spinlock.h

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// Copyright 2013 Cloudera Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef IMPALA_UTIL_SPINLOCK_H
#define IMPALA_UTIL_SPINLOCK_H

#include "common/atomic.h"
#include "common/logging.h"

namespace impala {

class SpinLock {
 public:
  SpinLock() : locked_(false) {}

  void lock() {
    if (!try_lock()) SlowAcquire();
  }

  void unlock() {
    // Memory barrier here. All updates before the unlock need to be made visible.
    __sync_synchronize();
    DCHECK(locked_);
    locked_ = false;
  }

  inline bool try_lock() { return __sync_bool_compare_and_swap(&locked_, false, true); }

  void DCheckLocked() { DCHECK(locked_); }

 private:

  void SlowAcquire();

  static const int NUM_SPIN_CYCLES = 70;
  bool locked_;
};

}
#endif