hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp - 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.
  *
  */

 class ConcurrentMarkSweepGeneration;
 class CMSCollector;

 // The Concurrent Mark Sweep GC Thread (could be several in the future).
 class ConcurrentMarkSweepThread: public ConcurrentGCThread {
   friend class VMStructs;
   friend class ConcurrentMarkSweepGeneration;   // XXX should remove friendship
   friend class CMSCollector;
  public:
   virtual void run();

  private:
   static ConcurrentMarkSweepThread*     _cmst;
   static CMSCollector*                  _collector;
   static SurrogateLockerThread*         _slt;
   static SurrogateLockerThread::SLT_msg_type _sltBuffer;
   static Monitor*                       _sltMonitor;

   ConcurrentMarkSweepThread*            _next;

   static bool _should_terminate;

   enum CMS_flag_type {
     CMS_nil             = NoBits,
     CMS_cms_wants_token = nth_bit(0),
     CMS_cms_has_token   = nth_bit(1),
     CMS_vm_wants_token  = nth_bit(2),
     CMS_vm_has_token    = nth_bit(3)
   };

   static int _CMS_flag;

   static bool CMS_flag_is_set(int b)        { return (_CMS_flag & b) != 0;   }
   static bool set_CMS_flag(int b)           { return (_CMS_flag |= b) != 0;  }
   static bool clear_CMS_flag(int b)         { return (_CMS_flag &= ~b) != 0; }
   void sleepBeforeNextCycle();

   // CMS thread should yield for a young gen collection, direct allocation,
   // and iCMS activity.
   static char _pad_1[64 - sizeof(jint)];    // prevent cache-line sharing
   static volatile jint _pending_yields;
   static volatile jint _pending_decrements; // decrements to _pending_yields
   static char _pad_2[64 - sizeof(jint)];    // prevent cache-line sharing

   // Tracing messages, enabled by CMSTraceThreadState.
   static inline void trace_state(const char* desc);

   static volatile bool _icms_enabled;   // iCMS enabled?
   static volatile bool _should_run;     // iCMS may run
   static volatile bool _should_stop;    // iCMS should stop

   // debugging
   void verify_ok_to_terminate() const PRODUCT_RETURN;

  public:
   // Constructor
   ConcurrentMarkSweepThread(CMSCollector* collector);

   static void makeSurrogateLockerThread(TRAPS);
   static SurrogateLockerThread* slt() { return _slt; }

   // Tester
   bool is_ConcurrentGC_thread() const { return true;       }

   static void threads_do(ThreadClosure* tc);

   // Printing
   void print_on(outputStream* st) const;
   void print() const                                  { print_on(tty); }
   static void print_all_on(outputStream* st);
   static void print_all()                             { print_all_on(tty); }

   // Returns the CMS Thread
   static ConcurrentMarkSweepThread* cmst()    { return _cmst; }
   static CMSCollector*         collector()    { return _collector;  }

   // Create and start the CMS Thread, or stop it on shutdown
   static ConcurrentMarkSweepThread* start(CMSCollector* collector);
   static void stop();
   static bool should_terminate() { return _should_terminate; }

   // Synchronization using CMS token
   static void synchronize(bool is_cms_thread);
   static void desynchronize(bool is_cms_thread);
   static bool vm_thread_has_cms_token() {
     return CMS_flag_is_set(CMS_vm_has_token);
   }
   static bool cms_thread_has_cms_token() {
     return CMS_flag_is_set(CMS_cms_has_token);
   }
   static bool vm_thread_wants_cms_token() {
     return CMS_flag_is_set(CMS_vm_wants_token);
   }
   static bool cms_thread_wants_cms_token() {
     return CMS_flag_is_set(CMS_cms_wants_token);
   }

   // Wait on CMS lock until the next synchronous GC
   // or given timeout, whichever is earlier.
   void    wait_on_cms_lock(long t); // milliseconds

