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8228748: Remove GCLocker::_doing_gc

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Reviewed-by: kbarrett, iwalulya, pliden, tschatzl
This commit is contained in:
Albert Mingkun Yang 2021-02-22 10:10:53 +00:00 committed by Thomas Schatzl
parent c20fb5db90
commit 6b7575bbb0
2 changed files with 11 additions and 12 deletions
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19
src/hotspot/share/gc/shared/gcLocker.cpp
View File

@ -36,7 +36,6 @@
volatile jint GCLocker::_jni_lock_count = 0;
volatile bool GCLocker::_needs_gc = false;
volatile bool GCLocker::_doing_gc = false;
unsigned int GCLocker::_total_collections = 0;
#ifdef ASSERT
@ -127,12 +126,16 @@ bool GCLocker::should_discard(GCCause::Cause cause, uint total_collections) {
void GCLocker::jni_lock(JavaThread* thread) {
assert(!thread->in_critical(), "shouldn't currently be in a critical region");
MonitorLocker ml(JNICritical_lock);
// Block entering threads if we know at least one thread is in a
// JNI critical region and we need a GC.
// We check that at least one thread is in a critical region before
// blocking because blocked threads are woken up by a thread exiting
// a JNI critical region.
while (is_active_and_needs_gc() || _doing_gc) {
// Block entering threads if there's a pending GC request.
while (needs_gc()) {
// There's at least one thread that has not left the critical region (CR)
// completely. When that last thread (no new threads can enter CR due to the
// blocking) exits CR, it calls `jni_unlock`, which sets `_needs_gc`
// to false and wakes up all blocked threads.
// We would like to assert #threads in CR to be > 0, `_jni_lock_count > 0`
// in the code, but it's too strong; it's possible that the last thread
// has called `jni_unlock`, but not yet finished the call, e.g. initiating
// a GCCause::_gc_locker GC.
ml.wait();
}
thread->enter_critical();
@ -154,7 +157,6 @@ void GCLocker::jni_unlock(JavaThread* thread) {
// must not be a safepoint between the lock becoming inactive and
// getting the count, else there may be unnecessary GCLocker GCs.
_total_collections = Universe::heap()->total_collections();
_doing_gc = true;
GCLockerTracer::report_gc_locker();
{
// Must give up the lock while at a safepoint
@ -162,7 +164,6 @@ void GCLocker::jni_unlock(JavaThread* thread) {
log_debug_jni("Performing GC after exiting critical section.");
Universe::heap()->collect(GCCause::_gc_locker);
}
_doing_gc = false;
_needs_gc = false;
JNICritical_lock->notify_all();
}

4
src/hotspot/share/gc/shared/gcLocker.hpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 1997, 2020, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -44,8 +44,6 @@ class GCLocker: public AllStatic {
// unlocking.
static volatile jint _jni_lock_count; // number of jni active instances.
static volatile bool _needs_gc; // heap is filling, we need a GC
// note: bool is typedef'd as jint
static volatile bool _doing_gc; // unlock_critical() is doing a GC
static uint _total_collections; // value for _gc_locker collection
#ifdef ASSERT