*
* ---------------------------------------------------------------------------*/
+#include "PosixSource.h"
#include "Rts.h"
-#include "Storage.h"
+
#include "MarkWeak.h"
#include "GC.h"
#include "GCThread.h"
#include "Evac.h"
#include "Trace.h"
#include "Schedule.h"
+#include "Weak.h"
+#include "Storage.h"
+#include "Threads.h"
/* -----------------------------------------------------------------------------
Weak Pointers
// List of threads found to be unreachable
StgTSO *resurrected_threads;
-// List of blocked threads found to have pending throwTos
-StgTSO *exception_threads;
+static void resurrectUnreachableThreads (generation *gen);
+static rtsBool tidyThreadList (generation *gen);
void
initWeakForGC(void)
weak_ptr_list = NULL;
weak_stage = WeakPtrs;
resurrected_threads = END_TSO_QUEUE;
- exception_threads = END_TSO_QUEUE;
}
rtsBool
/* doesn't matter where we evacuate values/finalizers to, since
* these pointers are treated as roots (iff the keys are alive).
*/
- gct->evac_step = 0;
+ gct->evac_gen_no = 0;
last_w = &old_weak_ptr_list;
for (w = old_weak_ptr_list; w != NULL; w = next_w) {
continue;
}
- info = w->header.info;
- if (IS_FORWARDING_PTR(info)) {
- next_w = (StgWeak *)UN_FORWARDING_PTR(info);
- *last_w = next_w;
- continue;
- }
-
- switch (INFO_PTR_TO_STRUCT(info)->type) {
+ info = get_itbl(w);
+ switch (info->type) {
case WEAK:
/* Now, check whether the key is reachable.
return rtsTrue;
case WeakThreads:
- /* Now deal with the all_threads list, which behaves somewhat like
+ /* Now deal with the step->threads lists, which behave 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;
- nat g, s;
- step *stp;
+ {
+ nat g;
- // Traverse thread lists for generations we collected...
- for (g = 0; g <= N; g++) {
- for (s = 0; s < generations[g].n_steps; s++) {
- stp = &generations[g].steps[s];
-
- prev = &stp->old_threads;
-
- for (t = stp->old_threads; t != END_TSO_QUEUE; t = next) {
-
- tmp = (StgTSO *)isAlive((StgClosure *)t);
-
- if (tmp != NULL) {
- t = tmp;
- }
-
- ASSERT(get_itbl(t)->type == TSO);
- if (t->what_next == ThreadRelocated) {
- next = t->_link;
- *prev = next;
- continue;
- }
-
- next = t->global_link;
-
- // This is a good place to check for blocked
- // exceptions. It might be the case that a thread is
- // blocked on delivering an exception to a thread that
- // is also blocked - we try to ensure that this
- // doesn't happen in throwTo(), but it's too hard (or
- // impossible) to close all the race holes, so we
- // accept that some might get through and deal with
- // them here. A GC will always happen at some point,
- // even if the system is otherwise deadlocked.
- //
- // If an unreachable thread has blocked
- // exceptions, we really want to perform the
- // blocked exceptions rather than throwing
- // BlockedIndefinitely exceptions. This is the
- // only place we can discover such threads.
- // The target thread might even be
- // ThreadFinished or ThreadKilled. Bugs here
- // will only be seen when running on a
- // multiprocessor.
- if (t->blocked_exceptions != END_TSO_QUEUE) {
- if (tmp == NULL) {
- evacuate((StgClosure **)&t);
- flag = rtsTrue;
- }
- t->global_link = exception_threads;
- exception_threads = t;
- *prev = next;
- continue;
- }
-
- if (tmp == NULL) {
- // not alive (yet): leave this thread on the
- // old_all_threads list.
- prev = &(t->global_link);
- }
- else {
- // alive
- *prev = next;
-
- // move this thread onto the correct threads list.
