The emulation uses native InitOnce* APIs on Windows Vista+, and a
lock-free/allocation-free approach using atomics and spinning for Windows XP.
---
This is in preparation to use pthread_once for global static init functions,
and eventually removing the global lock in avcodec_open2
compat/w32pthreads.h | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 68 insertions(+)
diff --git a/compat/w32pthreads.h b/compat/w32pthreads.h
index 3748289..ef28036 100644
--- a/compat/w32pthreads.h
+++ b/compat/w32pthreads.h
@@ -145,6 +145,19 @@ static inline void pthread_cond_signal(pthread_cond_t
*cond)
WakeConditionVariable(cond);
}
+typedef INIT_ONCE pthread_once_t;
+#define PTHREAD_ONCE_INIT INIT_ONCE_STATIC_INIT
+
+static av_unused int pthread_once(pthread_once_t *once_control, void
(*init_routine)(void))
+{
+ BOOL pending = FALSE;
+ InitOnceBeginInitialize(once_control, 0, &pending, NULL);
+ if (pending)
+ init_routine();
+ InitOnceComplete(once_control, 0, NULL);
+ return 0;
+}
+
#else // _WIN32_WINNT < 0x0600
/* for pre-Windows 6.0 platforms we need to define and use our own condition
* variable and api */
@@ -291,6 +304,57 @@ static av_unused void pthread_cond_signal(pthread_cond_t
*cond)
pthread_mutex_unlock(&win32_cond->mtx_broadcast);
}
+
+/* for pre-Windows 6.0 platforms, define INIT_ONCE struct,
+ * compatible to the one used in the native API */
+
+typedef union pthread_once_t {
+ void * Ptr; ///< For the Windows 6.0+ native functions
+ LONG state; ///< For the pre-Windows 6.0 compat code
+} pthread_once_t;
+
+#define PTHREAD_ONCE_INIT {0}
+
+/* function pointers to init once API on windows 6.0+ kernels */
+static BOOL (WINAPI *initonce_begin)(pthread_once_t *lpInitOnce, DWORD
dwFlags, BOOL *fPending, void **lpContext);
+static BOOL (WINAPI *initonce_complete)(pthread_once_t *lpInitOnce, DWORD
dwFlags, void *lpContext);
+
+static av_unused int pthread_once(pthread_once_t *once_control, void
(*init_routine)(void))
+{
+ /* Use native functions on Windows 6.0+ */
+ if (initonce_begin && initonce_complete)
+ {
+ BOOL pending = FALSE;
+ initonce_begin(once_control, 0, &pending, NULL);
+ if (pending)
+ init_routine();
+ initonce_complete(once_control, 0, NULL);
+ return 0;
+ }
+
+ /* pre-Windows 6.0 compat using a spin-lock */
+ switch (InterlockedCompareExchange(&once_control->state, 1, 0))
+ {
+ /* Initial run */
+ case 0:
+ init_routine();
+ InterlockedExchange(&once_control->state, 2);
+ break;
+ /* Another thread is running init */
+ case 1:
+ while (1) {
+ MemoryBarrier();
+ if (once_control->state == 2)
+ break;
+ Sleep(0);
+ }
+ break;
+ /* Initialization complete */
+ case 2:
+ break;
+ }
+ return 0;
+}
#endif
static av_unused void w32thread_init(void)
@@ -306,6 +370,10 @@ static av_unused void w32thread_init(void)
(void*)GetProcAddress(kernel_dll, "WakeConditionVariable");
cond_wait =
(void*)GetProcAddress(kernel_dll, "SleepConditionVariableCS");
+ initonce_begin =
+ (void*)GetProcAddress(kernel_dll, "InitOnceBeginInitialize");
+ initonce_complete =
+ (void*)GetProcAddress(kernel_dll, "InitOnceComplete");
#endif
}
--
2.5.3.windows.1
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