2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1993, 1998-1999, 2001-2012 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 the dumped Emacs is made.
16 * Pure Storage:: Kludge to make preloaded Lisp functions shareable.
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 @section 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 developers.
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
36 I/O routines, but not the editing commands.
38 @cindex @file{loadup.el}
39 The command @w{@command{temacs -l loadup}} would run @file{temacs}
40 and direct it to load @file{loadup.el}. The @code{loadup} library
41 loads additional Lisp libraries, which set up the normal Emacs editing
42 environment. After this step, the Emacs executable is no longer
46 Because it takes some time to load the standard Lisp files, the
47 @file{temacs} executable usually isn't run directly by users.
48 Instead, as one of the last steps of building Emacs, the command
49 @samp{temacs -batch -l loadup dump} is run. The special @samp{dump}
50 argument causes @command{temacs} to dump out an executable program,
51 called @file{emacs}, which has all the standard Lisp files preloaded.
52 (The @samp{-batch} argument prevents @file{temacs} from trying to
53 initialize any of its data on the terminal, so that the tables of
54 terminal information are empty in the dumped Emacs.)
56 @cindex preloaded Lisp files
57 @vindex preloaded-file-list
58 The dumped @file{emacs} executable (also called a @dfn{pure} Emacs)
59 is the one which is installed. The variable
60 @code{preloaded-file-list} stores a list of the Lisp files preloaded
61 into the dumped Emacs. If you port Emacs to a new operating system,
62 and are not able to implement dumping, then Emacs must load
63 @file{loadup.el} each time it starts.
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 rebuild Emacs
68 with an added definition
71 #define SITELOAD_PURESIZE_EXTRA @var{n}
75 to make @var{n} added bytes of pure space to hold the additional files;
76 see @file{src/puresize.h}.
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
84 calling @code{Snarf-documentation} (@pxref{Definition of
85 Snarf-documentation,, Accessing Documentation}).
87 @cindex @file{site-init.el}
88 @cindex preloading additional functions and variables
89 You can specify other Lisp expressions to execute just before dumping
90 by putting them in a library named @file{site-init.el}. This file is
91 executed after the documentation strings are found.
93 If you want to preload function or variable definitions, there are
94 three ways you can do this and make their documentation strings
95 accessible when you subsequently run Emacs:
99 Arrange to scan these files when producing the @file{etc/DOC} file,
100 and load them with @file{site-load.el}.
103 Load the files with @file{site-init.el}, then copy the files into the
104 installation directory for Lisp files when you install Emacs.
107 Specify a @code{nil} value for @code{byte-compile-dynamic-docstrings}
108 as a local variable in each of these files, and load them with either
109 @file{site-load.el} or @file{site-init.el}. (This method has the
110 drawback that the documentation strings take up space in Emacs all the
114 It is not advisable to put anything in @file{site-load.el} or
115 @file{site-init.el} that would alter any of the features that users
116 expect in an ordinary unmodified Emacs. If you feel you must override
117 normal features for your site, do it with @file{default.el}, so that
118 users can override your changes if they wish. @xref{Startup Summary}.
120 In a package that can be preloaded, it is sometimes necessary (or
121 useful) to delay certain evaluations until Emacs subsequently starts
122 up. The vast majority of such cases relate to the values of
123 customizable variables. For example, @code{tutorial-directory} is a
124 variable defined in @file{startup.el}, which is preloaded. The default
125 value is set based on @code{data-directory}. The variable needs to
126 access the value of @code{data-directory} when Emacs starts, not when
127 it is dumped, because the Emacs executable has probably been installed
128 in a different location since it was dumped.
130 @defun custom-initialize-delay symbol value
131 This function delays the initialization of @var{symbol} to the next
132 Emacs start. You normally use this function by specifying it as the
133 @code{:initialize} property of a customizable variable. (The argument
134 @var{value} is unused, and is provided only for compatibility with the
135 form Custom expects.)
138 In the unlikely event that you need a more general functionality than
139 @code{custom-initialize-delay} provides, you can use
140 @code{before-init-hook} (@pxref{Startup Summary}).
142 @defun dump-emacs to-file from-file
144 This function dumps the current state of Emacs into an executable file
145 @var{to-file}. It takes symbols from @var{from-file} (this is normally
146 the executable file @file{temacs}).
148 If you want to use this function in an Emacs that was already dumped,
149 you must run Emacs with @samp{-batch}.
153 @section Pure Storage
156 Emacs Lisp uses two kinds of storage for user-created Lisp objects:
157 @dfn{normal storage} and @dfn{pure storage}. Normal storage is where
158 all the new data created during an Emacs session are kept
159 (@pxref{Garbage Collection}). Pure storage is used for certain data
160 in the preloaded standard Lisp files---data that should never change
161 during actual use of Emacs.
163 Pure storage is allocated only while @command{temacs} is loading the
164 standard preloaded Lisp libraries. In the file @file{emacs}, it is
165 marked as read-only (on operating systems that permit this), so that
166 the memory space can be shared by all the Emacs jobs running on the
167 machine at once. Pure storage is not expandable; a fixed amount is
168 allocated when Emacs is compiled, and if that is not sufficient for
169 the preloaded libraries, @file{temacs} allocates dynamic memory for
170 the part that didn't fit. The resulting image will work, but garbage
171 collection (@pxref{Garbage Collection}) is disabled in this situation,
172 causing a memory leak. Such an overflow normally won't happen unless
173 you try to preload additional libraries or add features to the
174 standard ones. Emacs will display a warning about the overflow when
175 it starts. If this happens, you should increase the compilation
176 parameter @code{SYSTEM_PURESIZE_EXTRA} in the file
177 @file{src/puresize.h} and rebuild Emacs.
