, &y)) |
649 | @{ | |
650 | case 0: /* NOT in window at all. */ | |
651 | return Qnil; | |
a44af9f2 | 652 | @end group |
969fe9b5 | 653 | |
a44af9f2 | 654 | @group |
969fe9b5 RS |
655 | case 1: /* In text part of window. */ |
656 | return Fcons (make_number (x), make_number (y)); | |
a44af9f2 | 657 | @end group |
969fe9b5 | 658 | |
a44af9f2 | 659 | @group |
969fe9b5 RS |
660 | case 2: /* In mode line of window. */ |
661 | return Qmode_line; | |
a44af9f2 | 662 | @end group |
969fe9b5 | 663 | |
a44af9f2 | 664 | @group |
969fe9b5 RS |
665 | case 3: /* On right border of window. */ |
666 | return Qvertical_line; | |
667 | @end group | |
668 | ||
669 | @group | |
670 | default: | |
671 | abort (); | |
672 | @} | |
a44af9f2 RS |
673 | @} |
674 | @end group | |
675 | @end smallexample | |
676 | ||
a890e1b0 RS |
677 | Note that C code cannot call functions by name unless they are defined |
678 | in C. The way to call a function written in Lisp is to use | |
679 | @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since | |
680 | the Lisp function @code{funcall} accepts an unlimited number of | |
681 | arguments, in C it takes two: the number of Lisp-level arguments, and a | |
682 | one-dimensional array containing their values. The first Lisp-level | |
683 | argument is the Lisp function to call, and the rest are the arguments to | |
684 | pass to it. Since @code{Ffuncall} can call the evaluator, you must | |
685 | protect pointers from garbage collection around the call to | |
686 | @code{Ffuncall}. | |
687 | ||
688 | The C functions @code{call0}, @code{call1}, @code{call2}, and so on, | |
689 | provide handy ways to call a Lisp function conveniently with a fixed | |
690 | number of arguments. They work by calling @code{Ffuncall}. | |
a44af9f2 RS |
691 | |
692 | @file{eval.c} is a very good file to look through for examples; | |
693 | @file{lisp.h} contains the definitions for some important macros and | |
694 | functions. | |
695 | ||
8241495d RS |
696 | If you define a function which is side-effect free, update the code in |
697 | @file{byte-opt.el} which binds @code{side-effect-free-fns} and | |
698 | @code{side-effect-and-error-free-fns} to include it. This will help the | |
699 | optimizer. | |
700 | ||
969fe9b5 | 701 | @node Object Internals |
a44af9f2 RS |
702 | @appendixsec Object Internals |
703 | @cindex object internals | |
704 | ||
705 | GNU Emacs Lisp manipulates many different types of data. The actual | |
f9f59935 RS |
706 | data are stored in a heap and the only access that programs have to it |
707 | is through pointers. Pointers are thirty-two bits wide in most | |
a44af9f2 | 708 | implementations. Depending on the operating system and type of machine |
f9f59935 RS |
709 | for which you compile Emacs, twenty-eight bits are used to address the |
710 | object, and the remaining four bits are used for a GC mark bit and the | |
a44af9f2 RS |
711 | tag that identifies the object's type. |
712 | ||
a890e1b0 RS |
713 | Because Lisp objects are represented as tagged pointers, it is always |
714 | possible to determine the Lisp data type of any object. The C data type | |
715 | @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary | |
716 | variables have type @code{Lisp_Object}, which means they can hold any | |
717 | type of Lisp value; you can determine the actual data type only at run | |
718 | time. The same is true for function arguments; if you want a function | |
719 | to accept only a certain type of argument, you must check the type | |
720 | explicitly using a suitable predicate (@pxref{Type Predicates}). | |
a44af9f2 RS |
721 | @cindex type checking internals |
722 | ||
723 | @menu | |
724 | * Buffer Internals:: Components of a buffer structure. | |
725 | * Window Internals:: Components of a window structure. | |
726 | * Process Internals:: Components of a process structure. | |
727 | @end menu | |
728 | ||
969fe9b5 | 729 | @node Buffer Internals |
a44af9f2 RS |
730 | @appendixsubsec Buffer Internals |
731 | @cindex internals, of buffer | |
732 | @cindex buffer internals | |
