promise.h

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// Copyright 2012 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_PROMISE_H
#define IMPALA_UTIL_PROMISE_H

#include <boost/thread.hpp>

#include "common/logging.h"
#include "runtime/timestamp-value.h"
#include "util/time.h"

namespace impala {

template <typename T>
class Promise {
 public:
  Promise() : val_is_set_(false) { }

  void Set(const T& val) {
    boost::unique_lock<boost::mutex> l(val_lock_);
    DCHECK(!val_is_set_) << "Called Set(..) twice on the same Promise";
    val_ = val;
    val_is_set_ = true;

    val_set_cond_.notify_all();
  }

  const T& Get() {
    boost::unique_lock<boost::mutex> l(val_lock_);
    while (!val_is_set_) {
      val_set_cond_.wait(l);
    }
    return val_;
  }

  const T& Get(int64_t timeout_millis, bool* timed_out) {
    DCHECK_GT(timeout_millis, 0);
    int64_t timeout_micros = timeout_millis * 1000;
    DCHECK(timed_out != NULL);
    boost::unique_lock<boost::mutex> l(val_lock_);
    int64_t start;
    int64_t now;
    now = start = MonotonicMicros();
    while (!val_is_set_ && (now - start) < timeout_micros) {
      boost::posix_time::microseconds wait_time =
          boost::posix_time::microseconds(std::max(1L, timeout_micros - (now - start)));
      val_set_cond_.timed_wait(l, wait_time);
      now = MonotonicMicros();
    }
    *timed_out = !val_is_set_;
    return val_;
  }

  bool IsSet() {
    boost::lock_guard<boost::mutex> l(val_lock_);
    return val_is_set_;
  }

 private:
  boost::condition_variable val_set_cond_;
  bool val_is_set_;
  boost::mutex val_lock_;

  T val_;
};

}

#endif