Use message-passing to implement throwTo in the RTS

This replaces some complicated locking schemes with message-passing
in the implementation of throwTo. The benefits are

 - previously it was impossible to guarantee that a throwTo from
   a thread running on one CPU to a thread running on another CPU
   would be noticed, and we had to rely on the GC to pick up these
   forgotten exceptions. This no longer happens.

 - the locking regime is simpler (though the code is about the same
   size)

 - threads can be unblocked from a blocked_exceptions queue without
   having to traverse the whole queue now.  It's a rare case, but
   replaces an O(n) operation with an O(1).

 - generally we move in the direction of sharing less between
   Capabilities (aka HECs), which will become important with other
   changes we have planned.

Also in this patch I replaced several STM-specific closure types with
a generic MUT_PRIM closure type, which allowed a lot of code in the GC
and other places to go away, hence the line-count reduction.  The
message-passing changes resulted in about a net zero line-count
difference.

1 files changed, 4 insertions, 2 deletions

diff --git a/includes/stg/MiscClosures.h b/includes/stg/MiscClosures.h
index e68282ebc0..42e878f945 100644
--- a/includes/stg/MiscClosures.h
+++ b/includes/stg/MiscClosures.h
@@ -114,6 +114,8 @@ RTS_INFO(stg_MUT_ARR_PTRS_FROZEN0_info);
 RTS_INFO(stg_MUT_VAR_CLEAN_info);
 RTS_INFO(stg_MUT_VAR_DIRTY_info);
 RTS_INFO(stg_END_TSO_QUEUE_info);
+RTS_INFO(stg_MSG_WAKEUP_info);
+RTS_INFO(stg_MSG_THROWTO_info);
 RTS_INFO(stg_MUT_CONS_info);
 RTS_INFO(stg_catch_info);
 RTS_INFO(stg_PAP_info);
@@ -163,6 +165,8 @@ RTS_ENTRY(stg_MUT_ARR_PTRS_FROZEN0_entry);
 RTS_ENTRY(stg_MUT_VAR_CLEAN_entry);
 RTS_ENTRY(stg_MUT_VAR_DIRTY_entry);
 RTS_ENTRY(stg_END_TSO_QUEUE_entry);
+RTS_ENTRY(stg_MSG_WAKEUP_entry);
+RTS_ENTRY(stg_MSG_THROWTO_entry);
 RTS_ENTRY(stg_MUT_CONS_entry);
 RTS_ENTRY(stg_catch_entry);
 RTS_ENTRY(stg_PAP_entry);
@@ -205,8 +209,6 @@ RTS_CLOSURE(stg_END_STM_CHUNK_LIST_closure);
 RTS_CLOSURE(stg_NO_TREC_closure);
 
 RTS_ENTRY(stg_NO_FINALIZER_entry);
-RTS_ENTRY(stg_END_EXCEPTION_LIST_entry);
-RTS_ENTRY(stg_EXCEPTION_CONS_entry);
 
 #if IN_STG_CODE
 extern DLL_IMPORT_RTS StgWordArray stg_CHARLIKE_closure;