-/* Convenient once-only execution.
- *
- *
- * Problem
- * =======
- *
- * POSIX provides pthread_once_t and pthread_once() as primitives for running a
- * set of code only once per process execution. They are used like this:
- *
- * static void run_once(void) { ...initialization... }
- * static pthread_once_t once = PTHREAD_ONCE_INIT;
- * ...
- * pthread_once(&once, run_once);
- *
- * pthread_once() does not allow passing any parameters to the initialization
- * function, which is often inconvenient, because it means that the function
- * can only access data declared at file scope.
- *
- *
- * Solution
- * ========
- *
- * Use ovsthread_once, like this, instead:
- *
- * static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
- *
- * if (ovsthread_once_start(&once)) {
- * ...initialization...
- * ovsthread_once_done(&once);
- * }
- */
-
-struct ovsthread_once {
- bool done; /* Non-atomic, false negatives possible. */
- struct ovs_mutex mutex;
-};
-
-#define OVSTHREAD_ONCE_INITIALIZER \
- { \
- false, \
- OVS_MUTEX_INITIALIZER, \
- }
-
-static inline bool ovsthread_once_start(struct ovsthread_once *once)
- OVS_TRY_LOCK(true, once->mutex);
-void ovsthread_once_done(struct ovsthread_once *once)
- OVS_RELEASES(once->mutex);
-
-bool ovsthread_once_start__(struct ovsthread_once *once)
- OVS_TRY_LOCK(true, once->mutex);
-
-/* Returns true if this is the first call to ovsthread_once_start() for
- * 'once'. In this case, the caller should perform whatever initialization
- * actions it needs to do, then call ovsthread_once_done() for 'once'.
- *
- * Returns false if this is not the first call to ovsthread_once_start() for
- * 'once'. In this case, the call will not return until after
- * ovsthread_once_done() has been called. */
-static inline bool
-ovsthread_once_start(struct ovsthread_once *once)
-{
- /* We may be reading 'done' at the same time as the first thread
- * is writing on it, or we can be using a stale copy of it. The
- * worst that can happen is that we call ovsthread_once_start__()
- * once when strictly not necessary. */
- return OVS_UNLIKELY(!once->done && ovsthread_once_start__(once));
-}
-\f