733 | ||
734 | Buffers contain fields not directly accessible by the Lisp programmer. | |
735 | We describe them here, naming them by the names used in the C code. | |
736 | Many are accessible indirectly in Lisp programs via Lisp primitives. | |
737 | ||
95260b26 GM |
738 | Two structures are used to represent buffers in C. The |
739 | @code{buffer_text} structure contains fields describing the text of a | |
740 | buffer; the @code{buffer} structure holds other fields. In the case | |
741 | of indirect buffers, two or more @code{buffer} structures reference | |
742 | the same @code{buffer_text} structure. | |
743 | ||
744 | Here is a list of the @code{struct buffer_text} fields: | |
745 | ||
a44af9f2 | 746 | @table @code |
95260b26 | 747 | @item beg |
05aea714 | 748 | This field contains the actual address of the buffer contents. |
95260b26 GM |
749 | |
750 | @item got | |
751 | This holds the character position of the gap in the buffer. | |
752 | ||
753 | @item z | |
754 | This field contains the character position of the end of the buffer | |
755 | text. | |
756 | ||
757 | @item gpt_byte | |
758 | Contains the byte position of the gap. | |
759 | ||
760 | @item z_byte | |
761 | Holds the byte position of the end of the buffer text. | |
762 | ||
763 | @item gap_size | |
764 | Contains the size of buffer's gap. | |
765 | ||
766 | @item modiff | |
767 | This field counts buffer-modification events for this buffer. It is | |
768 | incremented for each such event, and never otherwise changed. | |
769 | ||
770 | @item save_modiff | |
771 | Contains the previous value of @code{modiff}, as of the last time a | |
772 | buffer was visited or saved in a file. | |
773 | ||
774 | @item overlay_modiff | |
775 | Counts modifications to overlays analogous to @code{modiff}. | |
776 | ||
777 | @item beg_unchanged | |
778 | Holds the number of characters at the start of the text that are known | |
779 | to be unchanged since the last redisplay that finished. | |
780 | ||
781 | @item end_unchanged | |
782 | Holds the number of characters at the end of the text that are known to | |
783 | be unchanged since the last redisplay that finished. | |
784 | ||
785 | @item unchanged_modified | |
786 | Contains the value of @code{modiff} at the time of the last redisplay | |
787 | that finished. If this value matches @code{modiff}, | |
788 | @code{beg_unchanged} and @code{end_unchanged} contain no useful | |
789 | information. | |
790 | ||
791 | @item overlay_unchanged_modified | |
792 | Contains the value of @code{overlay_modiff} at the time of the last | |
793 | redisplay that finished. If this value matches @code{overlay_modiff}, | |
794 | @code{beg_unchanged} and @code{end_unchanged} contain no useful | |
795 | information. | |
796 | ||
797 | @item markers | |
798 | The markers that refer to this buffer. This is actually a single | |
799 | marker, and successive elements in its marker @code{chain} are the other | |
800 | markers referring to this buffer text. | |
a44af9f2 | 801 | |
95260b26 GM |
802 | @item intervals |
803 | Contains the interval tree which records the text properties of this | |
804 | buffer. | |
805 | @end table | |
806 | ||
807 | The fields of @code{struct buffer} are: | |
808 | ||
809 | @table @code | |
810 | @item next | |
811 | Points to the next buffer, in the chain of all buffers including killed | |
812 | buffers. This chain is used only for garbage collection, in order to | |
813 | collect killed buffers properly. Note that vectors, and most kinds of | |
814 | objects allocated as vectors, are all on one chain, but buffers are on a | |
815 | separate chain of their own. | |
816 | ||
817 | @item own_text | |
818 | This is a @code{struct buffer_text} structure. In an ordinary buffer, | |
819 | it holds the buffer contents. In indirect buffers, this field is not | |
820 | used. | |
821 | ||
822 | @item text | |
823 | This points to the @code{buffer_text} structure that is used for this | |
824 | buffer. In an ordinary buffer, this is the @code{own_text} field above. | |
