2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993 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 preload Lisp libraries into Emacs.
16 * Pure Storage:: A kludge to make preloaded Lisp functions sharable.
17 * Garbage Collection:: Reclaiming space for Lisp objects no longer used.
18 * Writing Emacs Primitives:: Writing C code for Emacs.
19 * Object Internals:: Data formats of buffers, windows, processes.
22 @node Building Emacs, Pure Storage, GNU Emacs Internals, GNU Emacs Internals
23 @appendixsec Building Emacs
24 @cindex building Emacs
27 This section explains the steps involved in building the Emacs
28 executable. You don't have to know this material to build and install
29 Emacs, since the makefiles do all these things automatically. This
30 information is pertinent to Emacs maintenance.
32 Compilation of the C source files in the @file{src} directory
33 produces an executable file called @file{temacs}, also called a
34 @dfn{bare impure Emacs}. It contains the Emacs Lisp interpreter and I/O
35 routines, but not the editing commands.
37 @cindex @file{loadup.el}
38 The command @w{@samp{temacs -l loadup}} uses @file{temacs} to create
39 the real runnable Emacs executable. These arguments direct
40 @file{temacs} to evaluate the Lisp files specified in the file
41 @file{loadup.el}. These files set up the normal Emacs editing
42 environment, resulting in an Emacs that is still impure but no longer
45 It takes a substantial time to load the standard Lisp files. Luckily,
46 you don't have to do this each time you run Emacs; @file{temacs} can
47 dump out an executable program called @file{emacs} that has these files
48 preloaded. @file{emacs} starts more quickly because it does not need to
49 load the files. This is the Emacs executable that is normally
52 To create @file{emacs}, use the command @samp{temacs -batch -l loadup
53 dump}. The purpose of @samp{-batch} here is to prevent @file{temacs}
54 from trying to initialize any of its data on the terminal; this ensures
55 that the tables of terminal information are empty in the dumped Emacs.
56 The argument @samp{dump} tells @file{loadup.el} to dump a new executable
59 Some operating systems don't support dumping. On those systems, you
60 must start Emacs with the @samp{temacs -l loadup} command each time you
61 use it. This takes a substantial time, but since you need to start
62 Emacs once a day at most---or once a week if you never log out---the
63 extra time is not too severe a problem.
65 @cindex @file{site-load.el}
66 You can specify additional files to preload by writing a library named
67 @file{site-load.el} that loads them. You may need to increase the
68 value of @code{PURESIZE}, in @file{src/puresize.h}, to make room for the
69 additional files. (Try adding increments of 20000 until it is big
70 enough.) However, the advantage of preloading additional files
71 decreases as machines get faster. On modern machines, it is usually not
74 @cindex @file{site-init.el}
75 You can specify other Lisp expressions to execute just before dumping
76 by putting them in a library named @file{site-init.el}. However, if
77 they might alter the behavior that users expect from an ordinary
78 unmodified Emacs, it is better to put them in @file{default.el}, so that
79 users can override them if they wish. @xref{Start-up Summary}.
81 Before @file{loadup.el} dumps the new executable, it finds the
82 documentation strings for primitive and preloaded functions (and
83 variables) in the file where they are stored, by calling
84 @code{Snarf-documentation} (@pxref{Accessing Documentation}). These
85 strings were moved out of the @file{emacs} executable to make it
86 smaller. @xref{Documentation Basics}.
88 @defun dump-emacs to-file from-file
90 This function dumps the current state of Emacs into an executable file
91 @var{to-file}. It takes symbols from @var{from-file} (this is normally
92 the executable file @file{temacs}).
94 If you use this function in an Emacs that was already dumped, you must
95 set @code{command-line-processed} to @code{nil} first for good results.
96 @xref{Command Line Arguments}.
99 @deffn Command emacs-version
100 This function returns a string describing the version of Emacs that is
101 running. It is useful to include this string in bug reports.
106 @result{} "GNU Emacs 19.29.1 (i386-debian-linux) \
107 of Tue Jun 6 1995 on balloon"
111 Called interactively, the function prints the same information in the
115 @defvar emacs-build-time
116 The value of this variable is the time at which Emacs was built at the
122 @result{} "Tue Jun 6 14:55:57 1995"
127 @defvar emacs-version
128 The value of this variable is the version of Emacs being run. It is a
129 string such as @code{"19.29.1"}.
