/*

 * Copyright (c) 2018, 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 "utilities/globalCounter.hpp"

#include "runtime/orderAccess.inline.hpp"

#include "runtime/thread.hpp"

#include "runtime/threadSMR.inline.hpp"

#include "runtime/vmThread.hpp"

#include "utilities/spinYield.hpp"

GlobalCounter::PaddedCounter GlobalCounter::_global_counter;

class GlobalCounter::CounterThreadCheck : public ThreadClosure {

 private:

  uintx _gbl_cnt;

 public:

  CounterThreadCheck(uintx gbl_cnt) : _gbl_cnt(gbl_cnt) {}

  void do_thread(Thread* thread) {

    SpinYield yield;

    // Loops on this thread until it has exited the critical read section.

    while(true) {

      uintx cnt = OrderAccess::load_acquire(thread->get_rcu_counter());

      // This checks if the thread's counter is active. And if so is the counter

      // for a pre-existing reader (belongs to this grace period). A pre-existing

      // reader will have a lower counter than the global counter version for this

      // generation. If the counter is larger than the global counter version this

      //  is a new reader and we can continue.

      if (((cnt & COUNTER_ACTIVE) != 0) && (cnt - _gbl_cnt) > (max_uintx / 2)) {

        yield.wait();

      } else {

        break;

      }

    }

  }

};

void GlobalCounter::write_synchronize() {

  assert((*Thread::current()->get_rcu_counter() & COUNTER_ACTIVE) == 0x0, "must be outside a critcal section");

  // Atomic::add must provide fence since we have storeload dependency.

  volatile uintx gbl_cnt = Atomic::add((uintx)COUNTER_INCREMENT, &_global_counter._counter,

                                       memory_order_conservative);

  // Do all RCU threads.

  CounterThreadCheck ctc(gbl_cnt);

  for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {

    ctc.do_thread(thread);

  }

  ctc.do_thread(VMThread::vm_thread());

}