825 | In an indirect buffer, this is the @code{own_text} field of the base | |
826 | buffer. | |
827 | ||
828 | @item pt | |
829 | Contains the character position of point in a buffer. | |
830 | ||
831 | @item pt_byte | |
832 | Contains the byte position of point in a buffer. | |
833 | ||
834 | @item begv | |
835 | This field contains the character position of the beginning of the | |
836 | accessible range of text in the buffer. | |
837 | ||
838 | @item begv_byte | |
839 | This field contains the byte position of the beginning of the | |
840 | accessible range of text in the buffer. | |
841 | ||
842 | @item zv | |
843 | This field contains the character position of the end of the | |
844 | accessible range of text in the buffer. | |
845 | ||
846 | @item zv_byte | |
847 | This field contains the byte position of the end of the | |
848 | accessible range of text in the buffer. | |
849 | ||
850 | @item base_buffer | |
851 | In an indirect buffer, this points to the base buffer. In an ordinary | |
852 | buffer, it is null. | |
853 | ||
854 | @item local_var_flags | |
855 | This field contains flags indicating that certain variables are local in | |
856 | this buffer. Such variables are declared in the C code using | |
857 | @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored in | |
858 | fields in the buffer structure itself. (Some of these fields are | |
859 | described in this table.) | |
a44af9f2 RS |
860 | |
861 | @item modtime | |
862 | This field contains the modification time of the visited file. It is | |
8241495d RS |
863 | set when the file is written or read. Before writing the buffer into a |
864 | file, this field is compared to the modification time of the file to see | |
865 | if the file has changed on disk. @xref{Buffer Modification}. | |
a44af9f2 RS |
866 | |
867 | @item auto_save_modified | |
868 | This field contains the time when the buffer was last auto-saved. | |
869 | ||
95260b26 GM |
870 | @item auto_save_failure_time |
871 | The time at which we detected a failure to auto-save, or -1 if we didn't | |
872 | have a failure. | |
873 | ||
a44af9f2 RS |
874 | @item last_window_start |
875 | This field contains the @code{window-start} position in the buffer as of | |
876 | the last time the buffer was displayed in a window. | |
877 | ||
95260b26 GM |
878 | @item clip_changed |
879 | This flag is set when narrowing changes in a buffer. | |
880 | ||
881 | @item prevent_redisplay_optimizations_p | |
05aea714 | 882 | this flag indicates that redisplay optimizations should not be used |
95260b26 GM |
883 | to display this buffer. |
884 | ||
a890e1b0 RS |
885 | @item undo_list |
886 | This field points to the buffer's undo list. @xref{Undo}. | |
a44af9f2 | 887 | |
95260b26 GM |
888 | @item name |
889 | The buffer name is a string that names the buffer. It is guaranteed to | |
890 | be unique. @xref{Buffer Names}. | |
891 | ||
892 | @item filename | |
893 | The name of the file visited in this buffer, or @code{nil}. | |
894 | ||
895 | @item directory | |
896 | The directory for expanding relative file names. | |
897 | ||
898 | @item save_length | |
899 | Length of the file this buffer is visiting, when last read or saved. | |
900 | This and other fields concerned with saving are not kept in the | |
901 | @code{buffer_text} structure because indirect buffers are never saved. | |
902 | ||
903 | @item auto_save_file_name | |
904 | File name used for auto-saving this buffer. This is not in the | |
905 | @code{buffer_text} because it's not used in indirect buffers at all. | |
906 | ||
907 | @item read_only | |
908 | Non-@code{nil} means this buffer is read-only. | |
909 | ||
910 | @item mark | |
911 | This field contains the mark for the buffer. The mark is a marker, | |
912 | hence it is also included on the list @code{markers}. @xref{The Mark}. | |
913 | ||
914 | @item local_var_alist | |
915 | This field contains the association list describing the buffer-local | |
916 | variable bindings of this buffer, not including the built-in | |
917 | buffer-local bindings that have special slots in the buffer object. | |
