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8297487: G1 Remark: no need to keep alive oop constants of nmethods on stack #11314

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8297487: G1 Remark: no need to keep alive oop constants of nmethods on stack #11314

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37ee165
G1 Remark: no need to keep alive const oops for nmethods on stack
reinrich Nov 15, 2022
54f2e80
Merge branch 'master'
reinrich Jan 9, 2023
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13 changes: 0 additions & 13 deletions src/hotspot/share/gc/g1/g1ConcurrentMark.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1779,30 +1779,17 @@ class G1CMSATBBufferClosure : public SATBBufferClosure {

class G1RemarkThreadsClosure : public ThreadClosure {
G1SATBMarkQueueSet& _qset;
G1CMOopClosure _cm_cl;
MarkingCodeBlobClosure _code_cl;
uintx _claim_token;

public:
G1RemarkThreadsClosure(G1CollectedHeap* g1h, G1CMTask* task) :
_qset(G1BarrierSet::satb_mark_queue_set()),
_cm_cl(g1h, task),
_code_cl(&_cm_cl, !CodeBlobToOopClosure::FixRelocations, true /* keepalive nmethods */),
_claim_token(Threads::thread_claim_token()) {}

void do_thread(Thread* thread) {
if (thread->claim_threads_do(true, _claim_token)) {
// Transfer any partial buffer to the qset for completed buffer processing.
_qset.flush_queue(G1ThreadLocalData::satb_mark_queue(thread));
if (thread->is_Java_thread()) {
// In theory it should not be necessary to explicitly walk the nmethods to find roots for concurrent marking
// however the liveness of oops reachable from nmethods have very complex lifecycles:
// * Alive if on the stack of an executing method
// * Weakly reachable otherwise
// Some objects reachable from nmethods, such as the class loader (or klass_holder) of the receiver should be
// live by the SATB invariant but other oops recorded in nmethods may behave differently.
JavaThread::cast(thread)->nmethods_do(&_code_cl);
}
}
}
};
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5 changes: 3 additions & 2 deletions src/hotspot/share/gc/shared/barrierSet.cpp
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Expand Up @@ -57,8 +57,9 @@ static BarrierSetNMethod* select_barrier_set_nmethod(BarrierSetNMethod* barrier_
// The GC needs nmethod entry barriers to do concurrent GC
return barrier_set_nmethod;
} else {
// The GC needs nmethod entry barriers to deal with continuations
// and code cache unloading
// The GC needs nmethod entry barriers for code cache unloading (recently
// used heuristics) and, if it's a SATB GC, to keep alive constant objects
// of nmethods because they are weakly referenced.
return new BarrierSetNMethod();
}
}
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