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 @node GNU Emacs Internals, Standard Errors, Tips, Top
6 @comment node-name, next, previous, up
7 @appendix GNU Emacs Internals
9 This chapter describes how the runnable Emacs executable is dumped with
10 the preloaded Lisp libraries in it, how storage is allocated, and some
11 internal aspects of GNU Emacs that may be of interest to C programmers.
14 * Building Emacs:: How the dumped Emacs is made.
15 * Pure Storage:: Kludge to make preloaded Lisp functions shareable.
16 * Garbage Collection:: Reclaiming space for Lisp objects no longer used.
17 * Memory Usage:: Info about total size of Lisp objects made so far.
18 * Writing Emacs Primitives:: Writing C code for Emacs.
19 * Object Internals:: Data formats of buffers, windows, processes.
23 @section 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 developers.
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
35 I/O routines, but not the editing commands.
37 @cindex @file{loadup.el}
38 The command @w{@command{temacs -l loadup}} would run @file{temacs}
39 and direct it to load @file{loadup.el}. The @code{loadup} library
40 loads additional Lisp libraries, which set up the normal Emacs editing
41 environment. After this step, the Emacs executable is no longer
45 Because it takes some time to load the standard Lisp files, the
46 @file{temacs} executable usually isn't run directly by users.
47 Instead, as one of the last steps of building Emacs, the command
48 @samp{temacs -batch -l loadup dump} is run. The special @samp{dump}
49 argument causes @command{temacs} to dump out an executable program,
50 called @file{emacs}, which has all the standard Lisp files preloaded.
51 (The @samp{-batch} argument prevents @file{temacs} from trying to
52 initialize any of its data on the terminal, so that the tables of
53 terminal information are empty in the dumped Emacs.)
55 @cindex preloaded Lisp files
56 @vindex preloaded-file-list
57 The dumped @file{emacs} executable (also called a @dfn{pure} Emacs)
58 is the one which is installed. The variable
59 @code{preloaded-file-list} stores a list of the Lisp files preloaded
60 into the dumped Emacs. If you port Emacs to a new operating system,
61 and are not able to implement dumping, then Emacs must load
62 @file{loadup.el} each time it starts.
64 @cindex @file{site-load.el}
65 You can specify additional files to preload by writing a library named
66 @file{site-load.el} that loads them. You may need to rebuild Emacs
67 with an added definition
70 #define SITELOAD_PURESIZE_EXTRA @var{n}
74 to make @var{n} added bytes of pure space to hold the additional files;
75 see @file{src/puresize.h}.
76 (Try adding increments of 20000 until it is big enough.) However, the
77 advantage of preloading additional files decreases as machines get
78 faster. On modern machines, it is usually not advisable.
80 After @file{loadup.el} reads @file{site-load.el}, it finds the
81 documentation strings for primitive and preloaded functions (and
82 variables) in the file @file{etc/DOC} where they are stored, by
83 calling @code{Snarf-documentation} (@pxref{Definition of
84 Snarf-documentation,, Accessing Documentation}).
86 @cindex @file{site-init.el}
87 @cindex preloading additional functions and variables
88 You can specify other Lisp expressions to execute just before dumping
89 by putting them in a library named @file{site-init.el}. This file is
90 executed after the documentation strings are found.
92 If you want to preload function or variable definitions, there are
93 three ways you can do this and make their documentation strings
94 accessible when you subsequently run Emacs:
98 Arrange to scan these files when producing the @file{etc/DOC} file,
99 and load them with @file{site-load.el}.
102 Load the files with @file{site-init.el}, then copy the files into the
103 installation directory for Lisp files when you install Emacs.
106 Specify a @code{nil} value for @code{byte-compile-dynamic-docstrings}
107 as a local variable in each of these files, and load them with either
108 @file{site-load.el} or @file{site-init.el}. (This method has the
109 drawback that the documentation strings take up space in Emacs all the
113 It is not advisable to put anything in @file{site-load.el} or
114 @file{site-init.el} that would alter any of the features that users
115 expect in an ordinary unmodified Emacs. If you feel you must override
116 normal features for your site, do it with @file{default.el}, so that
117 users can override your changes if they wish. @xref{Startup Summary}.
119 In a package that can be preloaded, it is sometimes necessary (or
120 useful) to delay certain evaluations until Emacs subsequently starts
121 up. The vast majority of such cases relate to the values of
122 customizable variables. For example, @code{tutorial-directory} is a
123 variable defined in @file{startup.el}, which is preloaded. The default
124 value is set based on @code{data-directory}. The variable needs to
125 access the value of @code{data-directory} when Emacs starts, not when
126 it is dumped, because the Emacs executable has probably been installed
127 in a different location since it was dumped.
129 @defun custom-initialize-delay symbol value
130 This function delays the initialization of @var{symbol} to the next
131 Emacs start. You normally use this function by specifying it as the
132 @code{:initialize} property of a customizable variable. (The argument
133 @var{value} is unused, and is provided only for compatibility with the
134 form Custom expects.)
137 In the unlikely event that you need a more general functionality than
138 @code{custom-initialize-delay} provides, you can use
139 @code{before-init-hook} (@pxref{Startup Summary}).
141 @defun dump-emacs to-file from-file
143 This function dumps the current state of Emacs into an executable file
144 @var{to-file}. It takes symbols from @var{from-file} (this is normally
145 the executable file @file{temacs}).
147 If you want to use this function in an Emacs that was already dumped,
148 you must run Emacs with @samp{-batch}.