918 | (Those slots are omitted from this table.) @xref{Buffer-Local | |
919 | Variables}. | |
920 | ||
921 | @item major_mode | |
922 | Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}. | |
923 | ||
924 | @item mode_name | |
925 | Pretty name of major mode, e.g., @code{"Lisp"}. | |
926 | ||
927 | @item mode_line_format | |
928 | Mode line element that controls the format of the mode line. If this | |
929 | is @code{nil}, no mode line will be displayed. | |
930 | ||
931 | @item header_line_format | |
932 | This field is analoguous to @code{mode_line_format} for the mode | |
933 | line displayed at the top of windows. | |
934 | ||
935 | @item keymap | |
936 | This field holds the buffer's local keymap. @xref{Keymaps}. | |
937 | ||
938 | @item abbrev_table | |
939 | This buffer's local abbrevs. | |
940 | ||
941 | @item syntax_table | |
a44af9f2 RS |
942 | This field contains the syntax table for the buffer. @xref{Syntax Tables}. |
943 | ||
95260b26 GM |
944 | @item category_table |
945 | This field contains the category table for the buffer. | |
946 | ||
947 | @item case_fold_search | |
948 | The value of @code{case-fold-search} in this buffer. | |
949 | ||
950 | @item tab_width | |
951 | The value of @code{tab-width} in this buffer. | |
952 | ||
953 | @item fill_column | |
954 | The value of @code{fill-column} in this buffer. | |
955 | ||
956 | @item left_margin | |
957 | The value of @code{left-margin} in this buffer. | |
958 | ||
959 | @item auto_fill_function | |
960 | The value of @code{auto-fill-function} in this buffer. | |
961 | ||
a44af9f2 RS |
962 | @item downcase_table |
963 | This field contains the conversion table for converting text to lower case. | |
969fe9b5 | 964 | @xref{Case Tables}. |
a44af9f2 RS |
965 | |
966 | @item upcase_table | |
967 | This field contains the conversion table for converting text to upper case. | |
969fe9b5 | 968 | @xref{Case Tables}. |
a44af9f2 RS |
969 | |
970 | @item case_canon_table | |
971 | This field contains the conversion table for canonicalizing text for | |
969fe9b5 | 972 | case-folding search. @xref{Case Tables}. |
a44af9f2 RS |
973 | |
974 | @item case_eqv_table | |
975 | This field contains the equivalence table for case-folding search. | |
969fe9b5 | 976 | @xref{Case Tables}. |
a44af9f2 | 977 | |
95260b26 GM |
978 | @item truncate_lines |
979 | The value of @code{truncate-lines} in this buffer. | |
a44af9f2 | 980 | |
95260b26 GM |
981 | @item ctl_arrow |
982 | The value of @code{ctl-arrow} in this buffer. | |
a44af9f2 | 983 | |
95260b26 GM |
984 | @item selective_display |
985 | The value of @code{selective-display} in this buffer. | |
a44af9f2 | 986 | |
95260b26 GM |
987 | @item selective_display_ellipsis |
988 | The value of @code{selective-display-ellipsis} in this buffer. | |
a44af9f2 | 989 | |
95260b26 GM |
990 | @item minor_modes |
991 | An alist of the minor modes of this buffer. | |
a890e1b0 | 992 | |
95260b26 GM |
993 | @item overwrite_mode |
994 | The value of @code{overwrite_mode} in this buffer. | |
a890e1b0 | 995 | |
95260b26 GM |
996 | @item abbrev_mode |
997 | The value of @code{abbrev-mode} in this buffer. | |
bfe721d1 | 998 | |
95260b26 GM |
999 | @item display_table |
1000 | This field contains the buffer's display table, or @code{nil} if it doesn't | |
1001 | have one. @xref{Display Tables}. | |
a890e1b0 | 1002 | |
95260b26 GM |
1003 | @item save_modified |
1004 | This field contains the time when the buffer was last saved, as an integer. | |
1005 | @xref{Buffer Modification}. | |
1006 | ||
1007 | @item mark_active | |
1008 | This field is non-@code{nil} if the buffer's mark is active. | |
a890e1b0 RS |
1009 | |
1010 | @item overlays_before | |
1011 | This field holds a list of the overlays in this buffer that end at or | |
1012 | before the current overlay center position. They are sorted in order of | |
1013 | decreasing end position. | |
1014 | ||
1015 | @item overlays_after | |
1016 | This field holds a list of the overlays in this buffer that end after | |
