/*

 * 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

 * 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.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

  // The CMS thread will yield during the work portion of its cycle

  // only when requested to.  Both synchronous and asychronous requests

  // are provided:

  // (1) A synchronous request is used for young gen collections and

  //     for direct allocations.  The requesting thread increments

  //     _pending_yields at the beginning of an operation, and decrements

  //     _pending_yields when that operation is completed.

  //     In turn, the CMS thread yields when _pending_yields is positive,

  //     and continues to yield until the value reverts to 0.

  // (2) An asynchronous request, on the other hand, is used by iCMS

  //     for the stop_icms() operation. A single yield satisfies all of

  //     the outstanding asynch yield requests, of which there may

  //     occasionally be several in close succession. To accomplish

  //     this, an asynch-requesting thread atomically increments both

  //     _pending_yields and _pending_decrements. An asynchr requesting

  //     thread does not wait and "acknowledge" completion of an operation

  //     and deregister the request, like the synchronous version described

  //     above does. In turn, after yielding, the CMS thread decrements both

  //     _pending_yields and _pending_decrements by the value seen in

  //     _pending_decrements before the decrement.

  //  NOTE: The above scheme is isomorphic to having two request counters,

  //  one for async requests and one for sync requests, and for the CMS thread

  //  to check the sum of the two counters to decide whether it should yield

  //  and to clear only the async counter when it yields. However, it turns out

  //  to be more efficient for CMS code to just check a single counter

  //  _pending_yields that holds the sum (of both sync and async requests), and

  //  a second counter _pending_decrements that only holds the async requests,

  //  for greater efficiency, since in a typical CMS run, there are many more

  //  pontential (i.e. static) yield points than there are actual

  //  (i.e. dynamic) yields because of requests, which are few and far between.

  //

  // 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() below 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() {

    assert(CMSIncrementalMode, "Currently only used w/iCMS");

    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) {

      assert(CMSIncrementalMode, "Currently only used w/iCMS");

      // 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 (synchronous) 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);

    }

  }

};