152 @section Pure Storage
155 Emacs Lisp uses two kinds of storage for user-created Lisp objects:
156 @dfn{normal storage} and @dfn{pure storage}. Normal storage is where
157 all the new data created during an Emacs session are kept
158 (@pxref{Garbage Collection}). Pure storage is used for certain data
159 in the preloaded standard Lisp files---data that should never change
160 during actual use of Emacs.
162 Pure storage is allocated only while @command{temacs} is loading the
163 standard preloaded Lisp libraries. In the file @file{emacs}, it is
164 marked as read-only (on operating systems that permit this), so that
165 the memory space can be shared by all the Emacs jobs running on the
166 machine at once. Pure storage is not expandable; a fixed amount is
167 allocated when Emacs is compiled, and if that is not sufficient for
168 the preloaded libraries, @file{temacs} allocates dynamic memory for
169 the part that didn't fit. The resulting image will work, but garbage
170 collection (@pxref{Garbage Collection}) is disabled in this situation,
171 causing a memory leak. Such an overflow normally won't happen unless
172 you try to preload additional libraries or add features to the
173 standard ones. Emacs will display a warning about the overflow when
174 it starts. If this happens, you should increase the compilation
175 parameter @code{SYSTEM_PURESIZE_EXTRA} in the file
176 @file{src/puresize.h} and rebuild Emacs.
178 @defun purecopy object
179 This function makes a copy in pure storage of @var{object}, and returns
180 it. It copies a string by simply making a new string with the same
181 characters, but without text properties, in pure storage. It
182 recursively copies the contents of vectors and cons cells. It does
183 not make copies of other objects such as symbols, but just returns
184 them unchanged. It signals an error if asked to copy markers.
186 This function is a no-op except while Emacs is being built and dumped;
187 it is usually called only in preloaded Lisp files.
190 @defvar pure-bytes-used
191 The value of this variable is the number of bytes of pure storage
192 allocated so far. Typically, in a dumped Emacs, this number is very
193 close to the total amount of pure storage available---if it were not,
194 we would preallocate less.
198 This variable determines whether @code{defun} should make a copy of the
199 function definition in pure storage. If it is non-@code{nil}, then the
200 function definition is copied into pure storage.
202 This flag is @code{t} while loading all of the basic functions for
203 building Emacs initially (allowing those functions to be shareable and
204 non-collectible). Dumping Emacs as an executable always writes
205 @code{nil} in this variable, regardless of the value it actually has
206 before and after dumping.
208 You should not change this flag in a running Emacs.
211 @node Garbage Collection
212 @section Garbage Collection
214 @cindex memory allocation
215 When a program creates a list or the user defines a new function
216 (such as by loading a library), that data is placed in normal storage.
217 If normal storage runs low, then Emacs asks the operating system to
218 allocate more memory. Different types of Lisp objects, such as
219 symbols, cons cells, markers, etc., are segregated in distinct blocks
220 in memory. (Vectors, long strings, buffers and certain other editing
221 types, which are fairly large, are allocated in individual blocks, one
222 per object, while small strings are packed into blocks of 8k bytes.)
224 @cindex garbage collection
225 It is quite common to use some storage for a while, then release it
226 by (for example) killing a buffer or deleting the last pointer to an
227 object. Emacs provides a @dfn{garbage collector} to reclaim this
228 abandoned storage. The garbage collector operates by finding and
229 marking all Lisp objects that are still accessible to Lisp programs.
230 To begin with, it assumes all the symbols, their values and associated
231 function definitions, and any data presently on the stack, are
232 accessible. Any objects that can be reached indirectly through other
233 accessible objects are also accessible.
235 When marking is finished, all objects still unmarked are garbage. No
236 matter what the Lisp program or the user does, it is impossible to refer
237 to them, since there is no longer a way to reach them. Their space
238 might as well be reused, since no one will miss them. The second
239 (``sweep'') phase of the garbage collector arranges to reuse them.
241 @c ??? Maybe add something describing weak hash tables here?
244 The sweep phase puts unused cons cells onto a @dfn{free list}
245 for future allocation; likewise for symbols and markers. It compacts
246 the accessible strings so they occupy fewer 8k blocks; then it frees the
247 other 8k blocks. Vectors, buffers, windows, and other large objects are
248 individually allocated and freed using @code{malloc} and @code{free}.
250 @cindex CL note---allocate more storage
252 @b{Common Lisp note:} Unlike other Lisps, GNU Emacs Lisp does not
253 call the garbage collector when the free list is empty. Instead, it
254 simply requests the operating system to allocate more storage, and
255 processing continues until @code{gc-cons-threshold} bytes have been
258 This means that you can make sure that the garbage collector will not
259 run during a certain portion of a Lisp program by calling the garbage
260 collector explicitly just before it (provided that portion of the
261 program does not use so much space as to force a second garbage
265 @deffn Command garbage-collect
266 This command runs a garbage collection, and returns information on
267 the amount of space in use. (Garbage collection can also occur
268 spontaneously if you use more than @code{gc-cons-threshold} bytes of
269 Lisp data since the previous garbage collection.)
271 @code{garbage-collect} returns a list containing the following
276 ((@var{used-conses} . @var{free-conses})
277 (@var{used-syms} . @var{free-syms})
279 (@var{used-miscs} . @var{free-miscs})
280 @var{used-string-chars}
281 @var{used-vector-slots}
282 (@var{used-floats} . @var{free-floats})
283 (@var{used-intervals} . @var{free-intervals})
284 (@var{used-strings} . @var{free-strings}))
292 @result{} ((106886 . 13184) (9769 . 0)
293 (7731 . 4651) 347543 121628
294 (31 . 94) (1273 . 168)
299 Here is a table explaining each element:
303 The number of cons cells in use.
306 The number of cons cells for which space has been obtained from the
307 operating system, but that are not currently being used.