179 @defun purecopy object
180 This function makes a copy in pure storage of @var{object}, and returns
181 it. It copies a string by simply making a new string with the same
182 characters, but without text properties, in pure storage. It
183 recursively copies the contents of vectors and cons cells. It does
184 not make copies of other objects such as symbols, but just returns
185 them unchanged. It signals an error if asked to copy markers.
187 This function is a no-op except while Emacs is being built and dumped;
188 it is usually called only in preloaded Lisp files.
191 @defvar pure-bytes-used
192 The value of this variable is the number of bytes of pure storage
193 allocated so far. Typically, in a dumped Emacs, this number is very
194 close to the total amount of pure storage available---if it were not,
195 we would preallocate less.
199 This variable determines whether @code{defun} should make a copy of the
200 function definition in pure storage. If it is non-@code{nil}, then the
201 function definition is copied into pure storage.
203 This flag is @code{t} while loading all of the basic functions for
204 building Emacs initially (allowing those functions to be shareable and
205 non-collectible). Dumping Emacs as an executable always writes
206 @code{nil} in this variable, regardless of the value it actually has
207 before and after dumping.
209 You should not change this flag in a running Emacs.
212 @node Garbage Collection
213 @section Garbage Collection
215 @cindex memory allocation
216 When a program creates a list or the user defines a new function
217 (such as by loading a library), that data is placed in normal storage.
218 If normal storage runs low, then Emacs asks the operating system to
219 allocate more memory. Different types of Lisp objects, such as
220 symbols, cons cells, markers, etc., are segregated in distinct blocks
221 in memory. (Vectors, long strings, buffers and certain other editing
222 types, which are fairly large, are allocated in individual blocks, one
223 per object, while small strings are packed into blocks of 8k bytes.)
225 @cindex garbage collection
226 It is quite common to use some storage for a while, then release it
227 by (for example) killing a buffer or deleting the last pointer to an
228 object. Emacs provides a @dfn{garbage collector} to reclaim this
229 abandoned storage. The garbage collector operates by finding and
230 marking all Lisp objects that are still accessible to Lisp programs.
231 To begin with, it assumes all the symbols, their values and associated
232 function definitions, and any data presently on the stack, are
233 accessible. Any objects that can be reached indirectly through other
234 accessible objects are also accessible.
236 When marking is finished, all objects still unmarked are garbage. No
237 matter what the Lisp program or the user does, it is impossible to refer
238 to them, since there is no longer a way to reach them. Their space
239 might as well be reused, since no one will miss them. The second
240 (``sweep'') phase of the garbage collector arranges to reuse them.
242 @c ??? Maybe add something describing weak hash tables here?
245 The sweep phase puts unused cons cells onto a @dfn{free list}
246 for future allocation; likewise for symbols and markers. It compacts
247 the accessible strings so they occupy fewer 8k blocks; then it frees the
248 other 8k blocks. Vectors, buffers, windows, and other large objects are
249 individually allocated and freed using @code{malloc} and @code{free}.
251 @cindex CL note---allocate more storage
253 @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not
254 call the garbage collector when the free list is empty. Instead, it
255 simply requests the operating system to allocate more storage, and
256 processing continues until @code{gc-cons-threshold} bytes have been
259 This means that you can make sure that the garbage collector will not
260 run during a certain portion of a Lisp program by calling the garbage
261 collector explicitly just before it (provided that portion of the
262 program does not use so much space as to force a second garbage
266 @deffn Command garbage-collect
267 This command runs a garbage collection, and returns information on
268 the amount of space in use. (Garbage collection can also occur
269 spontaneously if you use more than @code{gc-cons-threshold} bytes of
270 Lisp data since the previous garbage collection.)
272 @code{garbage-collect} returns a list containing the following
277 ((@var{used-conses} . @var{free-conses})
278 (@var{used-syms} . @var{free-syms})
280 (@var{used-miscs} . @var{free-miscs})
281 @var{used-string-chars}
282 @var{used-vector-slots}
283 (@var{used-floats} . @var{free-floats})
284 (@var{used-intervals} . @var{free-intervals})
285 (@var{used-strings} . @var{free-strings}))
293 @result{} ((106886 . 13184) (9769 . 0)
294 (7731 . 4651) 347543 121628
295 (31 . 94) (1273 . 168)
300 Here is a table explaining each element:
304 The number of cons cells in use.
307 The number of cons cells for which space has been obtained from the
308 operating system, but that are not currently being used.
311 The number of symbols in use.
314 The number of symbols for which space has been obtained from the
315 operating system, but that are not currently being used.
318 The number of miscellaneous objects in use. These include markers and
319 overlays, plus certain objects not visible to users.
322 The number of miscellaneous objects for which space has been obtained
323 from the operating system, but that are not currently being used.
325 @item used-string-chars
326 The total size of all strings, in characters.
328 @item used-vector-slots
329 The total number of elements of existing vectors.
332 The number of floats in use.
335 The number of floats for which space has been obtained from the
336 operating system, but that are not currently being used.
