/* -----------------------------------------------------------------------------
- * $Id: GC.c,v 1.128 2001/11/26 16:54:21 simonmar Exp $
+ * $Id: GC.c,v 1.133 2002/04/13 05:16:25 sof Exp $
*
* (c) The GHC Team 1998-1999
*
/* Weak pointers
*/
StgWeak *old_weak_ptr_list; // also pending finaliser list
-static rtsBool weak_done; // all done for this pass
+
+/* Which stage of processing various kinds of weak pointer are we at?
+ * (see traverse_weak_ptr_list() below for discussion).
+ */
+typedef enum { WeakPtrs, WeakThreads, WeakDone } WeakStage;
+static WeakStage weak_stage;
/* List of all threads during GC
*/
static StgTSO *old_all_threads;
-static StgTSO *resurrected_threads;
+StgTSO *resurrected_threads;
/* Flag indicating failure to evacuate an object to the desired
* generation.
- free from-space in each step, and set from-space = to-space.
+ Locks held: sched_mutex
+
-------------------------------------------------------------------------- */
void
mark_weak_ptr_list(&weak_ptr_list);
old_weak_ptr_list = weak_ptr_list;
weak_ptr_list = NULL;
- weak_done = rtsFalse;
+ weak_stage = WeakPtrs;
/* The all_threads list is like the weak_ptr_list.
* See traverse_weak_ptr_list() for the details.
if (flag) { goto loop; }
- // must be last...
+ // must be last... invariant is that everything is fully
+ // scavenged at this point.
if (traverse_weak_ptr_list()) { // returns rtsTrue if evaced something
goto loop;
}
}
+ /* Update the pointers from the "main thread" list - these are
+ * treated as weak pointers because we want to allow a main thread
+ * to get a BlockedOnDeadMVar exception in the same way as any other
+ * thread. Note that the threads should all have been retained by
+ * GC by virtue of being on the all_threads list, we're just
+ * updating pointers here.
+ */
+ {
+ StgMainThread *m;
+ StgTSO *tso;
+ for (m = main_threads; m != NULL; m = m->link) {
+ tso = (StgTSO *) isAlive((StgClosure *)m->tso);
+ if (tso == NULL) {
+ barf("main thread has been GC'd");
+ }
+ m->tso = tso;
+ }
+ }
+
#if defined(PAR)
// Reconstruct the Global Address tables used in GUM
rebuildGAtables(major_gc);
#ifdef PROFILING
// We call processHeapClosureForDead() on every closure destroyed during
// the current garbage collection, so we invoke LdvCensusForDead().
- if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV)
+ if (RtsFlags.ProfFlags.doHeapProfile == HEAP_BY_LDV
+ || RtsFlags.ProfFlags.bioSelector != NULL)
LdvCensusForDead(N);
#endif
// Reset the nursery
resetNurseries();
+ RELEASE_LOCK(&sched_mutex);
+
// start any pending finalizers
scheduleFinalizers(old_weak_ptr_list);
+ ACQUIRE_LOCK(&sched_mutex);
+
// send exceptions to any threads which were about to die
resurrectThreads(resurrected_threads);
-
+
// Update the stable pointer hash table.
updateStablePtrTable(major_gc);
older generations than the one we're collecting. This could
probably be optimised by keeping per-generation lists of weak
pointers, but for a few weak pointers this scheme will work.
+
+ There are three distinct stages to processing weak pointers:
+
+ - weak_stage == WeakPtrs
+
+ We process all the weak pointers whos keys are alive (evacuate
+ their values and finalizers), and repeat until we can find no new
+ live keys. If no live keys are found in this pass, then we
+ evacuate the finalizers of all the dead weak pointers in order to
+ run them.
+
+ - weak_stage == WeakThreads
+
+ Now, we discover which *threads* are still alive. Pointers to
+ threads from the all_threads and main thread lists are the
+ weakest of all: a pointers from the finalizer of a dead weak
+ pointer can keep a thread alive. Any threads found to be unreachable
+ are evacuated and placed on the resurrected_threads list so we
+ can send them a signal later.
+
+ - weak_stage == WeakDone
+
+ No more evacuation is done.
