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Clarify a subtle issue in the Internals chapter of lispref

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* doc/lispref/internals.texi (Writing Emacs Primitives):
Clarify the issue with relocation of buffer or string text as
side effect of Lisp evaluation.  (Bug#36392)
This commit is contained in:
Eli Zaretskii 2019-06-26 18:02:26 +03:00
parent e62ad04963
commit 7648c125df
1 changed files with 8 additions and 4 deletions
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12
doc/lispref/internals.texi
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@ -825,10 +825,14 @@ the type explicitly using a suitable predicate (@pxref{Type Predicates}).
@code{args} refers to objects controlled by Emacs's stack-marking
garbage collector. Although the garbage collector does not reclaim
objects reachable from C @code{Lisp_Object} stack variables, it may
move non-object components of an object, such as string contents; so
functions that access non-object components must take care to refetch
their addresses after performing Lisp evaluation. Lisp evaluation can
occur via calls to @code{eval_sub} or @code{Feval}, either directly or
move some of the components of an object, such as the contents of a
string or the text of a buffer. Therefore, functions that access
these components must take care to refetch their addresses after
performing Lisp evaluation. This means that instead of keeping C
pointers to string contents or buffer text, the code should keep the
buffer or string position, and recompute the C pointer from the
position after performing Lisp evaluation. Lisp evaluation can occur
via calls to @code{eval_sub} or @code{Feval}, either directly or
indirectly.
@cindex @code{maybe_quit}, use in Lisp primitives