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Support for one-time initialization functions. (#69668, Sebastian

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2003-07-09  Matthias Clasen  <maclas@gmx.de>

	Support for one-time initialization functions.  (#69668, Sebastian Wilhelmi)

	* configure.in: Check whether double checked locking is safe, define g_once() in
	glibconfig.h accordingly.
	* glib/gthread.h: Add GOnce, GOnceStatus, G_ONCE_INIT and g_once_impl.
	* glib/gthread.c (g_once_impl): Fallback implementation using a mutex if double checked
	locking is unsafe.
	* tests/thread-test.c: Add tests for g_once().
This commit is contained in:
Matthias Clasen
2003-07-08 23:43:48 +00:00
committed by Matthias Clasen
parent 238c7c368b
commit 876f907863
12 changed files with 329 additions and 11 deletions
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7
docs/reference/glib/glib-sections.txt
View File

@@ -554,6 +554,12 @@ g_static_private_get
g_static_private_set
g_static_private_free
<SUBSECTION>
GOnce
GOnceStatus
G_ONCE_INIT
g_once
<SUBSECTION Private>
G_THREAD_ECF
G_THREAD_CF
@@ -569,6 +575,7 @@ g_threads_got_initialized
g_thread_functions_for_glib_use
g_thread_init_glib
g_thread_error_quark
g_once_impl
</SECTION>
<SECTION>

69
docs/reference/glib/tmpl/threads.sgml
View File

@@ -1606,3 +1606,72 @@ you should also free the #GStaticPrivate.
@private_key: a #GStaticPrivate to be freed.
<!-- ##### STRUCT GOnce ##### -->
<para>
A <structname>GOnce</structname> struct controls a one-time initialization function.
Any one-time initialization function must have its own unique <structname>GOnce</structname>
struct.
</para>
@Since: 2.4
<!-- ##### ENUM GOnceStatus ##### -->
<para>
The possible stati of a one-time initialization function controlled by a #GOnce struct.
</para>
@G_ONCE_STATUS_NOTCALLED: the function has not been called yet.
@G_ONCE_STATUS_PROGRESS: the function call is currently in progress.
@G_ONCE_STATUS_READY: the function has been called.
<!-- ##### MACRO G_ONCE_INIT ##### -->
<para>
A #GOnce must be initialized with this macro, before it can be used.
</para>
<para>
<informalexample>
<programlisting>
GOnce my_once = G_ONCE_INIT;
</programlisting>
</informalexample>
</para>
<!-- ##### MACRO g_once ##### -->
<para>
The first call to this routine by a process with a given #GOnce struct calls @func with the given
argument. Thereafter, subsequent calls to g_once() with the same #GOnce struct do not call @func
again, but return the stored result of the first call. On return from g_once(), the status of @once
will be %G_ONCE_STATUS_READY.
</para>
<para>
For example, a mutex or a thread-specific data key must be created exactly once. In a threaded
environment, calling g_once() ensures that the initialization is serialized across multiple threads.
</para>
<note><para>
Calling g_once() recursively on the same #GOnce struct in @func will lead to a deadlock.
</para></note>
<para>
<informalexample>
<programlisting>
gpointer
get_debug_flags ()
{
static GOnce my_once = G_ONCE_INIT;
g_once (&my_once, parse_debug_flags, NULL);
return my_once.retval;
}
</programlisting>
</informalexample>
</para>
@once: a #GOnce structure
@func: the function associated to @once. This function is called only once, regardless of the
number of times it and its associated #GOnce struct are passed to g_once() .
@arg: data to be passed to @func
@Since: 2.4