1017 | the current overlay center position. They are sorted in order of | |
1018 | increasing beginning position. | |
969fe9b5 | 1019 | |
95260b26 GM |
1020 | @item overlay_center |
1021 | This field holds the current overlay center position. @xref{Overlays}. | |
1022 | ||
969fe9b5 RS |
1023 | @item enable_multibyte_characters |
1024 | This field holds the buffer's local value of | |
1025 | @code{enable-multibyte-characters}---either @code{t} or @code{nil}. | |
95260b26 GM |
1026 | |
1027 | @item buffer_file_coding_system | |
1028 | The value of @code{buffer-file-coding-system} in this buffer. | |
1029 | ||
1030 | @item file_format | |
1031 | The value of @code{buffer-file-format} in this buffer. | |
1032 | ||
1033 | @item pt_marker | |
1034 | In an indirect buffer, or a buffer that is the base of an indirect | |
1035 | buffer, this holds a marker that records point for this buffer when the | |
1036 | buffer is not current. | |
1037 | ||
1038 | @item begv_marker | |
1039 | In an indirect buffer, or a buffer that is the base of an indirect | |
1040 | buffer, this holds a marker that records @code{begv} for this buffer | |
1041 | when the buffer is not current. | |
1042 | ||
1043 | @item zv_marker | |
1044 | In an indirect buffer, or a buffer that is the base of an indirect | |
1045 | buffer, this holds a marker that records @code{zv} for this buffer when | |
1046 | the buffer is not current. | |
1047 | ||
1048 | @item file_truename | |
1049 | The truename of the visited file, or @code{nil}. | |
1050 | ||
1051 | @item invisibility_spec | |
1052 | The value of @code{buffer-invisibility-spec} in this buffer. | |
1053 | ||
1054 | @item last_selected_window | |
1055 | This is the last window that was selected with this buffer in it, or @code{nil} | |
1056 | if that window no longer displays this buffer. | |
1057 | ||
1058 | @item display_count | |
1059 | This field is incremented each time the buffer is displayed in a window. | |
1060 | ||
1061 | @item left_margin_width | |
1062 | The value of @code{left-margin-width} in this buffer. | |
1063 | ||
1064 | @item right_margin_width | |
1065 | The value of @code{right-margin-width} in this buffer. | |
1066 | ||
1067 | @item indicate_empty_lines | |
1068 | Non-@code{nil} means indicate empty lines (lines with no text) with a | |
1069 | small bitmap in the fringe, when using a window system that can do it. | |
1070 | ||
1071 | @item display_time | |
1072 | This holds a time stamp that is updated each time this buffer is | |
1073 | displayed in a window. | |
1074 | ||
1075 | @item scroll_up_aggressively | |
1076 | The value of @code{scroll-up-aggressively} in this buffer. | |
1077 | ||
1078 | @item scroll_down_aggressively | |
1079 | The value of @code{scroll-down-aggressively} in this buffer. | |
a44af9f2 RS |
1080 | @end table |
1081 | ||
969fe9b5 | 1082 | @node Window Internals |
a44af9f2 RS |
1083 | @appendixsubsec Window Internals |
1084 | @cindex internals, of window | |
1085 | @cindex window internals | |
1086 | ||
1087 | Windows have the following accessible fields: | |
1088 | ||
1089 | @table @code | |
1090 | @item frame | |
a890e1b0 | 1091 | The frame that this window is on. |
a44af9f2 RS |
1092 | |
1093 | @item mini_p | |
a890e1b0 | 1094 | Non-@code{nil} if this window is a minibuffer window. |
a44af9f2 | 1095 | |
95260b26 GM |
1096 | @item parent |
1097 | Internally, Emacs arranges windows in a tree; each group of siblings has | |
1098 | a parent window whose area includes all the siblings. This field points | |
1099 | to a window's parent. | |
1100 | ||
1101 | Parent windows do not display buffers, and play little role in display | |
1102 | except to shape their child windows. Emacs Lisp programs usually have | |
1103 | no access to the parent windows; they operate on the windows at the | |
1104 | leaves of the tree, which actually display buffers. | |
1105 | ||
1106 | The following four fields also describe the window tree structure. | |
1107 | ||
1108 | @item hchild | |
1109 | In a window subdivided horizontally by child windows, the leftmost child. | |
