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 which 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} which 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} which 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 19.22.1 of Fri Feb 27 1994 \
107 on slug (berkeley-unix)"
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{} "Fri Feb 27 14:55:57 1994"
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{"19.22.1"}.
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.
140 @defvar emacs-minor-version
141 The minor version number of Emacs, as an integer. For Emacs version
142 19.23, the value is 23.
145 @node Pure Storage, Garbage Collection, Building Emacs, GNU Emacs Internals
146 @appendixsec Pure Storage
149 Emacs Lisp uses two kinds of storage for user-created Lisp objects:
150 @dfn{normal storage} and @dfn{pure storage}. Normal storage is where
151 all the new data which is created during an Emacs session is kept; see
152 the following section for information on normal storage. Pure storage
153 is used for certain data in the preloaded standard Lisp files---data
154 that should never change during actual use of Emacs.
156 Pure storage is allocated only while @file{temacs} is loading the
157 standard preloaded Lisp libraries. In the file @file{emacs}, it is
158 marked as read-only (on operating systems which permit this), so that
159 the memory space can be shared by all the Emacs jobs running on the
160 machine at once. Pure storage is not expandable; a fixed amount is
161 allocated when Emacs is compiled, and if that is not sufficient for the
162 preloaded libraries, @file{temacs} crashes. If that happens, you must
163 increase the compilation parameter @code{PURESIZE} in the file
164 @file{src/puresize.h}. This normally won't happen unless you try to
165 preload additional libraries or add features to the standard ones.
167 @defun purecopy object
168 This function makes a copy of @var{object} in pure storage and returns
169 it. It copies strings by simply making a new string with the same
170 characters in pure storage. It recursively copies the contents of
171 vectors and cons cells. It does not make copies of other objects such
172 as symbols, but just returns them unchanged. It signals an error if
173 asked to copy markers.
175 This function is used only while Emacs is being built and dumped; it is
176 called only in the file @file{emacs/lisp/loaddefs.el}.
179 @defvar pure-bytes-used
180 The value of this variable is the number of bytes of pure storage
181 allocated so far. Typically, in a dumped Emacs, this number is very
182 close to the total amount of pure storage available---if it were not,
183 we would preallocate less.
187 This variable determines whether @code{defun} should make a copy of the
188 function definition in pure storage. If it is non-@code{nil}, then the
189 function definition is copied into pure storage.
191 This flag is @code{t} while loading all of the basic functions for
192 building Emacs initially (allowing those functions to be sharable and
193 non-collectible). Dumping Emacs as an executable always writes
194 @code{nil} in this variable, regardless of the value it actually has
195 before and after dumping.
197 You should not change this flag in a running Emacs.
200 @node Garbage Collection, Writing Emacs Primitives, Pure Storage, GNU Emacs Internals
201 @appendixsec Garbage Collection
202 @cindex garbage collector
204 @cindex memory allocation
205 When a program creates a list or the user defines a new function (such
206 as by loading a library), that data is placed in normal storage. If
207 normal storage runs low, then Emacs asks the operating system to
208 allocate more memory in blocks of 1k bytes. Each block is used for one
209 type of Lisp object, so symbols, cons cells, markers, etc., are
210 segregated in distinct blocks in memory. (Vectors, long strings,
211 buffers and certain other editing types, which are fairly large, are
212 allocated in individual blocks, one per object, while small strings are
213 packed into blocks of 8k bytes.)
215 It is quite common to use some storage for a while, then release it by
216 (for example) killing a buffer or deleting the last pointer to an
217 object. Emacs provides a @dfn{garbage collector} to reclaim this
218 abandoned storage. (This name is traditional, but ``garbage recycler''
219 might be a more intuitive metaphor for this facility.)
