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6992998: CMSWaitDuration=0 causes hangs with +ExplicitGCInvokesConcurrent

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Closed a timing hole during which concurrent full gc requests can be missed. The hole can increase the latency of the response to a full gc request by up to the value of CMSWaitDuration. If CMSWaitDuration=0 is, as currently, interpreted as an unbounded wait, suitable in certain tuning scenarios, the application can potentially hang. Made two obscure tunables, including CMSWaitDuration, manageable.

Reviewed-by: jcoomes, tonyp
This commit is contained in:
Y. Srinivas Ramakrishna 2010-10-21 17:29:24 -07:00
parent 0c660e1f60
commit 554e77efb4
3 changed files with 16 additions and 9 deletions
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15
hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2001, 2006, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2001, 2010, 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
@ -272,12 +272,16 @@ void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
}
}
// Wait until the next synchronous GC or a timeout, whichever is earlier.
void ConcurrentMarkSweepThread::wait_on_cms_lock(long t) {
// Wait until the next synchronous GC, a concurrent full gc request,
// or a timeout, whichever is earlier.
void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
MutexLockerEx x(CGC_lock,
Mutex::_no_safepoint_check_flag);
if (_should_terminate || _collector->_full_gc_requested) {
return;
}
set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
CGC_lock->wait(Mutex::_no_safepoint_check_flag, t);
CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
clear_CMS_flag(CMS_cms_wants_token);
assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
"Should not be set");
@ -289,7 +293,8 @@ void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
icms_wait();
return;
} else {
// Wait until the next synchronous GC or a timeout, whichever is earlier
// Wait until the next synchronous GC, a concurrent full gc
// request or a timeout, whichever is earlier.
wait_on_cms_lock(CMSWaitDuration);
}
// Check if we should start a CMS collection cycle