X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2Fsm%2FMarkWeak.c;h=7b7187c94d58e10392ec52c71fd18e41386b4691;hb=b84ba676034763b3082bbd9405794a4fde499d14;hp=eca5c54b138fc4b7f658936182b6b9f36a0739c5;hpb=c357244371ca5eeaa0d56a6bd349e26a3b16b7dc;p=ghc-hetmet.git diff --git a/rts/sm/MarkWeak.c b/rts/sm/MarkWeak.c index eca5c54..7b7187c 100644 --- a/rts/sm/MarkWeak.c +++ b/rts/sm/MarkWeak.c @@ -1,6 +1,6 @@ /* ----------------------------------------------------------------------------- * - * (c) The GHC Team 1998-2006 + * (c) The GHC Team 1998-2008 * * Weak pointers and weak-like things in the GC * @@ -11,13 +11,17 @@ * * ---------------------------------------------------------------------------*/ +#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" /* ----------------------------------------------------------------------------- Weak Pointers @@ -73,10 +77,14 @@ static WeakStage weak_stage; */ StgWeak *old_weak_ptr_list; // also pending finaliser list -/* List of all threads during GC - */ +// List of threads found to be unreachable StgTSO *resurrected_threads; -static StgTSO *old_all_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) @@ -84,13 +92,8 @@ initWeakForGC(void) old_weak_ptr_list = weak_ptr_list; weak_ptr_list = NULL; weak_stage = WeakPtrs; - - /* The all_threads list is like the weak_ptr_list. - * See traverseWeakPtrList() for the details. - */ - old_all_threads = all_threads; - all_threads = END_TSO_QUEUE; resurrected_threads = END_TSO_QUEUE; + exception_threads = END_TSO_QUEUE; } rtsBool @@ -99,6 +102,7 @@ traverseWeakPtrList(void) StgWeak *w, **last_w, *next_w; StgClosure *new; rtsBool flag = rtsFalse; + const StgInfoTable *info; switch (weak_stage) { @@ -109,7 +113,7 @@ traverseWeakPtrList(void) /* 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 = 0; last_w = &old_weak_ptr_list; for (w = old_weak_ptr_list; w != NULL; w = next_w) { @@ -123,12 +127,8 @@ traverseWeakPtrList(void) continue; } - switch (get_itbl(w)->type) { - - case EVACUATED: - next_w = (StgWeak *)((StgEvacuated *)w)->evacuee; - *last_w = next_w; - continue; + info = get_itbl(w); + switch (info->type) { case WEAK: /* Now, check whether the key is reachable. @@ -180,57 +180,26 @@ traverseWeakPtrList(void) 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; - prev = &old_all_threads; - for (t = old_all_threads; t != END_TSO_QUEUE; t = next) { - - tmp = (StgTSO *)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; - } - } + // 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; + } } - + /* If we evacuated any threads, we need to go back to the scavenger. */ if (flag) return rtsTrue; @@ -238,16 +207,12 @@ traverseWeakPtrList(void) /* 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; - tmp = t; - evacuate((StgClosure **)&tmp); - tmp->global_link = resurrected_threads; - resurrected_threads = tmp; - } + nat g; + for (g = 0; g <= N; g++) { + 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 @@ -257,20 +222,118 @@ traverseWeakPtrList(void) */ { StgTSO **pt; - for (pt = &blackhole_queue; *pt != END_TSO_QUEUE; pt = &((*pt)->link)) { + 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; + } + } +} +static rtsBool tidyThreadList (generation *gen) +{ + 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); + 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. + generation *new_gen; + new_gen = Bdescr((P_)t)->gen; + t->global_link = new_gen->threads; + new_gen->threads = t; + } + } + + return flag; } /* ----------------------------------------------------------------------------- @@ -290,7 +353,7 @@ traverseBlackholeQueue (void) flag = rtsFalse; prev = NULL; - for (t = blackhole_queue; t != END_TSO_QUEUE; prev=t, t = t->link) { + 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 @@ -302,9 +365,14 @@ traverseBlackholeQueue (void) continue; } } - tmp = t; - evacuate((StgClosure **)&tmp); - if (prev) prev->link = t; + 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; } } @@ -312,31 +380,31 @@ traverseBlackholeQueue (void) } /* ----------------------------------------------------------------------------- - 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(w->header.info == &stg_DEAD_WEAK_info - || get_itbl(w)->type == WEAK || get_itbl(w)->type == EVACUATED); - tmp = w; - evacuate((StgClosure **)&tmp); - *last_w = w; - last_w = &(w->link); + ASSERT(IS_FORWARDING_PTR(w->header.info) + || w->header.info == &stg_DEAD_WEAK_info + || get_itbl(w)->type == WEAK); + 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); + } } }