| 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, |
| 4 | @c 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Free Software Foundation, Inc. |
| 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 |
| 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 | @vindex preloaded-file-list |
| 56 | @cindex dumped Lisp files |
| 57 | To create @file{emacs}, use the command @samp{temacs -batch -l loadup |
| 58 | dump}. The purpose of @samp{-batch} here is to prevent @file{temacs} |
| 59 | from trying to initialize any of its data on the terminal; this ensures |
| 60 | that the tables of terminal information are empty in the dumped Emacs. |
| 61 | The argument @samp{dump} tells @file{loadup.el} to dump a new executable |
| 62 | named @file{emacs}. The variable @code{preloaded-file-list} stores a |
| 63 | list of the Lisp files that were dumped with the @file{emacs} executable. |
| 64 | |
| 65 | Some operating systems don't support dumping. On those systems, you |
| 66 | must start Emacs with the @samp{temacs -l loadup} command each time you |
| 67 | use it. This takes a substantial time, but since you need to start |
| 68 | Emacs once a day at most---or once a week if you never log out---the |
| 69 | extra time is not too severe a problem. |
| 70 | |
| 71 | @cindex @file{site-load.el} |
| 72 | |
| 73 | You can specify additional files to preload by writing a library named |
| 74 | @file{site-load.el} that loads them. You may need to add a definition |
| 75 | |
| 76 | @example |
| 77 | #define SITELOAD_PURESIZE_EXTRA @var{n} |
| 78 | @end example |
| 79 | |
| 80 | @noindent |
| 81 | to make @var{n} added bytes of pure space to hold the additional files. |
| 82 | (Try adding increments of 20000 until it is big enough.) However, the |
| 83 | advantage of preloading additional files decreases as machines get |
| 84 | faster. On modern machines, it is usually not advisable. |
| 85 | |
| 86 | After @file{loadup.el} reads @file{site-load.el}, it finds the |
| 87 | documentation strings for primitive and preloaded functions (and |
| 88 | variables) in the file @file{etc/DOC} where they are stored, by |
| 89 | calling @code{Snarf-documentation} (@pxref{Definition of |
| 90 | Snarf-documentation,, Accessing Documentation}). |
| 91 | |
| 92 | @cindex @file{site-init.el} |
| 93 | @cindex preloading additional functions and variables |
| 94 | You can specify other Lisp expressions to execute just before dumping |
| 95 | by putting them in a library named @file{site-init.el}. This file is |
| 96 | executed after the documentation strings are found. |
| 97 | |
| 98 | If you want to preload function or variable definitions, there are |
| 99 | three ways you can do this and make their documentation strings |
| 100 | accessible when you subsequently run Emacs: |
| 101 | |
| 102 | @itemize @bullet |
| 103 | @item |
| 104 | Arrange to scan these files when producing the @file{etc/DOC} file, |
| 105 | and load them with @file{site-load.el}. |
| 106 | |
| 107 | @item |
| 108 | Load the files with @file{site-init.el}, then copy the files into the |
| 109 | installation directory for Lisp files when you install Emacs. |
| 110 | |
| 111 | @item |
| 112 | Specify a non-@code{nil} value for |
| 113 | @code{byte-compile-dynamic-docstrings} as a local variable in each of these |
| 114 | files, and load them with either @file{site-load.el} or |
| 115 | @file{site-init.el}. (This method has the drawback that the |
| 116 | documentation strings take up space in Emacs all the time.) |
| 117 | @end itemize |
| 118 | |
| 119 | It is not advisable to put anything in @file{site-load.el} or |
| 120 | @file{site-init.el} that would alter any of the features that users |
| 121 | expect in an ordinary unmodified Emacs. If you feel you must override |
| 122 | normal features for your site, do it with @file{default.el}, so that |
| 123 | users can override your changes if they wish. @xref{Startup Summary}. |
| 124 | |
| 125 | In a package that can be preloaded, it is sometimes useful to |
| 126 | specify a computation to be done when Emacs subsequently starts up. |
| 127 | For this, use @code{eval-at-startup}: |
| 128 | |
| 129 | @defmac eval-at-startup body@dots{} |
| 130 | This evaluates the @var{body} forms, either immediately if running in |
| 131 | an Emacs that has already started up, or later when Emacs does start |
| 132 | up. Since the value of the @var{body} forms is not necessarily |
| 133 | available when the @code{eval-at-startup} form is run, that form |
| 134 | always returns @code{nil}. |
| 135 | @end defmac |
| 136 | |
| 137 | @defun dump-emacs to-file from-file |
| 138 | @cindex unexec |
| 139 | This function dumps the current state of Emacs into an executable file |
| 140 | @var{to-file}. It takes symbols from @var{from-file} (this is normally |
| 141 | the executable file @file{temacs}). |
| 142 | |
| 143 | If you want to use this function in an Emacs that was already dumped, |
| 144 | you must run Emacs with @samp{-batch}. |
| 145 | @end defun |
| 146 | |
| 147 | @node Pure Storage |
| 148 | @appendixsec Pure Storage |
| 149 | @cindex pure storage |
| 150 | |
| 151 | Emacs Lisp uses two kinds of storage for user-created Lisp objects: |
| 152 | @dfn{normal storage} and @dfn{pure storage}. Normal storage is where |
| 153 | all the new data created during an Emacs session are kept; see the |
| 154 | following section for information on normal storage. Pure storage is |
| 155 | used for certain data in the preloaded standard Lisp files---data that |
| 156 | should never change during actual use of Emacs. |
| 157 | |
| 158 | Pure storage is allocated only while @file{temacs} is loading the |
| 159 | standard preloaded Lisp libraries. In the file @file{emacs}, it is |
| 160 | marked as read-only (on operating systems that permit this), so that |
| 161 | the memory space can be shared by all the Emacs jobs running on the |
| 162 | machine at once. Pure storage is not expandable; a fixed amount is |
| 163 | allocated when Emacs is compiled, and if that is not sufficient for |
| 164 | the preloaded libraries, @file{temacs} allocates dynamic memory for |
| 165 | the part that didn't fit. If that happens, you should increase the |
| 166 | compilation parameter @code{PURESIZE} in the file |
| 167 | @file{src/puresize.h} and rebuild Emacs, even though the resulting |
| 168 | image will work: garbage collection is disabled in this situation, |
| 169 | causing a memory leak. Such an overflow normally won't happen unless you |
| 170 | try to preload additional libraries or add features to the standard |
| 171 | ones. Emacs will display a warning about the overflow when it |
| 172 | starts. |
| 173 | |
| 174 | @defun purecopy object |
| 175 | This function makes a copy in pure storage of @var{object}, and returns |
| 176 | it. It copies a string by simply making a new string with the same |
| 177 | characters, but without text properties, in pure storage. It |
| 178 | recursively copies the contents of vectors and cons cells. It does |
| 179 | not make copies of other objects such as symbols, but just returns |
| 180 | them unchanged. It signals an error if asked to copy markers. |
| 181 | |
| 182 | This function is a no-op except while Emacs is being built and dumped; |
| 183 | it is usually called only in the file @file{emacs/lisp/loaddefs.el}, but |
| 184 | a few packages call it just in case you decide to preload them. |
| 185 | @end defun |
| 186 | |
| 187 | @defvar pure-bytes-used |
| 188 | The value of this variable is the number of bytes of pure storage |
| 189 | allocated so far. Typically, in a dumped Emacs, this number is very |
| 190 | close to the total amount of pure storage available---if it were not, |
| 191 | we would preallocate less. |