339 The number of intervals in use. Intervals are an internal
340 data structure used for representing text properties.
343 The number of intervals for which space has been obtained
344 from the operating system, but that are not currently being used.
347 The number of strings in use.
350 The number of string headers for which the space was obtained from the
351 operating system, but which are currently not in use. (A string
352 object consists of a header and the storage for the string text
353 itself; the latter is only allocated when the string is created.)
356 If there was overflow in pure space (@pxref{Pure Storage}),
357 @code{garbage-collect} returns @code{nil}, because a real garbage
358 collection cannot be done.
361 @defopt garbage-collection-messages
362 If this variable is non-@code{nil}, Emacs displays a message at the
363 beginning and end of garbage collection. The default value is
368 This is a normal hook that is run at the end of garbage collection.
369 Garbage collection is inhibited while the hook functions run, so be
370 careful writing them.
373 @defopt gc-cons-threshold
374 The value of this variable is the number of bytes of storage that must
375 be allocated for Lisp objects after one garbage collection in order to
376 trigger another garbage collection. A cons cell counts as eight bytes,
377 a string as one byte per character plus a few bytes of overhead, and so
378 on; space allocated to the contents of buffers does not count. Note
379 that the subsequent garbage collection does not happen immediately when
380 the threshold is exhausted, but only the next time the Lisp evaluator is
383 The initial threshold value is 800,000. If you specify a larger
384 value, garbage collection will happen less often. This reduces the
385 amount of time spent garbage collecting, but increases total memory use.
386 You may want to do this when running a program that creates lots of
389 You can make collections more frequent by specifying a smaller value,
390 down to 10,000. A value less than 10,000 will remain in effect only
391 until the subsequent garbage collection, at which time
392 @code{garbage-collect} will set the threshold back to 10,000.
395 @defopt gc-cons-percentage
396 The value of this variable specifies the amount of consing before a
397 garbage collection occurs, as a fraction of the current heap size.
398 This criterion and @code{gc-cons-threshold} apply in parallel, and
399 garbage collection occurs only when both criteria are satisfied.
401 As the heap size increases, the time to perform a garbage collection
402 increases. Thus, it can be desirable to do them less frequently in
406 The value returned by @code{garbage-collect} describes the amount of
407 memory used by Lisp data, broken down by data type. By contrast, the
408 function @code{memory-limit} provides information on the total amount of
409 memory Emacs is currently using.
412 This function returns the address of the last byte Emacs has allocated,
413 divided by 1024. We divide the value by 1024 to make sure it fits in a
416 You can use this to get a general idea of how your actions affect the
421 This variable is @code{t} if Emacs is nearly out of memory for Lisp
422 objects, and @code{nil} otherwise.
425 @defun memory-use-counts
426 This returns a list of numbers that count the number of objects
427 created in this Emacs session. Each of these counters increments for
428 a certain kind of object. See the documentation string for details.
432 This variable contains the total number of garbage collections
433 done so far in this Emacs session.
437 This variable contains the total number of seconds of elapsed time
438 during garbage collection so far in this Emacs session, as a floating
443 @section Memory Usage
446 These functions and variables give information about the total amount
447 of memory allocation that Emacs has done, broken down by data type.
448 Note the difference between these and the values returned by
449 @code{garbage-collect}; those count objects that currently exist, but
450 these count the number or size of all allocations, including those for
451 objects that have since been freed.
453 @defvar cons-cells-consed
454 The total number of cons cells that have been allocated so far
455 in this Emacs session.
458 @defvar floats-consed
459 The total number of floats that have been allocated so far
460 in this Emacs session.
463 @defvar vector-cells-consed
464 The total number of vector cells that have been allocated so far
465 in this Emacs session.
468 @defvar symbols-consed
469 The total number of symbols that have been allocated so far
470 in this Emacs session.
473 @defvar string-chars-consed
474 The total number of string characters that have been allocated so far
478 @defvar misc-objects-consed
479 The total number of miscellaneous objects that have been allocated so
480 far in this session. These include markers and overlays, plus
481 certain objects not visible to users.
484 @defvar intervals-consed
485 The total number of intervals that have been allocated so far
486 in this Emacs session.
489 @defvar strings-consed
490 The total number of strings that have been allocated so far in this
494 @node Writing Emacs Primitives
495 @section Writing Emacs Primitives
496 @cindex primitive function internals
497 @cindex writing Emacs primitives
499 Lisp primitives are Lisp functions implemented in C. The details of
500 interfacing the C function so that Lisp can call it are handled by a few
501 C macros. The only way to really understand how to write new C code is
502 to read the source, but we can explain some things here.
504 An example of a special form is the definition of @code{or}, from
505 @file{eval.c}. (An ordinary function would have the same general
508 @cindex garbage collection protection
511 DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
512 doc: /* Eval args until one of them yields non-nil, then return
514 The remaining args are not evalled at all.
515 If all args return nil, return nil.
518 usage: (or CONDITIONS ...) */)
521 register Lisp_Object val = Qnil;
532 val = eval_sub (XCAR (args));
546 @cindex @code{DEFUN}, C macro to define Lisp primitives
547 Let's start with a precise explanation of the arguments to the
548 @code{DEFUN} macro. Here is a template for them:
551 DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc})
556 This is the name of the Lisp symbol to define as the function name; in
557 the example above, it is @code{or}.
