6992998: CMSWaitDuration=0 causes hangs with +ExplicitGCInvokesConcurrent
Summary: 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
--- a/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.cpp Sat Oct 16 17:12:19 2010 -0400
+++ b/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.cpp Thu Oct 21 17:29:24 2010 -0700
@@ -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 @@
}
}
-// 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 @@
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
--- a/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp Sat Oct 16 17:12:19 2010 -0400
+++ b/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp Thu Oct 21 17:29:24 2010 -0700
@@ -120,8 +120,10 @@
}
// Wait on CMS lock until the next synchronous GC
- // or given timeout, whichever is earlier.
- void wait_on_cms_lock(long t); // milliseconds
+ // or given timeout, whichever is earlier. A timeout value
+ // of 0 indicates that there is no upper bound on the wait time.
+ // A concurrent full gc request terminates the wait.
+ void wait_on_cms_lock(long t_millis);
// The CMS thread will yield during the work portion of its cycle
// only when requested to. Both synchronous and asychronous requests
--- a/hotspot/src/share/vm/runtime/globals.hpp Sat Oct 16 17:12:19 2010 -0400
+++ b/hotspot/src/share/vm/runtime/globals.hpp Thu Oct 21 17:29:24 2010 -0700
@@ -1585,7 +1585,7 @@
"(Temporary, subject to experimentation)" \
"Nominal minimum work per abortable preclean iteration") \
\
- product(intx, CMSAbortablePrecleanWaitMillis, 100, \
+ manageable(intx, CMSAbortablePrecleanWaitMillis, 100, \
"(Temporary, subject to experimentation)" \
" Time that we sleep between iterations when not given" \
" enough work per iteration") \
@@ -1677,7 +1677,7 @@
product(uintx, CMSWorkQueueDrainThreshold, 10, \
"Don't drain below this size per parallel worker/thief") \
\
- product(intx, CMSWaitDuration, 2000, \
+ manageable(intx, CMSWaitDuration, 2000, \
"Time in milliseconds that CMS thread waits for young GC") \
\
product(bool, CMSYield, true, \