| 192 | @end defvar |
| 193 | |
| 194 | @defvar purify-flag |
| 195 | This variable determines whether @code{defun} should make a copy of the |
| 196 | function definition in pure storage. If it is non-@code{nil}, then the |
| 197 | function definition is copied into pure storage. |
| 198 | |
| 199 | This flag is @code{t} while loading all of the basic functions for |
| 200 | building Emacs initially (allowing those functions to be sharable and |
| 201 | non-collectible). Dumping Emacs as an executable always writes |
| 202 | @code{nil} in this variable, regardless of the value it actually has |
| 203 | before and after dumping. |
| 204 | |
| 205 | You should not change this flag in a running Emacs. |
| 206 | @end defvar |
| 207 | |
| 208 | @node Garbage Collection |
| 209 | @appendixsec Garbage Collection |
| 210 | @cindex garbage collection |
| 211 | |
| 212 | @cindex memory allocation |
| 213 | When a program creates a list or the user defines a new function (such |
| 214 | as by loading a library), that data is placed in normal storage. If |
| 215 | normal storage runs low, then Emacs asks the operating system to |
| 216 | allocate more memory in blocks of 1k bytes. Each block is used for one |
| 217 | type of Lisp object, so symbols, cons cells, markers, etc., are |
| 218 | segregated in distinct blocks in memory. (Vectors, long strings, |
| 219 | buffers and certain other editing types, which are fairly large, are |
| 220 | allocated in individual blocks, one per object, while small strings are |
| 221 | packed into blocks of 8k bytes.) |
| 222 | |
| 223 | It is quite common to use some storage for a while, then release it by |
| 224 | (for example) killing a buffer or deleting the last pointer to an |
| 225 | object. Emacs provides a @dfn{garbage collector} to reclaim this |
| 226 | abandoned storage. (This name is traditional, but ``garbage recycler'' |
| 227 | might be a more intuitive metaphor for this facility.) |
| 228 | |
| 229 | The garbage collector operates by finding and marking all Lisp objects |
| 230 | that are still accessible to Lisp programs. To begin with, it assumes |
| 231 | all the symbols, their values and associated function definitions, and |
| 232 | any data presently on the stack, are accessible. Any objects that can |
| 233 | be reached indirectly through other accessible objects are also |
| 234 | accessible. |
| 235 | |
| 236 | When marking is finished, all objects still unmarked are garbage. No |
| 237 | matter what the Lisp program or the user does, it is impossible to refer |
| 238 | to them, since there is no longer a way to reach them. Their space |
| 239 | might as well be reused, since no one will miss them. The second |
| 240 | (``sweep'') phase of the garbage collector arranges to reuse them. |
| 241 | |
| 242 | @c ??? Maybe add something describing weak hash tables here? |
| 243 | |
| 244 | @cindex free list |
| 245 | The sweep phase puts unused cons cells onto a @dfn{free list} |
| 246 | for future allocation; likewise for symbols and markers. It compacts |
| 247 | the accessible strings so they occupy fewer 8k blocks; then it frees the |
| 248 | other 8k blocks. Vectors, buffers, windows, and other large objects are |
| 249 | individually allocated and freed using @code{malloc} and @code{free}. |
| 250 | |
| 251 | @cindex CL note---allocate more storage |
| 252 | @quotation |
| 253 | @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not |
| 254 | call the garbage collector when the free list is empty. Instead, it |
| 255 | simply requests the operating system to allocate more storage, and |
| 256 | processing continues until @code{gc-cons-threshold} bytes have been |
| 257 | used. |
| 258 | |
| 259 | This means that you can make sure that the garbage collector will not |
| 260 | run during a certain portion of a Lisp program by calling the garbage |
| 261 | collector explicitly just before it (provided that portion of the |
| 262 | program does not use so much space as to force a second garbage |
| 263 | collection). |
| 264 | @end quotation |
| 265 | |
| 266 | @deffn Command garbage-collect |
| 267 | This command runs a garbage collection, and returns information on |
| 268 | the amount of space in use. (Garbage collection can also occur |
| 269 | spontaneously if you use more than @code{gc-cons-threshold} bytes of |
| 270 | Lisp data since the previous garbage collection.) |
| 271 | |
| 272 | @code{garbage-collect} returns a list containing the following |
| 273 | information: |
| 274 | |
| 275 | @example |
| 276 | @group |
| 277 | ((@var{used-conses} . @var{free-conses}) |
| 278 | (@var{used-syms} . @var{free-syms}) |
| 279 | @end group |
| 280 | (@var{used-miscs} . @var{free-miscs}) |
| 281 | @var{used-string-chars} |
| 282 | @var{used-vector-slots} |
| 283 | (@var{used-floats} . @var{free-floats}) |
| 284 | (@var{used-intervals} . @var{free-intervals}) |
| 285 | (@var{used-strings} . @var{free-strings})) |
| 286 | @end example |
| 287 | |
| 288 | Here is an example: |
| 289 | |
| 290 | @example |
| 291 | @group |
| 292 | (garbage-collect) |
| 293 | @result{} ((106886 . 13184) (9769 . 0) |
| 294 | (7731 . 4651) 347543 121628 |
| 295 | (31 . 94) (1273 . 168) |
| 296 | (25474 . 3569)) |
| 297 | @end group |
| 298 | @end example |
| 299 | |
| 300 | Here is a table explaining each element: |
| 301 | |
| 302 | @table @var |
| 303 | @item used-conses |
| 304 | The number of cons cells in use. |
| 305 | |
| 306 | @item free-conses |
| 307 | The number of cons cells for which space has been obtained from the |
| 308 | operating system, but that are not currently being used. |
| 309 | |
| 310 | @item used-syms |
| 311 | The number of symbols in use. |
| 312 | |
| 313 | @item free-syms |
| 314 | The number of symbols for which space has been obtained from the |
| 315 | operating system, but that are not currently being used. |
| 316 | |
| 317 | @item used-miscs |
| 318 | The number of miscellaneous objects in use. These include markers and |
| 319 | overlays, plus certain objects not visible to users. |
| 320 | |
| 321 | @item free-miscs |
| 322 | The number of miscellaneous objects for which space has been obtained |
| 323 | from the operating system, but that are not currently being used. |
| 324 | |
| 325 | @item used-string-chars |
| 326 | The total size of all strings, in characters. |
| 327 | |
| 328 | @item used-vector-slots |
| 329 | The total number of elements of existing vectors. |
| 330 | |
| 331 | @item used-floats |
| 332 | @c Emacs 19 feature |
| 333 | The number of floats in use. |
| 334 | |
| 335 | @item free-floats |
| 336 | @c Emacs 19 feature |
| 337 | The number of floats for which space has been obtained from the |
| 338 | operating system, but that are not currently being used. |
| 339 | |
| 340 | @item used-intervals |
| 341 | The number of intervals in use. Intervals are an internal |
| 342 | data structure used for representing text properties. |
| 343 | |
| 344 | @item free-intervals |
| 345 | The number of intervals for which space has been obtained |
| 346 | from the operating system, but that are not currently being used. |
| 347 | |
| 348 | @item used-strings |
| 349 | The number of strings in use. |
| 350 | |
| 351 | @item free-strings |
| 352 | The number of string headers for which the space was obtained from the |
| 353 | operating system, but which are currently not in use. (A string |
| 354 | object consists of a header and the storage for the string text |
| 355 | itself; the latter is only allocated when the string is created.) |
| 356 | @end table |
| 357 | |
| 358 | If there was overflow in pure space (see the previous section), |
| 359 | @code{garbage-collect} returns @code{nil}, because a real garbage |
| 360 | collection can not be done in this situation. |