+
-------------------------------------------------------------------------- */
static rtsBool
StgClosure *new;
rtsBool flag = rtsFalse;
- if (weak_done) { return rtsFalse; }
-
- /* doesn't matter where we evacuate values/finalizers to, since
- * these pointers are treated as roots (iff the keys are alive).
- */
- evac_gen = 0;
-
- last_w = &old_weak_ptr_list;
- for (w = old_weak_ptr_list; w != NULL; w = next_w) {
-
- /* There might be a DEAD_WEAK on the list if finalizeWeak# was
- * called on a live weak pointer object. Just remove it.
- */
- if (w->header.info == &stg_DEAD_WEAK_info) {
- next_w = ((StgDeadWeak *)w)->link;
- *last_w = next_w;
- continue;
- }
-
- ASSERT(get_itbl(w)->type == WEAK);
-
- /* Now, check whether the key is reachable.
- */
- new = isAlive(w->key);
- if (new != NULL) {
- w->key = new;
- // evacuate the value and finalizer
- w->value = evacuate(w->value);
- w->finalizer = evacuate(w->finalizer);
- // remove this weak ptr from the old_weak_ptr list
- *last_w = w->link;
- // and put it on the new weak ptr list
- next_w = w->link;
- w->link = weak_ptr_list;
- weak_ptr_list = w;
- flag = rtsTrue;
- IF_DEBUG(weak, belch("Weak pointer still alive at %p -> %p", w, w->key));
- continue;
- }
- else {
- last_w = &(w->link);
- next_w = w->link;
- continue;
- }
- }
+ switch (weak_stage) {
- /* Now deal with the all_threads list, which behaves somewhat like
- * the weak ptr list. If we discover any threads that are about to
- * become garbage, we wake them up and administer an exception.
- */
- {
- StgTSO *t, *tmp, *next, **prev;
-
- prev = &old_all_threads;
- for (t = old_all_threads; t != END_TSO_QUEUE; t = next) {
+ case WeakDone:
+ return rtsFalse;
- (StgClosure *)tmp = isAlive((StgClosure *)t);
+ case WeakPtrs:
+ /* doesn't matter where we evacuate values/finalizers to, since
+ * these pointers are treated as roots (iff the keys are alive).
+ */
+ evac_gen = 0;
- if (tmp != NULL) {
- t = tmp;
- }
-
- ASSERT(get_itbl(t)->type == TSO);
- switch (t->what_next) {
- case ThreadRelocated:
- next = t->link;
- *prev = next;
- continue;
- case ThreadKilled:
- case ThreadComplete:
- // finshed or died. The thread might still be alive, but we
- // don't keep it on the all_threads list. Don't forget to
- // stub out its global_link field.
- next = t->global_link;
- t->global_link = END_TSO_QUEUE;
- *prev = next;
- continue;
- default:
- ;
+ last_w = &old_weak_ptr_list;
+ for (w = old_weak_ptr_list; w != NULL; w = next_w) {
+
+ /* There might be a DEAD_WEAK on the list if finalizeWeak# was
+ * called on a live weak pointer object. Just remove it.
+ */
+ if (w->header.info == &stg_DEAD_WEAK_info) {
+ next_w = ((StgDeadWeak *)w)->link;
+ *last_w = next_w;
+ continue;
+ }
+
+ ASSERT(get_itbl(w)->type == WEAK);
+
+ /* Now, check whether the key is reachable.
+ */
+ new = isAlive(w->key);
+ if (new != NULL) {
+ w->key = new;
+ // evacuate the value and finalizer
+ w->value = evacuate(w->value);
+ w->finalizer = evacuate(w->finalizer);
+ // remove this weak ptr from the old_weak_ptr list
+ *last_w = w->link;
+ // and put it on the new weak ptr list
+ next_w = w->link;
+ w->link = weak_ptr_list;
+ weak_ptr_list = w;
+ flag = rtsTrue;
+ IF_DEBUG(weak, belch("Weak pointer still alive at %p -> %p",
+ w, w->key));
+ continue;
+ }
+ else {
+ last_w = &(w->link);
+ next_w = w->link;
+ continue;
+ }
}
+
+ /* If we didn't make any changes, then we can go round and kill all
+ * the dead weak pointers. The old_weak_ptr list is used as a list
+ * of pending finalizers later on.
