summaryrefslogtreecommitdiff
path: root/absl/synchronization/notification_test.cc
blob: 059d4cd2521deadafdea6f17e88762b6c93c5cb2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
// Copyright 2017 The Abseil Authors.
//
// 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
//
//      https://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.

#include "absl/synchronization/notification.h"

#include <thread>  // NOLINT(build/c++11)
#include <vector>

#include "gtest/gtest.h"
#include "absl/synchronization/mutex.h"

namespace absl {

// A thread-safe class that holds a counter.
class ThreadSafeCounter {
 public:
  ThreadSafeCounter() : count_(0) {}

  void Increment() {
    MutexLock lock(&mutex_);
    ++count_;
  }

  int Get() const {
    MutexLock lock(&mutex_);
    return count_;
  }

  void WaitUntilGreaterOrEqual(int n) {
    MutexLock lock(&mutex_);
    auto cond = [this, n]() { return count_ >= n; };
    mutex_.Await(Condition(&cond));
  }

 private:
  mutable Mutex mutex_;
  int count_;
};

// Runs the |i|'th worker thread for the tests in BasicTests().  Increments the
// |ready_counter|, waits on the |notification|, and then increments the
// |done_counter|.
static void RunWorker(int i, ThreadSafeCounter* ready_counter,
                      Notification* notification,
                      ThreadSafeCounter* done_counter) {
  ready_counter->Increment();
  notification->WaitForNotification();
  done_counter->Increment();
}

// Tests that the |notification| properly blocks and awakens threads.  Assumes
// that the |notification| is not yet triggered.  If |notify_before_waiting| is
// true, the |notification| is triggered before any threads are created, so the
// threads never block in WaitForNotification().  Otherwise, the |notification|
// is triggered at a later point when most threads are likely to be blocking in
// WaitForNotification().
static void BasicTests(bool notify_before_waiting, Notification* notification) {
  EXPECT_FALSE(notification->HasBeenNotified());
  EXPECT_FALSE(
      notification->WaitForNotificationWithTimeout(absl::Milliseconds(0)));
  EXPECT_FALSE(notification->WaitForNotificationWithDeadline(absl::Now()));

  const absl::Duration delay = absl::Milliseconds(50);
  const absl::Time start = absl::Now();
  EXPECT_FALSE(notification->WaitForNotificationWithTimeout(delay));
  const absl::Duration elapsed = absl::Now() - start;

  // Allow for a slight early return, to account for quality of implementation
  // issues on various platforms.
  const absl::Duration slop = absl::Microseconds(200);
  EXPECT_LE(delay - slop, elapsed)
      << "WaitForNotificationWithTimeout returned " << delay - elapsed
      << " early (with " << slop << " slop), start time was " << start;

  ThreadSafeCounter ready_counter;
  ThreadSafeCounter done_counter;

  if (notify_before_waiting) {
    notification->Notify();
  }

  // Create a bunch of threads that increment the |done_counter| after being
  // notified.
  const int kNumThreads = 10;
  std::vector<std::thread> workers;
  for (int i = 0; i < kNumThreads; ++i) {
    workers.push_back(std::thread(&RunWorker, i, &ready_counter, notification,
                                  &done_counter));
  }

  if (!notify_before_waiting) {
    ready_counter.WaitUntilGreaterOrEqual(kNumThreads);

    // Workers have not been notified yet, so the |done_counter| should be
    // unmodified.
    EXPECT_EQ(0, done_counter.Get());

    notification->Notify();
  }

  // After notifying and then joining the workers, both counters should be
  // fully incremented.
  notification->WaitForNotification();  // should exit immediately
  EXPECT_TRUE(notification->HasBeenNotified());
  EXPECT_TRUE(notification->WaitForNotificationWithTimeout(absl::Seconds(0)));
  EXPECT_TRUE(notification->WaitForNotificationWithDeadline(absl::Now()));
  for (std::thread& worker : workers) {
    worker.join();
  }
  EXPECT_EQ(kNumThreads, ready_counter.Get());
  EXPECT_EQ(kNumThreads, done_counter.Get());
}

TEST(NotificationTest, SanityTest) {
  Notification local_notification1, local_notification2;
  BasicTests(false, &local_notification1);
  BasicTests(true, &local_notification2);
}

}  // namespace absl