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, 7 insertions, 9 deletions

diff --git a/rts/Printer.c b/rts/Printer.c
index e9813299d8..6eecfabbfb 100644
--- a/rts/Printer.c
+++ b/rts/Printer.c
@@ -257,6 +257,12 @@ printClosure( StgClosure *obj )
             debugBelch(")\n"); 
             break;
 
+    case BLACKHOLE:
+            debugBelch("BLACKHOLE("); 
+            printPtr((StgPtr)((StgInd*)obj)->indirectee);
+            debugBelch(")\n"); 
+            break;
+
     /* Cannot happen -- use default case.
     case RET_BCO:
     case RET_SMALL:
@@ -296,14 +302,6 @@ printClosure( StgClosure *obj )
             break;
         }
 
-    case CAF_BLACKHOLE:
-            debugBelch("CAF_BH"); 
-            break;
-
-    case BLACKHOLE:
-            debugBelch("BH\n"); 
-            break;
-
     case ARR_WORDS:
         {
             StgWord i;
@@ -1122,8 +1120,8 @@ char *closure_type_names[] = {
  [UPDATE_FRAME]          = "UPDATE_FRAME",
  [CATCH_FRAME]           = "CATCH_FRAME",
  [STOP_FRAME]            = "STOP_FRAME",
- [CAF_BLACKHOLE]         = "CAF_BLACKHOLE",
  [BLACKHOLE]             = "BLACKHOLE",
+ [BLOCKING_QUEUE]        = "BLOCKING_QUEUE",
  [MVAR_CLEAN]            = "MVAR_CLEAN",
  [MVAR_DIRTY]            = "MVAR_DIRTY",
  [ARR_WORDS]             = "ARR_WORDS",