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// 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
//
// 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.
#include "absl/base/call_once.h"
#include <thread>
#include <vector>
#include "gtest/gtest.h"
#include "absl/base/attributes.h"
#include "absl/base/thread_annotations.h"
#include "absl/synchronization/mutex.h"
namespace absl {
namespace {
absl::once_flag once;
Mutex counters_mu;
int running_thread_count GUARDED_BY(counters_mu) = 0;
int call_once_invoke_count GUARDED_BY(counters_mu) = 0;
int call_once_finished_count GUARDED_BY(counters_mu) = 0;
int call_once_return_count GUARDED_BY(counters_mu) = 0;
bool done_blocking GUARDED_BY(counters_mu) = false;
// Function to be called from absl::call_once. Waits for a notification.
void WaitAndIncrement() {
counters_mu.Lock();
++call_once_invoke_count;
counters_mu.Unlock();
counters_mu.LockWhen(Condition(&done_blocking));
++call_once_finished_count;
counters_mu.Unlock();
}
void ThreadBody() {
counters_mu.Lock();
++running_thread_count;
counters_mu.Unlock();
absl::call_once(once, WaitAndIncrement);
counters_mu.Lock();
++call_once_return_count;
counters_mu.Unlock();
}
// Returns true if all threads are set up for the test.
bool ThreadsAreSetup(void*) EXCLUSIVE_LOCKS_REQUIRED(counters_mu) {
// All ten threads must be running, and WaitAndIncrement should be blocked.
return running_thread_count == 10 && call_once_invoke_count == 1;
}
TEST(CallOnceTest, ExecutionCount) {
std::vector<std::thread> threads;
// Start 10 threads all calling call_once on the same once_flag.
for (int i = 0; i < 10; ++i) {
threads.emplace_back(ThreadBody);
}
// Wait until all ten threads have started, and WaitAndIncrement has been
// invoked.
counters_mu.LockWhen(Condition(ThreadsAreSetup, nullptr));
// WaitAndIncrement should have been invoked by exactly one call_once()
// instance. That thread should be blocking on a notification, and all other
// call_once instances should be blocking as well.
EXPECT_EQ(call_once_invoke_count, 1);
EXPECT_EQ(call_once_finished_count, 0);
EXPECT_EQ(call_once_return_count, 0);
// Allow WaitAndIncrement to finish executing. Once it does, the other
// call_once waiters will be unblocked.
done_blocking = true;
counters_mu.Unlock();
for (std::thread& thread : threads) {
thread.join();
}
counters_mu.Lock();
EXPECT_EQ(call_once_invoke_count, 1);
EXPECT_EQ(call_once_finished_count, 1);
EXPECT_EQ(call_once_return_count, 10);
counters_mu.Unlock();
}
} // namespace
} // namespace absl
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