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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/synchronization/cancelable_event.h"
#include <stdint.h>
#include <atomic>
#include <memory>
#include <tuple>
#include <vector>
#include "base/barrier_closure.h"
#include "base/functional/callback.h"
#include "base/logging.h"
#include "base/numerics/clamped_math.h"
#include "base/rand_util.h"
#include "base/strings/stringprintf.h"
#include "base/synchronization/lock.h"
#include "base/test/bind.h"
#include "base/test/test_timeouts.h"
#include "base/test/test_waitable_event.h"
#include "base/threading/thread.h"
#include "base/time/time.h"
#include "testing/gtest/include/gtest/gtest.h"
#include "testing/platform_test.h"
namespace base {
namespace {
class CancelableEventTest : public testing::Test {
protected:
raw_ptr<Thread> CreateThreadWithTask(RepeatingClosure& thread_task) {
std::unique_ptr<Thread> thread = std::make_unique<Thread>(
StringPrintf("CancelTestThread%d", threadcounter++));
thread->Start();
thread->task_runner()->PostTask(FROM_HERE, thread_task);
threads_.push_back(std::move(thread));
return threads_.back().get();
}
int threadcounter = 0;
WaitableEvent shutdown_event_;
std::vector<std::unique_ptr<Thread>> threads_;
};
} // namespace
TEST_F(CancelableEventTest, TimedWaitFail) {
CancelableEvent event;
RepeatingClosure task = BindLambdaForTesting([&]() {
TimeTicks start_time = TimeTicks::Now();
EXPECT_FALSE(event.TimedWait(TestTimeouts::tiny_timeout()));
EXPECT_GE(TimeTicks::Now() - start_time, TestTimeouts::tiny_timeout());
});
this->CreateThreadWithTask(task)->FlushForTesting();
}
TEST_F(CancelableEventTest, TimedWaitSuccess) {
CancelableEvent event;
RepeatingClosure task = BindLambdaForTesting(
[&]() { EXPECT_TRUE(event.TimedWait(TestTimeouts::tiny_timeout())); });
event.Signal();
this->CreateThreadWithTask(task)->FlushForTesting();
}
// These are the platforms on which a functional CancelableEvent is implemented.
#if BUILDFLAG(IS_WIN) || BUILDFLAG(IS_CHROMEOS) || BUILDFLAG(IS_LINUX) || \
BUILDFLAG(IS_ANDROID)
TEST_F(CancelableEventTest, CancelSucceedsWhenNoWaiterAndWaitTimesOut) {
CancelableEvent event;
event.Signal();
EXPECT_TRUE(event.Cancel());
EXPECT_FALSE(event.TimedWait(base::TimeDelta()));
}
TEST_F(CancelableEventTest, BothCancelFailureAndSucceedOccurWithOneWaiter) {
bool cancel_failed = false;
bool cancel_succeeded = false;
for (int i = 0; i < 100; ++i) {
CancelableEvent event;
TestWaitableEvent thread_running;
auto task = BindLambdaForTesting([&]() {
thread_running.Signal();
event.Wait();
});
auto thread = CreateThreadWithTask(task);
if (!cancel_failed) {
thread_running.Wait();
}
event.Signal();
#if BUILDFLAG(IS_POSIX)
// Posix implementations of Semaphores seem to be much less greedy in waking
// up threads currently waiting on the event - give the thread a few
// milliseconds to wake up and acquire the semaphore before us.
if (cancel_succeeded) {
PlatformThread::Sleep(Milliseconds(8));
}
#endif
if (event.Cancel()) {
cancel_succeeded = true;
event.Signal();
} else {
cancel_failed = true;
}
thread->FlushForTesting();
if (cancel_failed && cancel_succeeded) {
break;
}
}
EXPECT_TRUE(cancel_failed);
EXPECT_TRUE(cancel_succeeded);
}
TEST_F(CancelableEventTest, BothCancelFailureAndSucceedOccurUnderContention) {
// The following block is responsible for creating CPU contention - it creates
// 16 threads which run for the duration of the test, crunching CPU. None of
// the data here is used in any meaningful way in the rest of the test. beyond
// setting `busywork_threads_should_quit` to signal exit.
std::atomic_bool busywork_threads_should_quit = false;
// The arena lives for the duration of the test, and so must have test-wide
// scope, however it is only accessed by the busywork threads, and not by the
// rest of the test.
const int kNumThreads = 16;
std::atomic_char busywork_arena[kNumThreads];
{
TestWaitableEvent threads_running;
RepeatingClosure threads_running_barrier = BarrierClosure(
kNumThreads,
BindOnce(&TestWaitableEvent::Signal, Unretained(&threads_running)));
for (int i = 0; i < kNumThreads; ++i) {
auto task = BindLambdaForTesting([&]() {
threads_running_barrier.Run();
while (!busywork_threads_should_quit.load(std::memory_order_acquire)) {
// Busy loop. Only done to burn CPU.
uint64_t counter = 1;
for (auto& slot : busywork_arena) {
counter += slot + 1;
slot.store(static_cast<char>((counter & 0xf) + 1),
std::memory_order_release);
}
}
});
CreateThreadWithTask(task);
}
threads_running.Wait();
}
// Used to adjust race timings to favor the case which has not yet been seen
// (cancel fail/success).
internal::ClampedNumeric<unsigned int> wait_ms = 0;
bool succeeded = false;
bool failed = false;
for (int i = 0; i < 10 && (!failed || !succeeded); ++i) {
CancelableEvent event;
TestWaitableEvent thread_running;
std::atomic_bool thread_done = false;
auto task = BindLambdaForTesting([&]() {
thread_running.Signal();
EXPECT_TRUE(event.TimedWait(TestTimeouts::test_launcher_timeout()));
thread_done = true;
});
auto thread = CreateThreadWithTask(task);
PlatformThread::Sleep(Milliseconds(wait_ms));
event.Signal();
PlatformThread::Sleep(Milliseconds(wait_ms));
if (event.Cancel()) {
succeeded = true;
event.Signal();
wait_ms += 100;
} else {
failed = true;
wait_ms -= 50;
}
thread->FlushForTesting();
EXPECT_TRUE(thread_done);
}
busywork_threads_should_quit.store(true, std::memory_order_release);
for (auto& thread : threads_) {
thread->FlushForTesting();
}
EXPECT_TRUE(succeeded);
EXPECT_TRUE(failed);
}
#else
TEST_F(CancelableEventTest, CancelFailsOnUnsupportedPlatforms) {
CancelableEvent event;
event.Signal();
EXPECT_FALSE(event.Cancel());
EXPECT_TRUE(event.TimedWait(base::TimeDelta()));
}
#endif
} // namespace base
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