310 The number of symbols in use.
313 The number of symbols for which space has been obtained from the
314 operating system, but that are not currently being used.
317 The number of miscellaneous objects in use. These include markers and
318 overlays, plus certain objects not visible to users.
321 The number of miscellaneous objects for which space has been obtained
322 from the operating system, but that are not currently being used.
324 @item used-string-chars
325 The total size of all strings, in characters.
327 @item used-vector-slots
328 The total number of elements of existing vectors.
331 The number of floats in use.
334 The number of floats for which space has been obtained from the
335 operating system, but that are not currently being used.
338 The number of intervals in use. Intervals are an internal
339 data structure used for representing text properties.
342 The number of intervals for which space has been obtained
343 from the operating system, but that are not currently being used.
346 The number of strings in use.
349 The number of string headers for which the space was obtained from the
350 operating system, but which are currently not in use. (A string
351 object consists of a header and the storage for the string text
352 itself; the latter is only allocated when the string is created.)
355 If there was overflow in pure space (@pxref{Pure Storage}),
356 @code{garbage-collect} returns @code{nil}, because a real garbage
357 collection cannot be done.
360 @defopt garbage-collection-messages
361 If this variable is non-@code{nil}, Emacs displays a message at the
362 beginning and end of garbage collection. The default value is
367 This is a normal hook that is run at the end of garbage collection.
368 Garbage collection is inhibited while the hook functions run, so be
369 careful writing them.
372 @defopt gc-cons-threshold
373 The value of this variable is the number of bytes of storage that must
374 be allocated for Lisp objects after one garbage collection in order to
375 trigger another garbage collection. A cons cell counts as eight bytes,
376 a string as one byte per character plus a few bytes of overhead, and so
377 on; space allocated to the contents of buffers does not count. Note
378 that the subsequent garbage collection does not happen immediately when
379 the threshold is exhausted, but only the next time the Lisp evaluator is
382 The initial threshold value is 800,000. If you specify a larger
383 value, garbage collection will happen less often. This reduces the
384 amount of time spent garbage collecting, but increases total memory use.
385 You may want to do this when running a program that creates lots of
388 You can make collections more frequent by specifying a smaller value,
389 down to 10,000. A value less than 10,000 will remain in effect only
390 until the subsequent garbage collection, at which time
391 @code{garbage-collect} will set the threshold back to 10,000.
394 @defopt gc-cons-percentage
395 The value of this variable specifies the amount of consing before a
396 garbage collection occurs, as a fraction of the current heap size.
397 This criterion and @code{gc-cons-threshold} apply in parallel, and
398 garbage collection occurs only when both criteria are satisfied.
400 As the heap size increases, the time to perform a garbage collection
401 increases. Thus, it can be desirable to do them less frequently in
405 The value returned by @code{garbage-collect} describes the amount of
406 memory used by Lisp data, broken down by data type. By contrast, the
407 function @code{memory-limit} provides information on the total amount of
408 memory Emacs is currently using.
411 This function returns the address of the last byte Emacs has allocated,
412 divided by 1024. We divide the value by 1024 to make sure it fits in a
415 You can use this to get a general idea of how your actions affect the
420 This variable is @code{t} if Emacs is nearly out of memory for Lisp
421 objects, and @code{nil} otherwise.
424 @defun memory-use-counts
425 This returns a list of numbers that count the number of objects
426 created in this Emacs session. Each of these counters increments for
427 a certain kind of object. See the documentation string for details.
431 This variable contains the total number of garbage collections
432 done so far in this Emacs session.
436 This variable contains the total number of seconds of elapsed time
437 during garbage collection so far in this Emacs session, as a floating
442 @section Memory Usage
445 These functions and variables give information about the total amount
446 of memory allocation that Emacs has done, broken down by data type.
447 Note the difference between these and the values returned by
448 @code{garbage-collect}; those count objects that currently exist, but
449 these count the number or size of all allocations, including those for
450 objects that have since been freed.
452 @defvar cons-cells-consed
453 The total number of cons cells that have been allocated so far
454 in this Emacs session.
457 @defvar floats-consed
458 The total number of floats that have been allocated so far
459 in this Emacs session.
462 @defvar vector-cells-consed
463 The total number of vector cells that have been allocated so far
464 in this Emacs session.
467 @defvar symbols-consed
468 The total number of symbols that have been allocated so far
469 in this Emacs session.
472 @defvar string-chars-consed
473 The total number of string characters that have been allocated so far
477 @defvar misc-objects-consed
478 The total number of miscellaneous objects that have been allocated so
479 far in this session. These include markers and overlays, plus
480 certain objects not visible to users.
483 @defvar intervals-consed
484 The total number of intervals that have been allocated so far
485 in this Emacs session.
488 @defvar strings-consed
489 The total number of strings that have been allocated so far in this
493 @node Writing Emacs Primitives
494 @section Writing Emacs Primitives
495 @cindex primitive function internals
496 @cindex writing Emacs primitives
498 Lisp primitives are Lisp functions implemented in C. The details of
499 interfacing the C function so that Lisp can call it are handled by a few
500 C macros. The only way to really understand how to write new C code is
501 to read the source, but we can explain some things here.
