2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1998 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
5 @setfilename ../info/internals
6 @node GNU Emacs Internals, Standard Errors, Tips, Top
7 @comment node-name, next, previous, up
8 @appendix GNU Emacs Internals
10 This chapter describes how the runnable Emacs executable is dumped with
11 the preloaded Lisp libraries in it, how storage is allocated, and some
12 internal aspects of GNU Emacs that may be of interest to C programmers.
15 * Building Emacs:: How to the dumped Emacs is made.
16 * Pure Storage:: A kludge to make preloaded Lisp functions sharable.
17 * Garbage Collection:: Reclaiming space for Lisp objects no longer used.
18 * Memory Usage:: Info about total size of Lisp objects made so far.
19 * Writing Emacs Primitives:: Writing C code for Emacs.
20 * Object Internals:: Data formats of buffers, windows, processes.
24 @appendixsec Building Emacs
25 @cindex building Emacs
28 This section explains the steps involved in building the Emacs
29 executable. You don't have to know this material to build and install
30 Emacs, since the makefiles do all these things automatically. This
31 information is pertinent to Emacs maintenance.
33 Compilation of the C source files in the @file{src} directory
34 produces an executable file called @file{temacs}, also called a
35 @dfn{bare impure Emacs}. It contains the Emacs Lisp interpreter and I/O
36 routines, but not the editing commands.
38 @cindex @file{loadup.el}
39 The command @w{@samp{temacs -l loadup}} uses @file{temacs} to create
40 the real runnable Emacs executable. These arguments direct
41 @file{temacs} to evaluate the Lisp files specified in the file
42 @file{loadup.el}. These files set up the normal Emacs editing
43 environment, resulting in an Emacs that is still impure but no longer
46 It takes a substantial time to load the standard Lisp files. Luckily,
47 you don't have to do this each time you run Emacs; @file{temacs} can
48 dump out an executable program called @file{emacs} that has these files
49 preloaded. @file{emacs} starts more quickly because it does not need to
50 load the files. This is the Emacs executable that is normally
53 To create @file{emacs}, use the command @samp{temacs -batch -l loadup
54 dump}. The purpose of @samp{-batch} here is to prevent @file{temacs}
55 from trying to initialize any of its data on the terminal; this ensures
56 that the tables of terminal information are empty in the dumped Emacs.
57 The argument @samp{dump} tells @file{loadup.el} to dump a new executable
60 Some operating systems don't support dumping. On those systems, you
61 must start Emacs with the @samp{temacs -l loadup} command each time you
62 use it. This takes a substantial time, but since you need to start
63 Emacs once a day at most---or once a week if you never log out---the
64 extra time is not too severe a problem.
66 @cindex @file{site-load.el}
68 You can specify additional files to preload by writing a library named
69 @file{site-load.el} that loads them. You may need to add a definition
72 #define SITELOAD_PURESIZE_EXTRA @var{n}
76 to make @var{n} added bytes of pure space to hold the additional files.
77 (Try adding increments of 20000 until it is big enough.) However, the
78 advantage of preloading additional files decreases as machines get
79 faster. On modern machines, it is usually not advisable.
81 After @file{loadup.el} reads @file{site-load.el}, it finds the
82 documentation strings for primitive and preloaded functions (and
83 variables) in the file @file{etc/DOC} where they are stored, by calling
84 @code{Snarf-documentation} (@pxref{Accessing Documentation}).
86 @cindex @file{site-init.el}
87 You can specify other Lisp expressions to execute just before dumping
88 by putting them in a library named @file{site-init.el}. This file is
89 executed after the documentation strings are found.
91 If you want to preload function or variable definitions, there are
92 three ways you can do this and make their documentation strings
93 accessible when you subsequently run Emacs:
97 Arrange to scan these files when producing the @file{etc/DOC} file,
98 and load them with @file{site-load.el}.
101 Load the files with @file{site-init.el}, then copy the files into the
102 installation directory for Lisp files when you install Emacs.
105 Specify a non-@code{nil} value for
106 @code{byte-compile-dynamic-docstrings} as a local variable in each of these
107 files, and load them with either @file{site-load.el} or
108 @file{site-init.el}. (This method has the drawback that the
109 documentation strings take up space in Emacs all the time.)
112 It is not advisable to put anything in @file{site-load.el} or
113 @file{site-init.el} that would alter any of the features that users
114 expect in an ordinary unmodified Emacs. If you feel you must override
115 normal features for your site, do it with @file{default.el}, so that
116 users can override your changes if they wish. @xref{Startup Summary}.
118 @defun dump-emacs to-file from-file
120 This function dumps the current state of Emacs into an executable file
121 @var{to-file}. It takes symbols from @var{from-file} (this is normally
122 the executable file @file{temacs}).
124 If you want to use this function in an Emacs that was already dumped,
125 you must run Emacs with @samp{-batch}.
129 @appendixsec Pure Storage
132 Emacs Lisp uses two kinds of storage for user-created Lisp objects:
133 @dfn{normal storage} and @dfn{pure storage}. Normal storage is where
134 all the new data created during an Emacs session are kept; see the
135 following section for information on normal storage. Pure storage is
136 used for certain data in the preloaded standard Lisp files---data that
137 should never change during actual use of Emacs.