221 The garbage collector operates by finding and marking all Lisp objects
222 that are still accessible to Lisp programs. To begin with, it assumes
223 all the symbols, their values and associated function definitions, and
224 any data presently on the stack, are accessible. Any objects which can
225 be reached indirectly through other accessible objects are also
228 When marking is finished, all objects still unmarked are garbage. No
229 matter what the Lisp program or the user does, it is impossible to refer
230 to them, since there is no longer a way to reach them. Their space
231 might as well be reused, since no one will miss them. The second,
232 ``sweep'' phase of the garbage collector arranges to reuse them.
235 The sweep phase puts unused cons cells onto a @dfn{free list}
236 for future allocation; likewise for symbols and markers. It compacts
237 the accessible strings so they occupy fewer 8k blocks; then it frees the
238 other 8k blocks. Vectors, buffers, windows and other large objects are
239 individually allocated and freed using @code{malloc} and @code{free}.
241 @cindex CL note---allocate more storage
243 @b{Common Lisp note:} unlike other Lisps, GNU Emacs Lisp does not
244 call the garbage collector when the free list is empty. Instead, it
245 simply requests the operating system to allocate more storage, and
246 processing continues until @code{gc-cons-threshold} bytes have been
249 This means that you can make sure that the garbage collector will not
250 run during a certain portion of a Lisp program by calling the garbage
251 collector explicitly just before it (provided that portion of the
252 program does not use so much space as to force a second garbage
256 @deffn Command garbage-collect
257 This command runs a garbage collection, and returns information on
258 the amount of space in use. (Garbage collection can also occur
259 spontaneously if you use more than @code{gc-cons-threshold} bytes of
260 Lisp data since the previous garbage collection.)
262 @code{garbage-collect} returns a list containing the following
267 ((@var{used-conses} . @var{free-conses})
268 (@var{used-syms} . @var{free-syms})
270 (@var{used-markers} . @var{free-markers})
271 @var{used-string-chars}
272 @var{used-vector-slots}
273 (@var{used-floats} . @var{free-floats}))
277 @result{} ((3435 . 2332) (1688 . 0)
278 (57 . 417) 24510 3839 (4 . 1))
282 Here is a table explaining each element:
286 The number of cons cells in use.
289 The number of cons cells for which space has been obtained from the
290 operating system, but that are not currently being used.
293 The number of symbols in use.
296 The number of symbols for which space has been obtained from the
297 operating system, but that are not currently being used.
300 The number of markers in use.
303 The number of markers for which space has been obtained from the
304 operating system, but that are not currently being used.
306 @item used-string-chars
307 The total size of all strings, in characters.
309 @item used-vector-slots
310 The total number of elements of existing vectors.
314 The number of floats in use.
318 The number of floats for which space has been obtained from the
319 operating system, but that are not currently being used.
323 @defopt gc-cons-threshold
324 The value of this variable is the number of bytes of storage that must
325 be allocated for Lisp objects after one garbage collection in order to
326 trigger another garbage collection. A cons cell counts as eight bytes,
327 a string as one byte per character plus a few bytes of overhead, and so
328 on; space allocated to the contents of buffers does not count. Note
329 that the subsequent garbage collection does not happen immediately when
330 the threshold is exhausted, but only the next time the Lisp evaluator is
333 The initial threshold value is 100,000. If you specify a larger
334 value, garbage collection will happen less often. This reduces the
335 amount of time spent garbage collecting, but increases total memory use.
336 You may want to do this when running a program which creates lots of
339 You can make collections more frequent by specifying a smaller value,
340 down to 10,000. A value less than 10,000 will remain in effect only
341 until the subsequent garbage collection, at which time
342 @code{garbage-collect} will set the threshold back to 10,000.
347 This function returns the address of the last byte Emacs has allocated,
348 divided by 1024. We divide the value by 1024 to make sure it fits in a
351 You can use this to get a general idea of how your actions affect the
355 @node Writing Emacs Primitives, Object Internals, Garbage Collection, GNU Emacs Internals
356 @appendixsec Writing Emacs Primitives
357 @cindex primitive function internals
359 Lisp primitives are Lisp functions implemented in C. The details of
360 interfacing the C function so that Lisp can call it are handled by a few
361 C macros. The only way to really understand how to write new C code is
362 to read the source, but we can explain some things here.
