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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.
// A bunch of threads repeatedly hash an array of ints protected by a
// spinlock. If the spinlock is working properly, all elements of the
// array should be equal at the end of the test.
#include <cstdint>
#include <limits>
#include <random>
#include <thread> // NOLINT(build/c++11)
#include <vector>
#include "gtest/gtest.h"
#include "absl/base/attributes.h"
#include "absl/base/internal/low_level_scheduling.h"
#include "absl/base/internal/scheduling_mode.h"
#include "absl/base/internal/spinlock.h"
#include "absl/base/internal/sysinfo.h"
#include "absl/base/macros.h"
#include "absl/synchronization/blocking_counter.h"
#include "absl/synchronization/notification.h"
constexpr int32_t kNumThreads = 10;
constexpr int32_t kIters = 1000;
namespace absl {
namespace base_internal {
// This is defined outside of anonymous namespace so that it can be
// a friend of SpinLock to access protected methods for testing.
struct SpinLockTest {
static uint32_t EncodeWaitCycles(int64_t wait_start_time,
int64_t wait_end_time) {
return SpinLock::EncodeWaitCycles(wait_start_time, wait_end_time);
}
static uint64_t DecodeWaitCycles(uint32_t lock_value) {
return SpinLock::DecodeWaitCycles(lock_value);
}
};
namespace {
static constexpr int kArrayLength = 10;
static uint32_t values[kArrayLength];
static SpinLock static_spinlock(base_internal::kLinkerInitialized);
static SpinLock static_cooperative_spinlock(
base_internal::kLinkerInitialized,
base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL);
static SpinLock static_noncooperative_spinlock(
base_internal::kLinkerInitialized, base_internal::SCHEDULE_KERNEL_ONLY);
// Simple integer hash function based on the public domain lookup2 hash.
// http://burtleburtle.net/bob/c/lookup2.c
static uint32_t Hash32(uint32_t a, uint32_t c) {
uint32_t b = 0x9e3779b9UL; // The golden ratio; an arbitrary value.
a -= b; a -= c; a ^= (c >> 13);
b -= c; b -= a; b ^= (a << 8);
c -= a; c -= b; c ^= (b >> 13);
a -= b; a -= c; a ^= (c >> 12);
b -= c; b -= a; b ^= (a << 16);
c -= a; c -= b; c ^= (b >> 5);
a -= b; a -= c; a ^= (c >> 3);
b -= c; b -= a; b ^= (a << 10);
c -= a; c -= b; c ^= (b >> 15);
return c;
}
static void TestFunction(int thread_salt, SpinLock* spinlock) {
for (int i = 0; i < kIters; i++) {
SpinLockHolder h(spinlock);
for (int j = 0; j < kArrayLength; j++) {
const int index = (j + thread_salt) % kArrayLength;
values[index] = Hash32(values[index], thread_salt);
std::this_thread::yield();
}
}
}
static void ThreadedTest(SpinLock* spinlock) {
std::vector<std::thread> threads;
for (int i = 0; i < kNumThreads; ++i) {
threads.push_back(std::thread(TestFunction, i, spinlock));
}
for (auto& thread : threads) {
thread.join();
}
SpinLockHolder h(spinlock);
for (int i = 1; i < kArrayLength; i++) {
EXPECT_EQ(values[0], values[i]);
}
}
TEST(SpinLock, StackNonCooperativeDisablesScheduling) {
SpinLock spinlock(base_internal::SCHEDULE_KERNEL_ONLY);
spinlock.Lock();
EXPECT_FALSE(base_internal::SchedulingGuard::ReschedulingIsAllowed());
spinlock.Unlock();
}
TEST(SpinLock, StaticNonCooperativeDisablesScheduling) {
static_noncooperative_spinlock.Lock();
EXPECT_FALSE(base_internal::SchedulingGuard::ReschedulingIsAllowed());
static_noncooperative_spinlock.Unlock();
}
TEST(SpinLock, WaitCyclesEncoding) {
// These are implementation details not exported by SpinLock.
