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      1 /* Copyright 2015 The TensorFlow Authors. All Rights Reserved.
      2 
      3 Licensed under the Apache License, Version 2.0 (the "License");
      4 you may not use this file except in compliance with the License.
      5 You may obtain a copy of the License at
      6 
      7     http://www.apache.org/licenses/LICENSE-2.0
      8 
      9 Unless required by applicable law or agreed to in writing, software
     10 distributed under the License is distributed on an "AS IS" BASIS,
     11 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     12 See the License for the specific language governing permissions and
     13 limitations under the License.
     14 ==============================================================================*/
     15 
     16 #ifndef TENSORFLOW_CORE_PLATFORM_DEFAULT_NOTIFICATION_H_
     17 #define TENSORFLOW_CORE_PLATFORM_DEFAULT_NOTIFICATION_H_
     18 
     19 #include <assert.h>
     20 #include <atomic>              // NOLINT
     21 #include <chrono>              // NOLINT
     22 #include <condition_variable>  // NOLINT
     23 
     24 #include "tensorflow/core/platform/mutex.h"
     25 #include "tensorflow/core/platform/types.h"
     26 
     27 namespace tensorflow {
     28 
     29 class Notification {
     30  public:
     31   Notification() : notified_(0) {}
     32   ~Notification() {
     33     // In case the notification is being used to synchronize its own deletion,
     34     // force any prior notifier to leave its critical section before the object
     35     // is destroyed.
     36     mutex_lock l(mu_);
     37   }
     38 
     39   void Notify() {
     40     mutex_lock l(mu_);
     41     assert(!HasBeenNotified());
     42     notified_.store(true, std::memory_order_release);
     43     cv_.notify_all();
     44   }
     45 
     46   bool HasBeenNotified() const {
     47     return notified_.load(std::memory_order_acquire);
     48   }
     49 
     50   void WaitForNotification() {
     51     if (!HasBeenNotified()) {
     52       mutex_lock l(mu_);
     53       while (!HasBeenNotified()) {
     54         cv_.wait(l);
     55       }
     56     }
     57   }
     58 
     59  private:
     60   friend bool WaitForNotificationWithTimeout(Notification* n,
     61                                              int64 timeout_in_us);
     62   bool WaitForNotificationWithTimeout(int64 timeout_in_us) {
     63     bool notified = HasBeenNotified();
     64     if (!notified) {
     65       mutex_lock l(mu_);
     66       do {
     67         notified = HasBeenNotified();
     68       } while (!notified &&
     69                cv_.wait_for(l, std::chrono::microseconds(timeout_in_us)) !=
     70                    std::cv_status::timeout);
     71     }
     72     return notified;
     73   }
     74 
     75   mutex mu_;                    // protects mutations of notified_
     76   condition_variable cv_;       // signaled when notified_ becomes non-zero
     77   std::atomic<bool> notified_;  // mutations under mu_
     78 };
     79 
     80 inline bool WaitForNotificationWithTimeout(Notification* n,
     81                                            int64 timeout_in_us) {
     82   return n->WaitForNotificationWithTimeout(timeout_in_us);
     83 }
     84 
     85 }  // namespace tensorflow
     86 
     87 #endif  // TENSORFLOW_CORE_PLATFORM_DEFAULT_NOTIFICATION_H_
     88