503 An example of a special form is the definition of @code{or}, from
504 @file{eval.c}. (An ordinary function would have the same general
507 @cindex garbage collection protection
510 DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
511 doc: /* Eval args until one of them yields non-nil, then return
513 The remaining args are not evalled at all.
514 If all args return nil, return nil.
517 usage: (or CONDITIONS ...) */)
520 register Lisp_Object val = Qnil;
531 val = eval_sub (XCAR (args));
545 @cindex @code{DEFUN}, C macro to define Lisp primitives
546 Let's start with a precise explanation of the arguments to the
547 @code{DEFUN} macro. Here is a template for them:
550 DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc})
555 This is the name of the Lisp symbol to define as the function name; in
556 the example above, it is @code{or}.
559 This is the C function name for this function. This is the name that
560 is used in C code for calling the function. The name is, by
561 convention, @samp{F} prepended to the Lisp name, with all dashes
562 (@samp{-}) in the Lisp name changed to underscores. Thus, to call
563 this function from C code, call @code{For}.
566 This is a C variable name to use for a structure that holds the data for
567 the subr object that represents the function in Lisp. This structure
568 conveys the Lisp symbol name to the initialization routine that will
569 create the symbol and store the subr object as its definition. By
570 convention, this name is always @var{fname} with @samp{F} replaced with
574 This is the minimum number of arguments that the function requires. The
575 function @code{or} allows a minimum of zero arguments.
578 This is the maximum number of arguments that the function accepts, if
579 there is a fixed maximum. Alternatively, it can be @code{UNEVALLED},
580 indicating a special form that receives unevaluated arguments, or
581 @code{MANY}, indicating an unlimited number of evaluated arguments (the
582 equivalent of @code{&rest}). Both @code{UNEVALLED} and @code{MANY} are
583 macros. If @var{max} is a number, it must be more than @var{min} but
587 This is an interactive specification, a string such as might be used as
588 the argument of @code{interactive} in a Lisp function. In the case of
589 @code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be
590 called interactively. A value of @code{""} indicates a function that
591 should receive no arguments when called interactively. If the value
592 begins with a @samp{(}, the string is evaluated as a Lisp form.
593 For examples of the last two forms, see @code{widen} and
594 @code{narrow-to-region} in @file{editfns.c}.
597 This is the documentation string. It uses C comment syntax rather
598 than C string syntax because comment syntax requires nothing special
599 to include multiple lines. The @samp{doc:} identifies the comment
600 that follows as the documentation string. The @samp{/*} and @samp{*/}
601 delimiters that begin and end the comment are not part of the
602 documentation string.
604 If the last line of the documentation string begins with the keyword
605 @samp{usage:}, the rest of the line is treated as the argument list
606 for documentation purposes. This way, you can use different argument
607 names in the documentation string from the ones used in the C code.
608 @samp{usage:} is required if the function has an unlimited number of
611 All the usual rules for documentation strings in Lisp code
612 (@pxref{Documentation Tips}) apply to C code documentation strings
616 After the call to the @code{DEFUN} macro, you must write the
617 argument list for the C function, including the types for the
618 arguments. If the primitive accepts a fixed maximum number of Lisp
619 arguments, there must be one C argument for each Lisp argument, and
620 each argument must be of type @code{Lisp_Object}. (Various macros and
621 functions for creating values of type @code{Lisp_Object} are declared
622 in the file @file{lisp.h}.) If the primitive has no upper limit on
623 the number of Lisp arguments, it must have exactly two C arguments:
624 the first is the number of Lisp arguments, and the second is the
625 address of a block containing their values. These have types
626 @code{int} and @w{@code{Lisp_Object *}} respectively.
628 @cindex @code{GCPRO} and @code{UNGCPRO}
629 @cindex protect C variables from garbage collection
630 Within the function @code{For} itself, note the use of the macros
631 @code{GCPRO1} and @code{UNGCPRO}. These macros are defined for the
632 sake of the few platforms which do not use Emacs' default
633 stack-marking garbage collector. The @code{GCPRO1} macro ``protects''
634 a variable from garbage collection, explicitly informing the garbage
635 collector that that variable and all its contents must be as
636 accessible. GC protection is necessary in any function which can
637 perform Lisp evaluation by calling @code{eval_sub} or @code{Feval} as
638 a subroutine, either directly or indirectly.
640 It suffices to ensure that at least one pointer to each object is
641 GC-protected. Thus, a particular local variable can do without
642 protection if it is certain that the object it points to will be
643 preserved by some other pointer (such as another local variable that
644 has a @code{GCPRO}). Otherwise, the local variable needs a
647 The macro @code{GCPRO1} protects just one local variable. If you
648 want to protect two variables, use @code{GCPRO2} instead; repeating
649 @code{GCPRO1} will not work. Macros @code{GCPRO3}, @code{GCPRO4},
650 @code{GCPRO5}, and @code{GCPRO6} also exist. All these macros
651 implicitly use local variables such as @code{gcpro1}; you must declare
652 these explicitly, with type @code{struct gcpro}. Thus, if you use
653 @code{GCPRO2}, you must declare @code{gcpro1} and @code{gcpro2}.
655 @code{UNGCPRO} cancels the protection of the variables that are
656 protected in the current function. It is necessary to do this
659 You must not use C initializers for static or global variables unless
660 the variables are never written once Emacs is dumped. These variables
661 with initializers are allocated in an area of memory that becomes
662 read-only (on certain operating systems) as a result of dumping Emacs.
