X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Frts%2FStable.c;h=815bac7690549ffd5a998e31cc37aef93f09a4a3;hb=47ff06307547e20eff37477a9bc9be80a460917a;hp=52876bd7a65aceb87e493d7d79f27c53978ce7f0;hpb=bc5c802181b513216bc88f0d1ec9574157ee05fe;p=ghc-hetmet.git

diff --git a/ghc/rts/Stable.c b/ghc/rts/Stable.c
index 52876bd..815bac7 100644
--- a/ghc/rts/Stable.c
+++ b/ghc/rts/Stable.c
@@ -1,16 +1,18 @@
 /* -----------------------------------------------------------------------------
- * $Id: Stable.c,v 1.17 2001/08/14 13:40:09 sewardj Exp $
+ * $Id: Stable.c,v 1.29 2004/08/22 15:50:42 panne Exp $
  *
- * (c) The GHC Team, 1998-1999
+ * (c) The GHC Team, 1998-2002
  *
  * Stable names and stable pointers.
  *
  * ---------------------------------------------------------------------------*/
 
+// Make static versions of inline functions in Stable.h:
+#define RTS_STABLE_C
+
 #include "PosixSource.h"
 #include "Rts.h"
 #include "Hash.h"
-#include "StablePriv.h"
 #include "RtsUtils.h"
 #include "Storage.h"
 #include "RtsAPI.h"
@@ -70,32 +72,20 @@
   There may be additional functions on the C side to allow evaluation,
   application, etc of a stable pointer.
 
-  When Haskell calls C, it normally just passes over primitive integers,
-  floats, bools, strings, etc.  This doesn't cause any problems at all
-  for garbage collection because the act of passing them makes a copy
-  from the heap, stack or wherever they are onto the C-world stack.
-  However, if we were to pass a heap object such as a (Haskell) @String@
-  and a garbage collection occured before we finished using it, we'd run
-  into problems since the heap object might have been moved or even
-  deleted.
-
-  So, if a C call is able to cause a garbage collection or we want to
-  store a pointer to a heap object between C calls, we must be careful
-  when passing heap objects. Our solution is to keep a table of all
-  objects we've given to the C-world and to make sure that the garbage
-  collector collects these objects --- updating the table as required to
-  make sure we can still find the object.
 */
 
-snEntry *stable_ptr_table;
-snEntry *stable_ptr_free;
+snEntry *stable_ptr_table = NULL;
+static snEntry *stable_ptr_free = NULL;
 
-unsigned int SPT_size;
+static unsigned int SPT_size = 0;
 
 /* This hash table maps Haskell objects to stable names, so that every
  * call to lookupStableName on a given object will return the same
  * stable name.
  *
+ * OLD COMMENTS about reference counting follow.  The reference count
+ * in a stable name entry is now just a counter.
+ *
  * Reference counting
  * ------------------
  * A plain stable name entry has a zero reference count, which means
@@ -122,11 +112,11 @@ unsigned int SPT_size;
  * to the weight stored in the table entry.
  * */
 
-HashTable *addrToStableHash;
+static HashTable *addrToStableHash = NULL;
 
 #define INIT_SPT_SIZE 64
 
-static inline void
+STATIC_INLINE void
 initFreeList(snEntry *table, nat n, snEntry *free)
 {
   snEntry *p;
@@ -134,7 +124,7 @@ initFreeList(snEntry *table, nat n, snEntry *free)
   for (p = table + n - 1; p >= table; p--) {
     p->addr   = (P_)free;
     p->old    = NULL;
-    p->weight = 0;
+    p->ref    = 0;
     p->sn_obj = NULL;
     free = p;
   }
@@ -144,12 +134,9 @@ initFreeList(snEntry *table, nat n, snEntry *free)
 void
 initStablePtrTable(void)
 {
-  /* the table will be allocated the first time makeStablePtr is
-   * called */
-  stable_ptr_table = NULL;
-  stable_ptr_free  = NULL;
-  addrToStableHash = NULL;
-  SPT_size = 0;
+    // Nothing to do:
+    // the table will be allocated the first time makeStablePtr is
+    // called, and we want the table to persist through multiple inits.
 }
 
 /*
@@ -177,6 +164,7 @@ StgWord
 lookupStableName(StgPtr p)
 {
   StgWord sn;
+  void* sn_tmp;
 
   if (stable_ptr_free == NULL) {
     enlargeStablePtrTable();
@@ -187,7 +175,8 @@ lookupStableName(StgPtr p)
    */
   p = (StgPtr)removeIndirections((StgClosure*)p);
 
-  (void *)sn = lookupHashTable(addrToStableHash,(W_)p);
+  sn_tmp = lookupHashTable(addrToStableHash,(W_)p);
+  sn = (StgWord)sn_tmp;
   
   if (sn != 0) {
     ASSERT(stable_ptr_table[sn].addr == p);
@@ -195,8 +184,8 @@ lookupStableName(StgPtr p)
     return sn;
   } else {
     sn = stable_ptr_free - stable_ptr_table;
-    (P_)stable_ptr_free  = stable_ptr_free->addr;
-    stable_ptr_table[sn].weight = 0;
+    stable_ptr_free  = (snEntry*)(stable_ptr_free->addr);
+    stable_ptr_table[sn].ref = 0;
     stable_ptr_table[sn].addr = p;
     stable_ptr_table[sn].sn_obj = NULL;
     /* IF_DEBUG(stable,fprintf(stderr,"new stable name %d at
@@ -209,12 +198,12 @@ lookupStableName(StgPtr p)
   }
 }
 
