hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.cpp - platform/libcore - Git at Google

 /*
  * Copyright 2001-2006 Sun Microsystems, Inc.  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
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  * CA 95054 USA or visit www.sun.com if you need additional information or
  * have any questions.
  *
  */

 # include "incls/_precompiled.incl"
 # include "incls/_concurrentMarkSweepThread.cpp.incl"

 // ======= Concurrent Mark Sweep Thread ========

 // The CMS thread is created when Concurrent Mark Sweep is used in the
 // older of two generations in a generational memory system.

 ConcurrentMarkSweepThread*
      ConcurrentMarkSweepThread::_cmst     = NULL;
 CMSCollector* ConcurrentMarkSweepThread::_collector = NULL;
 bool ConcurrentMarkSweepThread::_should_terminate = false;
 int  ConcurrentMarkSweepThread::_CMS_flag         = CMS_nil;

 volatile jint ConcurrentMarkSweepThread::_pending_yields      = 0;
 volatile jint ConcurrentMarkSweepThread::_pending_decrements  = 0;

 volatile bool ConcurrentMarkSweepThread::_icms_enabled   = false;
 volatile bool ConcurrentMarkSweepThread::_should_run     = false;
 // When icms is enabled, the icms thread is stopped until explicitly
 // started.
 volatile bool ConcurrentMarkSweepThread::_should_stop    = true;

 SurrogateLockerThread*
      ConcurrentMarkSweepThread::_slt = NULL;
 SurrogateLockerThread::SLT_msg_type
      ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
 Monitor*
      ConcurrentMarkSweepThread::_sltMonitor = NULL;

 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
   : ConcurrentGCThread() {
   assert(UseConcMarkSweepGC,  "UseConcMarkSweepGC should be set");
   assert(_cmst == NULL, "CMS thread already created");
   _cmst = this;
   assert(_collector == NULL, "Collector already set");
   _collector = collector;

   set_name("Concurrent Mark-Sweep GC Thread");

   if (os::create_thread(this, os::cgc_thread)) {
     // XXX: need to set this to low priority
     // unless "agressive mode" set; priority
     // should be just less than that of VMThread.
     os::set_priority(this, NearMaxPriority);
     if (!DisableStartThread) {
       os::start_thread(this);
     }
   }
   _sltMonitor = SLT_lock;
   set_icms_enabled(CMSIncrementalMode);
 }

 void ConcurrentMarkSweepThread::run() {
   assert(this == cmst(), "just checking");

   this->record_stack_base_and_size();
   this->initialize_thread_local_storage();
   this->set_active_handles(JNIHandleBlock::allocate_block());
   // From this time Thread::current() should be working.
   assert(this == Thread::current(), "just checking");
   if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
     warning("Couldn't bind CMS thread to processor %u", CPUForCMSThread);
   }
   // Wait until Universe::is_fully_initialized()
   {
     CMSLoopCountWarn loopX("CMS::run", "waiting for "
                            "Universe::is_fully_initialized()", 2);
     MutexLockerEx x(CGC_lock, true);
     set_CMS_flag(CMS_cms_wants_token);
     // Wait until Universe is initialized and all initialization is completed.
     while (!is_init_completed() && !Universe::is_fully_initialized() &&
            !_should_terminate) {
       CGC_lock->wait(true, 200);
       loopX.tick();
     }
     // Wait until the surrogate locker thread that will do
     // pending list locking on our behalf has been created.
     // We cannot start the SLT thread ourselves since we need
     // to be a JavaThread to do so.
     CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
     while (_slt == NULL && !_should_terminate) {
       CGC_lock->wait(true, 200);
       loopY.tick();
     }
     clear_CMS_flag(CMS_cms_wants_token);
   }

   while (!_should_terminate) {
     sleepBeforeNextCycle();
     if (_should_terminate) break;
     _collector->collect_in_background(false);  // !clear_all_soft_refs
   }
   assert(_should_terminate, "just checking");
   // Check that the state of any protocol for synchronization
   // between background (CMS) and foreground collector is "clean"
   // (i.e. will not potentially block the foreground collector,
   // requiring action by us).
   verify_ok_to_terminate();
   // Signal that it is terminated
   {
     MutexLockerEx mu(Terminator_lock,
                      Mutex::_no_safepoint_check_flag);
     assert(_cmst == this, "Weird!");
     _cmst = NULL;
     Terminator_lock->notify();
   }

   // Thread destructor usually does this..
   ThreadLocalStorage::set_thread(NULL);
 }