665 @cindex @code{defsubr}, Lisp symbol for a primitive
666 Defining the C function is not enough to make a Lisp primitive
667 available; you must also create the Lisp symbol for the primitive and
668 store a suitable subr object in its function cell. The code looks like
672 defsubr (&@var{sname});
676 Here @var{sname} is the name you used as the third argument to @code{DEFUN}.
678 If you add a new primitive to a file that already has Lisp primitives
679 defined in it, find the function (near the end of the file) named
680 @code{syms_of_@var{something}}, and add the call to @code{defsubr}
681 there. If the file doesn't have this function, or if you create a new
682 file, add to it a @code{syms_of_@var{filename}} (e.g.,
683 @code{syms_of_myfile}). Then find the spot in @file{emacs.c} where all
684 of these functions are called, and add a call to
685 @code{syms_of_@var{filename}} there.
687 @anchor{Defining Lisp variables in C}
688 @vindex byte-boolean-vars
689 @cindex defining Lisp variables in C
690 @cindex @code{DEFVAR_INT}, @code{DEFVAR_LISP}, @code{DEFVAR_BOOL}
691 The function @code{syms_of_@var{filename}} is also the place to define
692 any C variables that are to be visible as Lisp variables.
693 @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible
694 in Lisp. @code{DEFVAR_INT} makes a C variable of type @code{int}
695 visible in Lisp with a value that is always an integer.
696 @code{DEFVAR_BOOL} makes a C variable of type @code{int} visible in Lisp
697 with a value that is either @code{t} or @code{nil}. Note that variables
698 defined with @code{DEFVAR_BOOL} are automatically added to the list
699 @code{byte-boolean-vars} used by the byte compiler.
701 @cindex defining customization variables in C
702 If you want to make a Lisp variables that is defined in C behave
703 like one declared with @code{defcustom}, add an appropriate entry to
706 @cindex @code{staticpro}, protection from GC
707 If you define a file-scope C variable of type @code{Lisp_Object},
708 you must protect it from garbage-collection by calling @code{staticpro}
709 in @code{syms_of_@var{filename}}, like this:
712 staticpro (&@var{variable});
715 Here is another example function, with more complicated arguments.
716 This comes from the code in @file{window.c}, and it demonstrates the use
717 of macros and functions to manipulate Lisp objects.
721 DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
722 Scoordinates_in_window_p, 2, 2, 0,
723 doc: /* Return non-nil if COORDINATES are in WINDOW.
727 or `right-margin' is returned. */)
728 (register Lisp_Object coordinates, Lisp_Object window)
737 CHECK_LIVE_WINDOW (window);
738 w = XWINDOW (window);
739 f = XFRAME (w->frame);
740 CHECK_CONS (coordinates);
741 lx = Fcar (coordinates);
742 ly = Fcdr (coordinates);
743 CHECK_NUMBER_OR_FLOAT (lx);
744 CHECK_NUMBER_OR_FLOAT (ly);
745 x = FRAME_PIXEL_X_FROM_CANON_X (f, lx) + FRAME_INTERNAL_BORDER_WIDTH(f);
746 y = FRAME_PIXEL_Y_FROM_CANON_Y (f, ly) + FRAME_INTERNAL_BORDER_WIDTH(f);
750 switch (coordinates_in_window (w, x, y))
752 case ON_NOTHING: /* NOT in window at all. */
759 case ON_MODE_LINE: /* In mode line of window. */
766 case ON_SCROLL_BAR: /* On scroll-bar of window. */
767 /* Historically we are supposed to return nil in this case. */
779 Note that C code cannot call functions by name unless they are defined
780 in C. The way to call a function written in Lisp is to use
781 @code{Ffuncall}, which embodies the Lisp function @code{funcall}. Since
782 the Lisp function @code{funcall} accepts an unlimited number of
783 arguments, in C it takes two: the number of Lisp-level arguments, and a
784 one-dimensional array containing their values. The first Lisp-level
785 argument is the Lisp function to call, and the rest are the arguments to
786 pass to it. Since @code{Ffuncall} can call the evaluator, you must
787 protect pointers from garbage collection around the call to
790 The C functions @code{call0}, @code{call1}, @code{call2}, and so on,
791 provide handy ways to call a Lisp function conveniently with a fixed
792 number of arguments. They work by calling @code{Ffuncall}.
794 @file{eval.c} is a very good file to look through for examples;
795 @file{lisp.h} contains the definitions for some important macros and
798 If you define a function which is side-effect free, update the code
799 in @file{byte-opt.el} that binds @code{side-effect-free-fns} and
800 @code{side-effect-and-error-free-fns} so that the compiler optimizer
803 @node Object Internals
804 @section Object Internals
805 @cindex object internals
807 @c FIXME Is this still true? Does --with-wide-int affect anything?
808 GNU Emacs Lisp manipulates many different types of data. The actual
809 data are stored in a heap and the only access that programs have to it
810 is through pointers. Each pointer is 32 bits wide on 32-bit machines,
811 and 64 bits wide on 64-bit machines; three of these bits are used for
812 the tag that identifies the object's type, and the remainder are used
813 to address the object.
815 Because Lisp objects are represented as tagged pointers, it is always
816 possible to determine the Lisp data type of any object. The C data type
817 @code{Lisp_Object} can hold any Lisp object of any data type. Ordinary
818 variables have type @code{Lisp_Object}, which means they can hold any
819 type of Lisp value; you can determine the actual data type only at run
820 time. The same is true for function arguments; if you want a function
821 to accept only a certain type of argument, you must check the type
822 explicitly using a suitable predicate (@pxref{Type Predicates}).
