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src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp@c99c53f07c14 (annotated)

src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp

Wed, 29 Sep 2010 16:17:02 -0700

author

ysr

date

Wed, 29 Sep 2010 16:17:02 -0700

changeset 2192

c99c53f07c14

parent 1907

c18cbe5936b8

child 2242

cd3ef3fd20dd

permissions

-rw-r--r--

6692906: CMS: parallel concurrent marking may be prone to hanging or stalling mutators for periods of time
Summary: Inserted missing yield(check)s in closures used during the work-stealing phase of parallel concurrent marking, a missing synchronous yield-request in the cms perm gen allocation path, and a terminator-terminator for the offer_termination invocation that monitors the yield status of the concurrent marking task. Elaborated some documentation comments and made some task queue termination loop flags configurable at start-up to aid debugging in the field.
Reviewed-by: jmasa, johnc, poonam

duke@435	1	/*
ysr@2192	2	* Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.
duke@435	3	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
duke@435	4	*
duke@435	5	* This code is free software; you can redistribute it and/or modify it
duke@435	6	* under the terms of the GNU General Public License version 2 only, as
duke@435	7	* published by the Free Software Foundation.
duke@435	8	*
duke@435	9	* This code is distributed in the hope that it will be useful, but WITHOUT
duke@435	10	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
duke@435	11	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
duke@435	12	* version 2 for more details (a copy is included in the LICENSE file that
duke@435	13	* accompanied this code).
duke@435	14	*
duke@435	15	* You should have received a copy of the GNU General Public License version
duke@435	16	* 2 along with this work; if not, write to the Free Software Foundation,
duke@435	17	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
duke@435	18	*
trims@1907	19	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
trims@1907	20	* or visit www.oracle.com if you need additional information or have any
trims@1907	21	* questions.
duke@435	22	*
duke@435	23	*/
duke@435	24
duke@435	25	class ConcurrentMarkSweepGeneration;
duke@435	26	class CMSCollector;
duke@435	27
duke@435	28	// The Concurrent Mark Sweep GC Thread (could be several in the future).
duke@435	29	class ConcurrentMarkSweepThread: public ConcurrentGCThread {
duke@435	30	friend class VMStructs;
duke@435	31	friend class ConcurrentMarkSweepGeneration; // XXX should remove friendship
duke@435	32	friend class CMSCollector;
duke@435	33	public:
duke@435	34	virtual void run();
duke@435	35
duke@435	36	private:
duke@435	37	static ConcurrentMarkSweepThread* _cmst;
duke@435	38	static CMSCollector* _collector;
duke@435	39	static SurrogateLockerThread* _slt;
duke@435	40	static SurrogateLockerThread::SLT_msg_type _sltBuffer;
duke@435	41	static Monitor* _sltMonitor;
duke@435	42
duke@435	43	ConcurrentMarkSweepThread* _next;
duke@435	44
duke@435	45	static bool _should_terminate;
duke@435	46
duke@435	47	enum CMS_flag_type {
duke@435	48	CMS_nil = NoBits,
duke@435	49	CMS_cms_wants_token = nth_bit(0),
duke@435	50	CMS_cms_has_token = nth_bit(1),
duke@435	51	CMS_vm_wants_token = nth_bit(2),
duke@435	52	CMS_vm_has_token = nth_bit(3)
duke@435	53	};
duke@435	54
duke@435	55	static int _CMS_flag;
duke@435	56
duke@435	57	static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; }
duke@435	58	static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; }
duke@435	59	static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; }
duke@435	60	void sleepBeforeNextCycle();
duke@435	61
duke@435	62	// CMS thread should yield for a young gen collection, direct allocation,
duke@435	63	// and iCMS activity.
duke@435	64	static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
duke@435	65	static volatile jint _pending_yields;
duke@435	66	static volatile jint _pending_decrements; // decrements to _pending_yields
duke@435	67	static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing
duke@435	68
duke@435	69	// Tracing messages, enabled by CMSTraceThreadState.
duke@435	70	static inline void trace_state(const char* desc);
duke@435	71
duke@435	72	static volatile bool _icms_enabled; // iCMS enabled?
duke@435	73	static volatile bool _should_run; // iCMS may run
duke@435	74	static volatile bool _should_stop; // iCMS should stop
duke@435	75
duke@435	76	// debugging