| 361 | @end deffn |
| 362 | |
| 363 | @defopt garbage-collection-messages |
| 364 | If this variable is non-@code{nil}, Emacs displays a message at the |
| 365 | beginning and end of garbage collection. The default value is |
| 366 | @code{nil}, meaning there are no such messages. |
| 367 | @end defopt |
| 368 | |
| 369 | @defvar post-gc-hook |
| 370 | This is a normal hook that is run at the end of garbage collection. |
| 371 | Garbage collection is inhibited while the hook functions run, so be |
| 372 | careful writing them. |
| 373 | @end defvar |
| 374 | |
| 375 | @defopt gc-cons-threshold |
| 376 | The value of this variable is the number of bytes of storage that must |
| 377 | be allocated for Lisp objects after one garbage collection in order to |
| 378 | trigger another garbage collection. A cons cell counts as eight bytes, |
| 379 | a string as one byte per character plus a few bytes of overhead, and so |
| 380 | on; space allocated to the contents of buffers does not count. Note |
| 381 | that the subsequent garbage collection does not happen immediately when |
| 382 | the threshold is exhausted, but only the next time the Lisp evaluator is |
| 383 | called. |
| 384 | |
| 385 | The initial threshold value is 400,000. If you specify a larger |
| 386 | value, garbage collection will happen less often. This reduces the |
| 387 | amount of time spent garbage collecting, but increases total memory use. |
| 388 | You may want to do this when running a program that creates lots of |
| 389 | Lisp data. |
| 390 | |
| 391 | You can make collections more frequent by specifying a smaller value, |
| 392 | down to 10,000. A value less than 10,000 will remain in effect only |
| 393 | until the subsequent garbage collection, at which time |
| 394 | @code{garbage-collect} will set the threshold back to 10,000. |
| 395 | @end defopt |
| 396 | |
| 397 | @defopt gc-cons-percentage |
| 398 | The value of this variable specifies the amount of consing before a |
| 399 | garbage collection occurs, as a fraction of the current heap size. |
| 400 | This criterion and @code{gc-cons-threshold} apply in parallel, and |
| 401 | garbage collection occurs only when both criteria are satisfied. |
| 402 | |
| 403 | As the heap size increases, the time to perform a garbage collection |
| 404 | increases. Thus, it can be desirable to do them less frequently in |
| 405 | proportion. |
| 406 | @end defopt |
| 407 | |
| 408 | The value returned by @code{garbage-collect} describes the amount of |
| 409 | memory used by Lisp data, broken down by data type. By contrast, the |
| 410 | function @code{memory-limit} provides information on the total amount of |
| 411 | memory Emacs is currently using. |
| 412 | |
| 413 | @c Emacs 19 feature |
| 414 | @defun memory-limit |
| 415 | This function returns the address of the last byte Emacs has allocated, |
| 416 | divided by 1024. We divide the value by 1024 to make sure it fits in a |
| 417 | Lisp integer. |
| 418 | |
| 419 | You can use this to get a general idea of how your actions affect the |
| 420 | memory usage. |
| 421 | @end defun |
| 422 | |
| 423 | @defvar memory-full |
| 424 | This variable is @code{t} if Emacs is close to out of memory for Lisp |
| 425 | objects, and @code{nil} otherwise. |
| 426 | @end defvar |
| 427 | |
| 428 | @defun memory-use-counts |
| 429 | This returns a list of numbers that count the number of objects |
| 430 | created in this Emacs session. Each of these counters increments for |
| 431 | a certain kind of object. See the documentation string for details. |
| 432 | @end defun |
| 433 | |
| 434 | @defvar gcs-done |
| 435 | This variable contains the total number of garbage collections |
| 436 | done so far in this Emacs session. |
| 437 | @end defvar |
| 438 | |
| 439 | @defvar gc-elapsed |
| 440 | This variable contains the total number of seconds of elapsed time |
| 441 | during garbage collection so far in this Emacs session, as a floating |
| 442 | point number. |
| 443 | @end defvar |
| 444 | |
| 445 | @node Memory Usage |
| 446 | @section Memory Usage |
| 447 | @cindex memory usage |
| 448 | |
| 449 | These functions and variables give information about the total amount |
| 450 | of memory allocation that Emacs has done, broken down by data type. |
| 451 | Note the difference between these and the values returned by |
| 452 | @code{(garbage-collect)}; those count objects that currently exist, but |
| 453 | these count the number or size of all allocations, including those for |
| 454 | objects that have since been freed. |
| 455 | |
| 456 | @defvar cons-cells-consed |
| 457 | The total number of cons cells that have been allocated so far |
| 458 | in this Emacs session. |
| 459 | @end defvar |
| 460 | |
| 461 | @defvar floats-consed |
| 462 | The total number of floats that have been allocated so far |
| 463 | in this Emacs session. |
| 464 | @end defvar |
| 465 | |
| 466 | @defvar vector-cells-consed |
| 467 | The total number of vector cells that have been allocated so far |
| 468 | in this Emacs session. |
| 469 | @end defvar |
| 470 | |
| 471 | @defvar symbols-consed |
| 472 | The total number of symbols that have been allocated so far |
| 473 | in this Emacs session. |
| 474 | @end defvar |
| 475 | |
| 476 | @defvar string-chars-consed |
| 477 | The total number of string characters that have been allocated so far |
| 478 | in this Emacs session. |
| 479 | @end defvar |
| 480 | |
| 481 | @defvar misc-objects-consed |
| 482 | The total number of miscellaneous objects that have been allocated so |
| 483 | far in this Emacs session. These include markers and overlays, plus |
| 484 | certain objects not visible to users. |
| 485 | @end defvar |
| 486 | |
| 487 | @defvar intervals-consed |
| 488 | The total number of intervals that have been allocated so far |
| 489 | in this Emacs session. |
| 490 | @end defvar |
| 491 | |
| 492 | @defvar strings-consed |
| 493 | The total number of strings that have been allocated so far in this |
| 494 | Emacs session. |
| 495 | @end defvar |
| 496 | |
| 497 | @node Writing Emacs Primitives |
| 498 | @appendixsec Writing Emacs Primitives |
| 499 | @cindex primitive function internals |
| 500 | @cindex writing Emacs primitives |
| 501 | |
| 502 | Lisp primitives are Lisp functions implemented in C. The details of |
| 503 | interfacing the C function so that Lisp can call it are handled by a few |
| 504 | C macros. The only way to really understand how to write new C code is |
| 505 | to read the source, but we can explain some things here. |
| 506 | |
| 507 | An example of a special form is the definition of @code{or}, from |
| 508 | @file{eval.c}. (An ordinary function would have the same general |
| 509 | appearance.) |
| 510 | |
| 511 | @cindex garbage collection protection |
| 512 | @smallexample |
| 513 | @group |
| 514 | DEFUN ("or", For, Sor, 0, UNEVALLED, 0, |
| 515 | doc: /* Eval args until one of them yields non-nil, then return that |
| 516 | value. The remaining args are not evalled at all. |
| 517 | If all args return nil, return nil. |
| 518 | @end group |
| 519 | @group |
| 520 | usage: (or CONDITIONS ...) */) |
| 521 | (args) |
| 522 | Lisp_Object args; |
| 523 | @{ |
| 524 | register Lisp_Object val = Qnil; |
| 525 | struct gcpro gcpro1; |
| 526 | @end group |
| 527 | |
| 528 | @group |
| 529 | GCPRO1 (args); |
| 530 | @end group |
| 531 | |
| 532 | @group |
| 533 | while (CONSP (args)) |
| 534 | @{ |
| 535 | val = Feval (XCAR (args)); |
| 536 | if (!NILP (val)) |
| 537 | break; |
| 538 | args = XCDR (args); |
| 539 | @} |
| 540 | @end group |
| 541 | |
| 542 | @group |
| 543 | UNGCPRO; |
| 544 | return val; |
| 545 | @} |
| 546 | @end group |
| 547 | @end smallexample |
| 548 | |
| 549 | @cindex @code{DEFUN}, C macro to define Lisp primitives |