823 @cindex type checking internals
826 * Buffer Internals:: Components of a buffer structure.
827 * Window Internals:: Components of a window structure.
828 * Process Internals:: Components of a process structure.
831 @node Buffer Internals
832 @subsection Buffer Internals
833 @cindex internals, of buffer
834 @cindex buffer internals
836 Two structures (see @file{buffer.h}) are used to represent buffers
837 in C. The @code{buffer_text} structure contains fields describing the
838 text of a buffer; the @code{buffer} structure holds other fields. In
839 the case of indirect buffers, two or more @code{buffer} structures
840 reference the same @code{buffer_text} structure.
842 Here are some of the fields in @code{struct buffer_text}:
846 The address of the buffer contents.
850 The character and byte positions of the buffer gap. @xref{Buffer
855 The character and byte positions of the end of the buffer text.
858 The size of buffer's gap. @xref{Buffer Gap}.
863 @itemx overlay_modiff
864 These fields count the number of buffer-modification events performed
865 in this buffer. @code{modiff} is incremented after each
866 buffer-modification event, and is never otherwise changed;
867 @code{save_modiff} contains the value of @code{modiff} the last time
868 the buffer was visited or saved; @code{chars_modiff} counts only
869 modifications to the characters in the buffer, ignoring all other
870 kinds of changes; and @code{overlay_modiff} counts only modifications
875 The number of characters at the start and end of the text that are
876 known to be unchanged since the last complete redisplay.
878 @item unchanged_modified
879 @itemx overlay_unchanged_modified
880 The values of @code{modiff} and @code{overlay_modiff}, respectively,
881 after the last complete redisplay. If their current values match
882 @code{modiff} or @code{overlay_modiff}, that means
883 @code{beg_unchanged} and @code{end_unchanged} contain no useful
887 The markers that refer to this buffer. This is actually a single
888 marker, and successive elements in its marker @code{chain} are the other
889 markers referring to this buffer text.
892 The interval tree which records the text properties of this buffer.
895 Some of the fields of @code{struct buffer} are:
899 A @code{struct vectorlike_header} structure where @code{header.next}
900 points to the next buffer, in the chain of all buffers (including
901 killed buffers). This chain is used only for garbage collection, in
902 order to collect killed buffers properly. Note that vectors, and most
903 kinds of objects allocated as vectors, are all on one chain, but
904 buffers are on a separate chain of their own.
907 A @code{struct buffer_text} structure that ordinarily holds the buffer
908 contents. In indirect buffers, this field is not used.
911 A pointer to the @code{buffer_text} structure for this buffer. In an
912 ordinary buffer, this is the @code{own_text} field above. In an
913 indirect buffer, this is the @code{own_text} field of the base buffer.
917 The character and byte positions of point in a buffer.
921 The character and byte positions of the beginning of the accessible
922 range of text in the buffer.
926 The character and byte positions of the end of the accessible range of
930 In an indirect buffer, this points to the base buffer. In an ordinary
934 This field contains flags indicating that certain variables are local
935 in this buffer. Such variables are declared in the C code using
936 @code{DEFVAR_PER_BUFFER}, and their buffer-local bindings are stored
937 in fields in the buffer structure itself. (Some of these fields are
938 described in this table.)
941 The modification time of the visited file. It is set when the file is
942 written or read. Before writing the buffer into a file, this field is
943 compared to the modification time of the file to see if the file has
944 changed on disk. @xref{Buffer Modification}.
946 @item auto_save_modified
947 The time when the buffer was last auto-saved.
949 @item last_window_start
950 The @code{window-start} position in the buffer as of the last time the
951 buffer was displayed in a window.
954 This flag indicates that narrowing has changed in the buffer.
957 @item prevent_redisplay_optimizations_p
958 This flag indicates that redisplay optimizations should not be used to
962 This field holds the current overlay center position. @xref{Managing
965 @item overlays_before
966 @itemx overlays_after
967 These fields hold, respectively, a list of overlays that end at or
968 before the current overlay center, and a list of overlays that end
969 after the current overlay center. @xref{Managing Overlays}.
970 @code{overlays_before} is sorted in order of decreasing end position,
971 and @code{overlays_after} is sorted in order of increasing beginning
974 @c FIXME? the following are now all Lisp_Object BUFFER_INTERNAL_FIELD (foo).
977 A Lisp string that names the buffer. It is guaranteed to be unique.
981 The length of the file this buffer is visiting, when last read or
982 saved. This and other fields concerned with saving are not kept in
983 the @code{buffer_text} structure because indirect buffers are never
987 The directory for expanding relative file names. This is the value of
988 the buffer-local variable @code{default-directory} (@pxref{File Name Expansion}).
991 The name of the file visited in this buffer, or @code{nil}. This is
992 the value of the buffer-local variable @code{buffer-file-name}
993 (@pxref{Buffer File Name}).
997 @itemx auto_save_file_name
998 @itemx auto_save_file_format
1001 @itemx file_truename
1002 @itemx invisibility_spec
1003 @itemx display_count
1005 These fields store the values of Lisp variables that are automatically
1006 buffer-local (@pxref{Buffer-Local Variables}), whose corresponding
1007 variable names have the additional prefix @code{buffer-} and have
1008 underscores replaced with dashes. For instance, @code{undo_list}
1009 stores the value of @code{buffer-undo-list}.
1012 The mark for the buffer. The mark is a marker, hence it is also
1013 included on the list @code{markers}. @xref{The Mark}.