364 An example of a special form is the definition of @code{or}, from
365 @file{eval.c}. (An ordinary function would have the same general
368 @cindex garbage collection protection
371 DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
372 "Eval args until one of them yields non-nil, then return that value.\n\
373 The remaining args are not evalled at all.\n\
376 If all args return nil, return nil.")
380 register Lisp_Object val;
381 Lisp_Object args_left;
396 val = Feval (Fcar (args_left));
399 args_left = Fcdr (args_left);
401 while (!NULL (args_left));
411 Let's start with a precise explanation of the arguments to the
412 @code{DEFUN} macro. Here is a template for them:
415 DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc})
420 This is the name of the Lisp symbol to define as the function name; in
421 the example above, it is @code{or}.
424 This is the C function name for this function. This is
425 the name that is used in C code for calling the function. The name is,
426 by convention, @samp{F} prepended to the Lisp name, with all dashes
427 (@samp{-}) in the Lisp name changed to underscores. Thus, to call this
428 function from C code, call @code{For}. Remember that the arguments must
429 be of type @code{Lisp_Object}; various macros and functions for creating
430 values of type @code{Lisp_Object} are declared in the file
434 This is a C variable name to use for a structure that holds the data for
435 the subr object that represents the function in Lisp. This structure
436 conveys the Lisp symbol name to the initialization routine that will
437 create the symbol and store the subr object as its definition. By
438 convention, this name is always @var{fname} with @samp{F} replaced with
442 This is the minimum number of arguments that the function requires. The
443 function @code{or} allows a minimum of zero arguments.
446 This is the maximum number of arguments that the function accepts, if
447 there is a fixed maximum. Alternatively, it can be @code{UNEVALLED},
448 indicating a special form that receives unevaluated arguments, or
449 @code{MANY}, indicating an unlimited number of evaluated arguments (the
450 equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are
451 macros. If @var{max} is a number, it may not be less than @var{min} and
452 it may not be greater than seven.
455 This is an interactive specification, a string such as might be used as
456 the argument of @code{interactive} in a Lisp function. In the case of
457 @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be
458 called interactively. A value of @code{""} indicates a function that
459 should receive no arguments when called interactively.
462 This is the documentation string. It is written just like a
463 documentation string for a function defined in Lisp, except you must
464 write @samp{\n\} at the end of each line. In particular, the first line
465 should be a single sentence.
468 After the call to the @code{DEFUN} macro, you must write the argument
469 name list that every C function must have, followed by ordinary C
470 declarations for the arguments. For a function with a fixed maximum
471 number of arguments, declare a C argument for each Lisp argument, and
472 give them all type @code{Lisp_Object}. If the function has no upper
473 limit on the number of arguments in Lisp, then in C it receives two
474 arguments: the first is the number of Lisp arguments, and the second is
475 the address of a block containing their values. They have types
476 @code{int} and @w{@code{Lisp_Object *}}.
478 Within the function @code{For} itself, note the use of the macros
479 @code{GCPRO1} and @code{UNGCPRO}. @code{GCPRO1} is used to ``protect''
480 a variable from garbage collection---to inform the garbage collector that
481 it must look in that variable and regard its contents as an accessible
482 object. This is necessary whenever you call @code{Feval} or anything
483 that can directly or indirectly call @code{Feval}. At such a time, any
484 Lisp object that you intend to refer to again must be protected somehow.
485 @code{UNGCPRO} cancels the protection of the variables that are
486 protected in the current function. It is necessary to do this explicitly.
488 For most data types, it suffices to protect at least one pointer to
489 the object; as long as the object is not recycled, all pointers to it
490 remain valid. This is not so for strings, because the garbage collector
491 can move them. When the garbage collector moves a string, it relocates
492 all the pointers it knows about; any other pointers become invalid.
493 Therefore, you must protect all pointers to strings across any point
494 where garbage collection may be possible.
