X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Frts%2FStable.c;h=5b2635b4ab8053057b5da3e04e0cd8c08177de73;hb=5acd2909936a1e56db8386ebccf66e0347012ad6;hp=206772f3346b04f97f2f8129fb60fe423cf99193;hpb=a59148d19c0252c616dbb67fc3998f8d5ffd1fd6;p=ghc-hetmet.git

diff --git a/ghc/rts/Stable.c b/ghc/rts/Stable.c
index 206772f..5b2635b 100644
--- a/ghc/rts/Stable.c
+++ b/ghc/rts/Stable.c
@@ -1,5 +1,5 @@
 /* -----------------------------------------------------------------------------
- * $Id: Stable.c,v 1.3 1999/02/26 12:46:48 simonm Exp $
+ * $Id: Stable.c,v 1.13 2000/09/04 15:17:03 simonmar Exp $
  *
  * (c) The GHC Team, 1998-1999
  *
@@ -107,7 +107,7 @@ unsigned int SPT_size;
  *
  * A stable pointer has a weighted reference count N attached to it
  * (actually in its upper 5 bits), which represents the weight
- * 2^N.  The stable name entry keeps a 32-bit reference count, which
+ * 2^(N-1).  The stable name entry keeps a 32-bit reference count, which
  * represents any weight between 1 and 2^32 (represented as zero).
  * When the weight is 2^32, the stable name table owns "all" of the
  * stable pointers to this object, and the entry can be garbage
@@ -133,7 +133,9 @@ initFreeList(snEntry *table, nat n, snEntry *free)
   snEntry *p;
 
   for (p = table + n - 1; p >= table; p--) {
-    p->addr = (P_)free;
+    p->addr   = (P_)free;
+    p->weight = 0;
+    p->sn_obj = NULL;
     free = p;
   }
   stable_ptr_free = table;
@@ -150,6 +152,27 @@ initStablePtrTable(void)
   SPT_size = 0;
 }
 
+/*
+ * get at the real stuff...remove indirections.
+ *
+ * ToDo: move to a better home.
+ */
+static
+StgClosure*
+removeIndirections(StgClosure* p)
+{
+  StgClosure* q = p;
+
+  while (get_itbl(q)->type == IND ||
+         get_itbl(q)->type == IND_STATIC ||
+         get_itbl(q)->type == IND_OLDGEN ||
+         get_itbl(q)->type == IND_PERM ||
+         get_itbl(q)->type == IND_OLDGEN_PERM ) {
+      q = ((StgInd *)q)->indirectee;
+  }
+  return q;
+}
+
 StgWord
 lookupStableName(StgPtr p)
 {
@@ -158,7 +181,13 @@ lookupStableName(StgPtr p)
   if (stable_ptr_free == NULL) {
     enlargeStablePtrTable();
   }
-    
+
+  /* removing indirections increases the likelihood
+   * of finding a match in the stable name
+   * hash table.
+   */
+  p = (StgPtr)removeIndirections((StgClosure*)p);
+
   (void *)sn = lookupHashTable(addrToStableHash,(W_)p);
   
   if (sn != 0) {
@@ -185,6 +214,9 @@ static inline void
 freeStableName(snEntry *sn)
 {
   ASSERT(sn->sn_obj == NULL);
+  if (sn->addr != NULL) {
+    removeHashTable(addrToStableHash, (W_)sn->addr, NULL);
+  }
   sn->addr = (P_)stable_ptr_free;
   stable_ptr_free = sn;
 }
@@ -193,13 +225,12 @@ StgStablePtr
 getStablePtr(StgPtr p)
 {
   StgWord sn = lookupStableName(p);
-  StgWord weight, weight_2;
-
+  StgWord weight, n;
   weight = stable_ptr_table[sn].weight;
   if (weight == 0) {
-    weight = 1 << (BITS_IN(StgWord)-1);
+    weight = (StgWord)1 << (BITS_IN(StgWord)-1);
     stable_ptr_table[sn].weight = weight;
-    return (StgStablePtr)(sn + ((BITS_IN(StgWord)-1) << STABLEPTR_WEIGHT_SHIFT));
+    return (StgStablePtr)(sn + (BITS_IN(StgWord) << STABLEPTR_WEIGHT_SHIFT));
   } 
   else if (weight == 1) {
     barf("getStablePtr: too light");
@@ -207,11 +238,11 @@ getStablePtr(StgPtr p)
   else {
     weight /= 2;
     /* find log2(weight) */
-    for (weight_2 = 1; weight != 1; weight_2++) {
+    for (n = 0; weight != 1; n++) {
       weight >>= 1;
     }
-    stable_ptr_table[sn].weight -= 2^weight_2;
-    return (StgStablePtr)(sn + (weight_2 << STABLEPTR_WEIGHT_SHIFT));
+    stable_ptr_table[sn].weight -= 1 << n;
+    return (StgStablePtr)(sn + ((n+1) << STABLEPTR_WEIGHT_SHIFT));
   }
 }
 
