Per-thread allocation counters and limits

This tracks the amount of memory allocation by each thread in a
counter stored in the TSO.  Optionally, when the counter drops below
zero (it counts down), the thread can be sent an asynchronous
exception: AllocationLimitExceeded.  When this happens, given a small
additional limit so that it can handle the exception.  See
documentation in GHC.Conc for more details.

Allocation limits are similar to timeouts, but

  - timeouts use real time, not CPU time.  Allocation limits do not
    count anything while the thread is blocked or in foreign code.

  - timeouts don't re-trigger if the thread catches the exception,
    allocation limits do.

  - timeouts can catch non-allocating loops, if you use
    -fno-omit-yields.  This doesn't work for allocation limits.

I couldn't measure any impact on benchmarks with these changes, even
for nofib/smp.

1 files changed, 6 insertions, 2 deletions

diff --git a/includes/rts/Threads.h b/includes/rts/Threads.h
index da6f7a4add..f6264adfb9 100644
--- a/includes/rts/Threads.h
+++ b/includes/rts/Threads.h
@@ -42,8 +42,12 @@ StgRegTable * resumeThread  (void *);
 //
 // Thread operations from Threads.c
 //
-int    cmp_thread      (StgPtr tso1, StgPtr tso2);
-int    rts_getThreadId (StgPtr tso);
+int     cmp_thread                       (StgPtr tso1, StgPtr tso2);
+int     rts_getThreadId                  (StgPtr tso);
+HsInt64 rts_getThreadAllocationCounter   (StgPtr tso);
+void    rts_setThreadAllocationCounter   (StgPtr tso, HsInt64 i);
+void    rts_enableThreadAllocationLimit  (StgPtr tso);
+void    rts_disableThreadAllocationLimit (StgPtr tso);
 
 #if !defined(mingw32_HOST_OS)
 pid_t  forkProcess     (HsStablePtr *entry);