jdk-sandbox: comparison hotspot/src/share/vm/gc_implementation/g1/concurrentMark.cpp

equal deleted inserted replaced

-:4d193fe22b76
+:6719a2e727c0
 };
 void ConcurrentMark::checkpointRootsInitialPost() {
 G1CollectedHeap*   g1h = G1CollectedHeap::heap();
+// If we force an overflow during remark, the remark operation will
+// actually abort and we'll restart concurrent marking. If we always
+// force an oveflow during remark we'll never actually complete the
+// marking phase. So, we initilize this here, at the start of the
+// cycle, so that at the remaining overflow number will decrease at
+// every remark and we'll eventually not need to cause one.
+force_overflow_stw()->init();
 // For each region note start of marking.
 NoteStartOfMarkHRClosure startcl;
 g1h->heap_region_iterate(&startcl);
 // Start weak-reference discovery.
 g1p->record_concurrent_mark_init_end();
 }
 /*
-Notice that in the next two methods, we actually leave the STS
+* Notice that in the next two methods, we actually leave the STS
-during the barrier sync and join it immediately afterwards. If we
+* during the barrier sync and join it immediately afterwards. If we
-do not do this, this then the following deadlock can occur: one
+* do not do this, the following deadlock can occur: one thread could
-thread could be in the barrier sync code, waiting for the other
+* be in the barrier sync code, waiting for the other thread to also
-thread to also sync up, whereas another one could be trying to
+* sync up, whereas another one could be trying to yield, while also
-yield, while also waiting for the other threads to sync up too.
+* waiting for the other threads to sync up too.
+*
-Because the thread that does the sync barrier has left the STS, it
+* Note, however, that this code is also used during remark and in
-is possible to be suspended for a Full GC or an evacuation pause
+* this case we should not attempt to leave / enter the STS, otherwise
-could occur. This is actually safe, since the entering the sync
+* we'll either hit an asseert (debug / fastdebug) or deadlock
-barrier is one of the last things do_marking_step() does, and it
+* (product). So we should only leave / enter the STS if we are
-doesn't manipulate any data structures afterwards.
+* operating concurrently.
-*/
+*
+* Because the thread that does the sync barrier has left the STS, it
+* is possible to be suspended for a Full GC or an evacuation pause
+* could occur. This is actually safe, since the entering the sync
+* barrier is one of the last things do_marking_step() does, and it
+* doesn't manipulate any data structures afterwards.
+*/
 void ConcurrentMark::enter_first_sync_barrier(int task_num) {
 if (verbose_low())
 gclog_or_tty->print_cr("[%d] entering first barrier", task_num);
-ConcurrentGCThread::stsLeave();
+if (concurrent()) {
+ConcurrentGCThread::stsLeave();
+}
 _first_overflow_barrier_sync.enter();
-ConcurrentGCThread::stsJoin();
+if (concurrent()) {
+ConcurrentGCThread::stsJoin();
+}
 // at this point everyone should have synced up and not be doing any
 // more work
 if (verbose_low())
 gclog_or_tty->print_cr("[%d] leaving first barrier", task_num);
 // let task 0 do this
 if (task_num == 0) {
 // task 0 is responsible for clearing the global data structures
-clear_marking_state();
+// We should be here because of an overflow. During STW we should
+// not clear the overflow flag since we rely on it being true when
+// we exit this method to abort the pause and restart concurent
+// marking.
+clear_marking_state(concurrent() /* clear_overflow */);
+force_overflow()->update();
 if (PrintGC) {
 gclog_or_tty->date_stamp(PrintGCDateStamps);
 gclog_or_tty->stamp(PrintGCTimeStamps);
 gclog_or_tty->print_cr("[GC concurrent-mark-reset-for-overflow]");
 void ConcurrentMark::enter_second_sync_barrier(int task_num) {
 if (verbose_low())
 gclog_or_tty->print_cr("[%d] entering second barrier", task_num);
-ConcurrentGCThread::stsLeave();
+if (concurrent()) {
+ConcurrentGCThread::stsLeave();
+}
 _second_overflow_barrier_sync.enter();
-ConcurrentGCThread::stsJoin();
+if (concurrent()) {
+ConcurrentGCThread::stsJoin();
+}
 // at this point everything should be re-initialised and ready to go
 if (verbose_low())
 gclog_or_tty->print_cr("[%d] leaving second barrier", task_num);
 }
+#ifndef PRODUCT
+void ForceOverflowSettings::init() {
+_num_remaining = G1ConcMarkForceOverflow;
+_force = false;
+update();
+}
+void ForceOverflowSettings::update() {
+if (_num_remaining > 0) {
+_num_remaining -= 1;
+_force = true;
+} else {
+_force = false;
+}
+}
+bool ForceOverflowSettings::should_force() {
+if (_force) {
+_force = false;
+return true;
+} else {
+return false;
+}
+}
+#endif // !PRODUCT
 void ConcurrentMark::grayRoot(oop p) {
 HeapWord* addr = (HeapWord*) p;
 // We can't really check against _heap_start and _heap_end, since it
 // is possible during an evacuation pause with piggy-backed
 // stop-the-world GC happens even as we mark in this generation.
 _restart_for_overflow = false;
 size_t active_workers = MAX2((size_t) 1, parallel_marking_threads());
+force_overflow_conc()->init();
 set_phase(active_workers, true /* concurrent */);
 CMConcurrentMarkingTask markingTask(this, cmThread());
 if (parallel_marking_threads() > 0)
 _parallel_workers->run_task(&markingTask);
 assert(_should_gray_objects, "invariant");
 }
 }
-void ConcurrentMark::clear_marking_state() {
+void ConcurrentMark::clear_marking_state(bool clear_overflow) {
 _markStack.setEmpty();
 _markStack.clear_overflow();
 _regionStack.setEmpty();
 _regionStack.clear_overflow();
-clear_has_overflown();
+if (clear_overflow) {
+clear_has_overflown();
+} else {
+assert(has_overflown(), "pre-condition");
+}
 _finger = _heap_start;
 for (int i = 0; i < (int)_max_task_num; ++i) {
 OopTaskQueue* queue = _task_queues->queue(i);
 queue->set_empty();
 break;
 }
 }
 }
+// If we are about to wrap up and go into termination, check if we
+// should raise the overflow flag.
+if (do_termination && !has_aborted()) {
+if (_cm->force_overflow()->should_force()) {
+_cm->set_has_overflown();
+regular_clock_call();
+}
+}
 // We still haven't aborted. Now, let's try to get into the
 // termination protocol.
 if (do_termination && !has_aborted()) {
 // We cannot check whether the global stack is empty, since other
 // tasks might be concurrently pushing objects on it. We also cannot

changeset 9417	6719a2e727c0
parent 8931	8e2b610bc48f
child 9418	32a87dd6b746