summaryrefslogtreecommitdiff
path: root/src/thread/pthread_once.c
diff options
context:
space:
mode:
Diffstat (limited to 'src/thread/pthread_once.c')
-rw-r--r--src/thread/pthread_once.c38
1 files changed, 38 insertions, 0 deletions
diff --git a/src/thread/pthread_once.c b/src/thread/pthread_once.c
new file mode 100644
index 00000000..72230054
--- /dev/null
+++ b/src/thread/pthread_once.c
@@ -0,0 +1,38 @@
+#include "pthread_impl.h"
+
+static void undo(void *control)
+{
+ a_store(control, 0);
+ __wake(control, 1, 0);
+}
+
+int pthread_once(pthread_once_t *control, void (*init)(void))
+{
+ static int waiters;
+
+ /* Return immediately if init finished before */
+ if (*control == 2) return 0;
+
+ /* Try to enter initializing state. Three possibilities:
+ * 0 - we're the first or the other cancelled; run init
+ * 1 - another thread is running init; wait
+ * 2 - another thread finished running init; just return */
+
+ for (;;) switch (a_swap(control, 1)) {
+ case 0:
+ break;
+ case 1:
+ __wait(control, &waiters, 1, 0);
+ continue;
+ case 2:
+ a_store(control, 2);
+ return 0;
+ }
+
+ pthread_cleanup_push(undo, control);
+ init();
+ pthread_cleanup_pop(0);
+
+ if (waiters) __wake(control, -1, 0);
+ return 0;
+}