132 The following two variables did not exist before Emacs version 19.23,
133 which reduces their usefulness at present, but we hope they will be
134 convenient in the future.
136 @defvar emacs-major-version
137 The major version number of Emacs, as an integer. For Emacs version
138 19.29, the value is 19.
141 @defvar emacs-minor-version
142 The minor version number of Emacs, as an integer. For Emacs version
143 19.29, the value is 29.
146 @node Pure Storage, Garbage Collection, Building Emacs, GNU Emacs Internals
147 @appendixsec Pure Storage
150 Emacs Lisp uses two kinds of storage for user-created Lisp objects:
151 @dfn{normal storage} and @dfn{pure storage}. Normal storage is where
152 all the new data created during an Emacs session is kept; see the
153 following section for information on normal storage. Pure storage is
154 used for certain data in the preloaded standard Lisp files---data that
155 should never change during actual use of Emacs.
157 Pure storage is allocated only while @file{temacs} is loading the
158 standard preloaded Lisp libraries. In the file @file{emacs}, it is
159 marked as read-only (on operating systems that permit this), so that
160 the memory space can be shared by all the Emacs jobs running on the
161 machine at once. Pure storage is not expandable; a fixed amount is
162 allocated when Emacs is compiled, and if that is not sufficient for the
163 preloaded libraries, @file{temacs} crashes. If that happens, you must
164 increase the compilation parameter @code{PURESIZE} in the file
165 @file{src/puresize.h}. This normally won't happen unless you try to
166 preload additional libraries or add features to the standard ones.
168 @defun purecopy object
169 This function makes a copy of @var{object} in pure storage and returns
170 it. It copies strings by simply making a new string with the same
171 characters in pure storage. It recursively copies the contents of
172 vectors and cons cells. It does not make copies of other objects such
173 as symbols, but just returns them unchanged. It signals an error if
174 asked to copy markers.
176 This function is a no-op except while Emacs is being built and dumped;
177 it is usually called only in the file @file{emacs/lisp/loaddefs.el}, but
178 a few packages call it just in case you decide to preload them.
181 @defvar pure-bytes-used
182 The value of this variable is the number of bytes of pure storage
183 allocated so far. Typically, in a dumped Emacs, this number is very
184 close to the total amount of pure storage available---if it were not,
185 we would preallocate less.
189 This variable determines whether @code{defun} should make a copy of the
190 function definition in pure storage. If it is non-@code{nil}, then the
191 function definition is copied into pure storage.
193 This flag is @code{t} while loading all of the basic functions for
194 building Emacs initially (allowing those functions to be sharable and
195 non-collectible). Dumping Emacs as an executable always writes
196 @code{nil} in this variable, regardless of the value it actually has
197 before and after dumping.
199 You should not change this flag in a running Emacs.
202 @node Garbage Collection, Writing Emacs Primitives, Pure Storage, GNU Emacs Internals
203 @appendixsec Garbage Collection
204 @cindex garbage collector
206 @cindex memory allocation
207 When a program creates a list or the user defines a new function (such
208 as by loading a library), that data is placed in normal storage. If
209 normal storage runs low, then Emacs asks the operating system to
210 allocate more memory in blocks of 1k bytes. Each block is used for one
211 type of Lisp object, so symbols, cons cells, markers, etc., are
212 segregated in distinct blocks in memory. (Vectors, long strings,
213 buffers and certain other editing types, which are fairly large, are
214 allocated in individual blocks, one per object, while small strings are
215 packed into blocks of 8k bytes.)
217 It is quite common to use some storage for a while, then release it by
218 (for example) killing a buffer or deleting the last pointer to an
219 object. Emacs provides a @dfn{garbage collector} to reclaim this
220 abandoned storage. (This name is traditional, but ``garbage recycler''
221 might be a more intuitive metaphor for this facility.)
