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, 12 insertions, 10 deletions

diff --git a/includes/rts/Constants.h b/includes/rts/Constants.h
index 54a1ca71ca..bfc77fa361 100644
--- a/includes/rts/Constants.h
+++ b/includes/rts/Constants.h
@@ -208,25 +208,27 @@
 #define NotBlocked          0
 #define BlockedOnMVar       1
 #define BlockedOnBlackHole  2
-#define BlockedOnException  3
-#define BlockedOnRead       4
-#define BlockedOnWrite      5
-#define BlockedOnDelay      6
-#define BlockedOnSTM        7
+#define BlockedOnRead       3
+#define BlockedOnWrite      4
+#define BlockedOnDelay      5
+#define BlockedOnSTM        6
 
 /* Win32 only: */
-#define BlockedOnDoProc     8
+#define BlockedOnDoProc     7
 
 /* Only relevant for PAR: */
   /* blocked on a remote closure represented by a Global Address: */
-#define BlockedOnGA         9
+#define BlockedOnGA         8
   /* same as above but without sending a Fetch message */
-#define BlockedOnGA_NoSend  10
+#define BlockedOnGA_NoSend  9
 /* Only relevant for THREADED_RTS: */
-#define BlockedOnCCall      11
-#define BlockedOnCCall_NoUnblockExc 12
+#define BlockedOnCCall      10
+#define BlockedOnCCall_NoUnblockExc 11
    /* same as above but don't unblock async exceptions in resumeThread() */
 
+/* Involved in a message sent to tso->msg_cap */
+#define BlockedOnMsgWakeup  12
+#define BlockedOnMsgThrowTo 13
 /*
  * These constants are returned to the scheduler by a thread that has
  * stopped for one reason or another.  See typedef StgThreadReturnCode