- step *new_step;
- new_step = Bdescr((P_)t)->step;
- t->global_link = new_step->threads;
- new_step->threads = t;
- }
- }
- }
+ // Traverse thread lists for generations we collected...
+// ToDo when we have one gen per capability:
+// for (n = 0; n < n_capabilities; n++) {
+// if (tidyThreadList(&nurseries[n])) {
+// flag = rtsTrue;
+// }
+// }
+ for (g = 0; g <= N; g++) {
+ if (tidyThreadList(&generations[g])) {
+ flag = rtsTrue;
}
}
/* And resurrect any threads which were about to become garbage.
*/
{
- nat g, s;
- step *stp;
- StgTSO *t, *tmp, *next;
-
+ nat g;
for (g = 0; g <= N; g++) {
- for (s = 0; s < generations[g].n_steps; s++) {
- stp = &generations[g].steps[s];
-
- for (t = stp->old_threads; t != END_TSO_QUEUE; t = next) {
- next = t->global_link;
-
- // ThreadFinished and ThreadComplete: we have to keep
- // these on the all_threads list until they
- // become garbage, because they might get
- // pending exceptions.
- switch (t->what_next) {
- case ThreadKilled:
- case ThreadComplete:
- continue;
- default:
- tmp = t;
- evacuate((StgClosure **)&tmp);
- tmp->global_link = resurrected_threads;
- resurrected_threads = tmp;
- }
- }
- }
+ resurrectUnreachableThreads(&generations[g]);
}
}
-
- /* Finally, we can update the blackhole_queue. This queue
- * simply strings together TSOs blocked on black holes, it is
- * not intended to keep anything alive. Hence, we do not follow
- * pointers on the blackhole_queue until now, when we have
- * determined which TSOs are otherwise reachable. We know at
- * this point that all TSOs have been evacuated, however.
- */
- {
- StgTSO **pt;
- for (pt = &blackhole_queue; *pt != END_TSO_QUEUE; pt = &((*pt)->_link)) {
- *pt = (StgTSO *)isAlive((StgClosure *)*pt);
- ASSERT(*pt != NULL);
- }
- }
-
+
weak_stage = WeakDone; // *now* we're done,
return rtsTrue; // but one more round of scavenging, please
-
+ }
+
default:
barf("traverse_weak_ptr_list");
return rtsTrue;
}
-
+}
+
+ static void resurrectUnreachableThreads (generation *gen)
+{
+ StgTSO *t, *tmp, *next;
+
+ for (t = gen->old_threads; t != END_TSO_QUEUE; t = next) {
+ next = t->global_link;
+
+ // ThreadFinished and ThreadComplete: we have to keep
+ // these on the all_threads list until they
+ // become garbage, because they might get
+ // pending exceptions.
+ switch (t->what_next) {
+ case ThreadKilled:
+ case ThreadComplete:
+ continue;
+ default:
+ tmp = t;
+ evacuate((StgClosure **)&tmp);
+ tmp->global_link = resurrected_threads;
+ resurrected_threads = tmp;
+ }
+ }
}
-/* -----------------------------------------------------------------------------
- The blackhole queue
-
- Threads on this list behave like weak pointers during the normal
- phase of garbage collection: if the blackhole is reachable, then
- the thread is reachable too.
- -------------------------------------------------------------------------- */
-rtsBool
-traverseBlackholeQueue (void)
+static rtsBool tidyThreadList (generation *gen)
{
- StgTSO *prev, *t, *tmp;
- rtsBool flag;
- nat type;
-
- flag = rtsFalse;
- prev = NULL;
-
- for (t = blackhole_queue; t != END_TSO_QUEUE; prev=t, t = t->_link) {
- // if the thread is not yet alive...
- if (! (tmp = (StgTSO *)isAlive((StgClosure*)t))) {
- // if the closure it is blocked on is either (a) a
- // reachable BLAKCHOLE or (b) not a BLACKHOLE, then we
- // make the thread alive.
