/*

 * 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

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 */

#include "gc/cms/concurrentMarkSweepGeneration.hpp"

#include "gc/shared/concurrentGCThread.hpp"

#include "runtime/thread.hpp"

class ConcurrentMarkSweepGeneration;

class CMSCollector;

// The Concurrent Mark Sweep GC Thread

class ConcurrentMarkSweepThread: public ConcurrentGCThread {

  friend class VMStructs;

  friend class ConcurrentMarkSweepGeneration;   // XXX should remove friendship

  friend class CMSCollector;

 private:

  static ConcurrentMarkSweepThread* _cmst;

  static CMSCollector*              _collector;

  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 and direct allocations

  static char _pad_1[64 - sizeof(jint)];    // prevent cache-line sharing

  static volatile jint _pending_yields;

  static char _pad_2[64 - sizeof(jint)];    // prevent cache-line sharing

  // debugging

  void verify_ok_to_terminate() const PRODUCT_RETURN;

  void run_service();

  void stop_service();

 public:

  // Constructor

  ConcurrentMarkSweepThread(CMSCollector* collector);

  static void threads_do(ThreadClosure* tc);

  // Printing

  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);

  // 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. 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);

  // Wait on CMS lock until the next synchronous GC

  // 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_for_scavenge(long t_millis);

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

  // only when requested to.

  // 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.

  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 bool should_yield()   { return _pending_yields > 0; }

};

// 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) {

      log_warning(gc)("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg);

    }

  }

};