RTS tidyup sweep, first phase

[ghc-hetmet.git] / includes / rts / SpinLock.h

diff --git a/includes/rts/SpinLock.h b/includes/rts/SpinLock.h
new file mode 100644 (file)
index 0000000..ea992a3
--- /dev/null
+++ b/includes/rts/SpinLock.h
@@ -0,0 +1,105 @@
+/* ----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team, 2006-2008
+ *
+ * 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).
+ *
+ * -------------------------------------------------------------------------- */
+
+#ifndef RTS_SPINLOCK_H
+#define RTS_SPINLOCK_H
+ 
+#if defined(THREADED_RTS)
+
+#if defined(PROF_SPIN)
+typedef struct SpinLock_
+{
+    StgWord   lock;
+    StgWord64 spin; // DEBUG version counts how much it spins
+} SpinLock;
+#else
+typedef StgWord SpinLock;
+#endif
+
+typedef lnat SpinLockCount;
+
+
+#if defined(PROF_SPIN)
+
+// PROF_SPIN enables counting the number of times we spin on a lock
+
+// acquire spin lock
+INLINE_HEADER void ACQUIRE_SPIN_LOCK(SpinLock * p)
+{
+    StgWord32 r = 0;
+spin:
+    r = cas((StgVolatilePtr)&(p->lock), 1, 0);
+    if (r == 0) {
+        p->spin++;
+        goto spin;
+    }
+}
+
+// release spin lock
+INLINE_HEADER void RELEASE_SPIN_LOCK(SpinLock * p)
+{
+    write_barrier();
+    p->lock = 1;
+}
+
+// initialise spin lock
+INLINE_HEADER void initSpinLock(SpinLock * p)
+{
+    write_barrier();
+    p->lock = 1;
+    p->spin = 0;
+}
+
+#else
+
+// acquire spin lock
+INLINE_HEADER void ACQUIRE_SPIN_LOCK(SpinLock * p)
+{
+    StgWord32 r = 0;
+    do {
+        r = cas((StgVolatilePtr)p, 1, 0);
+    } while(r == 0);
+}
+
+// release spin lock
+INLINE_HEADER void RELEASE_SPIN_LOCK(SpinLock * p)
+{
+    write_barrier();
+    (*p) = 1;
+}
+
+// init spin lock
+INLINE_HEADER void initSpinLock(SpinLock * p)
+{
+    write_barrier();
+    (*p) = 1;
+}
+
+#endif /* PROF_SPIN */
+
+#else /* !THREADED_RTS */
+
+// Using macros here means we don't have to ensure the argument is in scope
+#define ACQUIRE_SPIN_LOCK(p) /* nothing */
+#define RELEASE_SPIN_LOCK(p) /* nothing */
+
+INLINE_HEADER void initSpinLock(void * p STG_UNUSED)
+{ /* nothing */ }
+
+#endif /* THREADED_RTS */
+
+#endif /* RTS_SPINLOCK_H */
+