- if (!isAlive(t->block_info.closure)) {
- type = get_itbl(t->block_info.closure)->type;
- if (type == BLACKHOLE || type == CAF_BLACKHOLE) {
- continue;
- }
- }
- evacuate((StgClosure **)&t);
- if (prev) {
- prev->_link = t;
- } else {
- blackhole_queue = t;
- }
- // no write barrier when on the blackhole queue,
- // because we traverse the whole queue on every GC.
- flag = rtsTrue;
- }
+ StgTSO *t, *tmp, *next, **prev;
+ rtsBool flag = rtsFalse;
+
+ prev = &gen->old_threads;
+
+ for (t = gen->old_threads; t != END_TSO_QUEUE; t = next) {
+
+ tmp = (StgTSO *)isAlive((StgClosure *)t);
+
+ if (tmp != NULL) {
+ t = tmp;
+ }
+
+ ASSERT(get_itbl(t)->type == TSO);
+ next = t->global_link;
+
+ // if the thread is not masking exceptions but there are
+ // pending exceptions on its queue, then something has gone
+ // wrong. However, pending exceptions are OK if there is an
+ // FFI call.
+ ASSERT(t->blocked_exceptions == END_BLOCKED_EXCEPTIONS_QUEUE
+ || t->why_blocked == BlockedOnCCall
+ || t->why_blocked == BlockedOnCCall_Interruptible
+ || (t->flags & TSO_BLOCKEX));
+
+ if (tmp == NULL) {
+ // not alive (yet): leave this thread on the
+ // old_all_threads list.
+ prev = &(t->global_link);
+ }
+ else {
+ // alive
+ *prev = next;
+
+ // move this thread onto the correct threads list.
+ generation *new_gen;
+ new_gen = Bdescr((P_)t)->gen;
+ t->global_link = new_gen->threads;
+ new_gen->threads = t;
+ }
}
+
return flag;
}
/* -----------------------------------------------------------------------------
- After GC, the live weak pointer list may have forwarding pointers
- on it, because a weak pointer object was evacuated after being
- moved to the live weak pointer list. We remove those forwarding
- pointers here.
-
- Also, we don't consider weak pointer objects to be reachable, but
- we must nevertheless consider them to be "live" and retain them.
- Therefore any weak pointer objects which haven't as yet been
- evacuated need to be evacuated now.
+ Evacuate every weak pointer object on the weak_ptr_list, and update
+ the link fields.
+
+ ToDo: with a lot of weak pointers, this will be expensive. We
+ should have a per-GC weak pointer list, just like threads.
-------------------------------------------------------------------------- */
void
markWeakPtrList ( void )
{
- StgWeak *w, **last_w, *tmp;
+ StgWeak *w, **last_w;
last_w = &weak_ptr_list;
for (w = weak_ptr_list; w; w = w->link) {
// w might be WEAK, EVACUATED, or DEAD_WEAK (actually CON_STATIC) here
- ASSERT(IS_FORWARDING_PTR(w->header.info)
- || w->header.info == &stg_DEAD_WEAK_info
- || get_itbl(w)->type == WEAK);
- tmp = w;
- evacuate((StgClosure **)&tmp);
- *last_w = w;
- last_w = &(w->link);
+
+#ifdef DEBUG
+ { // careful to do this assertion only reading the info ptr
+ // once, because during parallel GC it might change under our feet.
+ const StgInfoTable *info;
+ info = w->header.info;
+ ASSERT(IS_FORWARDING_PTR(info)
+ || info == &stg_DEAD_WEAK_info
+ || INFO_PTR_TO_STRUCT(info)->type == WEAK);
+ }
+#endif
+
+ evacuate((StgClosure **)last_w);
+ w = *last_w;
+ if (w->header.info == &stg_DEAD_WEAK_info) {
+ last_w = &(((StgDeadWeak*)w)->link);
+ } else {
+ last_w = &(w->link);
+ }
}
}
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