1110 | Otherwise, @code{nil}. | |
1111 | ||
1112 | @item vchild | |
1113 | In a window subdivided vertically by child windows, the topmost child. | |
1114 | Otherwise, @code{nil}. | |
1115 | ||
1116 | @item next | |
1117 | The next sibling of this window. It is @code{nil} in a window that is | |
1118 | the rightmost or bottommost of a group of siblings. | |
1119 | ||
1120 | @item prev | |
1121 | The previous sibling of this window. It is @code{nil} in a window that | |
1122 | is the leftmost or topmost of a group of siblings. | |
1123 | ||
1124 | @item left | |
1125 | This is the left-hand edge of the window, measured in columns. (The | |
1126 | leftmost column on the screen is @w{column 0}.) | |
1127 | ||
1128 | @item top | |
1129 | This is the top edge of the window, measured in lines. (The top line on | |
1130 | the screen is @w{line 0}.) | |
1131 | ||
1132 | @item height | |
1133 | The height of the window, measured in lines. | |
1134 | ||
1135 | @item width | |
1136 | The width of the window, measured in columns. This width includes the | |
1137 | scroll bar and fringes, and/or the separator line on the right of the | |
1138 | window (if any). | |
1139 | ||
a44af9f2 | 1140 | @item buffer |
574efc83 | 1141 | The buffer that the window is displaying. This may change often during |
a44af9f2 RS |
1142 | the life of the window. |
1143 | ||
95260b26 GM |
1144 | @item start |
1145 | The position in the buffer that is the first character to be displayed | |
1146 | in the window. | |
a44af9f2 RS |
1147 | |
1148 | @item pointm | |
1149 | @cindex window point internals | |
a890e1b0 | 1150 | This is the value of point in the current buffer when this window is |
a44af9f2 RS |
1151 | selected; when it is not selected, it retains its previous value. |
1152 | ||
a890e1b0 RS |
1153 | @item force_start |
1154 | If this flag is non-@code{nil}, it says that the window has been | |
1155 | scrolled explicitly by the Lisp program. This affects what the next | |
1156 | redisplay does if point is off the screen: instead of scrolling the | |
1157 | window to show the text around point, it moves point to a location that | |
1158 | is on the screen. | |
1159 | ||
95260b26 GM |
1160 | @item frozen_window_start_p |
1161 | This field is set temporarily to 1 to indicate to redisplay that | |
1162 | @code{start} of this window should not be changed, even if point | |
1163 | gets invisible. | |
1164 | ||
1165 | @item start_at_line_beg | |
1166 | Non-@code{nil} means current value of @code{start} was the beginning of a line | |
1167 | when it was chosen. | |
1168 | ||
1169 | @item too_small_ok | |
1170 | Non-@code{nil} means don't delete this window for becoming ``too small''. | |
1171 | ||
1172 | @item height_fixed_p | |
1173 | This field is temporarily set to 1 to fix the height of the selected | |
1174 | window when the echo area is resized. | |
1175 | ||
1176 | @item use_time | |
1177 | This is the last time that the window was selected. The function | |
1178 | @code{get-lru-window} uses this field. | |
1179 | ||
1180 | @item sequence_number | |
1181 | A unique number assigned to this window when it was created. | |
1182 | ||
a890e1b0 | 1183 | @item last_modified |
95260b26 | 1184 | The @code{modiff} field of the window's buffer, as of the last time |
a890e1b0 RS |
1185 | a redisplay completed in this window. |
1186 | ||
95260b26 GM |
1187 | @item last_overlay_modified |
1188 | The @code{overlay_modiff} field of the window's buffer, as of the last | |
1189 | time a redisplay completed in this window. | |
1190 | ||
a890e1b0 | 1191 | @item last_point |
95260b26 GM |
1192 | The buffer's value of point, as of the last time a redisplay completed |
1193 | in this window. | |
a890e1b0 | 1194 | |
95260b26 GM |
1195 | @item last_had_star |
1196 | A non-@code{nil} value means the window's buffer was ``modified'' when the | |
1197 | window was last updated. | |
a44af9f2 | 1198 | |
95260b26 GM |
1199 | @item vertical_scroll_bar |
1200 | This window's vertical scroll bar. | |
a44af9f2 | 1201 | |
95260b26 GM |