1015 @item local_var_alist
1016 The association list describing the buffer-local variable bindings of
1017 this buffer, not including the built-in buffer-local bindings that
1018 have special slots in the buffer object. (Those slots are omitted
1019 from this table.) @xref{Buffer-Local Variables}.
1022 Symbol naming the major mode of this buffer, e.g., @code{lisp-mode}.
1025 Pretty name of the major mode, e.g., @code{"Lisp"}.
1030 @itemx category_table
1031 @itemx display_table
1032 These fields store the buffer's local keymap (@pxref{Keymaps}), abbrev
1033 table (@pxref{Abbrev Tables}), syntax table (@pxref{Syntax Tables}),
1034 category table (@pxref{Categories}), and display table (@pxref{Display
1037 @item downcase_table
1039 @itemx case_canon_table
1040 These fields store the conversion tables for converting text to lower
1041 case, upper case, and for canonicalizing text for case-fold search.
1045 An alist of the minor modes of this buffer.
1050 These fields are only used in an indirect buffer, or in a buffer that
1051 is the base of an indirect buffer. Each holds a marker that records
1052 @code{pt}, @code{begv}, and @code{zv} respectively, for this buffer
1053 when the buffer is not current.
1055 @item mode_line_format
1056 @itemx header_line_format
1057 @itemx case_fold_search
1061 @itemx auto_fill_function
1062 @itemx truncate_lines
1065 @itemx bidi_display_reordering
1066 @itemx bidi_paragraph_direction
1067 @itemx selective_display
1068 @itemx selective_display_ellipses
1069 @itemx overwrite_mode
1072 @itemx enable_multibyte_characters
1073 @itemx buffer_file_coding_system
1074 @itemx cache_long_line_scans
1075 @itemx point_before_scroll
1076 @itemx left_fringe_width
1077 @itemx right_fringe_width
1078 @itemx fringes_outside_margins
1079 @itemx scroll_bar_width
1080 @itemx indicate_empty_lines
1081 @itemx indicate_buffer_boundaries
1082 @itemx fringe_indicator_alist
1083 @itemx fringe_cursor_alist
1084 @itemx scroll_up_aggressively
1085 @itemx scroll_down_aggressively
1087 @itemx cursor_in_non_selected_windows
1088 These fields store the values of Lisp variables that are automatically
1089 buffer-local (@pxref{Buffer-Local Variables}), whose corresponding
1090 variable names have underscores replaced with dashes. For instance,
1091 @code{mode_line_format} stores the value of @code{mode-line-format}.
1093 @item last_selected_window
1094 This is the last window that was selected with this buffer in it, or @code{nil}
1095 if that window no longer displays this buffer.
1098 @node Window Internals
1099 @subsection Window Internals
1100 @cindex internals, of window
1101 @cindex window internals
1103 The fields of a window (for a complete list, see the definition of
1104 @code{struct window} in @file{window.h}) include:
1108 The frame that this window is on.
1111 Non-@code{nil} if this window is a minibuffer window.
1114 Internally, Emacs arranges windows in a tree; each group of siblings has
1115 a parent window whose area includes all the siblings. This field points
1116 to a window's parent.
1118 Parent windows do not display buffers, and play little role in display
1119 except to shape their child windows. Emacs Lisp programs usually have
1120 no access to the parent windows; they operate on the windows at the
1121 leaves of the tree, which actually display buffers.
1125 These fields contain the window's leftmost child and its topmost child
1126 respectively. @code{hchild} is used if the window is subdivided
1127 horizontally by child windows, and @code{vchild} if it is subdivided
1128 vertically. In a live window, only one of @code{hchild}, @code{vchild},
1129 and @code{buffer} (q.v.) is non-@code{nil}.
1133 The next sibling and previous sibling of this window. @code{next} is
1134 @code{nil} if the window is the right-most or bottom-most in its group;
1135 @code{prev} is @code{nil} if it is the left-most or top-most in its
1139 The left-hand edge of the window, measured in columns, relative to the
1140 leftmost column in the frame (column 0).
1143 The top edge of the window, measured in lines, relative to the topmost
1144 line in the frame (line 0).
1148 The width and height of the window, measured in columns and lines
1149 respectively. The width includes the scroll bar and fringes, and/or
1150 the separator line on the right of the window (if any).
1153 The buffer that the window is displaying.
1156 A marker pointing to the position in the buffer that is the first
1157 character displayed in the window.
1160 @cindex window point internals
1161 This is the value of point in the current buffer when this window is
1162 selected; when it is not selected, it retains its previous value.
1165 If this flag is non-@code{nil}, it says that the window has been
1166 scrolled explicitly by the Lisp program. This affects what the next
1167 redisplay does if point is off the screen: instead of scrolling the
1168 window to show the text around point, it moves point to a location that
1171 @item frozen_window_start_p
1172 This field is set temporarily to 1 to indicate to redisplay that
1173 @code{start} of this window should not be changed, even if point
1176 @item start_at_line_beg
1177 Non-@code{nil} means current value of @code{start} was the beginning of a line
1181 This is the last time that the window was selected. The function
1182 @code{get-lru-window} uses this field.
1184 @item sequence_number
1185 A unique number assigned to this window when it was created.
1188 The @code{modiff} field of the window's buffer, as of the last time
1189 a redisplay completed in this window.
1191 @item last_overlay_modified
1192 The @code{overlay_modiff} field of the window's buffer, as of the last
1193 time a redisplay completed in this window.
1196 The buffer's value of point, as of the last time a redisplay completed
1200 A non-@code{nil} value means the window's buffer was ``modified'' when the
1201 window was last updated.