223 The garbage collector operates by finding and marking all Lisp objects
224 that are still accessible to Lisp programs. To begin with, it assumes
225 all the symbols, their values and associated function definitions, and
226 any data presently on the stack, are accessible. Any objects that can
227 be reached indirectly through other accessible objects are also
230 When marking is finished, all objects still unmarked are garbage. No
231 matter what the Lisp program or the user does, it is impossible to refer
232 to them, since there is no longer a way to reach them. Their space
233 might as well be reused, since no one will miss them. The second
234 (``sweep'') phase of the garbage collector arranges to reuse them.
237 The sweep phase puts unused cons cells onto a @dfn{free list}
238 for future allocation; likewise for symbols and markers. It compacts
239 the accessible strings so they occupy fewer 8k blocks; then it frees the
240 other 8k blocks. Vectors, buffers, windows, and other large objects are
241 individually allocated and freed using @code{malloc} and @code{free}.
243 @cindex CL note---allocate more storage
245 @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not
246 call the garbage collector when the free list is empty. Instead, it
247 simply requests the operating system to allocate more storage, and
248 processing continues until @code{gc-cons-threshold} bytes have been
251 This means that you can make sure that the garbage collector will not
252 run during a certain portion of a Lisp program by calling the garbage
253 collector explicitly just before it (provided that portion of the
254 program does not use so much space as to force a second garbage
258 @deffn Command garbage-collect
259 This command runs a garbage collection, and returns information on
260 the amount of space in use. (Garbage collection can also occur
261 spontaneously if you use more than @code{gc-cons-threshold} bytes of
262 Lisp data since the previous garbage collection.)
264 @code{garbage-collect} returns a list containing the following
269 ((@var{used-conses} . @var{free-conses})
270 (@var{used-syms} . @var{free-syms})
272 (@var{used-markers} . @var{free-markers})
273 @var{used-string-chars}
274 @var{used-vector-slots}
275 (@var{used-floats} . @var{free-floats}))
279 @result{} ((3435 . 2332) (1688 . 0)
280 (57 . 417) 24510 3839 (4 . 1))
284 Here is a table explaining each element:
288 The number of cons cells in use.
291 The number of cons cells for which space has been obtained from the
292 operating system, but that are not currently being used.
295 The number of symbols in use.
298 The number of symbols for which space has been obtained from the
299 operating system, but that are not currently being used.
302 The number of markers in use.
305 The number of markers for which space has been obtained from the
306 operating system, but that are not currently being used.
308 @item used-string-chars
309 The total size of all strings, in characters.
311 @item used-vector-slots
312 The total number of elements of existing vectors.
316 The number of floats in use.
320 The number of floats for which space has been obtained from the
321 operating system, but that are not currently being used.
325 @defopt gc-cons-threshold
326 The value of this variable is the number of bytes of storage that must
327 be allocated for Lisp objects after one garbage collection in order to
328 trigger another garbage collection. A cons cell counts as eight bytes,
329 a string as one byte per character plus a few bytes of overhead, and so
330 on; space allocated to the contents of buffers does not count. Note
331 that the subsequent garbage collection does not happen immediately when
332 the threshold is exhausted, but only the next time the Lisp evaluator is
335 The initial threshold value is 300,000. If you specify a larger
336 value, garbage collection will happen less often. This reduces the
337 amount of time spent garbage collecting, but increases total memory use.
338 You may want to do this when running a program that creates lots of
341 You can make collections more frequent by specifying a smaller value,
342 down to 10,000. A value less than 10,000 will remain in effect only
343 until the subsequent garbage collection, at which time
344 @code{garbage-collect} will set the threshold back to 10,000.
349 This function returns the address of the last byte Emacs has allocated,
350 divided by 1024. We divide the value by 1024 to make sure it fits in a
353 You can use this to get a general idea of how your actions affect the
357 @node Writing Emacs Primitives, Object Internals, Garbage Collection, GNU Emacs Internals
358 @appendixsec Writing Emacs Primitives
359 @cindex primitive function internals
361 Lisp primitives are Lisp functions implemented in C. The details of
362 interfacing the C function so that Lisp can call it are handled by a few
363 C macros. The only way to really understand how to write new C code is
364 to read the source, but we can explain some things here.
