New implementation of BLACKHOLEs

This replaces the global blackhole_queue with a clever scheme that
enables us to queue up blocked threads on the closure that they are
blocked on, while still avoiding atomic instructions in the common
case.

Advantages:

 - gets rid of a locked global data structure and some tricky GC code
   (replacing it with some per-thread data structures and different
   tricky GC code :)

 - wakeups are more prompt: parallel/concurrent performance should
   benefit.  I haven't seen anything dramatic in the parallel
   benchmarks so far, but a couple of threading benchmarks do improve
   a bit.

 - waking up a thread blocked on a blackhole is now O(1) (e.g. if
   it is the target of throwTo).

 - less sharing and better separation of Capabilities: communication
   is done with messages, the data structures are strictly owned by a
   Capability and cannot be modified except by sending messages.

 - this change will utlimately enable us to do more intelligent
   scheduling when threads block on each other.  This is what started
   off the whole thing, but it isn't done yet (#3838).

I'll be documenting all this on the wiki in due course.

1 files changed, 3 insertions, 1 deletions

diff --git a/rts/Interpreter.c b/rts/Interpreter.c
index 9071912f2d..16a8e242bd 100644
--- a/rts/Interpreter.c
+++ b/rts/Interpreter.c
@@ -21,6 +21,7 @@
 #include "Disassembler.h"
 #include "Interpreter.h"
 #include "ThreadPaused.h"
+#include "Threads.h"
 
 #include <string.h>     /* for memcpy */
 #ifdef HAVE_ERRNO_H
@@ -443,7 +444,8 @@ do_return:
         // to a PAP by the GC, violating the invariant that PAPs
         // always contain a tagged pointer to the function.
 	INTERP_TICK(it_retto_UPDATE);
-	UPD_IND(cap, ((StgUpdateFrame *)Sp)->updatee, tagged_obj); 
+        updateThunk(cap, cap->r.rCurrentTSO, 
+                    ((StgUpdateFrame *)Sp)->updatee, tagged_obj);
 	Sp += sizeofW(StgUpdateFrame);
 	goto do_return;