560 This is the C function name for this function. This is the name that
561 is used in C code for calling the function. The name is, by
562 convention, @samp{F} prepended to the Lisp name, with all dashes
563 (@samp{-}) in the Lisp name changed to underscores. Thus, to call
564 this function from C code, call @code{For}.
567 This is a C variable name to use for a structure that holds the data for
568 the subr object that represents the function in Lisp. This structure
569 conveys the Lisp symbol name to the initialization routine that will
570 create the symbol and store the subr object as its definition. By
571 convention, this name is always @var{fname} with @samp{F} replaced with
575 This is the minimum number of arguments that the function requires. The
576 function @code{or} allows a minimum of zero arguments.
579 This is the maximum number of arguments that the function accepts, if
580 there is a fixed maximum. Alternatively, it can be @code{UNEVALLED},
581 indicating a special form that receives unevaluated arguments, or
582 @code{MANY}, indicating an unlimited number of evaluated arguments (the
583 equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are
584 macros. If @var{max} is a number, it must be more than @var{min} but
588 This is an interactive specification, a string such as might be used as
589 the argument of @code{interactive} in a Lisp function. In the case of
590 @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be
591 called interactively. A value of @code{""} indicates a function that
592 should receive no arguments when called interactively. If the value
593 begins with a @samp{(}, the string is evaluated as a Lisp form.
594 For examples of the last two forms, see @code{widen} and
595 @code{narrow-to-region} in @file{editfns.c}.
598 This is the documentation string. It uses C comment syntax rather
599 than C string syntax because comment syntax requires nothing special
600 to include multiple lines. The @samp{doc:} identifies the comment
601 that follows as the documentation string. The @samp{/*} and @samp{*/}
602 delimiters that begin and end the comment are not part of the
603 documentation string.
605 If the last line of the documentation string begins with the keyword
606 @samp{usage:}, the rest of the line is treated as the argument list
607 for documentation purposes. This way, you can use different argument
608 names in the documentation string from the ones used in the C code.
609 @samp{usage:} is required if the function has an unlimited number of
612 All the usual rules for documentation strings in Lisp code
613 (@pxref{Documentation Tips}) apply to C code documentation strings
617 After the call to the @code{DEFUN} macro, you must write the
618 argument list for the C function, including the types for the
619 arguments. If the primitive accepts a fixed maximum number of Lisp
620 arguments, there must be one C argument for each Lisp argument, and
621 each argument must be of type @code{Lisp_Object}. (Various macros and
622 functions for creating values of type @code{Lisp_Object} are declared
623 in the file @file{lisp.h}.) If the primitive has no upper limit on
624 the number of Lisp arguments, it must have exactly two C arguments:
625 the first is the number of Lisp arguments, and the second is the
626 address of a block containing their values. These have types
627 @code{int} and @w{@code{Lisp_Object *}} respectively.
629 @cindex @code{GCPRO} and @code{UNGCPRO}
630 @cindex protect C variables from garbage collection
631 Within the function @code{For} itself, note the use of the macros
632 @code{GCPRO1} and @code{UNGCPRO}. These macros are defined for the
633 sake of the few platforms which do not use Emacs' default
634 stack-marking garbage collector. The @code{GCPRO1} macro ``protects''
635 a variable from garbage collection, explicitly informing the garbage
636 collector that that variable and all its contents must be as
637 accessible. GC protection is necessary in any function which can
638 perform Lisp evaluation by calling @code{eval_sub} or @code{Feval} as
639 a subroutine, either directly or indirectly.
641 It suffices to ensure that at least one pointer to each object is
642 GC-protected. Thus, a particular local variable can do without
643 protection if it is certain that the object it points to will be
644 preserved by some other pointer (such as another local variable that
645 has a @code{GCPRO}). Otherwise, the local variable needs a
648 The macro @code{GCPRO1} protects just one local variable. If you
649 want to protect two variables, use @code{GCPRO2} instead; repeating
650 @code{GCPRO1} will not work. Macros @code{GCPRO3}, @code{GCPRO4},
651 @code{GCPRO5}, and @code{GCPRO6} also exist. All these macros
652 implicitly use local variables such as @code{gcpro1}; you must declare
653 these explicitly, with type @code{struct gcpro}. Thus, if you use
654 @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}.
656 @code{UNGCPRO} cancels the protection of the variables that are
657 protected in the current function. It is necessary to do this
660 You must not use C initializers for static or global variables unless
661 the variables are never written once Emacs is dumped. These variables
662 with initializers are allocated in an area of memory that becomes
663 read-only (on certain operating systems) as a result of dumping Emacs.
666 @cindex @code{defsubr}, Lisp symbol for a primitive
667 Defining the C function is not enough to make a Lisp primitive
668 available; you must also create the Lisp symbol for the primitive and
669 store a suitable subr object in its function cell. The code looks like
673 defsubr (&@var{sname});
677 Here @var{sname} is the name you used as the third argument to @code{DEFUN}.
679 If you add a new primitive to a file that already has Lisp primitives
680 defined in it, find the function (near the end of the file) named
681 @code{syms_of_@var{something}}, and add the call to @code{defsubr}
682 there. If the file doesn't have this function, or if you create a new
683 file, add to it a @code{syms_of_@var{filename}} (e.g.,
684 @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all
685 of these functions are called, and add a call to
686 @code{syms_of_@var{filename}} there.