366 An example of a special form is the definition of @code{or}, from
367 @file{eval.c}. (An ordinary function would have the same general
370 @cindex garbage collection protection
373 DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
374 "Eval args until one of them yields non-nil, then return that value.\n\
375 The remaining args are not evalled at all.\n\
378 If all args return nil, return nil.")
382 register Lisp_Object val;
383 Lisp_Object args_left;
398 val = Feval (Fcar (args_left));
401 args_left = Fcdr (args_left);
403 while (!NULL (args_left));
413 Let's start with a precise explanation of the arguments to the
414 @code{DEFUN} macro. Here is a template for them:
417 DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc})
422 This is the name of the Lisp symbol to define as the function name; in
423 the example above, it is @code{or}.
426 This is the C function name for this function. This is
427 the name that is used in C code for calling the function. The name is,
428 by convention, @samp{F} prepended to the Lisp name, with all dashes
429 (@samp{-}) in the Lisp name changed to underscores. Thus, to call this
430 function from C code, call @code{For}. Remember that the arguments must
431 be of type @code{Lisp_Object}; various macros and functions for creating
432 values of type @code{Lisp_Object} are declared in the file
436 This is a C variable name to use for a structure that holds the data for
437 the subr object that represents the function in Lisp. This structure
438 conveys the Lisp symbol name to the initialization routine that will
439 create the symbol and store the subr object as its definition. By
440 convention, this name is always @var{fname} with @samp{F} replaced with
444 This is the minimum number of arguments that the function requires. The
445 function @code{or} allows a minimum of zero arguments.
448 This is the maximum number of arguments that the function accepts, if
449 there is a fixed maximum. Alternatively, it can be @code{UNEVALLED},
450 indicating a special form that receives unevaluated arguments, or
451 @code{MANY}, indicating an unlimited number of evaluated arguments (the
452 equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are
453 macros. If @var{max} is a number, it may not be less than @var{min} and
454 it may not be greater than seven.
457 This is an interactive specification, a string such as might be used as
458 the argument of @code{interactive} in a Lisp function. In the case of
459 @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be
460 called interactively. A value of @code{""} indicates a function that
461 should receive no arguments when called interactively.
464 This is the documentation string. It is written just like a
465 documentation string for a function defined in Lisp, except you must
466 write @samp{\n\} at the end of each line. In particular, the first line
467 should be a single sentence.
470 After the call to the @code{DEFUN} macro, you must write the argument
471 name list that every C function must have, followed by ordinary C
472 declarations for the arguments. For a function with a fixed maximum
473 number of arguments, declare a C argument for each Lisp argument, and
474 give them all type @code{Lisp_Object}. When a Lisp function has no
475 upper limit on the number of arguments, its implementation in C actually
476 receives exactly two arguments: the first is the number of Lisp
477 arguments, and the second is the address of a block containing their
478 values. They have types @code{int} and @w{@code{Lisp_Object *}}.
480 Within the function @code{For} itself, note the use of the macros
481 @code{GCPRO1} and @code{UNGCPRO}. @code{GCPRO1} is used to ``protect''
482 a variable from garbage collection---to inform the garbage collector that
483 it must look in that variable and regard its contents as an accessible
484 object. This is necessary whenever you call @code{Feval} or anything
485 that can directly or indirectly call @code{Feval}. At such a time, any
486 Lisp object that you intend to refer to again must be protected somehow.
487 @code{UNGCPRO} cancels the protection of the variables that are
488 protected in the current function. It is necessary to do this explicitly.
490 For most data types, it suffices to protect at least one pointer to
491 the object; as long as the object is not recycled, all pointers to it
492 remain valid. This is not so for strings, because the garbage collector
493 can move them. When the garbage collector moves a string, it relocates
494 all the pointers it knows about; any other pointers become invalid.
495 Therefore, you must protect all pointers to strings across any point
496 where garbage collection may be possible.
498 The macro @code{GCPRO1} protects just one local variable. If you want
499 to protect two, use @code{GCPRO2} instead; repeating @code{GCPRO1} will
500 not work. Macros @code{GCPRO3} and @code{GCPRO4} also exist.
