Split part of the Task struct into a separate struct InCall

The idea is that this leaves Tasks and OSThread in one-to-one
correspondence.  The part of a Task that represents a call into
Haskell from C is split into a separate struct InCall, pointed to by
the Task and the TSO bound to it.  A given OSThread/Task thus always
uses the same mutex and condition variable, rather than getting a new
one for each callback.  Conceptually it is simpler, although there are
more types and indirections in a few places now.

This improves callback performance by removing some of the locks that
we had to take when making in-calls.  Now we also keep the current Task
in a thread-local variable if supported by the OS and gcc (currently
only Linux).

1 files changed, 7 insertions, 3 deletions

diff --git a/rts/sm/Compact.c b/rts/sm/Compact.c
index 315eda732d..e55ae2b7c2 100644
--- a/rts/sm/Compact.c
+++ b/rts/sm/Compact.c
@@ -1014,10 +1014,14 @@ compact(StgClosure *static_objects)
     // the task list
     {
 	Task *task;
+        InCall *incall;
 	for (task = all_tasks; task != NULL; task = task->all_link) {
-	    if (task->tso) {
-		thread_(&task->tso);
-	    }
+            for (incall = task->incall; incall != NULL; 
+                 incall = incall->prev_stack) {
+                if (incall->tso) {
+                    thread_(&incall->tso);
+                }
+            }
 	}
     }