From: Simon Marlow <marlowsd@gmail.com>
Date: Wed, 19 Aug 2009 14:11:06 +0000 (+0000)
Subject: use cas() to claim the closure in copyPart(), to match copy_tag()
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=68bc07fed38228a1f9fd1885333c7412f57c7e17

use cas() to claim the closure in copyPart(), to match copy_tag()

copyPart() was still using the old WHITEHOLE mechanism for locking the
closure.  I don't think this fixes any actual bugs, but it removes a
gratuitous difference between two functions that should look similar.
---

diff --git a/rts/sm/Evac.c b/rts/sm/Evac.c
index ae843bd..b711914 100644
--- a/rts/sm/Evac.c
+++ b/rts/sm/Evac.c
@@ -112,7 +112,8 @@ copy_tag(StgClosure **p, const StgInfoTable *info,
 #if defined(PARALLEL_GC)
     {
         const StgInfoTable *new_info;
-        new_info = (const StgInfoTable *)cas((StgPtr)&src->header.info, (W_)info, MK_FORWARDING_PTR(to));
+        new_info = (const StgInfoTable *)cas((StgPtr)&src->header.info,
+                                             (W_)info, MK_FORWARDING_PTR(to));
         if (new_info != info) {
             return evacuate(p); // does the failed_to_evac stuff
         } else {
@@ -168,46 +169,39 @@ copy_tag_nolock(StgClosure **p, const StgInfoTable *info,
  * used to optimise evacuation of BLACKHOLEs.
  */
 static rtsBool
-copyPart(StgClosure **p, StgClosure *src, nat size_to_reserve, nat size_to_copy, step *stp)
+copyPart(StgClosure **p, const StgInfoTable *info, StgClosure *src, 
+         nat size_to_reserve, nat size_to_copy, step *stp)
 {
     StgPtr to, from;
     nat i;
-    StgWord info;
     
-#if defined(PARALLEL_GC)
-spin:
-	info = xchg((StgPtr)&src->header.info, (W_)&stg_WHITEHOLE_info);
-	if (info == (W_)&stg_WHITEHOLE_info) {
-#ifdef PROF_SPIN
-	    whitehole_spin++;
-#endif
-	    goto spin;
-	}
-    if (IS_FORWARDING_PTR(info)) {
-	src->header.info = (const StgInfoTable *)info;
-	evacuate(p); // does the failed_to_evac stuff
-	return rtsFalse;
-    }
-#else
-    info = (W_)src->header.info;
-#endif
-
     to = alloc_for_copy(size_to_reserve, stp);
-    *p = (StgClosure *)to;
 
     TICK_GC_WORDS_COPIED(size_to_copy);
 
     from = (StgPtr)src;
-    to[0] = info;
+    to[0] = (W_)info;
     for (i = 1; i < size_to_copy; i++) { // unroll for small i
 	to[i] = from[i];
     }
     
 #if defined(PARALLEL_GC)
-    write_barrier();
+    {
+        const StgInfoTable *new_info;
+        new_info = (const StgInfoTable *)cas((StgPtr)&src->header.info, 
+                                             (W_)info, MK_FORWARDING_PTR(to));
+        if (new_info != info) {
+            evacuate(p); // does the failed_to_evac stuff
+            return rtsFalse;
+        } else {
+            *p = (StgClosure*)to;
+        }
+    }
+#else
+    src->header.info = (const StgInfoTable *)MK_FORWARDING_PTR(to);
+    *p = (StgClosure*)to;
 #endif
-    src->header.info = (const StgInfoTable*)MK_FORWARDING_PTR(to);
-    
+
 #ifdef PROFILING
     // We store the size of the just evacuated object in the LDV word so that
     // the profiler can guess the position of the next object later.
@@ -639,7 +633,7 @@ loop:
 
   case CAF_BLACKHOLE:
   case BLACKHOLE:
-      copyPart(p,q,BLACKHOLE_sizeW(),sizeofW(StgHeader),stp);
+      copyPart(p,info,q,BLACKHOLE_sizeW(),sizeofW(StgHeader),stp);
       return;
 
   case THUNK_SELECTOR:
@@ -711,7 +705,7 @@ loop:
 	  StgPtr r, s;
           rtsBool mine;
 
-	  mine = copyPart(p,(StgClosure *)tso, tso_sizeW(tso), 
+	  mine = copyPart(p,info,(StgClosure *)tso, tso_sizeW(tso), 
                           sizeofW(StgTSO), stp);
           if (mine) {
               new_tso = (StgTSO *)*p;