 #ifndef PRODUCT
 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
   assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
            cms_thread_wants_cms_token()),
          "Must renounce all worldly possessions and desires for nirvana");
   _collector->verify_ok_to_terminate();
 }
 #endif

 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
   if (!_should_terminate) {
     assert(cmst() == NULL, "start() called twice?");
     ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
     assert(cmst() == th, "Where did the just-created CMS thread go?");
     return th;
   }
   return NULL;
 }

 void ConcurrentMarkSweepThread::stop() {
   if (CMSIncrementalMode) {
     // Disable incremental mode and wake up the thread so it notices the change.
     disable_icms();
     start_icms();
   }
   // it is ok to take late safepoints here, if needed
   {
     MutexLockerEx x(Terminator_lock);
     _should_terminate = true;
   }
   { // Now post a notify on CGC_lock so as to nudge
     // CMS thread(s) that might be slumbering in
     // sleepBeforeNextCycle.
     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
     CGC_lock->notify_all();
   }
   { // Now wait until (all) CMS thread(s) have exited
     MutexLockerEx x(Terminator_lock);
     while(cmst() != NULL) {
       Terminator_lock->wait();
     }
   }
 }

 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
   assert(tc != NULL, "Null ThreadClosure");
   if (_cmst != NULL) {
     tc->do_thread(_cmst);
   }
   assert(Universe::is_fully_initialized(),
          "Called too early, make sure heap is fully initialized");
   if (_collector != NULL) {
     AbstractWorkGang* gang = _collector->conc_workers();
     if (gang != NULL) {
       gang->threads_do(tc);
     }
   }
 }

 void ConcurrentMarkSweepThread::print_on(outputStream* st) const {
   st->print("\"%s\" ", name());
   Thread::print_on(st);
   st->cr();
 }

 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
   if (_cmst != NULL) {
     _cmst->print_on(st);
   }
   if (_collector != NULL) {
     AbstractWorkGang* gang = _collector->conc_workers();
     if (gang != NULL) {
       gang->print_worker_threads_on(st);
     }
   }
 }

 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
   assert(UseConcMarkSweepGC, "just checking");

   MutexLockerEx x(CGC_lock,
                   Mutex::_no_safepoint_check_flag);
   if (!is_cms_thread) {
     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
     CMSSynchronousYieldRequest yr;
     while (CMS_flag_is_set(CMS_cms_has_token)) {
       // indicate that we want to get the token
       set_CMS_flag(CMS_vm_wants_token);
       CGC_lock->wait(true);
     }
     // claim the token and proceed
     clear_CMS_flag(CMS_vm_wants_token);
     set_CMS_flag(CMS_vm_has_token);
   } else {
     assert(Thread::current()->is_ConcurrentGC_thread(),
            "Not a CMS thread");
     // The following barrier assumes there's only one CMS thread.
     // This will need to be modified is there are more CMS threads than one.
     while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
       set_CMS_flag(CMS_cms_wants_token);
       CGC_lock->wait(true);
     }
     // claim the token
     clear_CMS_flag(CMS_cms_wants_token);
     set_CMS_flag(CMS_cms_has_token);
   }
 }

 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
   assert(UseConcMarkSweepGC, "just checking");

   MutexLockerEx x(CGC_lock,
                   Mutex::_no_safepoint_check_flag);
   if (!is_cms_thread) {
     assert(Thread::current()->is_VM_thread(), "Not a VM thread");
     assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
     clear_CMS_flag(CMS_vm_has_token);
     if (CMS_flag_is_set(CMS_cms_wants_token)) {
       // wake-up a waiting CMS thread
       CGC_lock->notify();
     }
     assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
            "Should have been cleared");
   } else {
     assert(Thread::current()->is_ConcurrentGC_thread(),
            "Not a CMS thread");
     assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
     clear_CMS_flag(CMS_cms_has_token);
     if (CMS_flag_is_set(CMS_vm_wants_token)) {
       // wake-up a waiting VM thread
       CGC_lock->notify();
     }
     assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
            "Should have been cleared");
   }
 }

 // Wait until the next synchronous GC or a timeout, whichever is earlier.
 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t) {
   MutexLockerEx x(CGC_lock,
                   Mutex::_no_safepoint_check_flag);
   set_CMS_flag(CMS_cms_wants_token);   // to provoke notifies
   CGC_lock->wait(Mutex::_no_safepoint_check_flag, t);
   clear_CMS_flag(CMS_cms_wants_token);
   assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
          "Should not be set");
 }