139 Pure storage is allocated only while @file{temacs} is loading the
140 standard preloaded Lisp libraries. In the file @file{emacs}, it is
141 marked as read-only (on operating systems that permit this), so that
142 the memory space can be shared by all the Emacs jobs running on the
143 machine at once. Pure storage is not expandable; a fixed amount is
144 allocated when Emacs is compiled, and if that is not sufficient for the
145 preloaded libraries, @file{temacs} crashes. If that happens, you must
146 increase the compilation parameter @code{PURESIZE} in the file
147 @file{src/puresize.h}. This normally won't happen unless you try to
148 preload additional libraries or add features to the standard ones.
150 @defun purecopy object
151 This function makes a copy in pure storage of @var{object}, and returns
152 it. It copies a string by simply making a new string with the same
153 characters in pure storage. It recursively copies the contents of
154 vectors and cons cells. It does not make copies of other objects such
155 as symbols, but just returns them unchanged. It signals an error if
156 asked to copy markers.
158 This function is a no-op except while Emacs is being built and dumped;
159 it is usually called only in the file @file{emacs/lisp/loaddefs.el}, but
160 a few packages call it just in case you decide to preload them.
163 @defvar pure-bytes-used
164 The value of this variable is the number of bytes of pure storage
165 allocated so far. Typically, in a dumped Emacs, this number is very
166 close to the total amount of pure storage available---if it were not,
167 we would preallocate less.
171 This variable determines whether @code{defun} should make a copy of the
172 function definition in pure storage. If it is non-@code{nil}, then the
173 function definition is copied into pure storage.
175 This flag is @code{t} while loading all of the basic functions for
176 building Emacs initially (allowing those functions to be sharable and
177 non-collectible). Dumping Emacs as an executable always writes
178 @code{nil} in this variable, regardless of the value it actually has
179 before and after dumping.
181 You should not change this flag in a running Emacs.
184 @node Garbage Collection
185 @appendixsec Garbage Collection
186 @cindex garbage collector
188 @cindex memory allocation
189 When a program creates a list or the user defines a new function (such
190 as by loading a library), that data is placed in normal storage. If
191 normal storage runs low, then Emacs asks the operating system to
192 allocate more memory in blocks of 1k bytes. Each block is used for one
193 type of Lisp object, so symbols, cons cells, markers, etc., are
194 segregated in distinct blocks in memory. (Vectors, long strings,
195 buffers and certain other editing types, which are fairly large, are
196 allocated in individual blocks, one per object, while small strings are
197 packed into blocks of 8k bytes.)
199 It is quite common to use some storage for a while, then release it by
200 (for example) killing a buffer or deleting the last pointer to an
201 object. Emacs provides a @dfn{garbage collector} to reclaim this
202 abandoned storage. (This name is traditional, but ``garbage recycler''
203 might be a more intuitive metaphor for this facility.)
205 The garbage collector operates by finding and marking all Lisp objects
206 that are still accessible to Lisp programs. To begin with, it assumes
207 all the symbols, their values and associated function definitions, and
208 any data presently on the stack, are accessible. Any objects that can
209 be reached indirectly through other accessible objects are also
212 When marking is finished, all objects still unmarked are garbage. No
213 matter what the Lisp program or the user does, it is impossible to refer
214 to them, since there is no longer a way to reach them. Their space
215 might as well be reused, since no one will miss them. The second
216 (``sweep'') phase of the garbage collector arranges to reuse them.
218 ??? Maybe add something describing weak hash tables here?
221 The sweep phase puts unused cons cells onto a @dfn{free list}
222 for future allocation; likewise for symbols and markers. It compacts
223 the accessible strings so they occupy fewer 8k blocks; then it frees the
224 other 8k blocks. Vectors, buffers, windows, and other large objects are
225 individually allocated and freed using @code{malloc} and @code{free}.
227 @cindex CL note---allocate more storage
229 @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not
230 call the garbage collector when the free list is empty. Instead, it
231 simply requests the operating system to allocate more storage, and
232 processing continues until @code{gc-cons-threshold} bytes have been
235 This means that you can make sure that the garbage collector will not
236 run during a certain portion of a Lisp program by calling the garbage
237 collector explicitly just before it (provided that portion of the
238 program does not use so much space as to force a second garbage
242 @deffn Command garbage-collect
243 This command runs a garbage collection, and returns information on
244 the amount of space in use. (Garbage collection can also occur
245 spontaneously if you use more than @code{gc-cons-threshold} bytes of
246 Lisp data since the previous garbage collection.)
248 @code{garbage-collect} returns a list containing the following
253 ((@var{used-conses} . @var{free-conses})
254 (@var{used-syms} . @var{free-syms})
256 (@var{used-miscs} . @var{free-miscs})
257 @var{used-string-chars}
258 @var{used-vector-slots}
259 (@var{used-floats} . @var{free-floats})
260 (@var{used-intervals} . @var{free-intervals}))
268 @result{} ((106886 . 13184) (9769 . 0)
269 (7731 . 4651) 347543 121628
270 (31 . 94) (1273 . 168))
274 Here is a table explaining each element:
278 The number of cons cells in use.
281 The number of cons cells for which space has been obtained from the
282 operating system, but that are not currently being used.
