1 files changed, 62 insertions, 0 deletions
diff --git a/common/rwlock.c b/common/rwlock.c
new file mode 100644
index 00000000..b967db0a
--- /dev/null
+++ b/common/rwlock.c
@@ -0,0 +1,62 @@
+
+#include "config.h"
+
+#include "rwlock.h"
+
+#include "bool.h"
+#include "atomic.h"
+#include "threads.h"
+
+
+/* A simple spinlock. Yield the thread while the given integer is set by
+ * another. Could probably be improved... */
+static void Lock(volatile int *l)
+{
+    while(ExchangeInt(l, true) == true)
+        althrd_yield();
+}
+
+static void Unlock(volatile int *l)
+{
+    ExchangeInt(l, false);
+}
+
+
+void RWLockInit(RWLock *lock)
+{
+    lock->read_count = 0;
+    lock->write_count = 0;
+    lock->read_lock = false;
+    lock->read_entry_lock = false;
+    lock->write_lock = false;
+}
+
+void ReadLock(RWLock *lock)
+{
+    Lock(&lock->read_entry_lock);
+    Lock(&lock->read_lock);
+    if(IncrementRef(&lock->read_count) == 1)
+        Lock(&lock->write_lock);
+    Unlock(&lock->read_lock);
+    Unlock(&lock->read_entry_lock);
+}
+
+void ReadUnlock(RWLock *lock)
+{
+    if(DecrementRef(&lock->read_count) == 0)
+        Unlock(&lock->write_lock);
+}
+
+void WriteLock(RWLock *lock)
+{
+    if(IncrementRef(&lock->write_count) == 1)
+        Lock(&lock->read_lock);
+    Lock(&lock->write_lock);
+}
+
+void WriteUnlock(RWLock *lock)
+{
+    Unlock(&lock->write_lock);
+    if(DecrementRef(&lock->write_count) == 0)
+        Unlock(&lock->read_lock);
+}