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[Emacs-diffs] trunk r117987: * internals.texi (Stack-allocated Objects):
From: |
Dmitry Antipov |
Subject: |
[Emacs-diffs] trunk r117987: * internals.texi (Stack-allocated Objects): Describe this feature. |
Date: |
Tue, 30 Sep 2014 15:35:33 +0000 |
User-agent: |
Bazaar (2.6b2) |
------------------------------------------------------------
revno: 117987
revision-id: address@hidden
parent: address@hidden
committer: Dmitry Antipov <address@hidden>
branch nick: trunk
timestamp: Tue 2014-09-30 19:35:16 +0400
message:
* internals.texi (Stack-allocated Objects): Describe this feature.
modified:
doc/lispref/ChangeLog changelog-20091113204419-o5vbwnq5f7feedwu-6155
doc/lispref/internals.texi
internals.texi-20091113204419-o5vbwnq5f7feedwu-6188
=== modified file 'doc/lispref/ChangeLog'
--- a/doc/lispref/ChangeLog 2014-09-15 00:43:29 +0000
+++ b/doc/lispref/ChangeLog 2014-09-30 15:35:16 +0000
@@ -1,3 +1,7 @@
+2014-09-30 Dmitry Antipov <address@hidden>
+
+ * internals.texi (Stack-allocated Objects): Describe this feature.
+
2014-09-15 Daniel Colascione <address@hidden>
* text.texi (Registers): Make `insert-register' documentation
=== modified file 'doc/lispref/internals.texi'
--- a/doc/lispref/internals.texi 2014-07-11 12:49:49 +0000
+++ b/doc/lispref/internals.texi 2014-09-30 15:35:16 +0000
@@ -14,6 +14,7 @@
* 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.
* C Dialect:: What C variant Emacs is written in.
* Writing Emacs Primitives:: Writing C code for Emacs.
@@ -529,6 +530,31 @@
floating-point number.
@end defvar
address@hidden Stack-allocated Objects
address@hidden Stack-allocated Objects
+
address@hidden stack allocation overview
+ The garbage collector described above is used to manage data visible
+from Lisp program, as well as the most of data internally used by the
+interpreter. But sometimes it may be useful to allocate temporary
+internal (i.e. not visible for Lisp program) objects using C stack of
+an interpreter. Currently conses and strings are the only objects which
+can be allocated in that way. Strings are limited to ASCII characters
+only and should be treated as immutable (calling @code{ASET} on them is
+undefined).
+
address@hidden stack allocation internals
+ In C, this is implemented as a special macros which expands to
+a @code{Lisp_Object} with block-scoped semantics and lifetime (see
+the code around @code{USE_STACK_LISP_OBJECTS} in @file{lisp.h}). This
+means that these objects are not managed by the garbage collector;
+instead, they are allocated like local variables in C and automatically
+freed when an execution reaches an end of the corresponding scope. Thus,
+allocation and freeing are faster than using garbage collector. But
+remember that passing them out of their scope results in undefined
+behavior. Think twice before using this feature and carefully debug
+your code with @code{GC_CHECK_MARKED_OBJECTS} (see @file{alloc.c}).
+
@node Memory Usage
@section Memory Usage
@cindex memory usage
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