285 The number of symbols in use.
288 The number of symbols for which space has been obtained from the
289 operating system, but that are not currently being used.
292 The number of miscellaneous objects in use. These include markers and
293 overlays, plus certain objects not visible to users.
296 The number of miscellaneous objects for which space has been obtained
297 from the operating system, but that are not currently being used.
299 @item used-string-chars
300 The total size of all strings, in characters.
302 @item used-vector-slots
303 The total number of elements of existing vectors.
307 The number of floats in use.
311 The number of floats for which space has been obtained from the
312 operating system, but that are not currently being used.
315 The number of intervals in use. Intervals are an internal
316 data structure used for representing text properties.
319 The number of intervals for which space has been obtained
320 from the operating system, but that are not currently being used.
324 @defopt garbage-collection-messages
325 If this variable is non-@code{nil}, Emacs displays a message at the
326 beginning and end of garbage collection. The default value is
327 @code{nil}, meaning there are no such messages.
330 @defopt gc-cons-threshold
331 The value of this variable is the number of bytes of storage that must
332 be allocated for Lisp objects after one garbage collection in order to
333 trigger another garbage collection. A cons cell counts as eight bytes,
334 a string as one byte per character plus a few bytes of overhead, and so
335 on; space allocated to the contents of buffers does not count. Note
336 that the subsequent garbage collection does not happen immediately when
337 the threshold is exhausted, but only the next time the Lisp evaluator is
340 The initial threshold value is 400,000. If you specify a larger
341 value, garbage collection will happen less often. This reduces the
342 amount of time spent garbage collecting, but increases total memory use.
343 You may want to do this when running a program that creates lots of
346 You can make collections more frequent by specifying a smaller value,
347 down to 10,000. A value less than 10,000 will remain in effect only
348 until the subsequent garbage collection, at which time
349 @code{garbage-collect} will set the threshold back to 10,000.
352 The value return by @code{garbage-collect} describes the amount of
353 memory used by Lisp data, broken down by data type. By contrast, the
354 function @code{memory-limit} provides information on the total amount of
355 memory Emacs is currently using.
359 This function returns the address of the last byte Emacs has allocated,
360 divided by 1024. We divide the value by 1024 to make sure it fits in a
363 You can use this to get a general idea of how your actions affect the
368 @section Memory Usage
370 These functions and variables give information about the total amount
371 of memory allocation that Emacs has done, broken down by data type.
372 Note the difference between these and the values returned by
373 @code{(garbage-collect)}; those count objects that currently exist, but
374 these count the number or size of all allocations, including those for
375 objects that have since been freed.
377 @defvar cons-cells-consed
378 The total number of cons cells that have been allocated so far
379 in this Emacs session.
382 @defvar floats-consed
383 The total number of floats that have been allocated so far
384 in this Emacs session.
387 @defvar vector-cells-consed
388 The total number of vector cells that have been allocated so far
389 in this Emacs session.
392 @defvar symbols-consed
393 The total number of symbols that have been allocated so far
394 in this Emacs session.
397 @defvar string-chars-consed
398 The total number of string characters that have been allocated so far
399 in this Emacs session.
402 @defvar misc-objects-consed
403 The total number of miscellaneous objects that have been allocated so
404 far in this Emacs session. These include markers and overlays, plus
405 certain objects not visible to users.
408 @defvar intervals-consed
409 The total number of intervals that have been allocated so far
410 in this Emacs session.
413 @node Writing Emacs Primitives
414 @appendixsec Writing Emacs Primitives
415 @cindex primitive function internals
417 Lisp primitives are Lisp functions implemented in C. The details of
418 interfacing the C function so that Lisp can call it are handled by a few
419 C macros. The only way to really understand how to write new C code is
420 to read the source, but we can explain some things here.
422 An example of a special form is the definition of @code{or}, from
423 @file{eval.c}. (An ordinary function would have the same general
426 @cindex garbage collection protection
429 DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
430 "Eval args until one of them yields non-nil; return that value.\n\
431 The remaining args are not evalled at all.\n\
434 If all args return nil, return nil.")
438 register Lisp_Object val;
439 Lisp_Object args_left;
454 val = Feval (Fcar (args_left));
457 args_left = Fcdr (args_left);
459 while (!NILP (args_left));
469 Let's start with a precise explanation of the arguments to the
470 @code{DEFUN} macro. Here is a template for them:
473 DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc})
478 This is the name of the Lisp symbol to define as the function name; in
479 the example above, it is @code{or}.
482 This is the C function name for this function. This is
483 the name that is used in C code for calling the function. The name is,
484 by convention, @samp{F} prepended to the Lisp name, with all dashes
485 (@samp{-}) in the Lisp name changed to underscores. Thus, to call this
486 function from C code, call @code{For}. Remember that the arguments must
487 be of type @code{Lisp_Object}; various macros and functions for creating
488 values of type @code{Lisp_Object} are declared in the file
492 This is a C variable name to use for a structure that holds the data for
493 the subr object that represents the function in Lisp. This structure
494 conveys the Lisp symbol name to the initialization routine that will
495 create the symbol and store the subr object as its definition. By
496 convention, this name is always @var{fname} with @samp{F} replaced with
500 This is the minimum number of arguments that the function requires. The
501 function @code{or} allows a minimum of zero arguments.
