/* -----------------------------------------------------------------------------
- * $Id: Stable.c,v 1.5 1999/07/16 09:53:44 panne Exp $
+ * $Id: Stable.c,v 1.15 2001/07/23 17:23:19 simonmar Exp $
*
* (c) The GHC Team, 1998-1999
*
#include "Rts.h"
#include "Hash.h"
#include "StablePriv.h"
-#include "GC.h"
#include "RtsUtils.h"
#include "Storage.h"
#include "RtsAPI.h"
deRefStablePtr# :: StablePtr# a -> State# RealWorld ->
(# State# RealWorld, a #)
\end{verbatim}
- There is also a C procedure @FreeStablePtr@ which frees a stable pointer.
There may be additional functions on the C side to allow evaluation,
application, etc of a stable pointer.
*
* 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
for (p = table + n - 1; p >= table; p--) {
p->addr = (P_)free;
+ p->old = NULL;
p->weight = 0;
p->sn_obj = NULL;
free = p;
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)
{
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) {
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;
}
getStablePtr(StgPtr p)
{
StgWord sn = lookupStableName(p);
- StgWord weight, weight_2;
-
+ 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)-1) << STABLEPTR_WEIGHT_SHIFT));
+ return (StgStablePtr)(sn + (BITS_IN(StgWord) << STABLEPTR_WEIGHT_SHIFT));
}
else if (weight == 1) {
barf("getStablePtr: too light");
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));
}
}
nat old_SPT_size = SPT_size;
if (SPT_size == 0) {
- /* 1st time */
+ // 1st time
SPT_size = INIT_SPT_SIZE;
stable_ptr_table = stgMallocWords(SPT_size * sizeof(snEntry),
"initStablePtrTable");
- initFreeList(stable_ptr_table,INIT_SPT_SIZE,NULL);
+ /* 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();
}
else {
- /* 2nd and subsequent times */
+ // 2nd and subsequent times
SPT_size *= 2;
stable_ptr_table =
stgReallocWords(stable_ptr_table, SPT_size * sizeof(snEntry),
* -------------------------------------------------------------------------- */
void
-markStablePtrTable(rtsBool full)
+markStablePtrTable(evac_fn evac)
{
- snEntry *p, *end_stable_ptr_table;
- StgPtr q;
- StgClosure *new;
-
- if (SPT_size == 0)
- return;
-
- if (full) {
- freeHashTable(addrToStableHash,NULL);
- addrToStableHash = allocHashTable();
- }
+ snEntry *p, *end_stable_ptr_table;
+ StgPtr q;
+
+ end_stable_ptr_table = &stable_ptr_table[SPT_size];
+
+ // Mark all the stable *pointers* (not stable names).
+ // _starting_ at index 1; index 0 is unused.
+ for (p = stable_ptr_table+1; p < end_stable_ptr_table; p++) {
+ q = p->addr;
+
+ // internal pointers or NULL are free slots
+ if (q && (q < (P_)stable_ptr_table || q >= (P_)end_stable_ptr_table)) {
+
+ // save the current addr away: we need to be able to tell
+ // whether the objects moved in order to be able to update
+ // the hash table later.
+ p->old = p->addr;
+
+ // if the weight is non-zero, treat addr as a root
+ if (p->weight != 0) {
+ evac((StgClosure **)&p->addr);
+ }
+ }
+ }
+}
- end_stable_ptr_table = &stable_ptr_table[SPT_size];
+/* -----------------------------------------------------------------------------
+ * Thread the stable pointer table for compacting GC.
+ *
+ * Here we must call the supplied evac function for each pointer into
+ * the heap from the stable pointer table, because the compacting
+ * collector may move the object it points to.
+ * -------------------------------------------------------------------------- */
- /* Mark all the stable *pointers* (not stable names)
- */
- for (p = stable_ptr_table; p < end_stable_ptr_table; p++) {
- q = p->addr;
- /* internal pointers or NULL are free slots
- */
- if (q && (q < (P_)stable_ptr_table || q >= (P_)end_stable_ptr_table)) {
- if (p->weight != 0) {
- new = MarkRoot((StgClosure *)q);
- /* Update the hash table */
- if (full) {
- insertHashTable(addrToStableHash, (W_)new,
- (void *)(p - stable_ptr_table));
- (StgClosure *)p->addr = new;
- } else if ((P_)new != q) {
- removeHashTable(addrToStableHash, (W_)q, NULL);
- insertHashTable(addrToStableHash, (W_)new,
- (void *)(p - stable_ptr_table));
- (StgClosure *)p->addr = new;
+void
+threadStablePtrTable( evac_fn evac )
+{
+ snEntry *p, *end_stable_ptr_table;
+ StgPtr q;
+
+ end_stable_ptr_table = &stable_ptr_table[SPT_size];
+
+ for (p = stable_ptr_table+1; p < end_stable_ptr_table; p++) {
+ q = p->addr;
+
+ // internal pointers or NULL are free slots
+ if (q && (q < (P_)stable_ptr_table || q >= (P_)end_stable_ptr_table)) {
+ if (p->weight != 0) {
+ evac((StgClosure **)&p->addr);
+ }
+ if (p->sn_obj != NULL) {
+ evac((StgClosure **)&p->sn_obj);
+ }
}
- IF_DEBUG(stable, fprintf(stderr,"Stable ptr %d still alive at %p, weight %d\n", p - stable_ptr_table, new, p->weight));
- }
}
- }
}
/* -----------------------------------------------------------------------------
* name table entry. We can re-use stable name table entries for live
* heap objects, as long as the program has no StableName objects that
* refer to the entry.