 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
   while (!_should_terminate) {
     if (CMSIncrementalMode) {
       icms_wait();
       return;
     } else {
       // Wait until the next synchronous GC or a timeout, whichever is earlier
       wait_on_cms_lock(CMSWaitDuration);
     }
     // Check if we should start a CMS collection cycle
     if (_collector->shouldConcurrentCollect()) {
       return;
     }
     // .. collection criterion not yet met, let's go back
     // and wait some more
   }
 }

 // Incremental CMS
 void ConcurrentMarkSweepThread::start_icms() {
   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
   MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
   trace_state("start_icms");
   _should_run = true;
   iCMS_lock->notify_all();
 }

 void ConcurrentMarkSweepThread::stop_icms() {
   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
   MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
   if (!_should_stop) {
     trace_state("stop_icms");
     _should_stop = true;
     _should_run = false;
     asynchronous_yield_request();
     iCMS_lock->notify_all();
   }
 }

 void ConcurrentMarkSweepThread::icms_wait() {
   assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
   if (_should_stop && icms_enabled()) {
     MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
     trace_state("pause_icms");
     _collector->stats().stop_cms_timer();
     while(!_should_run && icms_enabled()) {
       iCMS_lock->wait(Mutex::_no_safepoint_check_flag);
     }
     _collector->stats().start_cms_timer();
     _should_stop = false;
     trace_state("pause_icms end");
   }
 }

 // Note: this method, although exported by the ConcurrentMarkSweepThread,
 // which is a non-JavaThread, can only be called by a JavaThread.
 // Currently this is done at vm creation time (post-vm-init) by the
 // main/Primordial (Java)Thread.
 // XXX Consider changing this in the future to allow the CMS thread
 // itself to create this thread?
 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
   assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
   assert(_slt == NULL, "SLT already created");
   _slt = SurrogateLockerThread::make(THREAD);
 }
	/*
	* Copyright 2001-2006 Sun Microsystems, Inc. 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
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
	* CA 95054 USA or visit www.sun.com if you need additional information or
	* have any questions.
	*
	*/

	# include "incls/_precompiled.incl"
	# include "incls/_concurrentMarkSweepThread.cpp.incl"

	// ======= Concurrent Mark Sweep Thread ========

	// The CMS thread is created when Concurrent Mark Sweep is used in the
	// older of two generations in a generational memory system.

	ConcurrentMarkSweepThread*
	ConcurrentMarkSweepThread::_cmst = NULL;
	CMSCollector* ConcurrentMarkSweepThread::_collector = NULL;
	bool ConcurrentMarkSweepThread::_should_terminate = false;
	int ConcurrentMarkSweepThread::_CMS_flag = CMS_nil;

	volatile jint ConcurrentMarkSweepThread::_pending_yields = 0;
	volatile jint ConcurrentMarkSweepThread::_pending_decrements = 0;

	volatile bool ConcurrentMarkSweepThread::_icms_enabled = false;
	volatile bool ConcurrentMarkSweepThread::_should_run = false;
	// When icms is enabled, the icms thread is stopped until explicitly
	// started.
	volatile bool ConcurrentMarkSweepThread::_should_stop = true;

	SurrogateLockerThread*
	ConcurrentMarkSweepThread::_slt = NULL;
	SurrogateLockerThread::SLT_msg_type
	ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
	Monitor*
	ConcurrentMarkSweepThread::_sltMonitor = NULL;

	ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
	: ConcurrentGCThread() {
	assert(UseConcMarkSweepGC, "UseConcMarkSweepGC should be set");
	assert(_cmst == NULL, "CMS thread already created");
	_cmst = this;
	assert(_collector == NULL, "Collector already set");
	_collector = collector;

	set_name("Concurrent Mark-Sweep GC Thread");

	if (os::create_thread(this, os::cgc_thread)) {
	// XXX: need to set this to low priority
	// unless "agressive mode" set; priority
	// should be just less than that of VMThread.
	os::set_priority(this, NearMaxPriority);
	if (!DisableStartThread) {
	os::start_thread(this);
	}
	}
	_sltMonitor = SLT_lock;
	set_icms_enabled(CMSIncrementalMode);
	}

	void ConcurrentMarkSweepThread::run() {
	assert(this == cmst(), "just checking");