688 @anchor{Defining Lisp variables in C}
689 @vindex byte-boolean-vars
690 @cindex defining Lisp variables in C
691 @cindex @code{DEFVAR_INT}, @code{DEFVAR_LISP}, @code{DEFVAR_BOOL}
692 The function @code{syms_of_@var{filename}} is also the place to define
693 any C variables that are to be visible as Lisp variables.
694 @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible
695 in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int}
696 visible in Lisp with a value that is always an integer.
697 @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp
698 with a value that is either @code{t} or @code{nil}. Note that variables
699 defined with @code{DEFVAR_BOOL} are automatically added to the list
700 @code{byte-boolean-vars} used by the byte compiler.
702 @cindex defining customization variables in C
703 If you want to make a Lisp variables that is defined in C behave
704 like one declared with @code{defcustom}, add an appropriate entry to
707 @cindex @code{staticpro}, protection from GC
708 If you define a file-scope C variable of type @code{Lisp_Object},
709 you must protect it from garbage-collection by calling @code{staticpro}
710 in @code{syms_of_@var{filename}}, like this:
713 staticpro (&@var{variable});
716 Here is another example function, with more complicated arguments.
717 This comes from the code in @file{window.c}, and it demonstrates the use
718 of macros and functions to manipulate Lisp objects.
722 DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
723 Scoordinates_in_window_p, 2, 2, 0,
724 doc: /* Return non-nil if COORDINATES are in WINDOW.
728 or `right-margin' is returned. */)
729 (register Lisp_Object coordinates, Lisp_Object window)
738 CHECK_LIVE_WINDOW (window);
739 w = XWINDOW (window);
740 f = XFRAME (w->frame);
741 CHECK_CONS (coordinates);
742 lx = Fcar (coordinates);
743 ly = Fcdr (coordinates);
744 CHECK_NUMBER_OR_FLOAT (lx);
745 CHECK_NUMBER_OR_FLOAT (ly);
746 x = FRAME_PIXEL_X_FROM_CANON_X (f, lx) + FRAME_INTERNAL_BORDER_WIDTH(f);
747 y = FRAME_PIXEL_Y_FROM_CANON_Y (f, ly) + FRAME_INTERNAL_BORDER_WIDTH(f);
751 switch (coordinates_in_window (w, x, y))
753 case ON_NOTHING: /* NOT in window at all. */
760 case ON_MODE_LINE: /* In mode line of window. */
767 case ON_SCROLL_BAR: /* On scroll-bar of window. */
768 /* Historically we are supposed to return nil in this case. */
780 Note that C code cannot call functions by name unless they are defined
781 in C. The way to call a function written in Lisp is to use
782 @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since
783 the Lisp function @code{funcall} accepts an unlimited number of
784 arguments, in C it takes two: the number of Lisp-level arguments, and a
785 one-dimensional array containing their values. The first Lisp-level
786 argument is the Lisp function to call, and the rest are the arguments to
787 pass to it. Since @code{Ffuncall} can call the evaluator, you must
788 protect pointers from garbage collection around the call to
791 The C functions @code{call0}, @code{call1}, @code{call2}, and so on,
792 provide handy ways to call a Lisp function conveniently with a fixed
793 number of arguments. They work by calling @code{Ffuncall}.
795 @file{eval.c} is a very good file to look through for examples;
796 @file{lisp.h} contains the definitions for some important macros and
799 If you define a function which is side-effect free, update the code
800 in @file{byte-opt.el} that binds @code{side-effect-free-fns} and
801 @code{side-effect-and-error-free-fns} so that the compiler optimizer
804 @node Object Internals
805 @section Object Internals
806 @cindex object internals
808 @c FIXME Is this still true? Does --with-wide-int affect anything?
809 GNU Emacs Lisp manipulates many different types of data. The actual
810 data are stored in a heap and the only access that programs have to it
811 is through pointers. Each pointer is 32 bits wide on 32-bit machines,
812 and 64 bits wide on 64-bit machines; three of these bits are used for
813 the tag that identifies the object's type, and the remainder are used
814 to address the object.
816 Because Lisp objects are represented as tagged pointers, it is always
817 possible to determine the Lisp data type of any object. The C data type
818 @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary
819 variables have type @code{Lisp_Object}, which means they can hold any
820 type of Lisp value; you can determine the actual data type only at run
821 time. The same is true for function arguments; if you want a function
822 to accept only a certain type of argument, you must check the type
823 explicitly using a suitable predicate (@pxref{Type Predicates}).
824 @cindex type checking internals
827 * Buffer Internals:: Components of a buffer structure.
828 * Window Internals:: Components of a window structure.
829 * Process Internals:: Components of a process structure.
832 @node Buffer Internals
833 @subsection Buffer Internals
834 @cindex internals, of buffer
835 @cindex buffer internals
837 Two structures (see @file{buffer.h}) are used to represent buffers
838 in C. The @code{buffer_text} structure contains fields describing the
839 text of a buffer; the @code{buffer} structure holds other fields. In
840 the case of indirect buffers, two or more @code{buffer} structures
841 reference the same @code{buffer_text} structure.
