@menu
* Building Emacs:: How the dumped Emacs is made.
-* Pure Storage:: Kludge to make preloaded Lisp functions shareable.
* Garbage Collection:: Reclaiming space for Lisp objects no longer used.
* Stack-allocated Objects:: Temporary conses and strings on C stack.
* Memory Usage:: Info about total size of Lisp objects made so far.
value is @code{nil}.
@end defun
-@node Pure Storage
-@section Pure Storage
-@cindex pure storage
-
- Emacs Lisp uses two kinds of storage for user-created Lisp objects:
-@dfn{normal storage} and @dfn{pure storage}. Normal storage is where
-all the new data created during an Emacs session are kept
-(@pxref{Garbage Collection}). Pure storage is used for certain data
-in the preloaded standard Lisp files---data that should never change
-during actual use of Emacs.
-
- Pure storage is allocated only while @command{temacs} is loading the
-standard preloaded Lisp libraries. In the file @file{emacs}, it is
-marked as read-only (on operating systems that permit this), so that
-the memory space can be shared by all the Emacs jobs running on the
-machine at once. Pure storage is not expandable; a fixed amount is
-allocated when Emacs is compiled, and if that is not sufficient for
-the preloaded libraries, @file{temacs} allocates dynamic memory for
-the part that didn't fit. If Emacs will be dumped using the
-@code{pdump} method (@pxref{Building Emacs}), the pure-space overflow
-is of no special importance (it just means some of the preloaded stuff
-cannot be shared with other Emacs jobs). However, if Emacs will be
-dumped using the now obsolete @code{unexec} method, the resulting
-image will work, but garbage collection (@pxref{Garbage Collection})
-is disabled in this situation, causing a memory leak. Such an
-overflow normally won't happen unless you try to preload additional
-libraries or add features to the standard ones. Emacs will display a
-warning about the overflow when it starts, if it was dumped using
-@code{unexec}. If this happens, you should increase the compilation
-parameter @code{SYSTEM_PURESIZE_EXTRA} in the file
-@file{src/puresize.h} and rebuild Emacs.
-
-@defun purecopy object
-This function makes a copy in pure storage of @var{object}, and returns
-it. It copies a string by simply making a new string with the same
-characters, but without text properties, in pure storage. It
-recursively copies the contents of vectors and cons cells. It does
-not make copies of other objects such as symbols, but just returns
-them unchanged. It signals an error if asked to copy markers.
-
-This function is a no-op except while Emacs is being built and dumped;
-it is usually called only in preloaded Lisp files.
-@end defun
-
-@defvar pure-bytes-used
-The value of this variable is the number of bytes of pure storage
-allocated so far. Typically, in a dumped Emacs, this number is very
-close to the total amount of pure storage available---if it were not,
-we would preallocate less.
-@end defvar
-
-@defvar purify-flag
-This variable determines whether @code{defun} should make a copy of the
-function definition in pure storage. If it is non-@code{nil}, then the
-function definition is copied into pure storage.
-
-This flag is @code{t} while loading all of the basic functions for
-building Emacs initially (allowing those functions to be shareable and
-non-collectible). Dumping Emacs as an executable always writes
-@code{nil} in this variable, regardless of the value it actually has
-before and after dumping.
-
-You should not change this flag in a running Emacs.
-@end defvar
-
@node Garbage Collection
@section Garbage Collection
@item free-size
Heap space which is not currently used, in @var{unit-size} units.
@end table
-
-If there was overflow in pure space (@pxref{Pure Storage}), and Emacs
-was dumped using the (now obsolete) @code{unexec} method
-(@pxref{Building Emacs}), then @code{garbage-collect} returns
-@code{nil}, because a real garbage collection cannot be done in that
-case.
@end deffn
@defopt garbage-collection-messages
the variables are never written once Emacs is dumped. These variables
with initializers are allocated in an area of memory that becomes
read-only (on certain operating systems) as a result of dumping Emacs.
-@xref{Pure Storage}.
@cindex @code{defsubr}, Lisp symbol for a primitive
Defining the C function is not enough to make a Lisp primitive
projects / emacs.git / commitdiff