	this->record_stack_base_and_size();
	this->initialize_thread_local_storage();
	this->set_active_handles(JNIHandleBlock::allocate_block());
	// From this time Thread::current() should be working.
	assert(this == Thread::current(), "just checking");
	if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
	warning("Couldn't bind CMS thread to processor %u", CPUForCMSThread);
	}
	// Wait until Universe::is_fully_initialized()
	{
	CMSLoopCountWarn loopX("CMS::run", "waiting for "
	"Universe::is_fully_initialized()", 2);
	MutexLockerEx x(CGC_lock, true);
	set_CMS_flag(CMS_cms_wants_token);
	// Wait until Universe is initialized and all initialization is completed.
	while (!is_init_completed() && !Universe::is_fully_initialized() &&
	!_should_terminate) {
	CGC_lock->wait(true, 200);
	loopX.tick();
	}
	// Wait until the surrogate locker thread that will do
	// pending list locking on our behalf has been created.
	// We cannot start the SLT thread ourselves since we need
	// to be a JavaThread to do so.
	CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
	while (_slt == NULL && !_should_terminate) {
	CGC_lock->wait(true, 200);
	loopY.tick();
	}
	clear_CMS_flag(CMS_cms_wants_token);
	}

	while (!_should_terminate) {
	sleepBeforeNextCycle();
	if (_should_terminate) break;
	_collector->collect_in_background(false); // !clear_all_soft_refs
	}
	assert(_should_terminate, "just checking");
	// Check that the state of any protocol for synchronization
	// between background (CMS) and foreground collector is "clean"
	// (i.e. will not potentially block the foreground collector,
	// requiring action by us).
	verify_ok_to_terminate();
	// Signal that it is terminated
	{
	MutexLockerEx mu(Terminator_lock,
	Mutex::_no_safepoint_check_flag);
	assert(_cmst == this, "Weird!");
	_cmst = NULL;
	Terminator_lock->notify();
	}

	// Thread destructor usually does this..
	ThreadLocalStorage::set_thread(NULL);
	}

	#ifndef PRODUCT
	void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
	assert(!(CGC_lock->owned_by_self() \|\| cms_thread_has_cms_token() \|\|
	cms_thread_wants_cms_token()),
	"Must renounce all worldly possessions and desires for nirvana");
	_collector->verify_ok_to_terminate();
	}
	#endif

	// create and start a new ConcurrentMarkSweep Thread for given CMS generation
	ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
	if (!_should_terminate) {
	assert(cmst() == NULL, "start() called twice?");
	ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
	assert(cmst() == th, "Where did the just-created CMS thread go?");
	return th;
	}
	return NULL;
	}

	void ConcurrentMarkSweepThread::stop() {
	if (CMSIncrementalMode) {
	// Disable incremental mode and wake up the thread so it notices the change.
	disable_icms();
	start_icms();
	}
	// it is ok to take late safepoints here, if needed
	{
	MutexLockerEx x(Terminator_lock);
	_should_terminate = true;
	}
	{ // Now post a notify on CGC_lock so as to nudge
	// CMS thread(s) that might be slumbering in
	// sleepBeforeNextCycle.
	MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
	CGC_lock->notify_all();
	}
	{ // Now wait until (all) CMS thread(s) have exited
	MutexLockerEx x(Terminator_lock);
	while(cmst() != NULL) {
	Terminator_lock->wait();
	}
	}
	}

	void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
	assert(tc != NULL, "Null ThreadClosure");
	if (_cmst != NULL) {
	tc->do_thread(_cmst);
	}
	assert(Universe::is_fully_initialized(),
	"Called too early, make sure heap is fully initialized");
	if (_collector != NULL) {
	AbstractWorkGang* gang = _collector->conc_workers();
	if (gang != NULL) {
	gang->threads_do(tc);
	}
	}
	}

	void ConcurrentMarkSweepThread::print_on(outputStream* st) const {
	st->print("\"%s\" ", name());
	Thread::print_on(st);
	st->cr();
	}

	void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
	if (_cmst != NULL) {
	_cmst->print_on(st);
	}
	if (_collector != NULL) {
	AbstractWorkGang* gang = _collector->conc_workers();
	if (gang != NULL) {
	gang->print_worker_threads_on(st);
	}
	}
	}

	void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
	assert(UseConcMarkSweepGC, "just checking");