504 This is the maximum number of arguments that the function accepts, if
505 there is a fixed maximum. Alternatively, it can be @code{UNEVALLED},
506 indicating a special form that receives unevaluated arguments, or
507 @code{MANY}, indicating an unlimited number of evaluated arguments (the
508 equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are
509 macros. If @var{max} is a number, it may not be less than @var{min} and
510 it may not be greater than seven.
513 This is an interactive specification, a string such as might be used as
514 the argument of @code{interactive} in a Lisp function. In the case of
515 @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be
516 called interactively. A value of @code{""} indicates a function that
517 should receive no arguments when called interactively.
520 This is the documentation string. It is written just like a
521 documentation string for a function defined in Lisp, except you must
522 write @samp{\n\} at the end of each line. In particular, the first line
523 should be a single sentence.
526 After the call to the @code{DEFUN} macro, you must write the argument
527 name list that every C function must have, followed by ordinary C
528 declarations for the arguments. For a function with a fixed maximum
529 number of arguments, declare a C argument for each Lisp argument, and
530 give them all type @code{Lisp_Object}. When a Lisp function has no
531 upper limit on the number of arguments, its implementation in C actually
532 receives exactly two arguments: the first is the number of Lisp
533 arguments, and the second is the address of a block containing their
534 values. They have types @code{int} and @w{@code{Lisp_Object *}}.
536 Within the function @code{For} itself, note the use of the macros
537 @code{GCPRO1} and @code{UNGCPRO}. @code{GCPRO1} is used to ``protect''
538 a variable from garbage collection---to inform the garbage collector that
539 it must look in that variable and regard its contents as an accessible
540 object. This is necessary whenever you call @code{Feval} or anything
541 that can directly or indirectly call @code{Feval}. At such a time, any
542 Lisp object that you intend to refer to again must be protected somehow.
543 @code{UNGCPRO} cancels the protection of the variables that are
544 protected in the current function. It is necessary to do this explicitly.
546 For most data types, it suffices to protect at least one pointer to
547 the object; as long as the object is not recycled, all pointers to it
548 remain valid. This is not so for strings, because the garbage collector
549 can move them. When the garbage collector moves a string, it relocates
550 all the pointers it knows about; any other pointers become invalid.
551 Therefore, you must protect all pointers to strings across any point
552 where garbage collection may be possible.
554 The macro @code{GCPRO1} protects just one local variable. If you want
555 to protect two, use @code{GCPRO2} instead; repeating @code{GCPRO1} will
556 not work. Macros @code{GCPRO3} and @code{GCPRO4} also exist.
558 These macros implicitly use local variables such as @code{gcpro1}; you
559 must declare these explicitly, with type @code{struct gcpro}. Thus, if
560 you use @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}.
561 Alas, we can't explain all the tricky details here.
563 You must not use C initializers for static or global variables unless
564 the variables are never stored in once Emacs is dumped. These variables
565 with initializers are allocated in an area of memory that becomes
566 read-only (on certain operating systems) as a result of dumping Emacs.
569 Do not use static variables within functions---place all static
570 variables at top level in the file. This is necessary because Emacs on
571 some operating systems defines the keyword @code{static} as a null
572 macro. (This definition is used because those systems put all variables
573 declared static in a place that becomes read-only after dumping, whether
574 they have initializers or not.)
576 Defining the C function is not enough to make a Lisp primitive
577 available; you must also create the Lisp symbol for the primitive and
578 store a suitable subr object in its function cell. The code looks like
582 defsubr (&@var{subr-structure-name});
586 Here @var{subr-structure-name} is the name you used as the third
587 argument to @code{DEFUN}.
589 If you add a new primitive to a file that already has Lisp primitives
590 defined in it, find the function (near the end of the file) named
591 @code{syms_of_@var{something}}, and add the call to @code{defsubr}
592 there. If the file doesn't have this function, or if you create a new
593 file, add to it a @code{syms_of_@var{filename}} (e.g.,
594 @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all
595 of these functions are called, and add a call to
596 @code{syms_of_@var{filename}} there.
598 @vindex byte-boolean-vars
599 The function @code{syms_of_@var{filename}} is also the place to define
600 any C variables that are to be visible as Lisp variables.
601 @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible
602 in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int}
603 visible in Lisp with a value that is always an integer.
604 @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp
605 with a value that is either @code{t} or @code{nil}. Note that variables
606 defined with @code{DEFVAR_BOOL} are automatically added to the list
607 @code{byte-boolean-vars} used by the byte compiler.
609 If you define a file-scope C variable of type @code{Lisp_Object},
610 you must protect it from garbage-collection by calling @code{staticpro}
611 in @code{syms_of_@var{filename}}, like this:
614 staticpro (&@var{variable});
617 Here is another example function, with more complicated arguments.
618 This comes from the code in @file{window.c}, and it demonstrates the use
619 of macros and functions to manipulate Lisp objects.
