Add a pthread_once() implementation for Win32 (untested on Win32).

src/xpdev/threadwrap.c

@@ -126,6 +126,28 @@ pthread_mutex_t DLLCALL pthread_mutex_initializer_np(BOOL recursive)
 
 #if !defined(_POSIX_THREADS)
 
+int DLLCALL pthread_once(pthread_once_t *oc, void (*init)(void))
+{
+	if (oc == NULL || init == NULL)
+		return EINVAL;
+	switch(InterlockedCompareExchange(&(oc->state), 1, 0)) {
+		case 0:	// Never called
+			init();
+			InterlockedIncrement(&(oc->state));
+			return 0;
+		case 1:	// In init function
+			/* We may not need to use InterlockedCompareExchange() here,
+			 * but I hate marking things as volatile, and hate tight loops
+			 * testing things that aren't marked volatile.
+			 */
+			while(InterlockedCompareExchange(&(oc->state), 1, 0) != 2)
+				SLEEP(1);
+			return 0;
+		case 2:	// Done.
+			return 0;
+	}
+}
+
 int DLLCALL pthread_mutex_init(pthread_mutex_t* mutex, void* attr)
 {
 	(void)attr;

src/xpdev/threadwrap.h

@@ -123,6 +123,14 @@ DLLEXPORT int DLLCALL pthread_mutex_destroy(pthread_mutex_t*);
 
 #define SetThreadName(c)
 
+// A structure in case we need to add an event or something...
+typedef struct {
+	uint32_t	state;
+} pthread_once_t;
+
+#define PTHREAD_ONCE_INIT	{0};
+DLLEXPORT int DLLCALL pthread_once(pthread_once_t *oc, void (*init)(void));
+
 #endif
 
 #if !defined(PTHREAD_MUTEX_INITIALIZER_NP)