502 These macros implicitly use local variables such as @code{gcpro1}; you
503 must declare these explicitly, with type @code{struct gcpro}. Thus, if
504 you use @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}.
505 Alas, we can't explain all the tricky details here.
507 You must not use C initializers for static or global variables unless
508 they are never written once Emacs is dumped. These variables with
509 initializers are allocated in an area of memory that becomes read-only
510 (on certain operating systems) as a result of dumping Emacs. @xref{Pure
513 Do not use static variables within functions---place all static
514 variables at top level in the file. This is necessary because Emacs on
515 some operating systems defines the keyword @code{static} as a null
516 macro. (This definition is used because those systems put all variables
517 declared static in a place that becomes read-only after dumping, whether
518 they have initializers or not.)
520 Defining the C function is not enough to make a Lisp primitive
521 available; you must also create the Lisp symbol for the primitive and
522 store a suitable subr object in its function cell. The code looks like
526 defsubr (&@var{subr-structure-name});
530 Here @var{subr-structure-name} is the name you used as the third
531 argument to @code{DEFUN}.
533 If you add a new primitive to a file that already has Lisp primitives
534 defined in it, find the function (near the end of the file) named
535 @code{syms_of_@var{something}}, and add the call to @code{defsubr}
536 there. If the file doesn't have this function, or if you create a new
537 file, add to it a @code{syms_of_@var{filename}} (e.g.,
538 @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all
539 of these functions are called, and add a call to
540 @code{syms_of_@var{filename}} there.
542 The function @code{syms_of_@var{filename}} is also the place to define
543 any C variables that are to be visible as Lisp variables.
544 @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible
545 in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int}
546 visible in Lisp with a value that is always an integer.
547 @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp
548 with a value that is either @code{t} or @code{nil}.
550 Here is another example function, with more complicated arguments.
551 This comes from the code for the X Window System, and it demonstrates
552 the use of macros and functions to manipulate Lisp objects.
556 DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
557 Scoordinates_in_window_p, 2, 2,
558 "xSpecify coordinate pair: \nXExpression which evals to window: ",
559 "Return non-nil if POSITIONS is in WINDOW.\n\
560 \(POSITIONS is a list, (SCREEN-X SCREEN-Y)\)\n\
563 Returned value is list of positions expressed\n\
564 relative to window upper left corner.")
566 register Lisp_Object coordinate, window;
568 register Lisp_Object xcoord, ycoord;
572 if (!CONSP (coordinate)) wrong_type_argument (Qlistp, coordinate);
573 CHECK_WINDOW (window, 2);
574 xcoord = Fcar (coordinate);
575 ycoord = Fcar (Fcdr (coordinate));
576 CHECK_NUMBER (xcoord, 0);
577 CHECK_NUMBER (ycoord, 1);
580 if ((XINT (xcoord) < XINT (XWINDOW (window)->left))
581 || (XINT (xcoord) >= (XINT (XWINDOW (window)->left)
582 + XINT (XWINDOW (window)->width))))
584 XFASTINT (xcoord) -= XFASTINT (XWINDOW (window)->left);
587 if (XINT (ycoord) == (screen_height - 1))
591 if ((XINT (ycoord) < XINT (XWINDOW (window)->top))
592 || (XINT (ycoord) >= (XINT (XWINDOW (window)->top)
593 + XINT (XWINDOW (window)->height)) - 1))
597 XFASTINT (ycoord) -= XFASTINT (XWINDOW (window)->top);
598 return (Fcons (xcoord, Fcons (ycoord, Qnil)));
603 Note that C code cannot call functions by name unless they are defined
604 in C. The way to call a function written in Lisp is to use
605 @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since
606 the Lisp function @code{funcall} accepts an unlimited number of
607 arguments, in C it takes two: the number of Lisp-level arguments, and a
608 one-dimensional array containing their values. The first Lisp-level
609 argument is the Lisp function to call, and the rest are the arguments to
610 pass to it. Since @code{Ffuncall} can call the evaluator, you must
611 protect pointers from garbage collection around the call to
614 The C functions @code{call0}, @code{call1}, @code{call2}, and so on,
615 provide handy ways to call a Lisp function conveniently with a fixed
616 number of arguments. They work by calling @code{Ffuncall}.