623 DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
624 Scoordinates_in_window_p, 2, 2,
625 "xSpecify coordinate pair: \nXExpression which evals to window: ",
626 "Return non-nil if COORDINATES is in WINDOW.\n\
627 COORDINATES is a cons of the form (X . Y), X and Y being distances\n\
631 If they are on the border between WINDOW and its right sibling,\n\
632 `vertical-line' is returned.")
633 (coordinates, window)
634 register Lisp_Object coordinates, window;
640 CHECK_LIVE_WINDOW (window, 0);
641 CHECK_CONS (coordinates, 1);
642 x = XINT (Fcar (coordinates));
643 y = XINT (Fcdr (coordinates));
647 switch (coordinates_in_window (XWINDOW (window), &x, &y))
649 case 0: /* NOT in window at all. */
654 case 1: /* In text part of window. */
655 return Fcons (make_number (x), make_number (y));
659 case 2: /* In mode line of window. */
664 case 3: /* On right border of window. */
665 return Qvertical_line;
676 Note that C code cannot call functions by name unless they are defined
677 in C. The way to call a function written in Lisp is to use
678 @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since
679 the Lisp function @code{funcall} accepts an unlimited number of
680 arguments, in C it takes two: the number of Lisp-level arguments, and a
681 one-dimensional array containing their values. The first Lisp-level
682 argument is the Lisp function to call, and the rest are the arguments to
683 pass to it. Since @code{Ffuncall} can call the evaluator, you must
684 protect pointers from garbage collection around the call to
687 The C functions @code{call0}, @code{call1}, @code{call2}, and so on,
688 provide handy ways to call a Lisp function conveniently with a fixed
689 number of arguments. They work by calling @code{Ffuncall}.
691 @file{eval.c} is a very good file to look through for examples;
692 @file{lisp.h} contains the definitions for some important macros and
695 If you define a function which is side-effect free, update the code in
696 @file{byte-opt.el} which binds @code{side-effect-free-fns} and
697 @code{side-effect-and-error-free-fns} to include it. This will help the
700 @node Object Internals
701 @appendixsec Object Internals
702 @cindex object internals
704 GNU Emacs Lisp manipulates many different types of data. The actual
705 data are stored in a heap and the only access that programs have to it
706 is through pointers. Pointers are thirty-two bits wide in most
707 implementations. Depending on the operating system and type of machine
708 for which you compile Emacs, twenty-eight bits are used to address the
709 object, and the remaining four bits are used for a GC mark bit and the
710 tag that identifies the object's type.
712 Because Lisp objects are represented as tagged pointers, it is always
713 possible to determine the Lisp data type of any object. The C data type
714 @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary
715 variables have type @code{Lisp_Object}, which means they can hold any
716 type of Lisp value; you can determine the actual data type only at run
717 time. The same is true for function arguments; if you want a function
718 to accept only a certain type of argument, you must check the type
719 explicitly using a suitable predicate (@pxref{Type Predicates}).
720 @cindex type checking internals
723 * Buffer Internals:: Components of a buffer structure.
724 * Window Internals:: Components of a window structure.
725 * Process Internals:: Components of a process structure.
728 @node Buffer Internals
729 @appendixsubsec Buffer Internals
730 @cindex internals, of buffer
731 @cindex buffer internals
733 Buffers contain fields not directly accessible by the Lisp programmer.
734 We describe them here, naming them by the names used in the C code.
735 Many are accessible indirectly in Lisp programs via Lisp primitives.
737 Two structures are used to represent buffers in C. The
738 @code{buffer_text} structure contains fields describing the text of a
739 buffer; the @code{buffer} structure holds other fields. In the case
740 of indirect buffers, two or more @code{buffer} structures reference
741 the same @code{buffer_text} structure.
743 Here is a list of the @code{struct buffer_text} fields:
747 This field contains the Actual address of the buffer contents.
750 This holds the character position of the gap in the buffer.
753 This field contains the character position of the end of the buffer
757 Contains the byte position of the gap.
760 Holds the byte position of the end of the buffer text.
763 Contains the size of buffer's gap.
766 This field counts buffer-modification events for this buffer. It is
767 incremented for each such event, and never otherwise changed.
770 Contains the previous value of @code{modiff}, as of the last time a
771 buffer was visited or saved in a file.
774 Counts modifications to overlays analogous to @code{modiff}.
777 Holds the number of characters at the start of the text that are known
778 to be unchanged since the last redisplay that finished.
781 Holds the number of characters at the end of the text that are known to
782 be unchanged since the last redisplay that finished.
784 @item unchanged_modified
785 Contains the value of @code{modiff} at the time of the last redisplay
786 that finished. If this value matches @code{modiff},
787 @code{beg_unchanged} and @code{end_unchanged} contain no useful
790 @item overlay_unchanged_modified
791 Contains the value of @code{overlay_modiff} at the time of the last
792 redisplay that finished. If this value matches @code{overlay_modiff},
793 @code{beg_unchanged} and @code{end_unchanged} contain no useful
797 The markers that refer to this buffer. This is actually a single
798 marker, and successive elements in its marker @code{chain} are the other
799 markers referring to this buffer text.
