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, 0 insertions, 1 deletions

diff --git a/compiler/codeGen/CgCallConv.hs b/compiler/codeGen/CgCallConv.hs
index 8a1ae8be0c..b8294ea326 100644
--- a/compiler/codeGen/CgCallConv.hs
+++ b/compiler/codeGen/CgCallConv.hs
@@ -284,7 +284,6 @@ getSequelAmode
 	    OnStack -> do { sp_rel <- getSpRelOffset virt_sp
 			  ; returnFC (CmmLoad sp_rel bWord) }
 
-	    UpdateCode 	      -> returnFC (CmmLit (CmmLabel mkUpdInfoLabel))
 	    CaseAlts lbl _ _  -> returnFC (CmmLit (CmmLabel lbl))
 	}