618 @file{eval.c} is a very good file to look through for examples;
619 @file{lisp.h} contains the definitions for some important macros and
622 @node Object Internals, , Writing Emacs Primitives, GNU Emacs Internals
623 @appendixsec Object Internals
624 @cindex object internals
626 GNU Emacs Lisp manipulates many different types of data. The actual
627 data are stored in a heap and the only access that programs have to it is
628 through pointers. Pointers are thirty-two bits wide in most
629 implementations. Depending on the operating system and type of machine
630 for which you compile Emacs, twenty-four to twenty-six bits are used to
631 address the object, and the remaining six to eight bits are used for a
632 tag that identifies the object's type.
634 Because Lisp objects are represented as tagged pointers, it is always
635 possible to determine the Lisp data type of any object. The C data type
636 @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary
637 variables have type @code{Lisp_Object}, which means they can hold any
638 type of Lisp value; you can determine the actual data type only at run
639 time. The same is true for function arguments; if you want a function
640 to accept only a certain type of argument, you must check the type
641 explicitly using a suitable predicate (@pxref{Type Predicates}).
642 @cindex type checking internals
645 * Buffer Internals:: Components of a buffer structure.
646 * Window Internals:: Components of a window structure.
647 * Process Internals:: Components of a process structure.
650 @node Buffer Internals, Window Internals, Object Internals, Object Internals
651 @appendixsubsec Buffer Internals
652 @cindex internals, of buffer
653 @cindex buffer internals
655 Buffers contain fields not directly accessible by the Lisp programmer.
656 We describe them here, naming them by the names used in the C code.
657 Many are accessible indirectly in Lisp programs via Lisp primitives.
661 The buffer name is a string that names the buffer. It is guaranteed to
662 be unique. @xref{Buffer Names}.
665 This field contains the time when the buffer was last saved, as an integer.
666 @xref{Buffer Modification}.
669 This field contains the modification time of the visited file. It is
670 set when the file is written or read. Every time the buffer is written
671 to the file, this field is compared to the modification time of the
672 file. @xref{Buffer Modification}.
674 @item auto_save_modified
675 This field contains the time when the buffer was last auto-saved.
677 @item last_window_start
678 This field contains the @code{window-start} position in the buffer as of
679 the last time the buffer was displayed in a window.
682 This field points to the buffer's undo list. @xref{Undo}.
685 This field contains the syntax table for the buffer. @xref{Syntax Tables}.
688 This field contains the conversion table for converting text to lower case.
692 This field contains the conversion table for converting text to upper case.
695 @item case_canon_table
696 This field contains the conversion table for canonicalizing text for
697 case-folding search. @xref{Case Table}.
700 This field contains the equivalence table for case-folding search.
704 This field contains the buffer's display table, or @code{nil} if it doesn't
705 have one. @xref{Display Tables}.
708 This field contains the chain of all markers that currently point into
709 the buffer. Deletion of text in the buffer, and motion of the buffer's
710 gap, must check each of these markers and perhaps update it.
714 This field is a flag that tells whether a backup file has been made
715 for the visited file of this buffer.
718 This field contains the mark for the buffer. The mark is a marker,
719 hence it is also included on the list @code{markers}. @xref{The Mark}.
722 This field is non-@code{nil} if the buffer's mark is active.
724 @item local_var_alist
725 This field contains the association list describing the variables local
726 in this buffer, and their values, with the exception of local variables
727 that have special slots in the buffer object. (Those slots are omitted
728 from this table.) @xref{Buffer-Local Variables}.
731 This field holds the buffer's base buffer (if it is an indirect buffer),
735 This field holds the buffer's local keymap. @xref{Keymaps}.
738 This field holds the current overlay center position. @xref{Overlays}.
740 @item overlays_before
741 This field holds a list of the overlays in this buffer that end at or
742 before the current overlay center position. They are sorted in order of
743 decreasing end position.
746 This field holds a list of the overlays in this buffer that end after
747 the current overlay center position. They are sorted in order of
748 increasing beginning position.