802 Contains the interval tree which records the text properties of this
806 The fields of @code{struct buffer} are:
810 Points to the next buffer, in the chain of all buffers including killed
811 buffers. This chain is used only for garbage collection, in order to
812 collect killed buffers properly. Note that vectors, and most kinds of
813 objects allocated as vectors, are all on one chain, but buffers are on a
814 separate chain of their own.
817 This is a @code{struct buffer_text} structure. In an ordinary buffer,
818 it holds the buffer contents. In indirect buffers, this field is not
822 This points to the @code{buffer_text} structure that is used for this
823 buffer. In an ordinary buffer, this is the @code{own_text} field above.
824 In an indirect buffer, this is the @code{own_text} field of the base
828 Contains the character position of point in a buffer.
831 Contains the byte position of point in a buffer.
834 This field contains the character position of the beginning of the
835 accessible range of text in the buffer.
838 This field contains the byte position of the beginning of the
839 accessible range of text in the buffer.
842 This field contains the character position of the end of the
843 accessible range of text in the buffer.
846 This field contains the byte position of the end of the
847 accessible range of text in the buffer.
850 In an indirect buffer, this points to the base buffer. In an ordinary
853 @item local_var_flags
854 This field contains flags indicating that certain variables are local in
855 this buffer. Such variables are declared in the C code using
856 @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored in
857 fields in the buffer structure itself. (Some of these fields are
858 described in this table.)
861 This field contains the modification time of the visited file. It is
862 set when the file is written or read. Before writing the buffer into a
863 file, this field is compared to the modification time of the file to see
864 if the file has changed on disk. @xref{Buffer Modification}.
866 @item auto_save_modified
867 This field contains the time when the buffer was last auto-saved.
869 @item auto_save_failure_time
870 The time at which we detected a failure to auto-save, or -1 if we didn't
873 @item last_window_start
874 This field contains the @code{window-start} position in the buffer as of
875 the last time the buffer was displayed in a window.
878 This flag is set when narrowing changes in a buffer.
880 @item prevent_redisplay_optimizations_p
881 A flag indicating the redisplay optiomizations should not be used
882 to display this buffer.
885 This field points to the buffer's undo list. @xref{Undo}.
888 The buffer name is a string that names the buffer. It is guaranteed to
889 be unique. @xref{Buffer Names}.
892 The name of the file visited in this buffer, or @code{nil}.
895 The directory for expanding relative file names.
898 Length of the file this buffer is visiting, when last read or saved.
899 This and other fields concerned with saving are not kept in the
900 @code{buffer_text} structure because indirect buffers are never saved.
902 @item auto_save_file_name
903 File name used for auto-saving this buffer. This is not in the
904 @code{buffer_text} because it's not used in indirect buffers at all.
907 Non-@code{nil} means this buffer is read-only.
910 This field contains the mark for the buffer. The mark is a marker,
911 hence it is also included on the list @code{markers}. @xref{The Mark}.
913 @item local_var_alist
914 This field contains the association list describing the buffer-local
915 variable bindings of this buffer, not including the built-in
916 buffer-local bindings that have special slots in the buffer object.
917 (Those slots are omitted from this table.) @xref{Buffer-Local
921 Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}.
924 Pretty name of major mode, e.g., @code{"Lisp"}.
926 @item mode_line_format
927 Mode line element that controls the format of the mode line. If this
928 is @code{nil}, no mode line will be displayed.
930 @item header_line_format
931 This field is analoguous to @code{mode_line_format} for the mode
932 line displayed at the top of windows.
935 This field holds the buffer's local keymap. @xref{Keymaps}.
938 This buffer's local abbrevs.
941 This field contains the syntax table for the buffer. @xref{Syntax Tables}.
944 This field contains the category table for the buffer.
946 @item case_fold_search
947 The value of @code{case-fold-search} in this buffer.
950 The value of @code{tab-width} in this buffer.
953 The value of @code{fill-column} in this buffer.
956 The value of @code{left-margin} in this buffer.
958 @item auto_fill_function
959 The value of @code{auto-fill-function} in this buffer.
962 This field contains the conversion table for converting text to lower case.
966 This field contains the conversion table for converting text to upper case.
969 @item case_canon_table
970 This field contains the conversion table for canonicalizing text for
971 case-folding search. @xref{Case Tables}.
974 This field contains the equivalence table for case-folding search.
978 The value of @code{truncate-lines} in this buffer.
981 The value of @code{ctl-arrow} in this buffer.
983 @item selective_display
984 The value of @code{selective-display} in this buffer.
986 @item selective_display_ellipsis
987 The value of @code{selective-display-ellipsis} in this buffer.
990 An alist of the minor modes of this buffer.
993 The value of @code{overwrite_mode} in this buffer.
996 The value of @code{abbrev-mode} in this buffer.
999 This field contains the buffer's display table, or @code{nil} if it doesn't
1000 have one. @xref{Display Tables}.
1003 This field contains the time when the buffer was last saved, as an integer.
1004 @xref{Buffer Modification}.