| 550 | Let's start with a precise explanation of the arguments to the |
| 551 | @code{DEFUN} macro. Here is a template for them: |
| 552 | |
| 553 | @example |
| 554 | DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc}) |
| 555 | @end example |
| 556 | |
| 557 | @table @var |
| 558 | @item lname |
| 559 | This is the name of the Lisp symbol to define as the function name; in |
| 560 | the example above, it is @code{or}. |
| 561 | |
| 562 | @item fname |
| 563 | This is the C function name for this function. This is |
| 564 | the name that is used in C code for calling the function. The name is, |
| 565 | by convention, @samp{F} prepended to the Lisp name, with all dashes |
| 566 | (@samp{-}) in the Lisp name changed to underscores. Thus, to call this |
| 567 | function from C code, call @code{For}. Remember that the arguments must |
| 568 | be of type @code{Lisp_Object}; various macros and functions for creating |
| 569 | values of type @code{Lisp_Object} are declared in the file |
| 570 | @file{lisp.h}. |
| 571 | |
| 572 | @item sname |
| 573 | This is a C variable name to use for a structure that holds the data for |
| 574 | the subr object that represents the function in Lisp. This structure |
| 575 | conveys the Lisp symbol name to the initialization routine that will |
| 576 | create the symbol and store the subr object as its definition. By |
| 577 | convention, this name is always @var{fname} with @samp{F} replaced with |
| 578 | @samp{S}. |
| 579 | |
| 580 | @item min |
| 581 | This is the minimum number of arguments that the function requires. The |
| 582 | function @code{or} allows a minimum of zero arguments. |
| 583 | |
| 584 | @item max |
| 585 | This is the maximum number of arguments that the function accepts, if |
| 586 | there is a fixed maximum. Alternatively, it can be @code{UNEVALLED}, |
| 587 | indicating a special form that receives unevaluated arguments, or |
| 588 | @code{MANY}, indicating an unlimited number of evaluated arguments (the |
| 589 | equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are |
| 590 | macros. If @var{max} is a number, it may not be less than @var{min} and |
| 591 | it may not be greater than eight. |
| 592 | |
| 593 | @item interactive |
| 594 | This is an interactive specification, a string such as might be used as |
| 595 | the argument of @code{interactive} in a Lisp function. In the case of |
| 596 | @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be |
| 597 | called interactively. A value of @code{""} indicates a function that |
| 598 | should receive no arguments when called interactively. If the value |
| 599 | begins with a @samp{(}, the string is evaluated as a Lisp form. |
| 600 | |
| 601 | @item doc |
| 602 | This is the documentation string. It uses C comment syntax rather |
| 603 | than C string syntax because comment syntax requires nothing special |
| 604 | to include multiple lines. The @samp{doc:} identifies the comment |
| 605 | that follows as the documentation string. The @samp{/*} and @samp{*/} |
| 606 | delimiters that begin and end the comment are not part of the |
| 607 | documentation string. |
| 608 | |
| 609 | If the last line of the documentation string begins with the keyword |
| 610 | @samp{usage:}, the rest of the line is treated as the argument list |
| 611 | for documentation purposes. This way, you can use different argument |
| 612 | names in the documentation string from the ones used in the C code. |
| 613 | @samp{usage:} is required if the function has an unlimited number of |
| 614 | arguments. |
| 615 | |
| 616 | All the usual rules for documentation strings in Lisp code |
| 617 | (@pxref{Documentation Tips}) apply to C code documentation strings |
| 618 | too. |
| 619 | @end table |
| 620 | |
| 621 | After the call to the @code{DEFUN} macro, you must write the argument |
| 622 | name list that every C function must have, followed by ordinary C |
| 623 | declarations for the arguments. For a function with a fixed maximum |
| 624 | number of arguments, declare a C argument for each Lisp argument, and |
| 625 | give them all type @code{Lisp_Object}. When a Lisp function has no |
| 626 | upper limit on the number of arguments, its implementation in C actually |
| 627 | receives exactly two arguments: the first is the number of Lisp |
| 628 | arguments, and the second is the address of a block containing their |
| 629 | values. They have types @code{int} and @w{@code{Lisp_Object *}}. |
| 630 | |
| 631 | @cindex @code{GCPRO} and @code{UNGCPRO} |
| 632 | @cindex protect C variables from garbage collection |
| 633 | Within the function @code{For} itself, note the use of the macros |
| 634 | @code{GCPRO1} and @code{UNGCPRO}. @code{GCPRO1} is used to |
| 635 | ``protect'' a variable from garbage collection---to inform the garbage |
| 636 | collector that it must look in that variable and regard its contents |
| 637 | as an accessible object. GC protection is necessary whenever you call |
| 638 | @code{Feval} or anything that can directly or indirectly call |
| 639 | @code{Feval}. At such a time, any Lisp object that this function may |
| 640 | refer to again must be protected somehow. |
| 641 | |
| 642 | It suffices to ensure that at least one pointer to each object is |
| 643 | GC-protected; that way, the object cannot be recycled, so all pointers |
| 644 | to it remain valid. Thus, a particular local variable can do without |
| 645 | protection if it is certain that the object it points to will be |
| 646 | preserved by some other pointer (such as another local variable which |
| 647 | has a @code{GCPRO})@footnote{Formerly, strings were a special |
| 648 | exception; in older Emacs versions, every local variable that might |
| 649 | point to a string needed a @code{GCPRO}.}. Otherwise, the local |
| 650 | variable needs a @code{GCPRO}. |
| 651 | |
| 652 | The macro @code{GCPRO1} protects just one local variable. If you |
| 653 | want to protect two variables, use @code{GCPRO2} instead; repeating |
| 654 | @code{GCPRO1} will not work. Macros @code{GCPRO3}, @code{GCPRO4}, |
| 655 | @code{GCPRO5}, and @code{GCPRO6} also exist. All these macros |
| 656 | implicitly use local variables such as @code{gcpro1}; you must declare |
| 657 | these explicitly, with type @code{struct gcpro}. Thus, if you use |
| 658 | @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}. |
| 659 | Alas, we can't explain all the tricky details here. |
| 660 | |
| 661 | @code{UNGCPRO} cancels the protection of the variables that are |
| 662 | protected in the current function. It is necessary to do this |
| 663 | explicitly. |
| 664 | |
| 665 | Built-in functions that take a variable number of arguments actually |
| 666 | accept two arguments at the C level: the number of Lisp arguments, and |
| 667 | a @code{Lisp_Object *} pointer to a C vector containing those Lisp |
| 668 | arguments. This C vector may be part of a Lisp vector, but it need |
| 669 | not be. The responsibility for using @code{GCPRO} to protect the Lisp |
| 670 | arguments from GC if necessary rests with the caller in this case, |
| 671 | since the caller allocated or found the storage for them. |
| 672 | |
| 673 | You must not use C initializers for static or global variables unless |
| 674 | the variables are never written once Emacs is dumped. These variables |
| 675 | with initializers are allocated in an area of memory that becomes |
| 676 | read-only (on certain operating systems) as a result of dumping Emacs. |
| 677 | @xref{Pure Storage}. |
| 678 | |
| 679 | Do not use static variables within functions---place all static |
| 680 | variables at top level in the file. This is necessary because Emacs on |
| 681 | some operating systems defines the keyword @code{static} as a null |
