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Use smobs as an example for 'remembering'. Mention continuation barriers.

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Marius Vollmer 2005-03-04 16:04:22 +00:00
parent a0f78c5085
commit 384138c496
1 changed files with 12 additions and 7 deletions
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19
doc/ref/libguile-concepts.texi
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@ -246,13 +246,13 @@ wanted.
There are situations, however, where a @code{SCM} object needs to be There are situations, however, where a @code{SCM} object needs to be
around longer than its reference from a local variable or function around longer than its reference from a local variable or function
parameter. This happens, for example, when you retrieve the array of parameter. This happens, for example, when you retrieve some pointer
characters from a Scheme string and work on that array directly. The from a smob and work with that pointer directly. The reference to the
reference to the @code{SCM} string object might be dead after the @code{SCM} smob object might be dead after the pointer has been
character array has been retrieved, but the array itself is still in use retrieved, but the pointer itself (and the memory pointed to) is still
and thus the string object must be protected. The compiler does not in use and thus the smob object must be protected. The compiler does
know about this connection and might overwrite the @code{SCM} reference not know about this connection and might overwrite the @code{SCM}
too early. reference too early.
To get around this problem, you can use @code{scm_remember_upto_here_1} To get around this problem, you can use @code{scm_remember_upto_here_1}
and its cousins. It will keep the compiler from overwriting the and its cousins. It will keep the compiler from overwriting the
@ -383,6 +383,11 @@ corresponding @code{scm_internal_dynamic_wind} function, but it might
prefer to use the @dfn{frames} concept that is more natural for C code, prefer to use the @dfn{frames} concept that is more natural for C code,
(@pxref{Frames}). (@pxref{Frames}).
Instead of coping with non-local control flow, you can also prevent it
by errecting a @emph{continuation barrier}, @xref{Continuation
Barriers}. The function @code{scm_c_with_continuation_barrier}, for
example, is guaranteed to return exactly once.
@node Asynchronous Signals @node Asynchronous Signals
@subsection Asynchronous Signals @subsection Asynchronous Signals