496 The macro @code{GCPRO1} protects just one local variable. If you want
497 to protect two, use @code{GCPRO2} instead; repeating @code{GCPRO1} will
498 not work. Macros @code{GCPRO3} and @code{GCPRO4} also exist.
500 These macros implicitly use local variables such as @code{gcpro1}; you
501 must declare these explicitly, with type @code{struct gcpro}. Thus, if
502 you use @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}.
503 Alas, we can't explain all the tricky details here.
505 Defining the C function is not enough to make a Lisp primitive
506 available; you must also create the Lisp symbol for the primitive and
507 store a suitable subr object in its function cell. The code looks like
511 defsubr (&@var{subr-structure-name});
515 Here @var{subr-structure-name} is the name you used as the third
516 argument to @code{DEFUN}.
518 If you add a new primitive to a file that already has Lisp primitives
519 defined in it, find the function (near the end of the file) named
520 @code{syms_of_@var{something}}, and add the call to @code{defsubr}
521 there. If the file doesn't have this function, or if you create a new
522 file, add to it a @code{syms_of_@var{filename}} (e.g.,
523 @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all
524 of these functions are called, and add a call to
525 @code{syms_of_@var{filename}} there.
527 This function @code{syms_of_@var{filename}} is also the place to
528 define any C variables which are to be visible as Lisp variables.
529 @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible
530 in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int}
531 visible in Lisp with a value that is always an integer.
532 @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp
533 with a value that is either @code{t} or @code{nil}.
535 Here is another example function, with more complicated arguments.
536 This comes from the code for the X Window System, and it demonstrates
537 the use of macros and functions to manipulate Lisp objects.
541 DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
542 Scoordinates_in_window_p, 2, 2,
543 "xSpecify coordinate pair: \nXExpression which evals to window: ",
544 "Return non-nil if POSITIONS is in WINDOW.\n\
545 \(POSITIONS is a list, (SCREEN-X SCREEN-Y)\)\n\
548 Returned value is list of positions expressed\n\
549 relative to window upper left corner.")
551 register Lisp_Object coordinate, window;
553 register Lisp_Object xcoord, ycoord;
557 if (!CONSP (coordinate)) wrong_type_argument (Qlistp, coordinate);
558 CHECK_WINDOW (window, 2);
559 xcoord = Fcar (coordinate);
560 ycoord = Fcar (Fcdr (coordinate));
561 CHECK_NUMBER (xcoord, 0);
562 CHECK_NUMBER (ycoord, 1);
565 if ((XINT (xcoord) < XINT (XWINDOW (window)->left))
566 || (XINT (xcoord) >= (XINT (XWINDOW (window)->left)
567 + XINT (XWINDOW (window)->width))))
569 XFASTINT (xcoord) -= XFASTINT (XWINDOW (window)->left);
572 if (XINT (ycoord) == (screen_height - 1))
576 if ((XINT (ycoord) < XINT (XWINDOW (window)->top))
577 || (XINT (ycoord) >= (XINT (XWINDOW (window)->top)
578 + XINT (XWINDOW (window)->height)) - 1))
582 XFASTINT (ycoord) -= XFASTINT (XWINDOW (window)->top);
583 return (Fcons (xcoord, Fcons (ycoord, Qnil)));
588 Note that C code cannot call functions by name unless they are defined
589 in C. The way to call a function written in Lisp is to use
590 @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since
591 the Lisp function @code{funcall} accepts an unlimited number of
592 arguments, in C it takes two: the number of Lisp-level arguments, and a
593 one-dimensional array containing their values. The first Lisp-level
594 argument is the Lisp function to call, and the rest are the arguments to
595 pass to it. Since @code{Ffuncall} can call the evaluator, you must
596 protect pointers from garbage collection around the call to
599 The C functions @code{call0}, @code{call1}, @code{call2}, and so on,
600 provide handy ways to call a Lisp function conveniently with a fixed
601 number of arguments. They work by calling @code{Ffuncall}.