843 Here are some of the fields in @code{struct buffer_text}:
847 The address of the buffer contents.
851 The character and byte positions of the buffer gap. @xref{Buffer
856 The character and byte positions of the end of the buffer text.
859 The size of buffer's gap. @xref{Buffer Gap}.
864 @itemx overlay_modiff
865 These fields count the number of buffer-modification events performed
866 in this buffer. @code{modiff} is incremented after each
867 buffer-modification event, and is never otherwise changed;
868 @code{save_modiff} contains the value of @code{modiff} the last time
869 the buffer was visited or saved; @code{chars_modiff} counts only
870 modifications to the characters in the buffer, ignoring all other
871 kinds of changes; and @code{overlay_modiff} counts only modifications
876 The number of characters at the start and end of the text that are
877 known to be unchanged since the last complete redisplay.
879 @item unchanged_modified
880 @itemx overlay_unchanged_modified
881 The values of @code{modiff} and @code{overlay_modiff}, respectively,
882 after the last complete redisplay. If their current values match
883 @code{modiff} or @code{overlay_modiff}, that means
884 @code{beg_unchanged} and @code{end_unchanged} contain no useful
888 The markers that refer to this buffer. This is actually a single
889 marker, and successive elements in its marker @code{chain} are the other
890 markers referring to this buffer text.
893 The interval tree which records the text properties of this buffer.
896 Some of the fields of @code{struct buffer} are:
900 A @code{struct vectorlike_header} structure where @code{header.next}
901 points to the next buffer, in the chain of all buffers (including
902 killed buffers). This chain is used only for garbage collection, in
903 order to collect killed buffers properly. Note that vectors, and most
904 kinds of objects allocated as vectors, are all on one chain, but
905 buffers are on a separate chain of their own.
908 A @code{struct buffer_text} structure that ordinarily holds the buffer
909 contents. In indirect buffers, this field is not used.
912 A pointer to the @code{buffer_text} structure for this buffer. In an
913 ordinary buffer, this is the @code{own_text} field above. In an
914 indirect buffer, this is the @code{own_text} field of the base buffer.
918 The character and byte positions of point in a buffer.
922 The character and byte positions of the beginning of the accessible
923 range of text in the buffer.
927 The character and byte positions of the end of the accessible range of
931 In an indirect buffer, this points to the base buffer. In an ordinary
935 This field contains flags indicating that certain variables are local
936 in this buffer. Such variables are declared in the C code using
937 @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored
938 in fields in the buffer structure itself. (Some of these fields are
939 described in this table.)
942 The modification time of the visited file. It is set when the file is
943 written or read. Before writing the buffer into a file, this field is
944 compared to the modification time of the file to see if the file has
945 changed on disk. @xref{Buffer Modification}.
947 @item auto_save_modified
948 The time when the buffer was last auto-saved.
950 @item last_window_start
951 The @code{window-start} position in the buffer as of the last time the
952 buffer was displayed in a window.
955 This flag indicates that narrowing has changed in the buffer.
958 @item prevent_redisplay_optimizations_p
959 This flag indicates that redisplay optimizations should not be used to
963 This field holds the current overlay center position. @xref{Managing
966 @item overlays_before
967 @itemx overlays_after
968 These fields hold, respectively, a list of overlays that end at or
969 before the current overlay center, and a list of overlays that end
970 after the current overlay center. @xref{Managing Overlays}.
971 @code{overlays_before} is sorted in order of decreasing end position,
972 and @code{overlays_after} is sorted in order of increasing beginning
975 @c FIXME? the following are now all Lisp_Object BUFFER_INTERNAL_FIELD (foo).
978 A Lisp string that names the buffer. It is guaranteed to be unique.
982 The length of the file this buffer is visiting, when last read or
983 saved. This and other fields concerned with saving are not kept in
984 the @code{buffer_text} structure because indirect buffers are never
988 The directory for expanding relative file names. This is the value of
989 the buffer-local variable @code{default-directory} (@pxref{File Name Expansion}).
992 The name of the file visited in this buffer, or @code{nil}. This is
993 the value of the buffer-local variable @code{buffer-file-name}
994 (@pxref{Buffer File Name}).
998 @itemx auto_save_file_name
999 @itemx auto_save_file_format
1002 @itemx file_truename
1003 @itemx invisibility_spec
1004 @itemx display_count
1006 These fields store the values of Lisp variables that are automatically
1007 buffer-local (@pxref{Buffer-Local Variables}), whose corresponding
1008 variable names have the additional prefix @code{buffer-} and have
1009 underscores replaced with dashes. For instance, @code{undo_list}
1010 stores the value of @code{buffer-undo-list}.
1013 The mark for the buffer. The mark is a marker, hence it is also
1014 included on the list @code{markers}. @xref{The Mark}.
1016 @item local_var_alist
1017 The association list describing the buffer-local variable bindings of
1018 this buffer, not including the built-in buffer-local bindings that
1019 have special slots in the buffer object. (Those slots are omitted
1020 from this table.) @xref{Buffer-Local Variables}.
1023 Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}.
