Implement aom_once using Win32 InitOnce functions.
On Windows Vista and later, we can use InitOnceBeginInitialize() and
InitOnceComplete() to implement aom_once().
BUG=aomedia:2224
Change-Id: I2f38c7f4386a618df07ab1e765889050f3f666c2
diff --git a/aom_ports/aom_once.h b/aom_ports/aom_once.h
index 4d77aac..d1a031b 100644
--- a/aom_ports/aom_once.h
+++ b/aom_ports/aom_once.h
@@ -40,56 +40,22 @@
#if CONFIG_MULTITHREAD && defined(_WIN32)
#include <windows.h>
-#include <stdlib.h>
/* Declare a per-compilation-unit state variable to track the progress
* of calling func() only once. This must be at global scope because
* local initializers are not thread-safe in MSVC prior to Visual
* Studio 2015.
- *
- * As a static, aom_once_state will be zero-initialized as program start.
*/
-static LONG aom_once_state;
+static INIT_ONCE aom_init_once = INIT_ONCE_STATIC_INIT;
+
static void aom_once(void (*func)(void)) {
- /* Try to advance aom_once_state from its initial value of 0 to 1.
- * Only one thread can succeed in doing so.
- */
- if (InterlockedCompareExchange(&aom_once_state, 1, 0) == 0) {
- /* We're the winning thread, having set aom_once_state to 1.
- * Call our function. */
- func();
- /* Now advance aom_once_state to 2, unblocking any other threads. */
- InterlockedIncrement(&aom_once_state);
+ BOOL pending;
+ InitOnceBeginInitialize(&aom_init_once, 0, &pending, NULL);
+ if (!pending) {
+ // Initialization has already completed.
return;
}
-
- /* We weren't the winning thread, but we want to block on
- * the state variable so we don't return before func()
- * has finished executing elsewhere.
- *
- * Try to advance aom_once_state from 2 to 2, which is only possible
- * after the winning thead advances it from 1 to 2.
- */
- while (InterlockedCompareExchange(&aom_once_state, 2, 2) != 2) {
- /* State isn't yet 2. Try again.
- *
- * We are used for singleton initialization functions,
- * which should complete quickly. Contention will likewise
- * be rare, so it's worthwhile to use a simple but cpu-
- * intensive busy-wait instead of successive backoff,
- * waiting on a kernel object, or another heavier-weight scheme.
- *
- * We can at least yield our timeslice.
- */
- Sleep(0);
- }
-
- /* We've seen aom_once_state advance to 2, so we know func()
- * has been called. And we've left aom_once_state as we found it,
- * so other threads will have the same experience.
- *
- * It's safe to return now.
- */
- return;
+ func();
+ InitOnceComplete(&aom_init_once, 0, NULL);
}
#elif CONFIG_MULTITHREAD && defined(__OS2__)