603 @file{eval.c} is a very good file to look through for examples;
604 @file{lisp.h} contains the definitions for some important macros and
607 @node Object Internals, , Writing Emacs Primitives, GNU Emacs Internals
608 @appendixsec Object Internals
609 @cindex object internals
611 GNU Emacs Lisp manipulates many different types of data. The actual
612 data are stored in a heap and the only access that programs have to it is
613 through pointers. Pointers are thirty-two bits wide in most
614 implementations. Depending on the operating system and type of machine
615 for which you compile Emacs, twenty-four to twenty-six bits are used to
616 address the object, and the remaining six to eight bits are used for a
617 tag that identifies the object's type.
619 Because Lisp objects are represented as tagged pointers, it is always
620 possible to determine the Lisp data type of any object. The C data type
621 @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary
622 variables have type @code{Lisp_Object}, which means they can hold any
623 type of Lisp value; you can determine the actual data type only at run
624 time. The same is true for function arguments; if you want a function
625 to accept only a certain type of argument, you must check the type
626 explicitly using a suitable predicate (@pxref{Type Predicates}).
627 @cindex type checking internals
630 * Buffer Internals:: Components of a buffer structure.
631 * Window Internals:: Components of a window structure.
632 * Process Internals:: Components of a process structure.
635 @node Buffer Internals, Window Internals, Object Internals, Object Internals
636 @appendixsubsec Buffer Internals
637 @cindex internals, of buffer
638 @cindex buffer internals
640 Buffers contain fields not directly accessible by the Lisp programmer.
641 We describe them here, naming them by the names used in the C code.
642 Many are accessible indirectly in Lisp programs via Lisp primitives.
646 The buffer name is a string which names the buffer. It is guaranteed to
647 be unique. @xref{Buffer Names}.
650 This field contains the time when the buffer was last saved, as an integer.
651 @xref{Buffer Modification}.
654 This field contains the modification time of the visited file. It is
655 set when the file is written or read. Every time the buffer is written
656 to the file, this field is compared to the modification time of the
657 file. @xref{Buffer Modification}.
659 @item auto_save_modified
660 This field contains the time when the buffer was last auto-saved.
662 @item last_window_start
663 This field contains the @code{window-start} position in the buffer as of
664 the last time the buffer was displayed in a window.
667 This field points to the buffer's undo list. @xref{Undo}.
670 This field contains the syntax table for the buffer. @xref{Syntax Tables}.
673 This field contains the conversion table for converting text to lower case.
677 This field contains the conversion table for converting text to upper case.
680 @item case_canon_table
681 This field contains the conversion table for canonicalizing text for
682 case-folding search. @xref{Case Table}.
685 This field contains the equivalence table for case-folding search.
689 This field contains the buffer's display table, or @code{nil} if it doesn't
690 have one. @xref{Display Tables}.
693 This field contains the chain of all markers that currently point into
694 the buffer. Deletion of text in the buffer, and motion of the buffer's
695 gap, must check each of these markers and perhaps update it.
699 This field is a flag which tells whether a backup file has been made
700 for the visited file of this buffer.
703 This field contains the mark for the buffer. The mark is a marker,
704 hence it is also included on the list @code{markers}. @xref{The Mark}.
707 This field is non-@code{nil} if the buffer's mark is active.
709 @item local_var_alist
710 This field contains the association list describing the variables local
711 in this buffer, and their values, with the exception of local variables
712 that have special slots in the buffer object. (Those slots are omitted
713 from this table.) @xref{Buffer-Local Variables}.
716 This field holds the buffer's local keymap. @xref{Keymaps}.
719 This field holds the current overlay center position. @xref{Overlays}.
721 @item overlays_before
722 This field holds a list of the overlays in this buffer that end at or
723 before the current overlay center position. They are sorted in order of
724 decreasing end position.
727 This field holds a list of the overlays in this buffer that end after
728 the current overlay center position. They are sorted in order of
729 increasing beginning position.