1026 Pretty name of the major mode, e.g., @code{"Lisp"}.
1031 @itemx category_table
1032 @itemx display_table
1033 These fields store the buffer's local keymap (@pxref{Keymaps}), abbrev
1034 table (@pxref{Abbrev Tables}), syntax table (@pxref{Syntax Tables}),
1035 category table (@pxref{Categories}), and display table (@pxref{Display
1038 @item downcase_table
1040 @itemx case_canon_table
1041 These fields store the conversion tables for converting text to lower
1042 case, upper case, and for canonicalizing text for case-fold search.
1046 An alist of the minor modes of this buffer.
1051 These fields are only used in an indirect buffer, or in a buffer that
1052 is the base of an indirect buffer. Each holds a marker that records
1053 @code{pt}, @code{begv}, and @code{zv} respectively, for this buffer
1054 when the buffer is not current.
1056 @item mode_line_format
1057 @itemx header_line_format
1058 @itemx case_fold_search
1062 @itemx auto_fill_function
1063 @itemx truncate_lines
1066 @itemx bidi_display_reordering
1067 @itemx bidi_paragraph_direction
1068 @itemx selective_display
1069 @itemx selective_display_ellipses
1070 @itemx overwrite_mode
1073 @itemx enable_multibyte_characters
1074 @itemx buffer_file_coding_system
1075 @itemx cache_long_line_scans
1076 @itemx point_before_scroll
1077 @itemx left_fringe_width
1078 @itemx right_fringe_width
1079 @itemx fringes_outside_margins
1080 @itemx scroll_bar_width
1081 @itemx indicate_empty_lines
1082 @itemx indicate_buffer_boundaries
1083 @itemx fringe_indicator_alist
1084 @itemx fringe_cursor_alist
1085 @itemx scroll_up_aggressively
1086 @itemx scroll_down_aggressively
1088 @itemx cursor_in_non_selected_windows
1089 These fields store the values of Lisp variables that are automatically
1090 buffer-local (@pxref{Buffer-Local Variables}), whose corresponding
1091 variable names have underscores replaced with dashes. For instance,
1092 @code{mode_line_format} stores the value of @code{mode-line-format}.
1094 @item last_selected_window
1095 This is the last window that was selected with this buffer in it, or @code{nil}
1096 if that window no longer displays this buffer.
1099 @node Window Internals
1100 @subsection Window Internals
1101 @cindex internals, of window
1102 @cindex window internals
1104 The fields of a window (for a complete list, see the definition of
1105 @code{struct window} in @file{window.h}) include:
1109 The frame that this window is on.
1112 Non-@code{nil} if this window is a minibuffer window.
1115 Internally, Emacs arranges windows in a tree; each group of siblings has
1116 a parent window whose area includes all the siblings. This field points
1117 to a window's parent.
1119 Parent windows do not display buffers, and play little role in display
1120 except to shape their child windows. Emacs Lisp programs usually have
1121 no access to the parent windows; they operate on the windows at the
1122 leaves of the tree, which actually display buffers.
1126 These fields contain the window's leftmost child and its topmost child
1127 respectively. @code{hchild} is used if the window is subdivided
1128 horizontally by child windows, and @code{vchild} if it is subdivided
1129 vertically. In a live window, only one of @code{hchild}, @code{vchild},
1130 and @code{buffer} (q.v.) is non-@code{nil}.
1134 The next sibling and previous sibling of this window. @code{next} is
1135 @code{nil} if the window is the right-most or bottom-most in its group;
1136 @code{prev} is @code{nil} if it is the left-most or top-most in its
1140 The left-hand edge of the window, measured in columns, relative to the
1141 leftmost column in the frame (column 0).
1144 The top edge of the window, measured in lines, relative to the topmost
1145 line in the frame (line 0).
1149 The width and height of the window, measured in columns and lines
1150 respectively. The width includes the scroll bar and fringes, and/or
1151 the separator line on the right of the window (if any).
1154 The buffer that the window is displaying.
1157 A marker pointing to the position in the buffer that is the first
1158 character displayed in the window.
1161 @cindex window point internals
1162 This is the value of point in the current buffer when this window is
1163 selected; when it is not selected, it retains its previous value.
1166 If this flag is non-@code{nil}, it says that the window has been
1167 scrolled explicitly by the Lisp program. This affects what the next
1168 redisplay does if point is off the screen: instead of scrolling the
1169 window to show the text around point, it moves point to a location that
1172 @item frozen_window_start_p
1173 This field is set temporarily to 1 to indicate to redisplay that
1174 @code{start} of this window should not be changed, even if point
1177 @item start_at_line_beg
1178 Non-@code{nil} means current value of @code{start} was the beginning of a line
1182 This is the last time that the window was selected. The function
1183 @code{get-lru-window} uses this field.
1185 @item sequence_number
1186 A unique number assigned to this window when it was created.
1189 The @code{modiff} field of the window's buffer, as of the last time
1190 a redisplay completed in this window.
1192 @item last_overlay_modified
1193 The @code{overlay_modiff} field of the window's buffer, as of the last
1194 time a redisplay completed in this window.
1197 The buffer's value of point, as of the last time a redisplay completed
1201 A non-@code{nil} value means the window's buffer was ``modified'' when the
1202 window was last updated.
1204 @item vertical_scroll_bar
1205 This window's vertical scroll bar.
1207 @item left_margin_cols
1208 @itemx right_margin_cols
1209 The widths of the left and right margins in this window. A value of
1210 @code{nil} means no margin.
