+/* -----------------------------------------------------------------------------
+ * Spin locks
+ *
+ * These are simple spin-only locks as opposed to Mutexes which
+ * probably spin for a while before blocking in the kernel. We use
+ * these when we are sure that all our threads are actively running on
+ * a CPU, eg. in the GC.
+ *
+ * TODO: measure whether we really need these, or whether Mutexes
+ * would do (and be a bit safer if a CPU becomes loaded).
+ * -------------------------------------------------------------------------- */
+
+#if defined(DEBUG)
+typedef struct StgSync_
+{
+ StgWord32 lock;
+ StgWord64 spin; // DEBUG version counts how much it spins
+} StgSync;
+#else
+typedef StgWord StgSync;
+#endif
+
+typedef lnat StgSyncCount;
+
+
+#if defined(DEBUG)
+
+// Debug versions of spin locks maintain a spin count
+
+// How to use:
+// To use the debug veriosn of the spin locks, a debug version of the program
+// can be run under a deugger with a break point on stat_exit. At exit time
+// of the program one can examine the state the spin count counts of various
+// spin locks to check for contention.
+
+// acquire spin lock
+INLINE_HEADER void ACQUIRE_SPIN_LOCK(StgSync * p)
+{
+ StgWord32 r = 0;
+ do {
+ p->spin++;
+ r = cas((StgVolatilePtr)&(p->lock), 1, 0);
+ } while(r == 0);
+ p->spin--;
+}
+
+// release spin lock
+INLINE_HEADER void RELEASE_SPIN_LOCK(StgSync * p)
+{
+ write_barrier();
+ p->lock = 1;
+}
+
+// initialise spin lock
+INLINE_HEADER void initSpinLock(StgSync * p)
+{
+ write_barrier();
+ p->lock = 1;
+ p->spin = 0;
+}
+
+#else
+
+// acquire spin lock
+INLINE_HEADER void ACQUIRE_SPIN_LOCK(StgSync * p)
+{
+ StgWord32 r = 0;
+ do {
+ r = cas((StgVolatilePtr)p, 1, 0);
+ } while(r == 0);
+}
+
+// release spin lock
+INLINE_HEADER void RELEASE_SPIN_LOCK(StgSync * p)
+{
+ write_barrier();
+ (*p) = 1;
+}
+
+// init spin lock
+INLINE_HEADER void initSpinLock(StgSync * p)
+{
+ write_barrier();
+ (*p) = 1;
+}
+
+#endif /* DEBUG */
+
+/* ---------------------------------------------------------------------- */