// Copyright 2008, Google Inc.
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#ifndef GEARS_DATABASE2_THREAD_SAFE_QUEUE_H__
#define GEARS_DATABASE2_THREAD_SAFE_QUEUE_H__

#include <queue>

#include "gears/base/common/common.h"
#include "gears/base/common/mutex.h"

template <class T>
class Database2ThreadSafeQueue {
 public:
  Database2ThreadSafeQueue() {};

  // Adds an item to the queue. If *first is non-null, returns whether the
  // pushed item is now first in the queue.
  void Push(T *t, bool *first) {
    MutexLock lock(&mutex_);
    if (first) {
      *first = queue_.empty();
    }
    queue_.push(t);
  }

  // Adds an item to the queue, but only if the queue is empty.
  bool PushIfEmpty(T *t) {
    MutexLock lock(&mutex_);
    if (!queue_.empty()) {
      return false;
    }

    queue_.push(t);
    return true;
  }

  // Removes and returns the front item from the queue. Returns NULL if there
  // are no items in the queue.
  T *Pop() {
    MutexLock lock(&mutex_);
    if (queue_.empty()) {
      return NULL;
    }

    T *t = queue_.front();
    queue_.pop();
    return t;
  }

 private:
  Mutex mutex_;
  std::queue<T*> queue_;

  DISALLOW_EVIL_CONSTRUCTORS(Database2ThreadSafeQueue);
};


#endif // GEARS_DATABASE2_THREAD_SAFE_QUEUE_H__