1212 @item left_fringe_width
1213 @itemx right_fringe_width
1214 The widths of the left and right fringes in this window. A value of
1215 @code{nil} or @code{t} means use the values of the frame.
1217 @item fringes_outside_margins
1218 A non-@code{nil} value means the fringes outside the display margins;
1219 othersize they are between the margin and the text.
1221 @item window_end_pos
1222 This is computed as @code{z} minus the buffer position of the last glyph
1223 in the current matrix of the window. The value is only valid if
1224 @code{window_end_valid} is not @code{nil}.
1226 @item window_end_bytepos
1227 The byte position corresponding to @code{window_end_pos}.
1229 @item window_end_vpos
1230 The window-relative vertical position of the line containing
1231 @code{window_end_pos}.
1233 @item window_end_valid
1234 This field is set to a non-@code{nil} value if @code{window_end_pos} is truly
1235 valid. This is @code{nil} if nontrivial redisplay is pre-empted, since in that
1236 case the display that @code{window_end_pos} was computed for did not get
1240 A structure describing where the cursor is in this window.
1243 The value of @code{cursor} as of the last redisplay that finished.
1246 A structure describing where the cursor of this window physically is.
1248 @item phys_cursor_type
1249 @c FIXME What is this?
1250 @c itemx phys_cursor_ascent
1251 @itemx phys_cursor_height
1252 @itemx phys_cursor_width
1253 The type, height, and width of the cursor that was last displayed on
1256 @item phys_cursor_on_p
1257 This field is non-zero if the cursor is physically on.
1260 Non-zero means the cursor in this window is logically off. This is
1261 used for blinking the cursor.
1263 @item last_cursor_off_p
1264 This field contains the value of @code{cursor_off_p} as of the time of
1267 @item must_be_updated_p
1268 This is set to 1 during redisplay when this window must be updated.
1271 This is the number of columns that the display in the window is scrolled
1272 horizontally to the left. Normally, this is 0.
1275 Vertical scroll amount, in pixels. Normally, this is 0.
1278 Non-@code{nil} if this window is dedicated to its buffer.
1281 The window's display table, or @code{nil} if none is specified for it.
1283 @item update_mode_line
1284 Non-@code{nil} means this window's mode line needs to be updated.
1286 @item base_line_number
1287 The line number of a certain position in the buffer, or @code{nil}.
1288 This is used for displaying the line number of point in the mode line.
1291 The position in the buffer for which the line number is known, or
1292 @code{nil} meaning none is known. If it is a buffer, don't display
1293 the line number as long as the window shows that buffer.
1295 @item region_showing
1296 If the region (or part of it) is highlighted in this window, this field
1297 holds the mark position that made one end of that region. Otherwise,
1298 this field is @code{nil}.
1300 @item column_number_displayed
1301 The column number currently displayed in this window's mode line, or @code{nil}
1302 if column numbers are not being displayed.
1304 @item current_matrix
1305 @itemx desired_matrix
1306 Glyph matrices describing the current and desired display of this window.
1309 @node Process Internals
1310 @subsection Process Internals
1311 @cindex internals, of process
1312 @cindex process internals
1314 The fields of a process (for a complete list, see the definition of
1315 @code{struct Lisp_Process} in @file{process.h}) include:
1319 A string, the name of the process.
1322 A list containing the command arguments that were used to start this
1323 process. For a network or serial process, it is @code{nil} if the
1324 process is running or @code{t} if the process is stopped.
1327 If non-@code{nil}, a function used to accept output from the process
1328 instead of a buffer.
1331 If non-@code{nil}, a function called whenever the state of the process
1335 The associated buffer of the process.
1338 An integer, the operating system's process @acronym{ID}.
1339 Pseudo-processes such as network or serial connections use a value of 0.
1342 A flag, @code{t} if this is really a child process. For a network or
1343 serial connection, it is a plist based on the arguments to
1344 @code{make-network-process} or @code{make-serial-process}.
1347 A marker indicating the position of the end of the last output from this
1348 process inserted into the buffer. This is often but not always the end
1351 @item kill_without_query
1352 If this is non-zero, killing Emacs while this process is still running
1353 does not ask for confirmation about killing the process.
1356 The raw process status, as returned by the @code{wait} system call.
1359 The process status, as @code{process-status} should return it.
1363 If these two fields are not equal, a change in the status of the process
1364 needs to be reported, either by running the sentinel or by inserting a
1365 message in the process buffer.
1368 Non-@code{nil} if communication with the subprocess uses a @acronym{PTY};
1369 @code{nil} if it uses a pipe.
1372 The file descriptor for input from the process.
1375 The file descriptor for output to the process.
1378 The name of the terminal that the subprocess is using,
1379 or @code{nil} if it is using pipes.
1381 @item decode_coding_system
1382 Coding-system for decoding the input from this process.
1385 A working buffer for decoding.
1387 @item decoding_carryover
1388 Size of carryover in decoding.
1390 @item encode_coding_system
1391 Coding-system for encoding the output to this process.
1394 A working buffer for encoding.
1396 @item inherit_coding_system_flag
1397 Flag to set @code{coding-system} of the process buffer from the
1398 coding system used to decode process output.
1401 Symbol indicating the type of process: @code{real}, @code{network},
1406 @c FIXME Mention src/globals.h somewhere in this file?