@@ -226,6 +257,10 @@ enlargeStablePtrTable(void)
     stable_ptr_table = stgMallocWords(SPT_size * sizeof(snEntry), 
 				      "initStablePtrTable");
     
+    /* we don't use index 0 in the stable name table, because that
+     * would conflict with the hash table lookup operations which
+     * return NULL if an entry isn't found in the hash table.
+     */
     initFreeList(stable_ptr_table+1,INIT_SPT_SIZE-1,NULL);
     addrToStableHash = allocHashTable();
   }
@@ -264,9 +299,10 @@ markStablePtrTable(rtsBool full)
 
   end_stable_ptr_table = &stable_ptr_table[SPT_size];
 
-  /* Mark all the stable *pointers* (not stable names) 
+  /* Mark all the stable *pointers* (not stable names).
+   * _starting_ at index 1; index 0 is unused.
    */
-  for (p = stable_ptr_table; p < end_stable_ptr_table; p++) {
+  for (p = stable_ptr_table+1; p < end_stable_ptr_table; p++) {
     q = p->addr;
     /* internal pointers or NULL are free slots 
      */
@@ -280,11 +316,13 @@ markStablePtrTable(rtsBool full)
 	  (StgClosure *)p->addr = new;
 	} else if ((P_)new != q) {
 	  removeHashTable(addrToStableHash, (W_)q, NULL);
-	  insertHashTable(addrToStableHash, (W_)new, 
-			  (void *)(p - stable_ptr_table));
+	  if (!lookupHashTable(addrToStableHash, (W_)new)) {
+	    insertHashTable(addrToStableHash, (W_)new, 
+			    (void *)(p - stable_ptr_table));
+	  }
 	  (StgClosure *)p->addr = new;
 	}
-	IF_DEBUG(stable, fprintf(stderr,"Stable ptr %d still alive at %p, weight %d\n", p - stable_ptr_table, new, p->weight));
+	IF_DEBUG(stable, fprintf(stderr,"Stable ptr %d still alive at %p, weight %u\n", p - stable_ptr_table, new, p->weight));
       }
     }
   }
@@ -321,7 +359,8 @@ gcStablePtrTable(rtsBool full)
 
   end_stable_ptr_table = &stable_ptr_table[SPT_size];
 
-  for (p = stable_ptr_table; p < end_stable_ptr_table; p++) {
+  /* NOTE: _starting_ at index 1; index 0 is unused. */
+  for (p = stable_ptr_table + 1; p < end_stable_ptr_table; p++) {
 
     /* Update the pointer to the StableName object, if there is one */
     if (p->sn_obj != NULL) {
@@ -345,9 +384,15 @@ gcStablePtrTable(rtsBool full)
 	  (StgClosure *)new = isAlive((StgClosure *)q);
 	  IF_DEBUG(stable, fprintf(stderr,"Stable name %d still alive at %p, weight %d\n", p - stable_ptr_table, new, p->weight));
 
-	  p->addr = new;
-	  if (new != NULL) {
-	    /* Re-hash this stable name */
+	  if (new == NULL) {
+	    /* The target has been garbage collected.  Remove its
+	     * entry from the hash table.
+	     */
+	    removeHashTable(addrToStableHash, (W_)q, NULL);
+
+	  } else {
+	    /* Target still alive, Re-hash this stable name 
+	     */
 	    if (full) {
 	      insertHashTable(addrToStableHash, (W_)new, (void *)(p - stable_ptr_table));
 	    } else if (new != q) {
@@ -355,6 +400,11 @@ gcStablePtrTable(rtsBool full)
 	      insertHashTable(addrToStableHash, (W_)new, (void *)(p - stable_ptr_table));
 	    }
 	  }
+
+	  /* finally update the address of the target to point to its
+	   * new location.
+	   */
+	  p->addr = new;
 	}
       }
     }