/*

 * Copyright (c) 2001, 2019, 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.

 *

 */

#include "precompiled.hpp"

#include "gc/shared/taskqueue.hpp"

#include "gc/shared/owstTaskTerminator.hpp"

#include "oops/oop.inline.hpp"

#include "logging/log.hpp"

#include "runtime/atomic.hpp"

#include "runtime/os.hpp"

#include "runtime/thread.inline.hpp"

#include "utilities/debug.hpp"

#include "utilities/stack.inline.hpp"

#ifdef TRACESPINNING

uint ParallelTaskTerminator::_total_yields = 0;

uint ParallelTaskTerminator::_total_spins = 0;

uint ParallelTaskTerminator::_total_peeks = 0;

#endif

#if TASKQUEUE_STATS

const char * const TaskQueueStats::_names[last_stat_id] = {

  "qpush", "qpop", "qpop-s", "qattempt", "qsteal", "opush", "omax"

};

TaskQueueStats & TaskQueueStats::operator +=(const TaskQueueStats & addend)

{

  for (unsigned int i = 0; i < last_stat_id; ++i) {

    _stats[i] += addend._stats[i];

  }

  return *this;

}

void TaskQueueStats::print_header(unsigned int line, outputStream* const stream,

                                  unsigned int width)

{

  // Use a width w: 1 <= w <= max_width

  const unsigned int max_width = 40;

  if (line == 0) { // spaces equal in width to the header

    const unsigned int hdr_width = w * last_stat_id + last_stat_id - 1;

    stream->print("%*s", hdr_width, " ");

  } else if (line == 1) { // labels

    stream->print("%*s", w, _names[0]);

    for (unsigned int i = 1; i < last_stat_id; ++i) {

      stream->print(" %*s", w, _names[i]);

    }

  } else if (line == 2) { // dashed lines

    char dashes[max_width + 1];

    memset(dashes, '-', w);

    dashes[w] = '\0';

    stream->print("%s", dashes);

    for (unsigned int i = 1; i < last_stat_id; ++i) {

      stream->print(" %s", dashes);

    }

  }

}

void TaskQueueStats::print(outputStream* stream, unsigned int width) const

{

  #define FMT SIZE_FORMAT_W(*)

  stream->print(FMT, width, _stats[0]);

  for (unsigned int i = 1; i < last_stat_id; ++i) {

    stream->print(" " FMT, width, _stats[i]);

  }

  #undef FMT

}

#ifdef ASSERT

// Invariants which should hold after a TaskQueue has been emptied and is

// quiescent; they do not hold at arbitrary times.

void TaskQueueStats::verify() const

{

  assert(get(push) == get(pop) + get(steal),

         "push=" SIZE_FORMAT " pop=" SIZE_FORMAT " steal=" SIZE_FORMAT,

         get(push), get(pop), get(steal));

  assert(get(pop_slow) <= get(pop),

         "pop_slow=" SIZE_FORMAT " pop=" SIZE_FORMAT,

         get(pop_slow), get(pop));

  assert(get(steal) <= get(steal_attempt),

         "steal=" SIZE_FORMAT " steal_attempt=" SIZE_FORMAT,

         get(steal), get(steal_attempt));

  assert(get(overflow) == 0 || get(push) != 0,

         "overflow=" SIZE_FORMAT " push=" SIZE_FORMAT,

         get(overflow), get(push));

  assert(get(overflow_max_len) == 0 || get(overflow) != 0,

         "overflow_max_len=" SIZE_FORMAT " overflow=" SIZE_FORMAT,

         get(overflow_max_len), get(overflow));

}

#endif // ASSERT

#endif // TASKQUEUE_STATS

ParallelTaskTerminator::

ParallelTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set) :

  _n_threads(n_threads),

  _queue_set(queue_set),

  _offered_termination(0) {}

ParallelTaskTerminator::~ParallelTaskTerminator() {

  assert(_offered_termination == 0 || !peek_in_queue_set(), "Precondition");

  assert(_offered_termination == 0 || _offered_termination == _n_threads, "Terminated or aborted" );

}

bool ParallelTaskTerminator::peek_in_queue_set() {

  return _queue_set->peek();

}

void ParallelTaskTerminator::yield() {

  assert(_offered_termination <= _n_threads, "Invariant");

  os::naked_yield();

}

void ParallelTaskTerminator::sleep(uint millis) {

  assert(_offered_termination <= _n_threads, "Invariant");

  os::naked_sleep(millis);

}

bool

ParallelTaskTerminator::offer_termination(TerminatorTerminator* terminator) {

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

  assert(_offered_termination < _n_threads, "Invariant");

  Atomic::inc(&_offered_termination);

  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) {

    assert(_offered_termination <= _n_threads, "Invariant");

    // Are all threads offering termination?

    if (_offered_termination == _n_threads) {

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

      return true;

    } else {

      // 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)("ParallelTaskTerminator::offer_termination() thread " PTR_FORMAT " sleeps after %u yields",

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

        yield_count = 0;

        // A sleep will cause this processor to seek work on another processor's

        // runqueue, if it has nothing else to run (as opposed to the yield

        // which may only move the thread to the end of the this processor's

        // runqueue).

        sleep(WorkStealingSleepMillis);

      }

#ifdef TRACESPINNING

      _total_peeks++;

#endif

      if (peek_in_queue_set() ||

          (terminator != NULL && terminator->should_exit_termination())) {

        return complete_or_exit_termination();

      }

    }

  }

}

#ifdef TRACESPINNING

void ParallelTaskTerminator::print_termination_counts() {

  log_trace(gc, task)("ParallelTaskTerminator Total yields: %u"

    " Total spins: %u Total peeks: %u",

    total_yields(),

    total_spins(),

    total_peeks());

}

#endif

bool ParallelTaskTerminator::complete_or_exit_termination() {

  // If termination is ever reached, terminator should stay in such state,

  // so that all threads see the same state

  uint current_offered = _offered_termination;

  uint expected_value;

  do {

    if (current_offered == _n_threads) {

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

      return true;

    }

    expected_value = current_offered;

  } while ((current_offered = Atomic::cmpxchg(current_offered - 1, &_offered_termination, current_offered)) != expected_value);

  assert(_offered_termination < _n_threads, "Invariant");

  return false;

}

void ParallelTaskTerminator::reset_for_reuse() {

  if (_offered_termination != 0) {

    assert(_offered_termination == _n_threads,

           "Terminator may still be in use");

    _offered_termination = 0;

  }

}

#ifdef ASSERT

bool ObjArrayTask::is_valid() const {

  return _obj != NULL && _obj->is_objArray() && _index >= 0 &&

      _index < objArrayOop(_obj)->length();

}

#endif // ASSERT

void ParallelTaskTerminator::reset_for_reuse(uint n_threads) {

  reset_for_reuse();

  _n_threads = n_threads;

}

TaskTerminator::TaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set) :

  _terminator(UseOWSTTaskTerminator ? new OWSTTaskTerminator(n_threads, queue_set)

                                    : new ParallelTaskTerminator(n_threads, queue_set)) {

}

TaskTerminator::~TaskTerminator() {

  if (_terminator != NULL) {

    delete _terminator;

  }

}