1007 This field is non-@code{nil} if the buffer's mark is active.
1009 @item overlays_before
1010 This field holds a list of the overlays in this buffer that end at or
1011 before the current overlay center position. They are sorted in order of
1012 decreasing end position.
1014 @item overlays_after
1015 This field holds a list of the overlays in this buffer that end after
1016 the current overlay center position. They are sorted in order of
1017 increasing beginning position.
1019 @item overlay_center
1020 This field holds the current overlay center position. @xref{Overlays}.
1022 @item enable_multibyte_characters
1023 This field holds the buffer's local value of
1024 @code{enable-multibyte-characters}---either @code{t} or @code{nil}.
1026 @item buffer_file_coding_system
1027 The value of @code{buffer-file-coding-system} in this buffer.
1030 The value of @code{buffer-file-format} in this buffer.
1033 In an indirect buffer, or a buffer that is the base of an indirect
1034 buffer, this holds a marker that records point for this buffer when the
1035 buffer is not current.
1038 In an indirect buffer, or a buffer that is the base of an indirect
1039 buffer, this holds a marker that records @code{begv} for this buffer
1040 when the buffer is not current.
1043 In an indirect buffer, or a buffer that is the base of an indirect
1044 buffer, this holds a marker that records @code{zv} for this buffer when
1045 the buffer is not current.
1048 The truename of the visited file, or @code{nil}.
1050 @item invisibility_spec
1051 The value of @code{buffer-invisibility-spec} in this buffer.
1053 @item last_selected_window
1054 This is the last window that was selected with this buffer in it, or @code{nil}
1055 if that window no longer displays this buffer.
1058 This field is incremented each time the buffer is displayed in a window.
1060 @item left_margin_width
1061 The value of @code{left-margin-width} in this buffer.
1063 @item right_margin_width
1064 The value of @code{right-margin-width} in this buffer.
1066 @item indicate_empty_lines
1067 Non-@code{nil} means indicate empty lines (lines with no text) with a
1068 small bitmap in the fringe, when using a window system that can do it.
1071 This holds a time stamp that is updated each time this buffer is
1072 displayed in a window.
1074 @item scroll_up_aggressively
1075 The value of @code{scroll-up-aggressively} in this buffer.
1077 @item scroll_down_aggressively
1078 The value of @code{scroll-down-aggressively} in this buffer.
1081 @node Window Internals
1082 @appendixsubsec Window Internals
1083 @cindex internals, of window
1084 @cindex window internals
1086 Windows have the following accessible fields:
1090 The frame that this window is on.
1093 Non-@code{nil} if this window is a minibuffer window.
1096 Internally, Emacs arranges windows in a tree; each group of siblings has
1097 a parent window whose area includes all the siblings. This field points
1098 to a window's parent.
1100 Parent windows do not display buffers, and play little role in display
1101 except to shape their child windows. Emacs Lisp programs usually have
1102 no access to the parent windows; they operate on the windows at the
1103 leaves of the tree, which actually display buffers.
1105 The following four fields also describe the window tree structure.
1108 In a window subdivided horizontally by child windows, the leftmost child.
1109 Otherwise, @code{nil}.
1112 In a window subdivided vertically by child windows, the topmost child.
1113 Otherwise, @code{nil}.
1116 The next sibling of this window. It is @code{nil} in a window that is
1117 the rightmost or bottommost of a group of siblings.
1120 The previous sibling of this window. It is @code{nil} in a window that
1121 is the leftmost or topmost of a group of siblings.
1124 This is the left-hand edge of the window, measured in columns. (The
1125 leftmost column on the screen is @w{column 0}.)
1128 This is the top edge of the window, measured in lines. (The top line on
1129 the screen is @w{line 0}.)
1132 The height of the window, measured in lines.
1135 The width of the window, measured in columns. This width includes the
1136 scroll bar and fringes, and/or the separator line on the right of the
1140 The buffer that the window is displaying. This may change often during
1141 the life of the window.
1144 The position in the buffer that is the first character to be displayed
1148 @cindex window point internals
1149 This is the value of point in the current buffer when this window is
1150 selected; when it is not selected, it retains its previous value.
1153 If this flag is non-@code{nil}, it says that the window has been
1154 scrolled explicitly by the Lisp program. This affects what the next
1155 redisplay does if point is off the screen: instead of scrolling the
1156 window to show the text around point, it moves point to a location that
1159 @item frozen_window_start_p
1160 This field is set temporarily to 1 to indicate to redisplay that
1161 @code{start} of this window should not be changed, even if point
1164 @item start_at_line_beg
1165 Non-@code{nil} means current value of @code{start} was the beginning of a line
1169 Non-@code{nil} means don't delete this window for becoming ``too small''.
1171 @item height_fixed_p
1172 This field is temporarily set to 1 to fix the height of the selected
1173 window when the echo area is resized.
1176 This is the last time that the window was selected. The function
1177 @code{get-lru-window} uses this field.
1179 @item sequence_number
1180 A unique number assigned to this window when it was created.
1183 The @code{modiff} field of the window's buffer, as of the last time
1184 a redisplay completed in this window.
1186 @item last_overlay_modified
1187 The @code{overlay_modiff} field of the window's buffer, as of the last
1188 time a redisplay completed in this window.