1203 @item vertical_scroll_bar
1204 This window's vertical scroll bar.
1206 @item left_margin_cols
1207 @itemx right_margin_cols
1208 The widths of the left and right margins in this window. A value of
1209 @code{nil} means no margin.
1211 @item left_fringe_width
1212 @itemx right_fringe_width
1213 The widths of the left and right fringes in this window. A value of
1214 @code{nil} or @code{t} means use the values of the frame.
1216 @item fringes_outside_margins
1217 A non-@code{nil} value means the fringes outside the display margins;
1218 othersize they are between the margin and the text.
1220 @item window_end_pos
1221 This is computed as @code{z} minus the buffer position of the last glyph
1222 in the current matrix of the window. The value is only valid if
1223 @code{window_end_valid} is not @code{nil}.
1225 @item window_end_bytepos
1226 The byte position corresponding to @code{window_end_pos}.
1228 @item window_end_vpos
1229 The window-relative vertical position of the line containing
1230 @code{window_end_pos}.
1232 @item window_end_valid
1233 This field is set to a non-@code{nil} value if @code{window_end_pos} is truly
1234 valid. This is @code{nil} if nontrivial redisplay is pre-empted, since in that
1235 case the display that @code{window_end_pos} was computed for did not get
1239 A structure describing where the cursor is in this window.
1242 The value of @code{cursor} as of the last redisplay that finished.
1245 A structure describing where the cursor of this window physically is.
1247 @item phys_cursor_type
1248 @c FIXME What is this?
1249 @c itemx phys_cursor_ascent
1250 @itemx phys_cursor_height
1251 @itemx phys_cursor_width
1252 The type, height, and width of the cursor that was last displayed on
1255 @item phys_cursor_on_p
1256 This field is non-zero if the cursor is physically on.
1259 Non-zero means the cursor in this window is logically off. This is
1260 used for blinking the cursor.
1262 @item last_cursor_off_p
1263 This field contains the value of @code{cursor_off_p} as of the time of
1266 @item must_be_updated_p
1267 This is set to 1 during redisplay when this window must be updated.
1270 This is the number of columns that the display in the window is scrolled
1271 horizontally to the left. Normally, this is 0.
1274 Vertical scroll amount, in pixels. Normally, this is 0.
1277 Non-@code{nil} if this window is dedicated to its buffer.
1280 The window's display table, or @code{nil} if none is specified for it.
1282 @item update_mode_line
1283 Non-@code{nil} means this window's mode line needs to be updated.
1285 @item base_line_number
1286 The line number of a certain position in the buffer, or @code{nil}.
1287 This is used for displaying the line number of point in the mode line.
1290 The position in the buffer for which the line number is known, or
1291 @code{nil} meaning none is known. If it is a buffer, don't display
1292 the line number as long as the window shows that buffer.
1294 @item region_showing
1295 If the region (or part of it) is highlighted in this window, this field
1296 holds the mark position that made one end of that region. Otherwise,
1297 this field is @code{nil}.
1299 @item column_number_displayed
1300 The column number currently displayed in this window's mode line, or @code{nil}
1301 if column numbers are not being displayed.
1303 @item current_matrix
1304 @itemx desired_matrix
1305 Glyph matrices describing the current and desired display of this window.
1308 @node Process Internals
1309 @subsection Process Internals
1310 @cindex internals, of process
1311 @cindex process internals
1313 The fields of a process (for a complete list, see the definition of
1314 @code{struct Lisp_Process} in @file{process.h}) include:
1318 A string, the name of the process.
1321 A list containing the command arguments that were used to start this
1322 process. For a network or serial process, it is @code{nil} if the
1323 process is running or @code{t} if the process is stopped.
1326 If non-@code{nil}, a function used to accept output from the process
1327 instead of a buffer.
1330 If non-@code{nil}, a function called whenever the state of the process
1334 The associated buffer of the process.
1337 An integer, the operating system's process @acronym{ID}.
1338 Pseudo-processes such as network or serial connections use a value of 0.
1341 A flag, @code{t} if this is really a child process. For a network or
1342 serial connection, it is a plist based on the arguments to
1343 @code{make-network-process} or @code{make-serial-process}.
1346 A marker indicating the position of the end of the last output from this
1347 process inserted into the buffer. This is often but not always the end
1350 @item kill_without_query
1351 If this is non-zero, killing Emacs while this process is still running
1352 does not ask for confirmation about killing the process.
1355 The raw process status, as returned by the @code{wait} system call.
1358 The process status, as @code{process-status} should return it.
1362 If these two fields are not equal, a change in the status of the process
1363 needs to be reported, either by running the sentinel or by inserting a
1364 message in the process buffer.
1367 Non-@code{nil} if communication with the subprocess uses a @acronym{PTY};
1368 @code{nil} if it uses a pipe.
1371 The file descriptor for input from the process.
1374 The file descriptor for output to the process.
1377 The name of the terminal that the subprocess is using,
1378 or @code{nil} if it is using pipes.
1380 @item decode_coding_system
1381 Coding-system for decoding the input from this process.
1384 A working buffer for decoding.
1386 @item decoding_carryover
1387 Size of carryover in decoding.
1389 @item encode_coding_system
1390 Coding-system for encoding the output to this process.
1393 A working buffer for encoding.
1395 @item inherit_coding_system_flag
1396 Flag to set @code{coding-system} of the process buffer from the
1397 coding system used to decode process output.
1400 Symbol indicating the type of process: @code{real}, @code{network},
1405 @c FIXME Mention src/globals.h somewhere in this file?