+ */
+ if (flag == rtsFalse) {
+ for (w = old_weak_ptr_list; w; w = w->link) {
+ w->finalizer = evacuate(w->finalizer);
+ }
- if (tmp == NULL) {
- // not alive (yet): leave this thread on the old_all_threads list.
- prev = &(t->global_link);
- next = t->global_link;
- }
- else {
- // alive: move this thread onto the all_threads list.
- next = t->global_link;
- t->global_link = all_threads;
- all_threads = t;
- *prev = next;
+ // Next, move to the WeakThreads stage after fully
+ // scavenging the finalizers we've just evacuated.
+ weak_stage = WeakThreads;
}
- }
- }
- /* If we didn't make any changes, then we can go round and kill all
- * the dead weak pointers. The old_weak_ptr list is used as a list
- * of pending finalizers later on.
- */
- if (flag == rtsFalse) {
- for (w = old_weak_ptr_list; w; w = w->link) {
- w->finalizer = evacuate(w->finalizer);
- }
+ return rtsTrue;
- /* And resurrect any threads which were about to become garbage.
- */
- {
- StgTSO *t, *tmp, *next;
- for (t = old_all_threads; t != END_TSO_QUEUE; t = next) {
- next = t->global_link;
- (StgClosure *)tmp = evacuate((StgClosure *)t);
- tmp->global_link = resurrected_threads;
- resurrected_threads = tmp;
+ case WeakThreads:
+ /* Now deal with the all_threads list, which behaves somewhat like
+ * the weak ptr list. If we discover any threads that are about to
+ * become garbage, we wake them up and administer an exception.
+ */
+ {
+ StgTSO *t, *tmp, *next, **prev;
+
+ prev = &old_all_threads;
+ for (t = old_all_threads; t != END_TSO_QUEUE; t = next) {
+
+ (StgClosure *)tmp = isAlive((StgClosure *)t);
+
+ if (tmp != NULL) {
+ t = tmp;
+ }
+
+ ASSERT(get_itbl(t)->type == TSO);
+ switch (t->what_next) {
+ case ThreadRelocated:
+ next = t->link;
+ *prev = next;
+ continue;
+ case ThreadKilled:
+ case ThreadComplete:
+ // finshed or died. The thread might still be alive, but we
+ // don't keep it on the all_threads list. Don't forget to
+ // stub out its global_link field.
+ next = t->global_link;
+ t->global_link = END_TSO_QUEUE;
+ *prev = next;
+ continue;
+ default:
+ ;
+ }
+
+ if (tmp == NULL) {
+ // not alive (yet): leave this thread on the
+ // old_all_threads list.
+ prev = &(t->global_link);
+ next = t->global_link;
+ }
+ else {
+ // alive: move this thread onto the all_threads list.
+ next = t->global_link;
+ t->global_link = all_threads;
+ all_threads = t;
+ *prev = next;
+ }
+ }
}
- }
+
+ /* And resurrect any threads which were about to become garbage.
+ */
+ {
+ StgTSO *t, *tmp, *next;
+ for (t = old_all_threads; t != END_TSO_QUEUE; t = next) {
+ next = t->global_link;
+ (StgClosure *)tmp = evacuate((StgClosure *)t);
+ tmp->global_link = resurrected_threads;
+ resurrected_threads = tmp;
+ }
+ }
+
+ weak_stage = WeakDone; // *now* we're done,
+ return rtsTrue; // but one more round of scavenging, please
- weak_done = rtsTrue;
+ default:
+ barf("traverse_weak_ptr_list");
}
- return rtsTrue;
}
/* -----------------------------------------------------------------------------
// perform the selection!
q = selectee->payload[offset];
+ if (major_gc==rtsTrue) {TICK_GC_SEL_MAJOR();} else {TICK_GC_SEL_MINOR();}
/* if we're already in to-space, there's no need to continue
* with the evacuation, just update the source address with
thunk_selector_depth--;
goto selector_loop;
}
- }
- // otherwise, fall through...
+ } else {
+ TICK_GC_SEL_ABANDONED();
+ // and fall through...
+ }
# endif
case AP_UPD:
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