   // The CMS thread will yield during the work portion of it's cycle
   // only when requested to.  Both synchronous and asychronous requests
   // are provided.  A synchronous request is used for young gen
   // collections and direct allocations.  The requesting thread increments
   // pending_yields at the beginning of an operation, and decrements it when
   // the operation is completed.  The CMS thread yields when pending_yields
   // is positive.  An asynchronous request is used by iCMS in the stop_icms()
   // operation. A single yield satisfies the outstanding asynch yield requests.
   // The requesting thread increments both pending_yields and pending_decrements.
   // After yielding, the CMS thread decrements both by the amount in
   // pending_decrements.
   // Note that, while "_pending_yields >= _pending_decrements" is an invariant,
   // we cannot easily test that invariant, since the counters are manipulated via
   // atomic instructions without explicit locking and we cannot read
   // the two counters atomically together: one suggestion is to
   // use (for example) 16-bit counters so as to be able to read the
   // two counters atomically even on 32-bit platforms. Notice that
   // the second assert in acknowledge_yield_request() does indeed
   // check a form of the above invariant, albeit indirectly.

   static void increment_pending_yields()   {
     Atomic::inc(&_pending_yields);
     assert(_pending_yields >= 0, "can't be negative");
   }
   static void decrement_pending_yields()   {
     Atomic::dec(&_pending_yields);
     assert(_pending_yields >= 0, "can't be negative");
   }
   static void asynchronous_yield_request() {
     increment_pending_yields();
     Atomic::inc(&_pending_decrements);
     assert(_pending_decrements >= 0, "can't be negative");
   }
   static void acknowledge_yield_request() {
     jint decrement = _pending_decrements;
     if (decrement > 0) {
       // Order important to preserve: _pending_yields >= _pending_decrements
       Atomic::add(-decrement, &_pending_decrements);
       Atomic::add(-decrement, &_pending_yields);
       assert(_pending_decrements >= 0, "can't be negative");
       assert(_pending_yields >= 0, "can't be negative");
     }
   }
   static bool should_yield()   { return _pending_yields > 0; }

   // CMS incremental mode.
   static void start_icms(); // notify thread to start a quantum of work
   static void stop_icms();  // request thread to stop working
   void icms_wait();         // if asked to stop, wait until notified to start

   // Incremental mode is enabled globally by the flag CMSIncrementalMode.  It
   // must also be enabled/disabled dynamically to allow foreground collections.
   static inline void enable_icms()              { _icms_enabled = true; }
   static inline void disable_icms()             { _icms_enabled = false; }
   static inline void set_icms_enabled(bool val) { _icms_enabled = val; }
   static inline bool icms_enabled()             { return _icms_enabled; }
 };

 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
   if (CMSTraceThreadState) {
     char buf[128];
     TimeStamp& ts = gclog_or_tty->time_stamp();
     if (!ts.is_updated()) {
       ts.update();
     }
     jio_snprintf(buf, sizeof(buf), " [%.3f:  CMSThread %s] ",
                  ts.seconds(), desc);
     buf[sizeof(buf) - 1] = '\0';
     gclog_or_tty->print(buf);
   }
 }

 // For scoped increment/decrement of yield requests
 class CMSSynchronousYieldRequest: public StackObj {
  public:
   CMSSynchronousYieldRequest() {
     ConcurrentMarkSweepThread::increment_pending_yields();
   }
   ~CMSSynchronousYieldRequest() {
     ConcurrentMarkSweepThread::decrement_pending_yields();
   }
 };

 // Used to emit a warning in case of unexpectedly excessive
 // looping (in "apparently endless loops") in CMS code.
 class CMSLoopCountWarn: public StackObj {
  private:
   const char* _src;
   const char* _msg;
   const intx  _threshold;
   intx        _ticks;

  public:
   inline CMSLoopCountWarn(const char* src, const char* msg,
                           const intx threshold) :
     _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }

   inline void tick() {
     _ticks++;
     if (CMSLoopWarn && _ticks % _threshold == 0) {
       warning("%s has looped %d times %s", _src, _ticks, _msg);
     }
   }
 };
	/*
	* 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.
	*
	*/

	class ConcurrentMarkSweepGeneration;
	class CMSCollector;