732 @node Window Internals, Process Internals, Buffer Internals, Object Internals
733 @appendixsubsec Window Internals
734 @cindex internals, of window
735 @cindex window internals
737 Windows have the following accessible fields:
741 The frame that this window is on.
744 Non-@code{nil} if this window is a minibuffer window.
747 The buffer which the window is displaying. This may change often during
748 the life of the window.
751 Non-@code{nil} if this window is dedicated to its buffer.
754 @cindex window point internals
755 This is the value of point in the current buffer when this window is
756 selected; when it is not selected, it retains its previous value.
759 he position in the buffer which is the first character to be displayed
763 If this flag is non-@code{nil}, it says that the window has been
764 scrolled explicitly by the Lisp program. This affects what the next
765 redisplay does if point is off the screen: instead of scrolling the
766 window to show the text around point, it moves point to a location that
770 The @code{modified} field of the window's buffer, as of the last time
771 a redisplay completed in this window.
774 The buffer's value of point, as of the last time
775 a redisplay completed in this window.
778 This is the left-hand edge of the window, measured in columns. (The
779 leftmost column on the screen is @w{column 0}.)
782 This is the top edge of the window, measured in lines. (The top line on
783 the screen is @w{line 0}.)
786 The height of the window, measured in lines.
789 The width of the window, measured in columns.
792 This is the window that is the next in the chain of siblings. It is
793 @code{nil} in a window that is the rightmost or bottommost of a group of
797 This is the window that is the previous in the chain of siblings. It is
798 @code{nil} in a window that is the leftmost or topmost of a group of
802 Internally, Emacs arranges windows in a tree; each group of siblings has
803 a parent window whose area includes all the siblings. This field points
804 to a window's parent.
806 Parent windows do not display buffers, and play little role in display
807 except to shape their child windows. Emacs Lisp programs usually have
808 no access to the parent windows; they operate on the windows at the
809 leaves of the tree, that actually display buffers.
812 This is the number of columns that the display in the window is scrolled
813 horizontally to the left. Normally, this is 0.
816 This is the last time that the window was selected. The function
817 @code{get-lru-window} uses this field.
820 The window's display table, or @code{nil} if none is specified for it.
822 @item update_mode_line
823 Non-@code{nil} means this window's mode line needs to be updated.
825 @item base_line_number
826 The line number of a certain position in the buffer, or @code{nil}.
827 This is used for displaying the line number of point in the mode line.
830 The position in the buffer for which the line number is known, or
831 @code{nil} meaning none is known.
834 If the region (or part of it) is highlighted in this window, this field
835 holds the mark position that made one end of that region. Otherwise,
836 this field is @code{nil}.
839 @node Process Internals, , Window Internals, Object Internals
840 @appendixsubsec Process Internals
841 @cindex internals, of process
842 @cindex process internals
844 The fields of a process are:
848 A string, the name of the process.
851 A list containing the command arguments that were used to start this
855 A function used to accept output from the process instead of a buffer,
859 A function called whenever the process receives a signal, or @code{nil}.
862 The associated buffer of the process.
865 An integer, the Unix process @sc{id}.
868 A flag, non-@code{nil} if this is really a child process.
869 It is @code{nil} for a network connection.
872 A marker indicating the position of end of last output from this process
873 inserted into the buffer. This is usually the end of the buffer.
875 @item kill_without_query
876 If this is non-@code{nil}, killing Emacs while this process is still
877 running does not ask for confirmation about killing the process.
880 @itemx raw_status_high
881 These two fields record 16 bits each of the process status returned by
882 the @code{wait} system call.
885 The process status, as @code{process-status} should return it.
889 If these two fields are not equal, a change in the status of the process
890 needs to be reported, either by running the sentinel or by inserting a
891 message in the process buffer.
894 Non-@code{nil} if communication with the subprocess uses a @sc{pty};
895 @code{nil} if it uses a pipe.
898 The file descriptor for input from the process.
901 The file descriptor for output to the process.
904 The file descriptor for the terminal that the subprocess is using. (On
905 some systems, there is no need to record this, so the value is