at basic locking/threading support

git-svn-id: file:///home/lennart/svn/public/libsydney/trunk@26 9ba3c220-e4d3-45a2-8aa3-73fcc9aff6ce

1 files changed, 58 insertions, 0 deletions

diff --git a/once.c b/once.c
new file mode 100644
index 0000000..de41be3
--- /dev/null
+++ b/once.c
@@ -0,0 +1,58 @@
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <pthread.h>
+#include <assert.h>
+
+#include "once.h"
+#include "mutex.h"
+#include "malloc.h"
+#include "macro.h"
+
+static sa_mutex_t *global_mutex; 
+static pthread_once_t global_mutex_once = PTHREAD_ONCE_INIT;
+
+static void global_mutex_once_func(void) { 
+    global_mutex = sa_mutex_new(0);
+} 
+
+int sa_once(sa_once_t *control, sa_once_func_t func) {
+    int r;
+    
+    assert(control); 
+    assert(func); 
+    
+    /* Create the global mutex */
+    sa_assert_success(pthread_once(&global_mutex_once, global_mutex_once_func));
+
+    if (!global_mutex)
+        return -1;
+
+    r = 0;
+    
+    /* Create the local mutex */
+    sa_mutex_lock(global_mutex); 
+    if (!control->mutex) {
+        if (!(control->mutex = sa_mutex_new(1)))
+            r = -1;
+    }
+    sa_mutex_unlock(global_mutex);
+
+    if (!r)
+        return -1;
+    
+    /* Execute function */
+    sa_mutex_lock(control->mutex);
+    if (!control->once_value) {
+        control->once_value = 1;
+        func();
+    }
+    sa_mutex_unlock(control->mutex); 
+
+    /* Caveat: We have to make sure that the once func has completed
+     * before returning, even if the once func is not actually
+     * executed by us. Hence the awkward locking. */
+
+    return 0;
+}