1202 | @item left_margin_width |
1203 | The width of the left margin in this window, or @code{nil} not to | |
1204 | specify it (in which case the buffer's value of @code{left-margin-width} | |
1205 | is used. | |
a890e1b0 | 1206 | |
95260b26 GM |
1207 | @item right_margin_width |
1208 | Likewise for the right margin. | |
a890e1b0 | 1209 | |
13ede7fc | 1210 | @ignore |
95260b26 GM |
1211 | @item last_mark_x |
1212 | @item last_mark_y | |
1213 | ???Not used. | |
1214 | @end ignore | |
a44af9f2 | 1215 | |
95260b26 GM |
1216 | @item window_end_pos |
1217 | This is computed as @code{z} minus the buffer position of the last glyph | |
1218 | in the current matrix of the window. The value is only valid if | |
1219 | @code{window_end_valid} is not @code{nil}. | |
a44af9f2 | 1220 | |
95260b26 GM |
1221 | @item window_end_bytepos |
1222 | The byte position corresponding to @code{window_end_pos}. | |
a890e1b0 | 1223 | |
95260b26 GM |
1224 | @item window_end_vpos |
1225 | The window-relative vertical position of the line containing | |
1226 | @code{window_end_pos}. | |
a44af9f2 | 1227 | |
95260b26 GM |
1228 | @item window_end_valid |
1229 | This field is set to a non-@code{nil} value if @code{window_end_pos} is truly | |
1230 | valid. This is @code{nil} if nontrivial redisplay is preempted since in that | |
1231 | case the display that @code{window_end_pos} was computed for did not get | |
1232 | onto the screen. | |
1233 | ||
1234 | @item redisplay_end_trigger | |
1235 | If redisplay in this window goes beyond this buffer position, it runs | |
1236 | run the @code{redisplay-end-trigger-hook}. | |
1237 | ||
13ede7fc | 1238 | @ignore |
95260b26 GM |
1239 | @item orig_height |
1240 | @item orig_top | |
1241 | ??? Are temporary storage areas. | |
1242 | @end ignore | |
1243 | ||
1244 | @item cursor | |
1245 | A structure describing where the cursor is in this window. | |
1246 | ||
1247 | @item last_cursor | |
1248 | The value of @code{cursor} as of the last redisplay that finished. | |
1249 | ||
1250 | @item phys_cursor | |
1251 | A structure describing where the cursor of this window physically is. | |
1252 | ||
1253 | @item phys_cursor_type | |
1254 | The type of cursor that was last displayed on this window. | |
1255 | ||
1256 | @item phys_cursor_on_p | |
1257 | This field is non-zero if the cursor is physically on. | |
1258 | ||
1259 | @item cursor_off_p | |
1260 | Non-zero means the cursor in this window is logically on. | |
1261 | ||
1262 | @item last_cursor_off_p | |
1263 | This field contains the value of @code{cursor_off_p} as of the time of | |
1264 | the last redisplay. | |
1265 | ||
1266 | @item must_be_updated_p | |
1267 | This is set to 1 during redisplay when this window must be updated. | |
1268 | ||
a44af9f2 | 1269 | @item hscroll |
a890e1b0 | 1270 | This is the number of columns that the display in the window is scrolled |
a44af9f2 RS |
1271 | horizontally to the left. Normally, this is 0. |
1272 | ||
95260b26 GM |
1273 | @item vscroll |
1274 | Vertical scroll amount, in pixels. Normally, this is 0. | |
1275 | ||
1276 | @item dedicated | |
1277 | Non-@code{nil} if this window is dedicated to its buffer. | |
a44af9f2 RS |
1278 | |
1279 | @item display_table | |
a890e1b0 RS |
1280 | The window's display table, or @code{nil} if none is specified for it. |
1281 | ||
1282 | @item update_mode_line | |
1283 | Non-@code{nil} means this window's mode line needs to be updated. | |
1284 | ||
1285 | @item base_line_number | |
1286 | The line number of a certain position in the buffer, or @code{nil}. | |
1287 | This is used for displaying the line number of point in the mode line. | |
1288 | ||
1289 | @item base_line_pos | |
1290 | The position in the buffer for which the line number is known, or | |
1291 | @code{nil} meaning none is known. | |
1292 | ||
1293 | @item region_showing | |
1294 | If the region (or part of it) is highlighted in this window, this field | |
1295 | holds the mark position that made one end of that region. Otherwise, | |
1296 | this field is @code{nil}. | |
95260b26 GM |
1297 | |