-static inline void
+STATIC_INLINE void
 freeStableName(snEntry *sn)
 {
   ASSERT(sn->sn_obj == NULL);
   if (sn->addr != NULL) {
-    removeHashTable(addrToStableHash, (W_)sn->addr, NULL);
+      removeHashTable(addrToStableHash, (W_)sn->addr, NULL);
   }
   sn->addr = (P_)stable_ptr_free;
   stable_ptr_free = sn;
@@ -223,26 +212,28 @@ freeStableName(snEntry *sn)
 StgStablePtr
 getStablePtr(StgPtr p)
 {
-  StgWord sn = lookupStableName(p);
-  StgWord weight, n;
-  weight = stable_ptr_table[sn].weight;
-  if (weight == 0) {
-    weight = (StgWord)1 << (BITS_IN(StgWord)-1);
-    stable_ptr_table[sn].weight = weight;
-    return (StgStablePtr)(sn + (BITS_IN(StgWord) << STABLEPTR_WEIGHT_SHIFT));
-  } 
-  else if (weight == 1) {
-    barf("getStablePtr: too light");
-  } 
-  else {
-    weight /= 2;
-    /* find log2(weight) */
-    for (n = 0; weight != 1; n++) {
-      weight >>= 1;
+  StgWord sn;
+
+  sn = lookupStableName(p);
+  stable_ptr_table[sn].ref++;
+  return (StgStablePtr)(sn);
+}
+
+void
+freeStablePtr(StgStablePtr sp)
+{
+    snEntry *sn = &stable_ptr_table[(StgWord)sp];
+    
+    ASSERT((StgWord)sp < SPT_size  &&  sn->addr != NULL  &&  sn->ref > 0);
+
+    sn->ref--;
+
+    // If this entry has no StableName attached, then just free it
+    // immediately.  This is important; it might be a while before the
+    // next major GC which actually collects the entry.
+    if (sn->sn_obj == NULL && sn->ref == 0) {
+	freeStableName(sn);
     }
-    stable_ptr_table[sn].weight -= 1 << n;
-    return (StgStablePtr)(sn + ((n+1) << STABLEPTR_WEIGHT_SHIFT));
-  }
 }
 
 void
@@ -253,8 +244,8 @@ enlargeStablePtrTable(void)
   if (SPT_size == 0) {
     // 1st time
     SPT_size = INIT_SPT_SIZE;
-    stable_ptr_table = stgMallocWords(SPT_size * sizeof(snEntry), 
-				      "initStablePtrTable");
+    stable_ptr_table = stgMallocBytes(SPT_size * sizeof(snEntry), 
+				      "enlargeStablePtrTable");
     
     /* we don't use index 0 in the stable name table, because that
      * would conflict with the hash table lookup operations which
@@ -267,9 +258,10 @@ enlargeStablePtrTable(void)
     // 2nd and subsequent times
     SPT_size *= 2;
     stable_ptr_table = 
-      stgReallocWords(stable_ptr_table, SPT_size * sizeof(snEntry),
+      stgReallocBytes(stable_ptr_table, 
+		      SPT_size * sizeof(snEntry),
 		      "enlargeStablePtrTable");
-    
+
     initFreeList(stable_ptr_table + old_SPT_size, old_SPT_size, NULL);
   }
 }
@@ -277,7 +269,7 @@ enlargeStablePtrTable(void)
 /* -----------------------------------------------------------------------------
  * Treat stable pointers as roots for the garbage collector.
  *
- * A stable pointer is any stable name entry with a weight > 0.  We'll
+ * A stable pointer is any stable name entry with a ref > 0.  We'll
  * take the opportunity to zero the "keep" flags at the same time.
  * -------------------------------------------------------------------------- */
 
@@ -304,8 +296,8 @@ markStablePtrTable(evac_fn evac)
 	    // the hash table later.
 	    p->old = p->addr;
 
-	    // if the weight is non-zero, treat addr as a root
-	    if (p->weight != 0) {
+	    // if the ref is non-zero, treat addr as a root
+	    if (p->ref != 0) {
 		evac((StgClosure **)&p->addr);
 	    }
 	}
@@ -346,7 +338,7 @@ threadStablePtrTable( evac_fn evac )
  *
  * A dead entry has:
  *
- *          - a weight of zero (i.e. 2^32)
+ *          - a zero reference count
  *          - a dead sn_obj
  *
  * Both of these conditions must be true in order to re-use the stable
@@ -378,7 +370,7 @@ gcStablePtrTable( void )
 	if (q && (q < (P_)stable_ptr_table || q >= (P_)end_stable_ptr_table)) {
 
 	    // StableNames only:
-	    if (p->weight == 0) {
+	    if (p->ref == 0) {
 		if (p->sn_obj == NULL) {
 		    // StableName object is dead
 		    freeStableName(p);
@@ -387,8 +379,8 @@ gcStablePtrTable( void )
 		    continue;
 		    
 		} else {
-		    (StgClosure *)p->addr = isAlive((StgClosure *)p->addr);
-		    IF_DEBUG(stable, fprintf(stderr,"Stable name %d still alive at %p, weight %d\n", p - stable_ptr_table, p->addr, p->weight));
+		  p->addr = (StgPtr)isAlive((StgClosure *)p->addr);
+		    IF_DEBUG(stable, fprintf(stderr,"Stable name %d still alive at %p, ref %d\n", p - stable_ptr_table, p->addr, p->ref));
 		}
 	    }
 	}