	// The Concurrent Mark Sweep GC Thread (could be several in the future).
	class ConcurrentMarkSweepThread: public ConcurrentGCThread {
	friend class VMStructs;
	friend class ConcurrentMarkSweepGeneration; // XXX should remove friendship
	friend class CMSCollector;
	public:
	virtual void run();

	private:
	static ConcurrentMarkSweepThread* _cmst;
	static CMSCollector* _collector;
	static SurrogateLockerThread* _slt;
	static SurrogateLockerThread::SLT_msg_type _sltBuffer;
	static Monitor* _sltMonitor;

	ConcurrentMarkSweepThread* _next;

	static bool _should_terminate;

	enum CMS_flag_type {
	CMS_nil = NoBits,
	CMS_cms_wants_token = nth_bit(0),
	CMS_cms_has_token = nth_bit(1),
	CMS_vm_wants_token = nth_bit(2),
	CMS_vm_has_token = nth_bit(3)
	};

	static int _CMS_flag;

	static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; }
	static bool set_CMS_flag(int b) { return (_CMS_flag \|= b) != 0; }
	static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; }
	void sleepBeforeNextCycle();

	// CMS thread should yield for a young gen collection, direct allocation,
	// and iCMS activity.
	static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
	static volatile jint _pending_yields;
	static volatile jint _pending_decrements; // decrements to _pending_yields
	static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing

	// Tracing messages, enabled by CMSTraceThreadState.
	static inline void trace_state(const char* desc);

	static volatile bool _icms_enabled; // iCMS enabled?
	static volatile bool _should_run; // iCMS may run
	static volatile bool _should_stop; // iCMS should stop

	// debugging
	void verify_ok_to_terminate() const PRODUCT_RETURN;

	public:
	// Constructor
	ConcurrentMarkSweepThread(CMSCollector* collector);

	static void makeSurrogateLockerThread(TRAPS);
	static SurrogateLockerThread* slt() { return _slt; }

	// Tester
	bool is_ConcurrentGC_thread() const { return true; }

	static void threads_do(ThreadClosure* tc);

	// Printing
	void print_on(outputStream* st) const;
	void print() const { print_on(tty); }
	static void print_all_on(outputStream* st);
	static void print_all() { print_all_on(tty); }

	// Returns the CMS Thread
	static ConcurrentMarkSweepThread* cmst() { return _cmst; }
	static CMSCollector* collector() { return _collector; }

	// Create and start the CMS Thread, or stop it on shutdown
	static ConcurrentMarkSweepThread* start(CMSCollector* collector);
	static void stop();
	static bool should_terminate() { return _should_terminate; }

	// Synchronization using CMS token
	static void synchronize(bool is_cms_thread);
	static void desynchronize(bool is_cms_thread);
	static bool vm_thread_has_cms_token() {
	return CMS_flag_is_set(CMS_vm_has_token);
	}
	static bool cms_thread_has_cms_token() {
	return CMS_flag_is_set(CMS_cms_has_token);
	}
	static bool vm_thread_wants_cms_token() {
	return CMS_flag_is_set(CMS_vm_wants_token);
	}
	static bool cms_thread_wants_cms_token() {
	return CMS_flag_is_set(CMS_cms_wants_token);
	}

	// Wait on CMS lock until the next synchronous GC
	// or given timeout, whichever is earlier.
	void wait_on_cms_lock(long t); // milliseconds

