semaphore: introduce static semaphores

src/pulsecore/semaphore-posix.c

@@ -65,3 +65,25 @@ void pa_semaphore_wait(pa_semaphore *s) {
 
     pa_assert(ret == 0);
 }
+
+pa_semaphore* pa_static_semaphore_get(pa_static_semaphore *s, unsigned value) {
+    pa_semaphore *m;
+
+    pa_assert(s);
+
+    /* First, check if already initialized and short cut */
+    if ((m = pa_atomic_ptr_load(&s->ptr)))
+        return m;
+
+    /* OK, not initialized, so let's allocate, and fill in */
+    m = pa_semaphore_new(value);
+    if ((pa_atomic_ptr_cmpxchg(&s->ptr, NULL, m)))
+        return m;
+
+    pa_semaphore_free(m);
+
+    /* Him, filling in failed, so someone else must have filled in
+     * already */
+    pa_assert_se(m = pa_atomic_ptr_load(&s->ptr));
+    return m;
+}

src/pulsecore/semaphore.h

@@ -22,6 +22,9 @@
   USA.
 ***/
 
+#include <pulsecore/macro.h>
+#include <pulsecore/atomic.h>
+
 typedef struct pa_semaphore pa_semaphore;
 
 pa_semaphore* pa_semaphore_new(unsigned value);
@@ -30,4 +33,16 @@ void pa_semaphore_free(pa_semaphore *m);
 void pa_semaphore_post(pa_semaphore *m);
 void pa_semaphore_wait(pa_semaphore *m);
 
+/* Static semaphores are basically just atomically updated pointers to
+ * pa_semaphore objects */
+
+typedef struct pa_static_semaphore {
+    pa_atomic_ptr_t ptr;
+} pa_static_semaphore;
+
+#define PA_STATIC_SEMAPHORE_INIT { PA_ATOMIC_PTR_INIT(NULL) }
+
+/* When you call this make sure to pass always the same value parameter! */
+pa_semaphore* pa_static_semaphore_get(pa_static_semaphore *m, unsigned value);
+
 #endif