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

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

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().