	// The CMS thread will yield during the work portion of it's cycle
	// only when requested to. Both synchronous and asychronous requests
	// are provided. A synchronous request is used for young gen
	// collections and direct allocations. The requesting thread increments
	// pending_yields at the beginning of an operation, and decrements it when
	// the operation is completed. The CMS thread yields when pending_yields
	// is positive. An asynchronous request is used by iCMS in the stop_icms()
	// operation. A single yield satisfies the outstanding asynch yield requests.
	// The requesting thread increments both pending_yields and pending_decrements.
	// After yielding, the CMS thread decrements both by the amount in
	// pending_decrements.
	// Note that, while "_pending_yields >= _pending_decrements" is an invariant,
	// we cannot easily test that invariant, since the counters are manipulated via
	// atomic instructions without explicit locking and we cannot read
	// the two counters atomically together: one suggestion is to
	// use (for example) 16-bit counters so as to be able to read the
	// two counters atomically even on 32-bit platforms. Notice that
	// the second assert in acknowledge_yield_request() does indeed
	// check a form of the above invariant, albeit indirectly.

	static void increment_pending_yields() {
	Atomic::inc(&_pending_yields);
	assert(_pending_yields >= 0, "can't be negative");
	}
	static void decrement_pending_yields() {
	Atomic::dec(&_pending_yields);
	assert(_pending_yields >= 0, "can't be negative");
	}
	static void asynchronous_yield_request() {
	increment_pending_yields();
	Atomic::inc(&_pending_decrements);
	assert(_pending_decrements >= 0, "can't be negative");
	}
	static void acknowledge_yield_request() {
	jint decrement = _pending_decrements;
	if (decrement > 0) {
	// Order important to preserve: _pending_yields >= _pending_decrements
	Atomic::add(-decrement, &_pending_decrements);
	Atomic::add(-decrement, &_pending_yields);
	assert(_pending_decrements >= 0, "can't be negative");
	assert(_pending_yields >= 0, "can't be negative");
	}
	}
	static bool should_yield() { return _pending_yields > 0; }

	// CMS incremental mode.
	static void start_icms(); // notify thread to start a quantum of work
	static void stop_icms(); // request thread to stop working
	void icms_wait(); // if asked to stop, wait until notified to start

	// Incremental mode is enabled globally by the flag CMSIncrementalMode. It
	// must also be enabled/disabled dynamically to allow foreground collections.
	static inline void enable_icms() { _icms_enabled = true; }
	static inline void disable_icms() { _icms_enabled = false; }
	static inline void set_icms_enabled(bool val) { _icms_enabled = val; }
	static inline bool icms_enabled() { return _icms_enabled; }
	};

	inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
	if (CMSTraceThreadState) {
	char buf[128];
	TimeStamp& ts = gclog_or_tty->time_stamp();
	if (!ts.is_updated()) {
	ts.update();
	}
	jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ",
	ts.seconds(), desc);
	buf[sizeof(buf) - 1] = '\0';
	gclog_or_tty->print(buf);
	}
	}

	// For scoped increment/decrement of yield requests
	class CMSSynchronousYieldRequest: public StackObj {
	public:
	CMSSynchronousYieldRequest() {
	ConcurrentMarkSweepThread::increment_pending_yields();
	}
	~CMSSynchronousYieldRequest() {
	ConcurrentMarkSweepThread::decrement_pending_yields();
	}
	};

	// Used to emit a warning in case of unexpectedly excessive
	// looping (in "apparently endless loops") in CMS code.
	class CMSLoopCountWarn: public StackObj {
	private:
	const char* _src;
	const char* _msg;
	const intx _threshold;
	intx _ticks;

	public:
	inline CMSLoopCountWarn(const char* src, const char* msg,
	const intx threshold) :
	_src(src), _msg(msg), _threshold(threshold), _ticks(0) { }

	inline void tick() {
	_ticks++;
	if (CMSLoopWarn && _ticks % _threshold == 0) {
	warning("%s has looped %d times %s", _src, _ticks, _msg);
	}
	}
	};