+ * -------------------------------------------------------------------------- */
+
+void
+gcStablePtrTable( void )
+{
+ snEntry *p, *end_stable_ptr_table;
+ StgPtr q;
+
+ end_stable_ptr_table = &stable_ptr_table[SPT_size];
+
+ // 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) {
+ p->sn_obj = isAlive(p->sn_obj);
+ }
+
+ q = p->addr;
+ if (q && (q < (P_)stable_ptr_table || q >= (P_)end_stable_ptr_table)) {
+
+ // StableNames only:
+ if (p->weight == 0) {
+ if (p->sn_obj == NULL) {
+ // StableName object is dead
+ freeStableName(p);
+ IF_DEBUG(stable, fprintf(stderr,"GC'd Stable name %d\n",
+ p - stable_ptr_table));
+ 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));
+ }
+ }
+ }
+ }
+}
+
+/* -----------------------------------------------------------------------------
+ * Update the StablePtr/StableName hash table
*
* The boolean argument 'full' indicates that a major collection is
* being done, so we might as well throw away the hash table and build
* -------------------------------------------------------------------------- */
void
-gcStablePtrTable(rtsBool full)
+updateStablePtrTable(rtsBool full)
{
- snEntry *p, *end_stable_ptr_table;
- StgPtr q, new;
-
- if (SPT_size == 0) {
- return;
- }
-
- end_stable_ptr_table = &stable_ptr_table[SPT_size];
-
- for (p = stable_ptr_table; p < end_stable_ptr_table; p++) {
-
- /* Update the pointer to the StableName object, if there is one */
- if (p->sn_obj != NULL) {
- p->sn_obj = isAlive(p->sn_obj);
+ snEntry *p, *end_stable_ptr_table;
+
+ if (full && addrToStableHash != NULL) {
+ freeHashTable(addrToStableHash,NULL);
+ addrToStableHash = allocHashTable();
}
-
- q = p->addr;
- if (q && (q < (P_)stable_ptr_table || q >= (P_)end_stable_ptr_table)) {
-
- /* We're only interested in Stable Names here. The weight != 0
- * case is handled in markStablePtrTable above.
- */
- if (p->weight == 0) {
+
+ end_stable_ptr_table = &stable_ptr_table[SPT_size];
+
+ // NOTE: _starting_ at index 1; index 0 is unused.
+ for (p = stable_ptr_table + 1; p < end_stable_ptr_table; p++) {
- if (p->sn_obj == NULL) {
- /* StableName object is dead */
- freeStableName(p);
- IF_DEBUG(stable, fprintf(stderr,"GC'd Stable name %d\n", p - stable_ptr_table));
- }
- else {
- (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 (p->addr == NULL) {
+ if (p->old != NULL) {
+ // The target has been garbage collected. Remove its
+ // entry from the hash table.
+ removeHashTable(addrToStableHash, (W_)p->old, NULL);
+ p->old = NULL;
+ }
+ }
+ else if (p->addr < (P_)stable_ptr_table
+ || p->addr >= (P_)end_stable_ptr_table) {
+ // Target still alive, Re-hash this stable name
if (full) {
- insertHashTable(addrToStableHash, (W_)new, (void *)(p - stable_ptr_table));
- } else if (new != q) {
- removeHashTable(addrToStableHash, (W_)q, NULL);
- insertHashTable(addrToStableHash, (W_)new, (void *)(p - stable_ptr_table));
+ insertHashTable(addrToStableHash, (W_)p->addr,
+ (void *)(p - stable_ptr_table));
+ } else if (p->addr != p->old) {
+ removeHashTable(addrToStableHash, (W_)p->old, NULL);
+ insertHashTable(addrToStableHash, (W_)p->addr,
+ (void *)(p - stable_ptr_table));
}
- }
}
- }
}
- }
}