Thu, 22 Sep 2011 10:57:37 -0700
6484982: G1: process references during evacuation pauses
Summary: G1 now uses two reference processors - one is used by concurrent marking and the other is used by STW GCs (both full and incremental evacuation pauses). In an evacuation pause, the reference processor is embedded into the closures used to scan objects. Doing so causes causes reference objects to be 'discovered' by the reference processor. At the end of the evacuation pause, these discovered reference objects are processed - preserving (and copying) referent objects (and their reachable graphs) as appropriate.
Reviewed-by: ysr, jwilhelm, brutisso, stefank, tonyp
1 /*
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25 #include "precompiled.hpp"
26 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
27 #include "gc_implementation/g1/g1CollectorPolicy.hpp"
28 #include "gc_implementation/g1/vm_operations_g1.hpp"
29 #include "gc_implementation/shared/isGCActiveMark.hpp"
30 #include "gc_implementation/g1/vm_operations_g1.hpp"
31 #include "runtime/interfaceSupport.hpp"
33 VM_G1CollectForAllocation::VM_G1CollectForAllocation(
34 unsigned int gc_count_before,
35 size_t word_size)
36 : VM_G1OperationWithAllocRequest(gc_count_before, word_size) {
37 guarantee(word_size > 0, "an allocation should always be requested");
38 }
40 void VM_G1CollectForAllocation::doit() {
41 G1CollectedHeap* g1h = G1CollectedHeap::heap();
42 _result = g1h->satisfy_failed_allocation(_word_size, &_pause_succeeded);
43 assert(_result == NULL || _pause_succeeded,
44 "if we get back a result, the pause should have succeeded");
45 }
47 void VM_G1CollectFull::doit() {
48 G1CollectedHeap* g1h = G1CollectedHeap::heap();
49 GCCauseSetter x(g1h, _gc_cause);
50 g1h->do_full_collection(false /* clear_all_soft_refs */);
51 }
53 VM_G1IncCollectionPause::VM_G1IncCollectionPause(
54 unsigned int gc_count_before,
55 size_t word_size,
56 bool should_initiate_conc_mark,
57 double target_pause_time_ms,
58 GCCause::Cause gc_cause)
59 : VM_G1OperationWithAllocRequest(gc_count_before, word_size),
60 _should_initiate_conc_mark(should_initiate_conc_mark),
61 _target_pause_time_ms(target_pause_time_ms),
62 _full_collections_completed_before(0) {
63 guarantee(target_pause_time_ms > 0.0,
64 err_msg("target_pause_time_ms = %1.6lf should be positive",
65 target_pause_time_ms));
66 guarantee(word_size == 0 || gc_cause == GCCause::_g1_inc_collection_pause,
67 "we can only request an allocation if the GC cause is for "
68 "an incremental GC pause");
69 _gc_cause = gc_cause;
70 }
72 void VM_G1IncCollectionPause::doit() {
73 G1CollectedHeap* g1h = G1CollectedHeap::heap();
74 assert(!_should_initiate_conc_mark ||
75 ((_gc_cause == GCCause::_gc_locker && GCLockerInvokesConcurrent) ||
76 (_gc_cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent)),
77 "only a GC locker or a System.gc() induced GC should start a cycle");
79 if (_word_size > 0) {
80 // An allocation has been requested. So, try to do that first.
81 _result = g1h->attempt_allocation_at_safepoint(_word_size,
82 false /* expect_null_cur_alloc_region */);
83 if (_result != NULL) {
84 // If we can successfully allocate before we actually do the
85 // pause then we will consider this pause successful.
86 _pause_succeeded = true;
87 return;
88 }
89 }
91 GCCauseSetter x(g1h, _gc_cause);
92 if (_should_initiate_conc_mark) {
93 // It's safer to read full_collections_completed() here, given
94 // that noone else will be updating it concurrently. Since we'll
95 // only need it if we're initiating a marking cycle, no point in
96 // setting it earlier.
97 _full_collections_completed_before = g1h->full_collections_completed();
99 // At this point we are supposed to start a concurrent cycle. We
100 // will do so if one is not already in progress.
101 bool res = g1h->g1_policy()->force_initial_mark_if_outside_cycle(_gc_cause);
103 // The above routine returns true if we were able to force the
104 // next GC pause to be an initial mark; it returns false if a
105 // marking cycle is already in progress.
106 //
107 // If a marking cycle is already in progress just return and skip
108 // the pause - the requesting thread should block in doit_epilogue
109 // until the marking cycle is complete.
110 if (!res) {
111 assert(_word_size == 0, "ExplicitGCInvokesConcurrent shouldn't be allocating");
112 return;
113 }
114 }
116 _pause_succeeded =
117 g1h->do_collection_pause_at_safepoint(_target_pause_time_ms);
118 if (_pause_succeeded && _word_size > 0) {
119 // An allocation had been requested.
120 _result = g1h->attempt_allocation_at_safepoint(_word_size,
121 true /* expect_null_cur_alloc_region */);
122 } else {
123 assert(_result == NULL, "invariant");
124 }
125 }
127 void VM_G1IncCollectionPause::doit_epilogue() {
128 VM_GC_Operation::doit_epilogue();
130 // If the pause was initiated by a System.gc() and
131 // +ExplicitGCInvokesConcurrent, we have to wait here for the cycle
132 // that just started (or maybe one that was already in progress) to
133 // finish.
134 if (_gc_cause == GCCause::_java_lang_system_gc &&
135 _should_initiate_conc_mark) {
136 assert(ExplicitGCInvokesConcurrent,
137 "the only way to be here is if ExplicitGCInvokesConcurrent is set");
139 G1CollectedHeap* g1h = G1CollectedHeap::heap();
141 // In the doit() method we saved g1h->full_collections_completed()
142 // in the _full_collections_completed_before field. We have to
143 // wait until we observe that g1h->full_collections_completed()
144 // has increased by at least one. This can happen if a) we started
145 // a cycle and it completes, b) a cycle already in progress
146 // completes, or c) a Full GC happens.
148 // If the condition has already been reached, there's no point in
149 // actually taking the lock and doing the wait.
150 if (g1h->full_collections_completed() <=
151 _full_collections_completed_before) {
152 // The following is largely copied from CMS
154 Thread* thr = Thread::current();
155 assert(thr->is_Java_thread(), "invariant");
156 JavaThread* jt = (JavaThread*)thr;
157 ThreadToNativeFromVM native(jt);
159 MutexLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
160 while (g1h->full_collections_completed() <=
161 _full_collections_completed_before) {
162 FullGCCount_lock->wait(Mutex::_no_safepoint_check_flag);
163 }
164 }
165 }
166 }
168 void VM_CGC_Operation::doit() {
169 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
170 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
171 TraceTime t(_printGCMessage, PrintGC, true, gclog_or_tty);
172 SharedHeap* sh = SharedHeap::heap();
173 // This could go away if CollectedHeap gave access to _gc_is_active...
174 if (sh != NULL) {
175 IsGCActiveMark x;
176 _cl->do_void();
177 } else {
178 _cl->do_void();
179 }
180 }
182 bool VM_CGC_Operation::doit_prologue() {
183 Heap_lock->lock();
184 SharedHeap::heap()->_thread_holds_heap_lock_for_gc = true;
185 return true;
186 }
188 void VM_CGC_Operation::doit_epilogue() {
189 SharedHeap::heap()->_thread_holds_heap_lock_for_gc = false;
190 Heap_lock->unlock();
191 }