Thu, 07 Apr 2011 09:53:20 -0700
7009266: G1: assert(obj->is_oop_or_null(true )) failed: Error
Summary: A referent object that is only weakly reachable at the start of concurrent marking but is re-attached to the strongly reachable object graph during marking may not be marked as live. This can cause the reference object to be processed prematurely and leave dangling pointers to the referent object. Implement a read barrier for the java.lang.ref.Reference::referent field by intrinsifying the Reference.get() method, and intercepting accesses though JNI, reflection, and Unsafe, so that when a non-null referent object is read it is also logged in an SATB buffer.
Reviewed-by: kvn, iveresov, never, tonyp, dholmes
1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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13 * accompanied this code).
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23 */
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();
102 }
104 _pause_succeeded =
105 g1h->do_collection_pause_at_safepoint(_target_pause_time_ms);
106 if (_pause_succeeded && _word_size > 0) {
107 // An allocation had been requested.
108 _result = g1h->attempt_allocation_at_safepoint(_word_size,
109 true /* expect_null_cur_alloc_region */);
110 } else {
111 assert(_result == NULL, "invariant");
112 }
113 }
115 void VM_G1IncCollectionPause::doit_epilogue() {
116 VM_GC_Operation::doit_epilogue();
118 // If the pause was initiated by a System.gc() and
119 // +ExplicitGCInvokesConcurrent, we have to wait here for the cycle
120 // that just started (or maybe one that was already in progress) to
121 // finish.
122 if (_gc_cause == GCCause::_java_lang_system_gc &&
123 _should_initiate_conc_mark) {
124 assert(ExplicitGCInvokesConcurrent,
125 "the only way to be here is if ExplicitGCInvokesConcurrent is set");
127 G1CollectedHeap* g1h = G1CollectedHeap::heap();
129 // In the doit() method we saved g1h->full_collections_completed()
130 // in the _full_collections_completed_before field. We have to
131 // wait until we observe that g1h->full_collections_completed()
132 // has increased by at least one. This can happen if a) we started
133 // a cycle and it completes, b) a cycle already in progress
134 // completes, or c) a Full GC happens.
136 // If the condition has already been reached, there's no point in
137 // actually taking the lock and doing the wait.
138 if (g1h->full_collections_completed() <=
139 _full_collections_completed_before) {
140 // The following is largely copied from CMS
142 Thread* thr = Thread::current();
143 assert(thr->is_Java_thread(), "invariant");
144 JavaThread* jt = (JavaThread*)thr;
145 ThreadToNativeFromVM native(jt);
147 MutexLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
148 while (g1h->full_collections_completed() <=
149 _full_collections_completed_before) {
150 FullGCCount_lock->wait(Mutex::_no_safepoint_check_flag);
151 }
152 }
153 }
154 }
156 void VM_CGC_Operation::doit() {
157 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
158 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
159 TraceTime t(_printGCMessage, PrintGC, true, gclog_or_tty);
160 SharedHeap* sh = SharedHeap::heap();
161 // This could go away if CollectedHeap gave access to _gc_is_active...
162 if (sh != NULL) {
163 IsGCActiveMark x;
164 _cl->do_void();
165 } else {
166 _cl->do_void();
167 }
168 }
170 bool VM_CGC_Operation::doit_prologue() {
171 Heap_lock->lock();
172 SharedHeap::heap()->_thread_holds_heap_lock_for_gc = true;
173 return true;
174 }
176 void VM_CGC_Operation::doit_epilogue() {
177 SharedHeap::heap()->_thread_holds_heap_lock_for_gc = false;
178 Heap_lock->unlock();
179 }