duke@435	77	void verify_ok_to_terminate() const PRODUCT_RETURN;
duke@435	78
duke@435	79	public:
duke@435	80	// Constructor
duke@435	81	ConcurrentMarkSweepThread(CMSCollector* collector);
duke@435	82
duke@435	83	static void makeSurrogateLockerThread(TRAPS);
duke@435	84	static SurrogateLockerThread* slt() { return _slt; }
duke@435	85
duke@435	86	// Tester
duke@435	87	bool is_ConcurrentGC_thread() const { return true; }
duke@435	88
duke@435	89	static void threads_do(ThreadClosure* tc);
duke@435	90
duke@435	91	// Printing
duke@435	92	void print_on(outputStream* st) const;
duke@435	93	void print() const { print_on(tty); }
duke@435	94	static void print_all_on(outputStream* st);
duke@435	95	static void print_all() { print_all_on(tty); }
duke@435	96
duke@435	97	// Returns the CMS Thread
duke@435	98	static ConcurrentMarkSweepThread* cmst() { return _cmst; }
duke@435	99	static CMSCollector* collector() { return _collector; }
duke@435	100
duke@435	101	// Create and start the CMS Thread, or stop it on shutdown
duke@435	102	static ConcurrentMarkSweepThread* start(CMSCollector* collector);
duke@435	103	static void stop();
duke@435	104	static bool should_terminate() { return _should_terminate; }
duke@435	105
duke@435	106	// Synchronization using CMS token
duke@435	107	static void synchronize(bool is_cms_thread);
duke@435	108	static void desynchronize(bool is_cms_thread);
duke@435	109	static bool vm_thread_has_cms_token() {
duke@435	110	return CMS_flag_is_set(CMS_vm_has_token);
duke@435	111	}
duke@435	112	static bool cms_thread_has_cms_token() {
duke@435	113	return CMS_flag_is_set(CMS_cms_has_token);
duke@435	114	}
duke@435	115	static bool vm_thread_wants_cms_token() {
duke@435	116	return CMS_flag_is_set(CMS_vm_wants_token);
duke@435	117	}
duke@435	118	static bool cms_thread_wants_cms_token() {
duke@435	119	return CMS_flag_is_set(CMS_cms_wants_token);
duke@435	120	}
duke@435	121
duke@435	122	// Wait on CMS lock until the next synchronous GC
duke@435	123	// or given timeout, whichever is earlier.
duke@435	124	void wait_on_cms_lock(long t); // milliseconds
duke@435	125
ysr@2192	126	// The CMS thread will yield during the work portion of its cycle
duke@435	127	// only when requested to. Both synchronous and asychronous requests
ysr@2192	128	// are provided:
ysr@2192	129	// (1) A synchronous request is used for young gen collections and
ysr@2192	130	// for direct allocations. The requesting thread increments
ysr@2192	131	// _pending_yields at the beginning of an operation, and decrements
ysr@2192	132	// _pending_yields when that operation is completed.
ysr@2192	133	// In turn, the CMS thread yields when _pending_yields is positive,
ysr@2192	134	// and continues to yield until the value reverts to 0.
ysr@2192	135	// (2) An asynchronous request, on the other hand, is used by iCMS
ysr@2192	136	// for the stop_icms() operation. A single yield satisfies all of
ysr@2192	137	// the outstanding asynch yield requests, of which there may
ysr@2192	138	// occasionally be several in close succession. To accomplish
ysr@2192	139	// this, an asynch-requesting thread atomically increments both
ysr@2192	140	// _pending_yields and _pending_decrements. An asynchr requesting
ysr@2192	141	// thread does not wait and "acknowledge" completion of an operation
ysr@2192	142	// and deregister the request, like the synchronous version described
ysr@2192	143	// above does. In turn, after yielding, the CMS thread decrements both
ysr@2192	144	// _pending_yields and _pending_decrements by the value seen in
ysr@2192	145	// _pending_decrements before the decrement.
ysr@2192	146	// NOTE: The above scheme is isomorphic to having two request counters,
ysr@2192	147	// one for async requests and one for sync requests, and for the CMS thread
ysr@2192	148	// to check the sum of the two counters to decide whether it should yield
ysr@2192	149	// and to clear only the async counter when it yields. However, it turns out
ysr@2192	150	// to be more efficient for CMS code to just check a single counter
ysr@2192	151	// _pending_yields that holds the sum (of both sync and async requests), and
ysr@2192	152	// a second counter _pending_decrements that only holds the async requests,
ysr@2192	153	// for greater efficiency, since in a typical CMS run, there are many more
ysr@2192	154	// pontential (i.e. static) yield points than there are actual
ysr@2192	155	// (i.e. dynamic) yields because of requests, which are few and far between.
ysr@2192	156	//
