Mon, 28 Jun 2010 14:13:17 -0400
6944166: G1: explicit GCs are not always handled correctly
Summary: G1 was not handling explicit GCs correctly in many ways. It does now. See the CR for the list of improvements contained in this changeset.
Reviewed-by: iveresov, ysr, johnc
1 /*
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25 #include "incls/_precompiled.incl"
26 #include "incls/_vm_operations_g1.cpp.incl"
28 void VM_G1CollectForAllocation::doit() {
29 JvmtiGCForAllocationMarker jgcm;
30 G1CollectedHeap* g1h = G1CollectedHeap::heap();
31 _res = g1h->satisfy_failed_allocation(_size);
32 assert(g1h->is_in_or_null(_res), "result not in heap");
33 }
35 void VM_G1CollectFull::doit() {
36 JvmtiGCFullMarker jgcm;
37 G1CollectedHeap* g1h = G1CollectedHeap::heap();
38 GCCauseSetter x(g1h, _gc_cause);
39 g1h->do_full_collection(false /* clear_all_soft_refs */);
40 }
42 void VM_G1IncCollectionPause::doit() {
43 JvmtiGCForAllocationMarker jgcm;
44 G1CollectedHeap* g1h = G1CollectedHeap::heap();
45 assert(!_should_initiate_conc_mark ||
46 ((_gc_cause == GCCause::_gc_locker && GCLockerInvokesConcurrent) ||
47 (_gc_cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent)),
48 "only a GC locker or a System.gc() induced GC should start a cycle");
50 GCCauseSetter x(g1h, _gc_cause);
51 if (_should_initiate_conc_mark) {
52 // It's safer to read full_collections_completed() here, given
53 // that noone else will be updating it concurrently. Since we'll
54 // only need it if we're initiating a marking cycle, no point in
55 // setting it earlier.
56 _full_collections_completed_before = g1h->full_collections_completed();
58 // At this point we are supposed to start a concurrent cycle. We
59 // will do so if one is not already in progress.
60 bool res = g1h->g1_policy()->force_initial_mark_if_outside_cycle();
61 }
62 g1h->do_collection_pause_at_safepoint(_target_pause_time_ms);
63 }
65 void VM_G1IncCollectionPause::doit_epilogue() {
66 VM_GC_Operation::doit_epilogue();
68 // If the pause was initiated by a System.gc() and
69 // +ExplicitGCInvokesConcurrent, we have to wait here for the cycle
70 // that just started (or maybe one that was already in progress) to
71 // finish.
72 if (_gc_cause == GCCause::_java_lang_system_gc &&
73 _should_initiate_conc_mark) {
74 assert(ExplicitGCInvokesConcurrent,
75 "the only way to be here is if ExplicitGCInvokesConcurrent is set");
77 G1CollectedHeap* g1h = G1CollectedHeap::heap();
79 // In the doit() method we saved g1h->full_collections_completed()
80 // in the _full_collections_completed_before field. We have to
81 // wait until we observe that g1h->full_collections_completed()
82 // has increased by at least one. This can happen if a) we started
83 // a cycle and it completes, b) a cycle already in progress
84 // completes, or c) a Full GC happens.
86 // If the condition has already been reached, there's no point in
87 // actually taking the lock and doing the wait.
88 if (g1h->full_collections_completed() <=
89 _full_collections_completed_before) {
90 // The following is largely copied from CMS
92 Thread* thr = Thread::current();
93 assert(thr->is_Java_thread(), "invariant");
94 JavaThread* jt = (JavaThread*)thr;
95 ThreadToNativeFromVM native(jt);
97 MutexLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
98 while (g1h->full_collections_completed() <=
99 _full_collections_completed_before) {
100 FullGCCount_lock->wait(Mutex::_no_safepoint_check_flag);
101 }
102 }
103 }
104 }
106 void VM_CGC_Operation::doit() {
107 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
108 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
109 TraceTime t(_printGCMessage, PrintGC, true, gclog_or_tty);
110 SharedHeap* sh = SharedHeap::heap();
111 // This could go away if CollectedHeap gave access to _gc_is_active...
112 if (sh != NULL) {
113 IsGCActiveMark x;
114 _cl->do_void();
115 } else {
116 _cl->do_void();
117 }
118 }
120 bool VM_CGC_Operation::doit_prologue() {
121 Heap_lock->lock();
122 SharedHeap::heap()->_thread_holds_heap_lock_for_gc = true;
123 return true;
124 }
126 void VM_CGC_Operation::doit_epilogue() {
127 SharedHeap::heap()->_thread_holds_heap_lock_for_gc = false;
128 Heap_lock->unlock();
129 }