1298 | @item column_number_displayed | |
1299 | The column number currently displayed in this window's mode line, or @code{nil} | |
1300 | if column numbers are not being displayed. | |
1301 | ||
1302 | @item current_matrix | |
1303 | A glyph matrix describing the current display of this window. | |
1304 | ||
1305 | @item desired_matrix | |
1306 | A glyph matrix describing the desired display of this window. | |
a44af9f2 RS |
1307 | @end table |
1308 | ||
969fe9b5 | 1309 | @node Process Internals |
a44af9f2 RS |
1310 | @appendixsubsec Process Internals |
1311 | @cindex internals, of process | |
1312 | @cindex process internals | |
1313 | ||
1314 | The fields of a process are: | |
1315 | ||
1316 | @table @code | |
1317 | @item name | |
1318 | A string, the name of the process. | |
1319 | ||
1320 | @item command | |
1321 | A list containing the command arguments that were used to start this | |
1322 | process. | |
1323 | ||
1324 | @item filter | |
1325 | A function used to accept output from the process instead of a buffer, | |
1326 | or @code{nil}. | |
1327 | ||
1328 | @item sentinel | |
1329 | A function called whenever the process receives a signal, or @code{nil}. | |
1330 | ||
1331 | @item buffer | |
1332 | The associated buffer of the process. | |
1333 | ||
1334 | @item pid | |
1335 | An integer, the Unix process @sc{id}. | |
1336 | ||
1337 | @item childp | |
1338 | A flag, non-@code{nil} if this is really a child process. | |
1339 | It is @code{nil} for a network connection. | |
1340 | ||
a44af9f2 | 1341 | @item mark |
574efc83 RS |
1342 | A marker indicating the position of the end of the last output from this |
1343 | process inserted into the buffer. This is often but not always the end | |
1344 | of the buffer. | |
a44af9f2 RS |
1345 | |
1346 | @item kill_without_query | |
a890e1b0 RS |
1347 | If this is non-@code{nil}, killing Emacs while this process is still |
1348 | running does not ask for confirmation about killing the process. | |
1349 | ||
1350 | @item raw_status_low | |
1351 | @itemx raw_status_high | |
1352 | These two fields record 16 bits each of the process status returned by | |
1353 | the @code{wait} system call. | |
1354 | ||
1355 | @item status | |
1356 | The process status, as @code{process-status} should return it. | |
1357 | ||
1358 | @item tick | |
1359 | @itemx update_tick | |
1360 | If these two fields are not equal, a change in the status of the process | |
1361 | needs to be reported, either by running the sentinel or by inserting a | |
1362 | message in the process buffer. | |
1363 | ||
1364 | @item pty_flag | |
1365 | Non-@code{nil} if communication with the subprocess uses a @sc{pty}; | |
1366 | @code{nil} if it uses a pipe. | |
1367 | ||
1368 | @item infd | |
1369 | The file descriptor for input from the process. | |
1370 | ||
1371 | @item outfd | |
1372 | The file descriptor for output to the process. | |
1373 | ||
1374 | @item subtty | |
1375 | The file descriptor for the terminal that the subprocess is using. (On | |
1376 | some systems, there is no need to record this, so the value is | |
1377 | @code{nil}.) | |
bfe721d1 KH |
1378 | |
1379 | @item tty_name | |
1380 | The name of the terminal that the subprocess is using, | |
1381 | or @code{nil} if it is using pipes. | |
95260b26 GM |
1382 | |
1383 | @item decode_coding_system | |
1384 | Coding-system for decoding the input from this process. | |
1385 | ||
1386 | @item decoding_buf | |
1387 | A working buffer for decoding. | |
1388 | ||
1389 | @item decoding_carryover | |
1390 | Size of carryover in decoding. | |
1391 | ||
1392 | @item encode_coding_system | |
1393 | Coding-system for encoding the output to this process. | |
1394 | ||
1395 | @item encoding_buf | |
1396 | A working buffer for enecoding. | |
1397 | ||
1398 | @item encoding_carryover | |
1399 | Size of carryover in encoding. | |
1400 | ||
1401 | @item inherit_coding_system_flag | |
1402 | Flag to set @code{coding-system} of the process buffer from the | |
1403 | coding system used to decode process output. | |
a44af9f2 | 1404 | @end table |