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
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#include "incls/_precompiled.incl"
#include "incls/_vm_operations_g1.cpp.incl"
void VM_G1CollectForAllocation::doit() {
JvmtiGCForAllocationMarker jgcm;
G1CollectedHeap* g1h = G1CollectedHeap::heap();
_res = g1h->satisfy_failed_allocation(_size);
assert(g1h->is_in_or_null(_res), "result not in heap");
}
void VM_G1CollectFull::doit() {
JvmtiGCFullMarker jgcm;
G1CollectedHeap* g1h = G1CollectedHeap::heap();
GCCauseSetter x(g1h, _gc_cause);
g1h->do_full_collection(false /* clear_all_soft_refs */);
}
void VM_G1IncCollectionPause::doit() {
JvmtiGCForAllocationMarker jgcm;
G1CollectedHeap* g1h = G1CollectedHeap::heap();
assert(!_should_initiate_conc_mark ||
((_gc_cause == GCCause::_gc_locker && GCLockerInvokesConcurrent) ||
(_gc_cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent)),
"only a GC locker or a System.gc() induced GC should start a cycle");
GCCauseSetter x(g1h, _gc_cause);
if (_should_initiate_conc_mark) {
// It's safer to read full_collections_completed() here, given
// that noone else will be updating it concurrently. Since we'll
// only need it if we're initiating a marking cycle, no point in
// setting it earlier.
_full_collections_completed_before = g1h->full_collections_completed();
// At this point we are supposed to start a concurrent cycle. We
// will do so if one is not already in progress.
bool res = g1h->g1_policy()->force_initial_mark_if_outside_cycle();
}
g1h->do_collection_pause_at_safepoint(_target_pause_time_ms);
}
void VM_G1IncCollectionPause::doit_epilogue() {
VM_GC_Operation::doit_epilogue();
// If the pause was initiated by a System.gc() and
// +ExplicitGCInvokesConcurrent, we have to wait here for the cycle
// that just started (or maybe one that was already in progress) to
// finish.
if (_gc_cause == GCCause::_java_lang_system_gc &&
_should_initiate_conc_mark) {
assert(ExplicitGCInvokesConcurrent,
"the only way to be here is if ExplicitGCInvokesConcurrent is set");
G1CollectedHeap* g1h = G1CollectedHeap::heap();
// In the doit() method we saved g1h->full_collections_completed()
// in the _full_collections_completed_before field. We have to
// wait until we observe that g1h->full_collections_completed()
// has increased by at least one. This can happen if a) we started
// a cycle and it completes, b) a cycle already in progress
// completes, or c) a Full GC happens.
// If the condition has already been reached, there's no point in
// actually taking the lock and doing the wait.
if (g1h->full_collections_completed() <=
_full_collections_completed_before) {
// The following is largely copied from CMS
Thread* thr = Thread::current();
assert(thr->is_Java_thread(), "invariant");
JavaThread* jt = (JavaThread*)thr;
ThreadToNativeFromVM native(jt);
MutexLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
while (g1h->full_collections_completed() <=
_full_collections_completed_before) {
FullGCCount_lock->wait(Mutex::_no_safepoint_check_flag);
}
}
}
}
void VM_CGC_Operation::doit() {
gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
TraceTime t(_printGCMessage, PrintGC, true, gclog_or_tty);
SharedHeap* sh = SharedHeap::heap();
// This could go away if CollectedHeap gave access to _gc_is_active...
if (sh != NULL) {
IsGCActiveMark x;
_cl->do_void();
} else {
_cl->do_void();
}
}
bool VM_CGC_Operation::doit_prologue() {
Heap_lock->lock();
SharedHeap::heap()->_thread_holds_heap_lock_for_gc = true;
return true;
}
void VM_CGC_Operation::doit_epilogue() {
SharedHeap::heap()->_thread_holds_heap_lock_for_gc = false;
Heap_lock->unlock();
}