Use message-passing to implement throwTo in the RTS

This replaces some complicated locking schemes with message-passing
in the implementation of throwTo. The benefits are

 - previously it was impossible to guarantee that a throwTo from
   a thread running on one CPU to a thread running on another CPU
   would be noticed, and we had to rely on the GC to pick up these
   forgotten exceptions. This no longer happens.

 - the locking regime is simpler (though the code is about the same
   size)

 - threads can be unblocked from a blocked_exceptions queue without
   having to traverse the whole queue now.  It's a rare case, but
   replaces an O(n) operation with an O(1).

 - generally we move in the direction of sharing less between
   Capabilities (aka HECs), which will become important with other
   changes we have planned.

Also in this patch I replaced several STM-specific closure types with
a generic MUT_PRIM closure type, which allowed a lot of code in the GC
and other places to go away, hence the line-count reduction.  The
message-passing changes resulted in about a net zero line-count
difference.

1 files changed, 10 insertions, 0 deletions

diff --git a/rts/Trace.h b/rts/Trace.h
index f8b6ad497d..69ea3d3d32 100644
--- a/rts/Trace.h
+++ b/rts/Trace.h
@@ -135,6 +135,15 @@ void traceUserMsg(Capability *cap, char *msg);
 #define debugTrace(class, str, ...) /* nothing */
 #endif
 
+#ifdef DEBUG
+#define debugTraceCap(class, cap, msg, ...)      \
+    if (RTS_UNLIKELY(class)) {                  \
+        traceCap_(cap, msg, ##__VA_ARGS__);     \
+    }
+#else
+#define debugTraceCap(class, cap, str, ...) /* nothing */
+#endif
+
 /* 
  * Emit a message/event describing the state of a thread
  */
@@ -152,6 +161,7 @@ void traceThreadStatus_ (StgTSO *tso);
 #define traceCap(class, cap, msg, ...) /* nothing */
 #define trace(class, msg, ...) /* nothing */
 #define debugTrace(class, str, ...) /* nothing */
+#define debugTraceCap(class, cap, str, ...) /* nothing */
 #define traceThreadStatus(class, tso) /* nothing */
 
 #endif /* TRACING */