	MutexLockerEx x(CGC_lock,
	Mutex::_no_safepoint_check_flag);
	if (!is_cms_thread) {
	assert(Thread::current()->is_VM_thread(), "Not a VM thread");
	CMSSynchronousYieldRequest yr;
	while (CMS_flag_is_set(CMS_cms_has_token)) {
	// indicate that we want to get the token
	set_CMS_flag(CMS_vm_wants_token);
	CGC_lock->wait(true);
	}
	// claim the token and proceed
	clear_CMS_flag(CMS_vm_wants_token);
	set_CMS_flag(CMS_vm_has_token);
	} else {
	assert(Thread::current()->is_ConcurrentGC_thread(),
	"Not a CMS thread");
	// The following barrier assumes there's only one CMS thread.
	// This will need to be modified is there are more CMS threads than one.
	while (CMS_flag_is_set(CMS_vm_has_token \| CMS_vm_wants_token)) {
	set_CMS_flag(CMS_cms_wants_token);
	CGC_lock->wait(true);
	}
	// claim the token
	clear_CMS_flag(CMS_cms_wants_token);
	set_CMS_flag(CMS_cms_has_token);
	}
	}

	void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
	assert(UseConcMarkSweepGC, "just checking");

	MutexLockerEx x(CGC_lock,
	Mutex::_no_safepoint_check_flag);
	if (!is_cms_thread) {
	assert(Thread::current()->is_VM_thread(), "Not a VM thread");
	assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
	clear_CMS_flag(CMS_vm_has_token);
	if (CMS_flag_is_set(CMS_cms_wants_token)) {
	// wake-up a waiting CMS thread
	CGC_lock->notify();
	}
	assert(!CMS_flag_is_set(CMS_vm_has_token \| CMS_vm_wants_token),
	"Should have been cleared");
	} else {
	assert(Thread::current()->is_ConcurrentGC_thread(),
	"Not a CMS thread");
	assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
	clear_CMS_flag(CMS_cms_has_token);
	if (CMS_flag_is_set(CMS_vm_wants_token)) {
	// wake-up a waiting VM thread
	CGC_lock->notify();
	}
	assert(!CMS_flag_is_set(CMS_cms_has_token \| CMS_cms_wants_token),
	"Should have been cleared");
	}
	}

	// Wait until the next synchronous GC or a timeout, whichever is earlier.
	void ConcurrentMarkSweepThread::wait_on_cms_lock(long t) {
	MutexLockerEx x(CGC_lock,
	Mutex::_no_safepoint_check_flag);
	set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
	CGC_lock->wait(Mutex::_no_safepoint_check_flag, t);
	clear_CMS_flag(CMS_cms_wants_token);
	assert(!CMS_flag_is_set(CMS_cms_has_token \| CMS_cms_wants_token),
	"Should not be set");
	}

	void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
	while (!_should_terminate) {
	if (CMSIncrementalMode) {
	icms_wait();
	return;
	} else {
	// Wait until the next synchronous GC or a timeout, whichever is earlier
	wait_on_cms_lock(CMSWaitDuration);
	}
	// Check if we should start a CMS collection cycle
	if (_collector->shouldConcurrentCollect()) {
	return;
	}
	// .. collection criterion not yet met, let's go back
	// and wait some more
	}
	}

	// Incremental CMS
	void ConcurrentMarkSweepThread::start_icms() {
	assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
	MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
	trace_state("start_icms");
	_should_run = true;
	iCMS_lock->notify_all();
	}

	void ConcurrentMarkSweepThread::stop_icms() {
	assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
	MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
	if (!_should_stop) {
	trace_state("stop_icms");
	_should_stop = true;
	_should_run = false;
	asynchronous_yield_request();
	iCMS_lock->notify_all();
	}
	}

	void ConcurrentMarkSweepThread::icms_wait() {
	assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
	if (_should_stop && icms_enabled()) {
	MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
	trace_state("pause_icms");
	_collector->stats().stop_cms_timer();
	while(!_should_run && icms_enabled()) {
	iCMS_lock->wait(Mutex::_no_safepoint_check_flag);
	}
	_collector->stats().start_cms_timer();
	_should_stop = false;
	trace_state("pause_icms end");
	}
	}

	// Note: this method, although exported by the ConcurrentMarkSweepThread,
	// which is a non-JavaThread, can only be called by a JavaThread.
	// Currently this is done at vm creation time (post-vm-init) by the
	// main/Primordial (Java)Thread.
	// XXX Consider changing this in the future to allow the CMS thread
	// itself to create this thread?
	void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
	assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
	assert(_slt == NULL, "SLT already created");
	_slt = SurrogateLockerThread::make(THREAD);
	}