| 682 | macro. (This definition is used because those systems put all variables |
| 683 | declared static in a place that becomes read-only after dumping, whether |
| 684 | they have initializers or not.) |
| 685 | |
| 686 | @cindex @code{defsubr}, Lisp symbol for a primitive |
| 687 | Defining the C function is not enough to make a Lisp primitive |
| 688 | available; you must also create the Lisp symbol for the primitive and |
| 689 | store a suitable subr object in its function cell. The code looks like |
| 690 | this: |
| 691 | |
| 692 | @example |
| 693 | defsubr (&@var{subr-structure-name}); |
| 694 | @end example |
| 695 | |
| 696 | @noindent |
| 697 | Here @var{subr-structure-name} is the name you used as the third |
| 698 | argument to @code{DEFUN}. |
| 699 | |
| 700 | If you add a new primitive to a file that already has Lisp primitives |
| 701 | defined in it, find the function (near the end of the file) named |
| 702 | @code{syms_of_@var{something}}, and add the call to @code{defsubr} |
| 703 | there. If the file doesn't have this function, or if you create a new |
| 704 | file, add to it a @code{syms_of_@var{filename}} (e.g., |
| 705 | @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all |
| 706 | of these functions are called, and add a call to |
| 707 | @code{syms_of_@var{filename}} there. |
| 708 | |
| 709 | @anchor{Defining Lisp variables in C} |
| 710 | @vindex byte-boolean-vars |
| 711 | @cindex defining Lisp variables in C |
| 712 | @cindex @code{DEFVAR_INT}, @code{DEFVAR_LISP}, @code{DEFVAR_BOOL} |
| 713 | The function @code{syms_of_@var{filename}} is also the place to define |
| 714 | any C variables that are to be visible as Lisp variables. |
| 715 | @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible |
| 716 | in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int} |
| 717 | visible in Lisp with a value that is always an integer. |
| 718 | @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp |
| 719 | with a value that is either @code{t} or @code{nil}. Note that variables |
| 720 | defined with @code{DEFVAR_BOOL} are automatically added to the list |
| 721 | @code{byte-boolean-vars} used by the byte compiler. |
| 722 | |
| 723 | @cindex @code{staticpro}, protection from GC |
| 724 | If you define a file-scope C variable of type @code{Lisp_Object}, |
| 725 | you must protect it from garbage-collection by calling @code{staticpro} |
| 726 | in @code{syms_of_@var{filename}}, like this: |
| 727 | |
| 728 | @example |
| 729 | staticpro (&@var{variable}); |
| 730 | @end example |
| 731 | |
| 732 | Here is another example function, with more complicated arguments. |
| 733 | This comes from the code in @file{window.c}, and it demonstrates the use |
| 734 | of macros and functions to manipulate Lisp objects. |
| 735 | |
| 736 | @smallexample |
| 737 | @group |
| 738 | DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p, |
| 739 | Scoordinates_in_window_p, 2, 2, |
| 740 | "xSpecify coordinate pair: \nXExpression which evals to window: ", |
| 741 | "Return non-nil if COORDINATES is in WINDOW.\n\ |
| 742 | COORDINATES is a cons of the form (X . Y), X and Y being distances\n\ |
| 743 | ... |
| 744 | @end group |
| 745 | @group |
| 746 | If they are on the border between WINDOW and its right sibling,\n\ |
| 747 | `vertical-line' is returned.") |
| 748 | (coordinates, window) |
| 749 | register Lisp_Object coordinates, window; |
| 750 | @{ |
| 751 | int x, y; |
| 752 | @end group |
| 753 | |
| 754 | @group |
| 755 | CHECK_LIVE_WINDOW (window, 0); |
| 756 | CHECK_CONS (coordinates, 1); |
| 757 | x = XINT (Fcar (coordinates)); |
| 758 | y = XINT (Fcdr (coordinates)); |
| 759 | @end group |
| 760 | |
| 761 | @group |
| 762 | switch (coordinates_in_window (XWINDOW (window), &x, &y)) |
| 763 | @{ |
| 764 | case 0: /* NOT in window at all. */ |
| 765 | return Qnil; |
| 766 | @end group |
| 767 | |
| 768 | @group |
| 769 | case 1: /* In text part of window. */ |
| 770 | return Fcons (make_number (x), make_number (y)); |
| 771 | @end group |
| 772 | |
| 773 | @group |
| 774 | case 2: /* In mode line of window. */ |
| 775 | return Qmode_line; |
| 776 | @end group |
| 777 | |
| 778 | @group |
| 779 | case 3: /* On right border of window. */ |
| 780 | return Qvertical_line; |
| 781 | @end group |
| 782 | |
| 783 | @group |
| 784 | default: |
| 785 | abort (); |
| 786 | @} |
| 787 | @} |
| 788 | @end group |
| 789 | @end smallexample |
| 790 | |
| 791 | Note that C code cannot call functions by name unless they are defined |
| 792 | in C. The way to call a function written in Lisp is to use |
| 793 | @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since |
| 794 | the Lisp function @code{funcall} accepts an unlimited number of |
| 795 | arguments, in C it takes two: the number of Lisp-level arguments, and a |
| 796 | one-dimensional array containing their values. The first Lisp-level |
| 797 | argument is the Lisp function to call, and the rest are the arguments to |
| 798 | pass to it. Since @code{Ffuncall} can call the evaluator, you must |
| 799 | protect pointers from garbage collection around the call to |
| 800 | @code{Ffuncall}. |
| 801 | |
| 802 | The C functions @code{call0}, @code{call1}, @code{call2}, and so on, |
| 803 | provide handy ways to call a Lisp function conveniently with a fixed |
| 804 | number of arguments. They work by calling @code{Ffuncall}. |
| 805 | |
| 806 | @file{eval.c} is a very good file to look through for examples; |
| 807 | @file{lisp.h} contains the definitions for some important macros and |
| 808 | functions. |
| 809 | |
| 810 | If you define a function which is side-effect free, update the code |
| 811 | in @file{byte-opt.el} which binds @code{side-effect-free-fns} and |
| 812 | @code{side-effect-and-error-free-fns} so that the compiler optimizer |
| 813 | knows about it. |
| 814 | |
| 815 | @node Object Internals |
| 816 | @appendixsec Object Internals |
| 817 | @cindex object internals |
| 818 | |
| 819 | GNU Emacs Lisp manipulates many different types of data. The actual |
| 820 | data are stored in a heap and the only access that programs have to it |
| 821 | is through pointers. Each pointer is 32 bits wide on 32-bit machines, |
| 822 | and 64 bits wide on 64-bit machines; three of these bits are used for |
| 823 | the tag that identifies the object's type, and the remainder are used |
| 824 | to address the object. |
| 825 | |
| 826 | Because Lisp objects are represented as tagged pointers, it is always |
| 827 | possible to determine the Lisp data type of any object. The C data type |
| 828 | @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary |
| 829 | variables have type @code{Lisp_Object}, which means they can hold any |
| 830 | type of Lisp value; you can determine the actual data type only at run |
| 831 | time. The same is true for function arguments; if you want a function |
| 832 | to accept only a certain type of argument, you must check the type |
| 833 | explicitly using a suitable predicate (@pxref{Type Predicates}). |
| 834 | @cindex type checking internals |
| 835 | |
| 836 | @menu |
| 837 | * Buffer Internals:: Components of a buffer structure. |
| 838 | * Window Internals:: Components of a window structure. |
| 839 | * Process Internals:: Components of a process structure. |
| 840 | @end menu |
| 841 | |
| 842 | @node Buffer Internals |
| 843 | @appendixsubsec Buffer Internals |
| 844 | @cindex internals, of buffer |
| 845 | @cindex buffer internals |
| 846 | |
| 847 | Two structures are used to represent buffers in C. The |
| 848 | @code{buffer_text} structure contains fields describing the text of a |
| 849 | buffer; the @code{buffer} structure holds other fields. In the case |
| 850 | of indirect buffers, two or more @code{buffer} structures reference |