duke@435	157	// Note that, while "_pending_yields >= _pending_decrements" is an invariant,
duke@435	158	// we cannot easily test that invariant, since the counters are manipulated via
duke@435	159	// atomic instructions without explicit locking and we cannot read
duke@435	160	// the two counters atomically together: one suggestion is to
duke@435	161	// use (for example) 16-bit counters so as to be able to read the
duke@435	162	// two counters atomically even on 32-bit platforms. Notice that
ysr@2192	163	// the second assert in acknowledge_yield_request() below does indeed
duke@435	164	// check a form of the above invariant, albeit indirectly.
duke@435	165
duke@435	166	static void increment_pending_yields() {
duke@435	167	Atomic::inc(&_pending_yields);
duke@435	168	assert(_pending_yields >= 0, "can't be negative");
duke@435	169	}
duke@435	170	static void decrement_pending_yields() {
duke@435	171	Atomic::dec(&_pending_yields);
duke@435	172	assert(_pending_yields >= 0, "can't be negative");
duke@435	173	}
duke@435	174	static void asynchronous_yield_request() {
ysr@2192	175	assert(CMSIncrementalMode, "Currently only used w/iCMS");
duke@435	176	increment_pending_yields();
duke@435	177	Atomic::inc(&_pending_decrements);
duke@435	178	assert(_pending_decrements >= 0, "can't be negative");
duke@435	179	}
duke@435	180	static void acknowledge_yield_request() {
duke@435	181	jint decrement = _pending_decrements;
duke@435	182	if (decrement > 0) {
ysr@2192	183	assert(CMSIncrementalMode, "Currently only used w/iCMS");
duke@435	184	// Order important to preserve: _pending_yields >= _pending_decrements
duke@435	185	Atomic::add(-decrement, &_pending_decrements);
duke@435	186	Atomic::add(-decrement, &_pending_yields);
duke@435	187	assert(_pending_decrements >= 0, "can't be negative");
duke@435	188	assert(_pending_yields >= 0, "can't be negative");
duke@435	189	}
duke@435	190	}
duke@435	191	static bool should_yield() { return _pending_yields > 0; }
duke@435	192
duke@435	193	// CMS incremental mode.
duke@435	194	static void start_icms(); // notify thread to start a quantum of work
duke@435	195	static void stop_icms(); // request thread to stop working
duke@435	196	void icms_wait(); // if asked to stop, wait until notified to start
duke@435	197
duke@435	198	// Incremental mode is enabled globally by the flag CMSIncrementalMode. It
duke@435	199	// must also be enabled/disabled dynamically to allow foreground collections.
duke@435	200	static inline void enable_icms() { _icms_enabled = true; }
duke@435	201	static inline void disable_icms() { _icms_enabled = false; }
duke@435	202	static inline void set_icms_enabled(bool val) { _icms_enabled = val; }
duke@435	203	static inline bool icms_enabled() { return _icms_enabled; }
duke@435	204	};
duke@435	205
duke@435	206	inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
duke@435	207	if (CMSTraceThreadState) {
duke@435	208	char buf[128];
duke@435	209	TimeStamp& ts = gclog_or_tty->time_stamp();
duke@435	210	if (!ts.is_updated()) {
duke@435	211	ts.update();
duke@435	212	}
duke@435	213	jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ",
duke@435	214	ts.seconds(), desc);
duke@435	215	buf[sizeof(buf) - 1] = '\0';
duke@435	216	gclog_or_tty->print(buf);
duke@435	217	}
duke@435	218	}
duke@435	219
ysr@2192	220	// For scoped increment/decrement of (synchronous) yield requests
duke@435	221	class CMSSynchronousYieldRequest: public StackObj {
duke@435	222	public:
duke@435	223	CMSSynchronousYieldRequest() {
duke@435	224	ConcurrentMarkSweepThread::increment_pending_yields();
duke@435	225	}
duke@435	226	~CMSSynchronousYieldRequest() {
duke@435	227	ConcurrentMarkSweepThread::decrement_pending_yields();
duke@435	228	}
duke@435	229	};
duke@435	230
duke@435	231	// Used to emit a warning in case of unexpectedly excessive
duke@435	232	// looping (in "apparently endless loops") in CMS code.
duke@435	233	class CMSLoopCountWarn: public StackObj {
duke@435	234	private:
duke@435	235	const char* _src;
duke@435	236	const char* _msg;
duke@435	237	const intx _threshold;
duke@435	238	intx _ticks;
duke@435	239
duke@435	240	public:
duke@435	241	inline CMSLoopCountWarn(const char* src, const char* msg,
duke@435	242	const intx threshold) :
duke@435	243	_src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
duke@435	244
duke@435	245	inline void tick() {
duke@435	246	_ticks++;
duke@435	247	if (CMSLoopWarn && _ticks % _threshold == 0) {
duke@435	248	warning("%s has looped %d times %s", _src, _ticks, _msg);
duke@435	249	}
duke@435	250	}
duke@435	251	};