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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
//
// 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/internal/per_thread_sem.h"
#include <atomic>
#include <condition_variable> // NOLINT(build/c++11)
#include <functional>
#include <limits>
#include <mutex> // NOLINT(build/c++11)
#include <string>
#include <thread> // NOLINT(build/c++11)
#include "gtest/gtest.h"
#include "absl/base/internal/cycleclock.h"
#include "absl/base/internal/thread_identity.h"
#include "absl/strings/str_cat.h"
#include "absl/time/clock.h"
#include "absl/time/time.h"
// In this test we explicitly avoid the use of synchronization
// primitives which might use PerThreadSem, most notably absl::Mutex.
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace synchronization_internal {
class SimpleSemaphore {
public:
SimpleSemaphore() : count_(0) {}
// Decrements (locks) the semaphore. If the semaphore's value is
// greater than zero, then the decrement proceeds, and the function
// returns, immediately. If the semaphore currently has the value
// zero, then the call blocks until it becomes possible to perform
// the decrement.
void Wait() {
std::unique_lock<std::mutex> lock(mu_);
cv_.wait(lock, [this]() { return count_ > 0; });
--count_;
cv_.notify_one();
}
// Increments (unlocks) the semaphore. If the semaphore's value
// consequently becomes greater than zero, then another thread
// blocked Wait() call will be woken up and proceed to lock the
// semaphore.
void Post() {
std::lock_guard<std::mutex> lock(mu_);
++count_;
cv_.notify_one();
}
private:
std::mutex mu_;
std::condition_variable cv_;
int count_;
};
struct ThreadData {
int num_iterations; // Number of replies to send.
SimpleSemaphore identity2_written; // Posted by thread writing identity2.
base_internal::ThreadIdentity *identity1; // First Post()-er.
base_internal::ThreadIdentity *identity2; // First Wait()-er.
KernelTimeout timeout;
};
// Need friendship with PerThreadSem.
class PerThreadSemTest : public testing::Test {
public:
static void TimingThread(ThreadData* t) {
t->identity2 = GetOrCreateCurrentThreadIdentity();
t->identity2_written.Post();
while (t->num_iterations--) {
Wait(t->timeout);
Post(t->identity1);
}
}
void TestTiming(const char *msg, bool timeout) {
static const int kNumIterations = 100;
ThreadData t;
t.num_iterations = kNumIterations;
t.timeout = timeout ?
KernelTimeout(absl::Now() + absl::Seconds(10000)) // far in the future
: KernelTimeout::Never();
t.identity1 = GetOrCreateCurrentThreadIdentity();
// We can't use the Thread class here because it uses the Mutex
// class which will invoke PerThreadSem, so we use std::thread instead.
std::thread partner_thread(std::bind(TimingThread, &t));
// Wait for our partner thread to register their identity.
t.identity2_written.Wait();
int64_t min_cycles = std::numeric_limits<int64_t>::max();
int64_t total_cycles = 0;
for (int i = 0; i < kNumIterations; ++i) {
absl::SleepFor(absl::Milliseconds(20));
int64_t cycles = base_internal::CycleClock::Now();
Post(t.identity2);
Wait(t.timeout);
cycles = base_internal::CycleClock::Now() - cycles;
min_cycles = std::min(min_cycles, cycles);
total_cycles += cycles;
}
std::string out = StrCat(
msg, "min cycle count=", min_cycles, " avg cycle count=",
absl::SixDigits(static_cast<double>(total_cycles) / kNumIterations));
printf("%s\n", out.c_str());
partner_thread.join();
}
protected:
static void Post(base_internal::ThreadIdentity *id) {
PerThreadSem::Post(id);
}
static bool Wait(KernelTimeout t) {
return PerThreadSem::Wait(t);
}
// convenience overload
static bool Wait(absl::Time t) {
return Wait(KernelTimeout(t));
}
static void Tick(base_internal::ThreadIdentity *identity) {
PerThreadSem::Tick(identity);
}
};
namespace {
TEST_F(PerThreadSemTest, WithoutTimeout) {
PerThreadSemTest::TestTiming("Without timeout: ", false);
}
TEST_F(PerThreadSemTest, WithTimeout) {
PerThreadSemTest::TestTiming("With timeout: ", true);
}
TEST_F(PerThreadSemTest, Timeouts) {
const absl::Duration delay = absl::Milliseconds(50);
const absl::Time start = absl::Now();
EXPECT_FALSE(Wait(start + 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)
<< "Wait returned " << delay - elapsed
<< " early (with " << slop << " slop), start time was " << start;
absl::Time negative_timeout = absl::UnixEpoch() - absl::Milliseconds(100);
EXPECT_FALSE(Wait(negative_timeout));
EXPECT_LE(negative_timeout, absl::Now() + slop); // trivially true :)
Post(GetOrCreateCurrentThreadIdentity());
// The wait here has an expired timeout, but we have a wake to consume,
// so this should succeed
EXPECT_TRUE(Wait(negative_timeout));
}
} // namespace
} // namespace synchronization_internal
ABSL_NAMESPACE_END
} // namespace absl
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