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, 8 insertions, 0 deletions

diff --git a/includes/Rts.h b/includes/Rts.h
index 3318402364..d79e9ad88e 100644
--- a/includes/Rts.h
+++ b/includes/Rts.h
@@ -106,10 +106,18 @@ void _assertFail(const char *filename, unsigned int linenum)
 	else					\
 	    _assertFail(__FILE__, __LINE__)
 
+#define CHECKM(predicate, msg, ...)             \
+	if (predicate)				\
+	    /*null*/;				\
+	else					\
+            barf(msg, ##__VA_ARGS__)
+
 #ifndef DEBUG
 #define ASSERT(predicate) /* nothing */
+#define ASSERTM(predicate,msg,...) /* nothing */
 #else
 #define ASSERT(predicate) CHECK(predicate)
+#define ASSERTM(predicate,msg,...) CHECKM(predicate,msg,##__VA_ARGS__)
 #endif /* DEBUG */
 
 /*