| 851 | the same @code{buffer_text} structure. |
| 852 | |
| 853 | Here are some of the fields in @code{struct buffer_text}: |
| 854 | |
| 855 | @table @code |
| 856 | @item beg |
| 857 | The address of the buffer contents. |
| 858 | |
| 859 | @item gpt |
| 860 | @itemx gpt_byte |
| 861 | The character and byte positions of the buffer gap. @xref{Buffer |
| 862 | Gap}. |
| 863 | |
| 864 | @item z |
| 865 | @itemx z_byte |
| 866 | The character and byte positions of the end of the buffer text. |
| 867 | |
| 868 | @item gap_size |
| 869 | The size of buffer's gap. @xref{Buffer Gap}. |
| 870 | |
| 871 | @item modiff |
| 872 | @itemx save_modiff |
| 873 | @itemx chars_modiff |
| 874 | @itemx overlay_modiff |
| 875 | These fields count the number of buffer-modification events performed |
| 876 | in this buffer. @code{modiff} is incremented after each |
| 877 | buffer-modification event, and is never otherwise changed; |
| 878 | @code{save_modiff} contains the value of @code{modiff} the last time |
| 879 | the buffer was visited or saved; @code{chars_modiff} counts only |
| 880 | modifications to the characters in the buffer, ignoring all other |
| 881 | kinds of changes; and @code{overlay_modiff} counts only modifications |
| 882 | to the overlays. |
| 883 | |
| 884 | @item beg_unchanged |
| 885 | @itemx end_unchanged |
| 886 | The number of characters at the start and end of the text that are |
| 887 | known to be unchanged since the last complete redisplay. |
| 888 | |
| 889 | @item unchanged_modified |
| 890 | @itemx overlay_unchanged_modified |
| 891 | The values of @code{modiff} and @code{overlay_modiff}, respectively, |
| 892 | after the last compelete redisplay. If their current values match |
| 893 | @code{modiff} or @code{overlay_modiff}, that means |
| 894 | @code{beg_unchanged} and @code{end_unchanged} contain no useful |
| 895 | information. |
| 896 | |
| 897 | @item markers |
| 898 | The markers that refer to this buffer. This is actually a single |
| 899 | marker, and successive elements in its marker @code{chain} are the other |
| 900 | markers referring to this buffer text. |
| 901 | |
| 902 | @item intervals |
| 903 | The interval tree which records the text properties of this buffer. |
| 904 | @end table |
| 905 | |
| 906 | Some of the fields of @code{struct buffer} are: |
| 907 | |
| 908 | @table @code |
| 909 | @item next |
| 910 | Points to the next buffer, in the chain of all buffers (including |
| 911 | killed buffers). This chain is used only for garbage collection, in |
| 912 | order to collect killed buffers properly. Note that vectors, and most |
| 913 | kinds of objects allocated as vectors, are all on one chain, but |
| 914 | buffers are on a separate chain of their own. |
| 915 | |
| 916 | @item own_text |
| 917 | A @code{struct buffer_text} structure that ordinarily holds the buffer |
| 918 | contents. In indirect buffers, this field is not used. |
| 919 | |
| 920 | @item text |
| 921 | A pointer to the @code{buffer_text} structure for this buffer. In an |
| 922 | ordinary buffer, this is the @code{own_text} field above. In an |
| 923 | indirect buffer, this is the @code{own_text} field of the base buffer. |
| 924 | |
| 925 | @item pt |
| 926 | @itemx pt_byte |
| 927 | The character and byte positions of point in a buffer. |
| 928 | |
| 929 | @item begv |
| 930 | @itemx begv_byte |
| 931 | The character and byte positions of the beginning of the accessible |
| 932 | range of text in the buffer. |
| 933 | |
| 934 | @item zv |
| 935 | @itemx zv_byte |
| 936 | The character and byte positions of the end of the accessible range of |
| 937 | text in the buffer. |
| 938 | |
| 939 | @item base_buffer |
| 940 | In an indirect buffer, this points to the base buffer. In an ordinary |
| 941 | buffer, it is null. |
| 942 | |
| 943 | @item local_flags |
| 944 | This field contains flags indicating that certain variables are local |
| 945 | in this buffer. Such variables are declared in the C code using |
| 946 | @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored |
| 947 | in fields in the buffer structure itself. (Some of these fields are |
| 948 | described in this table.) |
| 949 | |
| 950 | @item modtime |
| 951 | The modification time of the visited file. It is set when the file is |
| 952 | written or read. Before writing the buffer into a file, this field is |
| 953 | compared to the modification time of the file to see if the file has |
| 954 | changed on disk. @xref{Buffer Modification}. |
| 955 | |
| 956 | @item auto_save_modified |
| 957 | The time when the buffer was last auto-saved. |
| 958 | |
| 959 | @item last_window_start |
| 960 | The @code{window-start} position in the buffer as of the last time the |
| 961 | buffer was displayed in a window. |
| 962 | |
| 963 | @item clip_changed |
| 964 | This flag indicates that narrowing has changed in the buffer. |
| 965 | @xref{Narrowing}. |
| 966 | |
| 967 | @item prevent_redisplay_optimizations_p |
| 968 | This flag indicates that redisplay optimizations should not be used to |
| 969 | display this buffer. |
| 970 | |
| 971 | @item overlay_center |
| 972 | This field holds the current overlay center position. @xref{Managing |
| 973 | Overlays}. |
| 974 | |
| 975 | @item overlays_before |
| 976 | @itemx overlays_after |
| 977 | These fields hold, respectively, a list of overlays that end at or |
| 978 | before the current overlay center, and a list of overlays that end |
| 979 | after the current overlay center. @xref{Managing Overlays}. |
| 980 | @code{overlays_before} is sorted in order of decreasing end position, |
| 981 | and @code{overlays_after} is sorted in order of increasing beginning |
| 982 | position. |
| 983 | |
| 984 | @item name |
| 985 | A Lisp string that names the buffer. It is guaranteed to be unique. |
| 986 | @xref{Buffer Names}. |
| 987 | |
| 988 | @item save_length |
| 989 | The length of the file this buffer is visiting, when last read or |
| 990 | saved. This and other fields concerned with saving are not kept in |
| 991 | the @code{buffer_text} structure because indirect buffers are never |
| 992 | saved. |
| 993 | |
| 994 | @item directory |
| 995 | The directory for expanding relative file names. This is the value of |
| 996 | the buffer-local variable @code{default-directory} (@pxref{File Name Expansion}). |
| 997 | |
| 998 | @item filename |
| 999 | The name of the file visited in this buffer, or @code{nil}. This is |
| 1000 | the value of the buffer-local variable @code{buffer-file-name} |
| 1001 | (@pxref{Buffer File Name}). |
| 1002 | |
| 1003 | @item undo_list |
| 1004 | @itemx backed_up |
| 1005 | @itemx auto_save_file_name |
| 1006 | @itemx read_only |
| 1007 | @itemx file_format |
| 1008 | @itemx file_truename |
| 1009 | @itemx invisibility_spec |
| 1010 | @itemx display_count |
| 1011 | @itemx display_time |
| 1012 | These fields store the values of Lisp variables that are automatically |
| 1013 | buffer-local (@pxref{Buffer-Local Variables}), whose corresponding |
| 1014 | variable names have the additional prefix @code{buffer-} and have |
| 1015 | underscores replaced with dashes. For instance, @code{undo_list} |
| 1016 | stores the value of @code{buffer-undo-list}. @xref{Standard |
| 1017 | Buffer-Local Variables}. |
| 1018 | |
| 1019 | @item mark |
| 1020 | The mark for the buffer. The mark is a marker, hence it is also |
| 1021 | included on the list @code{markers}. @xref{The Mark}. |
| 1022 | |
| 1023 | @item local_var_alist |
| 1024 | The association list describing the buffer-local variable bindings of |
| 1025 | this buffer, not including the built-in buffer-local bindings that |
| 1026 | have special slots in the buffer object. (Those slots are omitted |
