/*

 * Copyright (c) 2018, 2019, Red Hat, Inc. All rights reserved.

 *

 * 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.

 *

 */

#include "precompiled.hpp"

#include "gc/shared/owstTaskTerminator.hpp"

#include "logging/log.hpp"

bool OWSTTaskTerminator::exit_termination(size_t tasks, TerminatorTerminator* terminator) {

  return tasks > 0 || (terminator != NULL && terminator->should_exit_termination());

}

bool OWSTTaskTerminator::offer_termination(TerminatorTerminator* terminator) {

  assert(_n_threads > 0, "Initialization is incorrect");

  assert(_offered_termination < _n_threads, "Invariant");

  assert(_blocker != NULL, "Invariant");

  // Single worker, done

  if (_n_threads == 1) {

    _offered_termination = 1;

    assert(!peek_in_queue_set(), "Precondition");

    return true;

  }

  _blocker->lock_without_safepoint_check();

  _offered_termination++;

  // All arrived, done

  if (_offered_termination == _n_threads) {

    _blocker->notify_all();

    _blocker->unlock();

    assert(!peek_in_queue_set(), "Precondition");

    return true;

  }

  Thread* the_thread = Thread::current();

  while (true) {

    if (_spin_master == NULL) {

      _spin_master = the_thread;

      _blocker->unlock();

      if (do_spin_master_work(terminator)) {

        assert(_offered_termination == _n_threads, "termination condition");

        assert(!peek_in_queue_set(), "Precondition");

        return true;

      } else {

        _blocker->lock_without_safepoint_check();

        // There is possibility that termination is reached between dropping the lock

        // before returning from do_spin_master_work() and acquiring lock above.

        if (_offered_termination == _n_threads) {

          _blocker->unlock();

          assert(!peek_in_queue_set(), "Precondition");

          return true;

        }

      }

    } else {

      _blocker->wait_without_safepoint_check(WorkStealingSleepMillis);

      if (_offered_termination == _n_threads) {

        _blocker->unlock();

        assert(!peek_in_queue_set(), "Precondition");

        return true;

      }

    }

    size_t tasks = tasks_in_queue_set();

    if (exit_termination(tasks, terminator)) {

      assert_lock_strong(_blocker);

      _offered_termination--;

      _blocker->unlock();

      return false;

    }

  }

}

bool OWSTTaskTerminator::do_spin_master_work(TerminatorTerminator* terminator) {

  uint yield_count = 0;

  // Number of hard spin loops done since last yield

  uint hard_spin_count = 0;

  // Number of iterations in the hard spin loop.

  uint hard_spin_limit = WorkStealingHardSpins;

  // If WorkStealingSpinToYieldRatio is 0, no hard spinning is done.

  // If it is greater than 0, then start with a small number

  // of spins and increase number with each turn at spinning until

  // the count of hard spins exceeds WorkStealingSpinToYieldRatio.

  // Then do a yield() call and start spinning afresh.

  if (WorkStealingSpinToYieldRatio > 0) {

    hard_spin_limit = WorkStealingHardSpins >> WorkStealingSpinToYieldRatio;

    hard_spin_limit = MAX2(hard_spin_limit, 1U);

  }

  // Remember the initial spin limit.

  uint hard_spin_start = hard_spin_limit;

  // Loop waiting for all threads to offer termination or

  // more work.

  while (true) {

    // Look for more work.

    // Periodically sleep() instead of yield() to give threads

    // waiting on the cores the chance to grab this code

    if (yield_count <= WorkStealingYieldsBeforeSleep) {

      // Do a yield or hardspin.  For purposes of deciding whether

      // to sleep, count this as a yield.

      yield_count++;

      // Periodically call yield() instead spinning

      // After WorkStealingSpinToYieldRatio spins, do a yield() call

      // and reset the counts and starting limit.

      if (hard_spin_count > WorkStealingSpinToYieldRatio) {

        yield();

        hard_spin_count = 0;

        hard_spin_limit = hard_spin_start;

#ifdef TRACESPINNING

        _total_yields++;

#endif

      } else {

        // Hard spin this time

        // Increase the hard spinning period but only up to a limit.

        hard_spin_limit = MIN2(2*hard_spin_limit,

                               (uint) WorkStealingHardSpins);

        for (uint j = 0; j < hard_spin_limit; j++) {

          SpinPause();

        }

        hard_spin_count++;

#ifdef TRACESPINNING

        _total_spins++;

#endif

      }

    } else {

      log_develop_trace(gc, task)("OWSTTaskTerminator::do_spin_master_work() thread " PTR_FORMAT " sleeps after %u yields",

                                  p2i(Thread::current()), yield_count);

      yield_count = 0;

      MonitorLocker locker(_blocker, Mutex::_no_safepoint_check_flag);

      _spin_master = NULL;

      locker.wait(WorkStealingSleepMillis);

      if (_spin_master == NULL) {

        _spin_master = Thread::current();

      } else {

        return false;

      }

    }

#ifdef TRACESPINNING

      _total_peeks++;

#endif

    size_t tasks = tasks_in_queue_set();

    bool exit = exit_termination(tasks, terminator);

    {

      MonitorLocker locker(_blocker, Mutex::_no_safepoint_check_flag);

      // Termination condition reached

      if (_offered_termination == _n_threads) {

        _spin_master = NULL;

        return true;

      } else if (exit) {

        if (tasks >= _offered_termination - 1) {

          locker.notify_all();

        } else {

          for (; tasks > 1; tasks--) {

            locker.notify();

          }

        }

        _spin_master = NULL;

        return false;

      }

    }

  }

}