/* -----------------------------------------------------------------------------
- * $Id: Stable.c,v 1.16 2001/08/08 16:03:47 simonmar Exp $
+ * $Id: Stable.c,v 1.26 2003/06/24 13:45:49 stolz 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"
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
* to the weight stored in the table entry.
* */
-HashTable *addrToStableHash;
+static HashTable *addrToStableHash = NULL;
#define INIT_SPT_SIZE 64
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;
}
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.
}
/*
} else {
sn = stable_ptr_free - stable_ptr_table;
(P_)stable_ptr_free = stable_ptr_free->addr;
- stable_ptr_table[sn].weight = 0;
+ 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
{
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;
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
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
// 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);
}
}
/* -----------------------------------------------------------------------------
* 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.
* -------------------------------------------------------------------------- */
// 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);
}
}
*
* 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
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);
} 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));
+ IF_DEBUG(stable, fprintf(stderr,"Stable name %d still alive at %p, ref %d\n", p - stable_ptr_table, p->addr, p->ref));
}
}
}