| 1027 | from this table.) @xref{Buffer-Local Variables}. |
| 1028 | |
| 1029 | @item major_mode |
| 1030 | Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}. |
| 1031 | |
| 1032 | @item mode_name |
| 1033 | Pretty name of the major mode, e.g., @code{"Lisp"}. |
| 1034 | |
| 1035 | @item keymap |
| 1036 | @itemx abbrev_table |
| 1037 | @itemx syntax_table |
| 1038 | @itemx category_table |
| 1039 | @itemx display_table |
| 1040 | These fields store the buffer's local keymap (@pxref{Keymaps}), abbrev |
| 1041 | table (@pxref{Abbrev Tables}), syntax table (@pxref{Syntax Tables}), |
| 1042 | category table (@pxref{Categories}), and display table (@pxref{Display |
| 1043 | Tables}). |
| 1044 | |
| 1045 | @item downcase_table |
| 1046 | @itemx upcase_table |
| 1047 | @itemx case_canon_table |
| 1048 | These fields store the conversion tables for converting text to lower |
| 1049 | case, upper case, and for canonicalizing text for case-fold search. |
| 1050 | @xref{Case Tables}. |
| 1051 | |
| 1052 | @item minor_modes |
| 1053 | An alist of the minor modes of this buffer. |
| 1054 | |
| 1055 | @item pt_marker |
| 1056 | @itemx begv_marker |
| 1057 | @itemx zv_marker |
| 1058 | These fields are only used in an indirect buffer, or in a buffer that |
| 1059 | is the base of an indirect buffer. Each holds a marker that records |
| 1060 | @code{pt}, @code{begv}, and @code{zv} respectively, for this buffer |
| 1061 | when the buffer is not current. |
| 1062 | |
| 1063 | @item mode_line_format |
| 1064 | @itemx header_line_format |
| 1065 | @itemx case_fold_search |
| 1066 | @itemx tab_width |
| 1067 | @itemx fill_column |
| 1068 | @itemx left_margin |
| 1069 | @itemx auto_fill_function |
| 1070 | @itemx truncate_lines |
| 1071 | @itemx word_wrap |
| 1072 | @itemx ctl_arrow |
| 1073 | @itemx selective_display |
| 1074 | @itemx selective_display_ellipses |
| 1075 | @itemx overwrite_mode |
| 1076 | @itemx abbrev_mode |
| 1077 | @itemx display_table |
| 1078 | @itemx mark_active |
| 1079 | @itemx enable_multibyte_characters |
| 1080 | @itemx buffer_file_coding_system |
| 1081 | @itemx auto_save_file_format |
| 1082 | @itemx cache_long_line_scans |
| 1083 | @itemx point_before_scroll |
| 1084 | @itemx left_fringe_width |
| 1085 | @itemx right_fringe_width |
| 1086 | @itemx fringes_outside_margins |
| 1087 | @itemx scroll_bar_width |
| 1088 | @itemx indicate_empty_lines |
| 1089 | @itemx indicate_buffer_boundaries |
| 1090 | @itemx fringe_indicator_alist |
| 1091 | @itemx fringe_cursor_alist |
| 1092 | @itemx scroll_up_aggressively |
| 1093 | @itemx scroll_down_aggressively |
| 1094 | @itemx cursor_type |
| 1095 | @itemx cursor_in_non_selected_windows |
| 1096 | These fields store the values of Lisp variables that are automatically |
| 1097 | buffer-local (@pxref{Buffer-Local Variables}), whose corresponding |
| 1098 | variable names have underscores replaced with dashes. For instance, |
| 1099 | @code{mode_line_format} stores the value of @code{mode-line-format}. |
| 1100 | @xref{Standard Buffer-Local Variables}. |
| 1101 | |
| 1102 | @item last_selected_window |
| 1103 | This is the last window that was selected with this buffer in it, or @code{nil} |
| 1104 | if that window no longer displays this buffer. |
| 1105 | @end table |
| 1106 | |
| 1107 | @node Window Internals |
| 1108 | @appendixsubsec Window Internals |
| 1109 | @cindex internals, of window |
| 1110 | @cindex window internals |
| 1111 | |
| 1112 | Windows have the following accessible fields: |
| 1113 | |
| 1114 | @table @code |
| 1115 | @item frame |
| 1116 | The frame that this window is on. |
| 1117 | |
| 1118 | @item mini_p |
| 1119 | Non-@code{nil} if this window is a minibuffer window. |
| 1120 | |
| 1121 | @item parent |
| 1122 | Internally, Emacs arranges windows in a tree; each group of siblings has |
| 1123 | a parent window whose area includes all the siblings. This field points |
| 1124 | to a window's parent. |
| 1125 | |
| 1126 | Parent windows do not display buffers, and play little role in display |
| 1127 | except to shape their child windows. Emacs Lisp programs usually have |
| 1128 | no access to the parent windows; they operate on the windows at the |
| 1129 | leaves of the tree, which actually display buffers. |
| 1130 | |
| 1131 | @item hchild |
| 1132 | @itemx vchild |
| 1133 | These fields contain the window's leftmost child and its topmost child |
| 1134 | respectively. @code{hchild} is used if the window is subdivided |
| 1135 | horizontally by child windows, and @code{vchild} if it is subdivided |
| 1136 | vertically. |
| 1137 | |
| 1138 | @item next |
| 1139 | @itemx prev |
| 1140 | The next sibling and previous sibling of this window. @code{next} is |
| 1141 | @code{nil} if the window is the rightmost or bottommost in its group; |
| 1142 | @code{prev} is @code{nil} if it is the leftmost or topmost in its |
| 1143 | group. |
| 1144 | |
| 1145 | @item left_col |
| 1146 | The left-hand edge of the window, measured in columns, relative to the |
| 1147 | leftmost column in the frame (column 0). |
| 1148 | |
| 1149 | @item top_line |
| 1150 | The top edge of the window, measured in lines, relative to the topmost |
| 1151 | line in the frame (line 0). |
| 1152 | |
| 1153 | @item total_cols |
| 1154 | @itemx total_lines |
| 1155 | The width and height of the window, measured in columns and lines |
| 1156 | respectively. The width includes the scroll bar and fringes, and/or |
| 1157 | the separator line on the right of the window (if any). |
| 1158 | |
| 1159 | @item buffer |
| 1160 | The buffer that the window is displaying. |
| 1161 | |
| 1162 | @item start |
| 1163 | A marker pointing to the position in the buffer that is the first |
| 1164 | character displayed in the window. |
| 1165 | |
| 1166 | @item pointm |
| 1167 | @cindex window point internals |
| 1168 | This is the value of point in the current buffer when this window is |
| 1169 | selected; when it is not selected, it retains its previous value. |
| 1170 | |
| 1171 | @item force_start |
| 1172 | If this flag is non-@code{nil}, it says that the window has been |
| 1173 | scrolled explicitly by the Lisp program. This affects what the next |
| 1174 | redisplay does if point is off the screen: instead of scrolling the |
| 1175 | window to show the text around point, it moves point to a location that |
| 1176 | is on the screen. |
| 1177 | |
| 1178 | @item frozen_window_start_p |
| 1179 | This field is set temporarily to 1 to indicate to redisplay that |
| 1180 | @code{start} of this window should not be changed, even if point |
| 1181 | gets invisible. |
| 1182 | |
| 1183 | @item start_at_line_beg |
| 1184 | Non-@code{nil} means current value of @code{start} was the beginning of a line |
| 1185 | when it was chosen. |
| 1186 | |
| 1187 | @item use_time |
| 1188 | This is the last time that the window was selected. The function |
| 1189 | @code{get-lru-window} uses this field. |
| 1190 | |
| 1191 | @item sequence_number |
| 1192 | A unique number assigned to this window when it was created. |
| 1193 | |
| 1194 | @item last_modified |
| 1195 | The @code{modiff} field of the window's buffer, as of the last time |
| 1196 | a redisplay completed in this window. |
| 1197 | |
| 1198 | @item last_overlay_modified |
| 1199 | The @code{overlay_modiff} field of the window's buffer, as of the last |
| 1200 | time a redisplay completed in this window. |
| 1201 | |
| 1202 | @item last_point |
| 1203 | The buffer's value of point, as of the last time a redisplay completed |
| 1204 | in this window. |
| 1205 | |
| 1206 | @item last_had_star |
| 1207 | A non-@code{nil} value means the window's buffer was ``modified'' when the |
| 1208 | window was last updated. |
| 1209 | |
| 1210 | @item vertical_scroll_bar |
| 1211 | This window's vertical scroll bar. |