1191 The buffer's value of point, as of the last time a redisplay completed
1195 A non-@code{nil} value means the window's buffer was ``modified'' when the
1196 window was last updated.
1198 @item vertical_scroll_bar
1199 This window's vertical scroll bar.
1201 @item left_margin_width
1202 The width of the left margin in this window, or @code{nil} not to
1203 specify it (in which case the buffer's value of @code{left-margin-width}
1206 @item right_margin_width
1207 Likewise for the right margin.
1215 @item window_end_pos
1216 This is computed as @code{z} minus the buffer position of the last glyph
1217 in the current matrix of the window. The value is only valid if
1218 @code{window_end_valid} is not @code{nil}.
1220 @item window_end_bytepos
1221 The byte position corresponding to @code{window_end_pos}.
1223 @item window_end_vpos
1224 The window-relative vertical position of the line containing
1225 @code{window_end_pos}.
1227 @item window_end_valid
1228 This field is set to a non-@code{nil} value if @code{window_end_pos} is truly
1229 valid. This is @code{nil} if nontrivial redisplay is preempted since in that
1230 case the display that @code{window_end_pos} was computed for did not get
1233 @item redisplay_end_trigger
1234 If redisplay in this window goes beyond this buffer position, it runs
1235 run the @code{redisplay-end-trigger-hook}.
1240 ??? Are temporary storage areas.
1244 A structure describing where the cursor is in this window.
1247 The value of @code{cursor} as of the last redisplay that finished.
1250 A structure describing where the cursor of this window physically is.
1252 @item phys_cursor_type
1253 The type of cursor that was last displayed on this window.
1255 @item phys_cursor_on_p
1256 This field is non-zero if the cursor is physically on.
1259 Non-zero means the cursor in this window is logically on.
1261 @item last_cursor_off_p
1262 This field contains the value of @code{cursor_off_p} as of the time of
1265 @item must_be_updated_p
1266 This is set to 1 during redisplay when this window must be updated.
1269 This is the number of columns that the display in the window is scrolled
1270 horizontally to the left. Normally, this is 0.
1273 Vertical scroll amount, in pixels. Normally, this is 0.
1276 Non-@code{nil} if this window is dedicated to its buffer.
1279 The window's display table, or @code{nil} if none is specified for it.
1281 @item update_mode_line
1282 Non-@code{nil} means this window's mode line needs to be updated.
1284 @item base_line_number
1285 The line number of a certain position in the buffer, or @code{nil}.
1286 This is used for displaying the line number of point in the mode line.
1289 The position in the buffer for which the line number is known, or
1290 @code{nil} meaning none is known.
1292 @item region_showing
1293 If the region (or part of it) is highlighted in this window, this field
1294 holds the mark position that made one end of that region. Otherwise,
1295 this field is @code{nil}.
1297 @item column_number_displayed
1298 The column number currently displayed in this window's mode line, or @code{nil}
1299 if column numbers are not being displayed.
1301 @item current_matrix
1302 A glyph matrix describing the current display of this window.
1304 @item desired_matrix
1305 A glyph matrix describing the desired display of this window.
1308 @node Process Internals
1309 @appendixsubsec Process Internals
1310 @cindex internals, of process
1311 @cindex process internals
1313 The fields of a process are:
1317 A string, the name of the process.
1320 A list containing the command arguments that were used to start this
1324 A function used to accept output from the process instead of a buffer,
1328 A function called whenever the process receives a signal, or @code{nil}.
1331 The associated buffer of the process.
1334 An integer, the Unix process @sc{id}.
1337 A flag, non-@code{nil} if this is really a child process.
1338 It is @code{nil} for a network connection.
1341 A marker indicating the position of the end of the last output from this
1342 process inserted into the buffer. This is often but not always the end
1345 @item kill_without_query
1346 If this is non-@code{nil}, killing Emacs while this process is still
1347 running does not ask for confirmation about killing the process.
1349 @item raw_status_low
1350 @itemx raw_status_high
1351 These two fields record 16 bits each of the process status returned by
1352 the @code{wait} system call.
1355 The process status, as @code{process-status} should return it.
1359 If these two fields are not equal, a change in the status of the process
1360 needs to be reported, either by running the sentinel or by inserting a
1361 message in the process buffer.
1364 Non-@code{nil} if communication with the subprocess uses a @sc{pty};
1365 @code{nil} if it uses a pipe.
1368 The file descriptor for input from the process.
1371 The file descriptor for output to the process.
1374 The file descriptor for the terminal that the subprocess is using. (On
1375 some systems, there is no need to record this, so the value is
1379 The name of the terminal that the subprocess is using,
1380 or @code{nil} if it is using pipes.
1382 @item decode_coding_system
1383 Coding-system for decoding the input from this process.
1386 A working buffer for decoding.
1388 @item decoding_carryover
1389 Size of carryover in decoding.
1391 @item encode_coding_system
1392 Coding-system for encoding the output to this process.
1395 A working buffer for enecoding.
1397 @item encoding_carryover
1398 Size of carryover in encoding.
1400 @item inherit_coding_system_flag
1401 Flag to set @code{coding-system} of the process buffer from the
1402 coding system used to decode process output.