/*

 * Copyright (c) 1997, 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/collectedHeap.hpp"

#include "gc/shared/gcLocker.hpp"

#include "memory/resourceArea.hpp"

#include "memory/universe.hpp"

#include "logging/log.hpp"

#include "runtime/atomic.hpp"

#include "runtime/safepoint.hpp"

#include "runtime/thread.inline.hpp"

#include "runtime/threadSMR.hpp"

volatile jint GCLocker::_jni_lock_count = 0;

volatile bool GCLocker::_needs_gc       = false;

volatile bool GCLocker::_doing_gc       = false;

#ifdef ASSERT

volatile jint GCLocker::_debug_jni_lock_count = 0;

#endif

#ifdef ASSERT

void GCLocker::verify_critical_count() {

  if (SafepointSynchronize::is_at_safepoint()) {

    assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");

    int count = 0;

    // Count the number of threads with critical operations in progress

    JavaThreadIteratorWithHandle jtiwh;

    for (; JavaThread *thr = jtiwh.next(); ) {

      if (thr->in_critical()) {

        count++;

      }

    }

    if (_jni_lock_count != count) {

      log_error(gc, verify)("critical counts don't match: %d != %d", _jni_lock_count, count);

      jtiwh.rewind();

      for (; JavaThread *thr = jtiwh.next(); ) {

        if (thr->in_critical()) {

          log_error(gc, verify)(INTPTR_FORMAT " in_critical %d", p2i(thr), thr->in_critical());

        }

      }

    }

    assert(_jni_lock_count == count, "must be equal");

  }

}

// In debug mode track the locking state at all times

void GCLocker::increment_debug_jni_lock_count() {

  assert(_debug_jni_lock_count >= 0, "bad value");

  Atomic::inc(&_debug_jni_lock_count);

}

void GCLocker::decrement_debug_jni_lock_count() {

  assert(_debug_jni_lock_count > 0, "bad value");

  Atomic::dec(&_debug_jni_lock_count);

}

#endif

void GCLocker::log_debug_jni(const char* msg) {

  Log(gc, jni) log;

  if (log.is_debug()) {

    ResourceMark rm; // JavaThread::name() allocates to convert to UTF8

    log.debug("%s Thread \"%s\" %d locked.", msg, Thread::current()->name(), _jni_lock_count);

  }

}

bool GCLocker::is_at_safepoint() {

  return SafepointSynchronize::is_at_safepoint();

}

bool GCLocker::check_active_before_gc() {

  assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");

  if (is_active() && !_needs_gc) {

    verify_critical_count();

    _needs_gc = true;

    log_debug_jni("Setting _needs_gc.");

  }

  return is_active();

}

void GCLocker::stall_until_clear() {

  assert(!JavaThread::current()->in_critical(), "Would deadlock");

  MonitorLocker ml(JNICritical_lock);

  if (needs_gc()) {

    log_debug_jni("Allocation failed. Thread stalled by JNI critical section.");

  }

  // Wait for _needs_gc  to be cleared

  while (needs_gc()) {

    ml.wait();

  }

}

void GCLocker::jni_lock(JavaThread* thread) {

  assert(!thread->in_critical(), "shouldn't currently be in a critical region");

  MonitorLocker ml(JNICritical_lock);

  // Block entering threads if we know at least one thread is in a

  // JNI critical region and we need a GC.

  // We check that at least one thread is in a critical region before

  // blocking because blocked threads are woken up by a thread exiting

  // a JNI critical region.

  while (is_active_and_needs_gc() || _doing_gc) {

    ml.wait();

  }

  thread->enter_critical();

  _jni_lock_count++;

  increment_debug_jni_lock_count();

}

void GCLocker::jni_unlock(JavaThread* thread) {

  assert(thread->in_last_critical(), "should be exiting critical region");

  MutexLocker mu(JNICritical_lock);

  _jni_lock_count--;

  decrement_debug_jni_lock_count();

  thread->exit_critical();

  if (needs_gc() && !is_active_internal()) {

    // We're the last thread out. Cause a GC to occur.

    _doing_gc = true;

    {

      // Must give up the lock while at a safepoint

      MutexUnlocker munlock(JNICritical_lock);

      log_debug_jni("Performing GC after exiting critical section.");

      Universe::heap()->collect(GCCause::_gc_locker);

    }

    _doing_gc = false;

    _needs_gc = false;

    JNICritical_lock->notify_all();

  }

}