751 @node Window Internals, Process Internals, Buffer Internals, Object Internals
752 @appendixsubsec Window Internals
753 @cindex internals, of window
754 @cindex window internals
756 Windows have the following accessible fields:
760 The frame that this window is on.
763 Non-@code{nil} if this window is a minibuffer window.
766 The buffer that the window is displaying. This may change often during
767 the life of the window.
770 Non-@code{nil} if this window is dedicated to its buffer.
773 @cindex window point internals
774 This is the value of point in the current buffer when this window is
775 selected; when it is not selected, it retains its previous value.
778 The position in the buffer that is the first character to be displayed
782 If this flag is non-@code{nil}, it says that the window has been
783 scrolled explicitly by the Lisp program. This affects what the next
784 redisplay does if point is off the screen: instead of scrolling the
785 window to show the text around point, it moves point to a location that
789 The @code{modified} field of the window's buffer, as of the last time
790 a redisplay completed in this window.
793 The buffer's value of point, as of the last time
794 a redisplay completed in this window.
797 This is the left-hand edge of the window, measured in columns. (The
798 leftmost column on the screen is @w{column 0}.)
801 This is the top edge of the window, measured in lines. (The top line on
802 the screen is @w{line 0}.)
805 The height of the window, measured in lines.
808 The width of the window, measured in columns.
811 This is the window that is the next in the chain of siblings. It is
812 @code{nil} in a window that is the rightmost or bottommost of a group of
816 This is the window that is the previous in the chain of siblings. It is
817 @code{nil} in a window that is the leftmost or topmost of a group of
821 Internally, Emacs arranges windows in a tree; each group of siblings has
822 a parent window whose area includes all the siblings. This field points
823 to a window's parent.
825 Parent windows do not display buffers, and play little role in display
826 except to shape their child windows. Emacs Lisp programs usually have
827 no access to the parent windows; they operate on the windows at the
828 leaves of the tree, which actually display buffers.
831 This is the number of columns that the display in the window is scrolled
832 horizontally to the left. Normally, this is 0.
835 This is the last time that the window was selected. The function
836 @code{get-lru-window} uses this field.
839 The window's display table, or @code{nil} if none is specified for it.
841 @item update_mode_line
842 Non-@code{nil} means this window's mode line needs to be updated.
844 @item base_line_number
845 The line number of a certain position in the buffer, or @code{nil}.
846 This is used for displaying the line number of point in the mode line.
849 The position in the buffer for which the line number is known, or
850 @code{nil} meaning none is known.
853 If the region (or part of it) is highlighted in this window, this field
854 holds the mark position that made one end of that region. Otherwise,
855 this field is @code{nil}.
858 @node Process Internals, , Window Internals, Object Internals
859 @appendixsubsec Process Internals
860 @cindex internals, of process
861 @cindex process internals
863 The fields of a process are:
867 A string, the name of the process.
870 A list containing the command arguments that were used to start this
874 A function used to accept output from the process instead of a buffer,
878 A function called whenever the process receives a signal, or @code{nil}.
881 The associated buffer of the process.
884 An integer, the Unix process @sc{id}.
887 A flag, non-@code{nil} if this is really a child process.
888 It is @code{nil} for a network connection.
891 A marker indicating the position of the end of the last output from this
892 process inserted into the buffer. This is often but not always the end
895 @item kill_without_query
896 If this is non-@code{nil}, killing Emacs while this process is still
897 running does not ask for confirmation about killing the process.
900 @itemx raw_status_high
901 These two fields record 16 bits each of the process status returned by
902 the @code{wait} system call.
905 The process status, as @code{process-status} should return it.
909 If these two fields are not equal, a change in the status of the process
910 needs to be reported, either by running the sentinel or by inserting a
911 message in the process buffer.
914 Non-@code{nil} if communication with the subprocess uses a @sc{pty};
915 @code{nil} if it uses a pipe.
918 The file descriptor for input from the process.
921 The file descriptor for output to the process.
924 The file descriptor for the terminal that the subprocess is using. (On
925 some systems, there is no need to record this, so the value is
929 The name of the terminal that the subprocess is using,
930 or @code{nil} if it is using pipes.