| 1212 | |
| 1213 | @item left_margin_width |
| 1214 | @itemx right_margin_width |
| 1215 | The widths of the left and right margins in this window. A value of |
| 1216 | @code{nil} means to use the buffer's value of @code{left-margin-width} |
| 1217 | or @code{right-margin-width}. |
| 1218 | |
| 1219 | @item window_end_pos |
| 1220 | This is computed as @code{z} minus the buffer position of the last glyph |
| 1221 | in the current matrix of the window. The value is only valid if |
| 1222 | @code{window_end_valid} is not @code{nil}. |
| 1223 | |
| 1224 | @item window_end_bytepos |
| 1225 | The byte position corresponding to @code{window_end_pos}. |
| 1226 | |
| 1227 | @item window_end_vpos |
| 1228 | The window-relative vertical position of the line containing |
| 1229 | @code{window_end_pos}. |
| 1230 | |
| 1231 | @item window_end_valid |
| 1232 | This field is set to a non-@code{nil} value if @code{window_end_pos} is truly |
| 1233 | valid. This is @code{nil} if nontrivial redisplay is preempted since in that |
| 1234 | case the display that @code{window_end_pos} was computed for did not get |
| 1235 | onto the screen. |
| 1236 | |
| 1237 | @item cursor |
| 1238 | A structure describing where the cursor is in this window. |
| 1239 | |
| 1240 | @item last_cursor |
| 1241 | The value of @code{cursor} as of the last redisplay that finished. |
| 1242 | |
| 1243 | @item phys_cursor |
| 1244 | A structure describing where the cursor of this window physically is. |
| 1245 | |
| 1246 | @item phys_cursor_type |
| 1247 | The type of cursor that was last displayed on this window. |
| 1248 | |
| 1249 | @item phys_cursor_on_p |
| 1250 | This field is non-zero if the cursor is physically on. |
| 1251 | |
| 1252 | @item cursor_off_p |
| 1253 | Non-zero means the cursor in this window is logically on. |
| 1254 | |
| 1255 | @item last_cursor_off_p |
| 1256 | This field contains the value of @code{cursor_off_p} as of the time of |
| 1257 | the last redisplay. |
| 1258 | |
| 1259 | @item must_be_updated_p |
| 1260 | This is set to 1 during redisplay when this window must be updated. |
| 1261 | |
| 1262 | @item hscroll |
| 1263 | This is the number of columns that the display in the window is scrolled |
| 1264 | horizontally to the left. Normally, this is 0. |
| 1265 | |
| 1266 | @item vscroll |
| 1267 | Vertical scroll amount, in pixels. Normally, this is 0. |
| 1268 | |
| 1269 | @item dedicated |
| 1270 | Non-@code{nil} if this window is dedicated to its buffer. |
| 1271 | |
| 1272 | @item display_table |
| 1273 | The window's display table, or @code{nil} if none is specified for it. |
| 1274 | |
| 1275 | @item update_mode_line |
| 1276 | Non-@code{nil} means this window's mode line needs to be updated. |
| 1277 | |
| 1278 | @item base_line_number |
| 1279 | The line number of a certain position in the buffer, or @code{nil}. |
| 1280 | This is used for displaying the line number of point in the mode line. |
| 1281 | |
| 1282 | @item base_line_pos |
| 1283 | The position in the buffer for which the line number is known, or |
| 1284 | @code{nil} meaning none is known. |
| 1285 | |
| 1286 | @item region_showing |
| 1287 | If the region (or part of it) is highlighted in this window, this field |
| 1288 | holds the mark position that made one end of that region. Otherwise, |
| 1289 | this field is @code{nil}. |
| 1290 | |
| 1291 | @item column_number_displayed |
| 1292 | The column number currently displayed in this window's mode line, or @code{nil} |
| 1293 | if column numbers are not being displayed. |
| 1294 | |
| 1295 | @item current_matrix |
| 1296 | A glyph matrix describing the current display of this window. |
| 1297 | |
| 1298 | @item desired_matrix |
| 1299 | A glyph matrix describing the desired display of this window. |
| 1300 | @end table |
| 1301 | |
| 1302 | @node Process Internals |
| 1303 | @appendixsubsec Process Internals |
| 1304 | @cindex internals, of process |
| 1305 | @cindex process internals |
| 1306 | |
| 1307 | The fields of a process are: |
| 1308 | |
| 1309 | @table @code |
| 1310 | @item name |
| 1311 | A string, the name of the process. |
| 1312 | |
| 1313 | @item command |
| 1314 | A list containing the command arguments that were used to start this |
| 1315 | process. For a network or serial process, it is @code{nil} if the |
| 1316 | process is running or @code{t} if the process is stopped. |
| 1317 | |
| 1318 | @item filter |
| 1319 | A function used to accept output from the process instead of a buffer, |
| 1320 | or @code{nil}. |
| 1321 | |
| 1322 | @item sentinel |
| 1323 | A function called whenever the process receives a signal, or @code{nil}. |
| 1324 | |
| 1325 | @item buffer |
| 1326 | The associated buffer of the process. |
| 1327 | |
| 1328 | @item pid |
| 1329 | An integer, the operating system's process @acronym{ID}. |
| 1330 | |
| 1331 | @item childp |
| 1332 | A flag, non-@code{nil} if this is really a child process. |
| 1333 | It is @code{nil} for a network or serial connection. |
| 1334 | |
| 1335 | @item mark |
| 1336 | A marker indicating the position of the end of the last output from this |
| 1337 | process inserted into the buffer. This is often but not always the end |
| 1338 | of the buffer. |
| 1339 | |
| 1340 | @item kill_without_query |
| 1341 | If this is non-zero, killing Emacs while this process is still running |
| 1342 | does not ask for confirmation about killing the process. |
| 1343 | |
| 1344 | @item raw_status_low |
| 1345 | @itemx raw_status_high |
| 1346 | These two fields record 16 bits each of the process status returned by |
| 1347 | the @code{wait} system call. |
| 1348 | |
| 1349 | @item status |
| 1350 | The process status, as @code{process-status} should return it. |
| 1351 | |
| 1352 | @item tick |
| 1353 | @itemx update_tick |
| 1354 | If these two fields are not equal, a change in the status of the process |
| 1355 | needs to be reported, either by running the sentinel or by inserting a |
| 1356 | message in the process buffer. |
| 1357 | |
| 1358 | @item pty_flag |
| 1359 | Non-@code{nil} if communication with the subprocess uses a @acronym{PTY}; |
| 1360 | @code{nil} if it uses a pipe. |
| 1361 | |
| 1362 | @item infd |
| 1363 | The file descriptor for input from the process. |
| 1364 | |
| 1365 | @item outfd |
| 1366 | The file descriptor for output to the process. |
| 1367 | |
| 1368 | @item subtty |
| 1369 | The file descriptor for the terminal that the subprocess is using. (On |
| 1370 | some systems, there is no need to record this, so the value is |
| 1371 | @code{nil}.) |
| 1372 | |
| 1373 | @item tty_name |
| 1374 | The name of the terminal that the subprocess is using, |
| 1375 | or @code{nil} if it is using pipes. |
| 1376 | |
| 1377 | @item decode_coding_system |
| 1378 | Coding-system for decoding the input from this process. |
| 1379 | |
| 1380 | @item decoding_buf |
| 1381 | A working buffer for decoding. |
| 1382 | |
| 1383 | @item decoding_carryover |
| 1384 | Size of carryover in decoding. |
| 1385 | |
| 1386 | @item encode_coding_system |
| 1387 | Coding-system for encoding the output to this process. |
| 1388 | |
| 1389 | @item encoding_buf |
| 1390 | A working buffer for encoding. |
| 1391 | |
| 1392 | @item encoding_carryover |
| 1393 | Size of carryover in encoding. |
| 1394 | |
| 1395 | @item inherit_coding_system_flag |
| 1396 | Flag to set @code{coding-system} of the process buffer from the |
| 1397 | coding system used to decode process output. |
| 1398 | |
| 1399 | @item type |
| 1400 | Symbol indicating the type of process: @code{real}, @code{network}, |
| 1401 | @code{serial} |
| 1402 | |
| 1403 | @end table |
| 1404 | |
| 1405 | @ignore |
| 1406 | arch-tag: 4b2c33bc-d7e4-43f5-bc20-27c0db52a53e |
| 1407 | @end ignore |