const int kProfileTimestampShift = 7;
const int kLockwordReservedShift = 3;
const uint32_t kSpinLockSleeper = 8;
// We should be able to encode up to (1^kMaxCycleBits - 1) without clamping
// but the lower kProfileTimestampShift will be dropped.
const int kMaxCyclesShift =
32 - kLockwordReservedShift + kProfileTimestampShift;
const uint64_t kMaxCycles = (int64_t{1} << kMaxCyclesShift) - 1;
// These bits should be zero after encoding.
const uint32_t kLockwordReservedMask = (1 << kLockwordReservedShift) - 1;
// These bits are dropped when wait cycles are encoded.
const uint64_t kProfileTimestampMask = (1 << kProfileTimestampShift) - 1;
// Test a bunch of random values
std::default_random_engine generator;
// Shift to avoid overflow below.
std::uniform_int_distribution<uint64_t> time_distribution(
0, std::numeric_limits<uint64_t>::max() >> 4);
std::uniform_int_distribution<uint64_t> cycle_distribution(0, kMaxCycles);
for (int i = 0; i < 100; i++) {
int64_t start_time = time_distribution(generator);
int64_t cycles = cycle_distribution(generator);
int64_t end_time = start_time + cycles;
uint32_t lock_value = SpinLockTest::EncodeWaitCycles(start_time, end_time);
EXPECT_EQ(0, lock_value & kLockwordReservedMask);
uint64_t decoded = SpinLockTest::DecodeWaitCycles(lock_value);
EXPECT_EQ(0, decoded & kProfileTimestampMask);
EXPECT_EQ(cycles & ~kProfileTimestampMask, decoded);
}
// Test corner cases
int64_t start_time = time_distribution(generator);
EXPECT_EQ(kSpinLockSleeper,
SpinLockTest::EncodeWaitCycles(start_time, start_time));
EXPECT_EQ(0, SpinLockTest::DecodeWaitCycles(0));
EXPECT_EQ(0, SpinLockTest::DecodeWaitCycles(kLockwordReservedMask));
EXPECT_EQ(kMaxCycles & ~kProfileTimestampMask,
SpinLockTest::DecodeWaitCycles(~kLockwordReservedMask));
// Check that we cannot produce kSpinLockSleeper during encoding.
int64_t sleeper_cycles =
kSpinLockSleeper << (kProfileTimestampShift - kLockwordReservedShift);
uint32_t sleeper_value =
SpinLockTest::EncodeWaitCycles(start_time, start_time + sleeper_cycles);
EXPECT_NE(sleeper_value, kSpinLockSleeper);
// Test clamping
uint32_t max_value =
SpinLockTest::EncodeWaitCycles(start_time, start_time + kMaxCycles);
uint64_t max_value_decoded = SpinLockTest::DecodeWaitCycles(max_value);
uint64_t expected_max_value_decoded = kMaxCycles & ~kProfileTimestampMask;
EXPECT_EQ(expected_max_value_decoded, max_value_decoded);
const int64_t step = (1 << kProfileTimestampShift);
uint32_t after_max_value =
SpinLockTest::EncodeWaitCycles(start_time, start_time + kMaxCycles + step);
uint64_t after_max_value_decoded =
SpinLockTest::DecodeWaitCycles(after_max_value);
EXPECT_EQ(expected_max_value_decoded, after_max_value_decoded);
uint32_t before_max_value = SpinLockTest::EncodeWaitCycles(
start_time, start_time + kMaxCycles - step);
uint64_t before_max_value_decoded =
SpinLockTest::DecodeWaitCycles(before_max_value);
EXPECT_GT(expected_max_value_decoded, before_max_value_decoded);
}
TEST(SpinLockWithThreads, StaticSpinLock) {
ThreadedTest(&static_spinlock);
}
TEST(SpinLockWithThreads, StackSpinLock) {
SpinLock spinlock;
ThreadedTest(&spinlock);
}
TEST(SpinLockWithThreads, StackCooperativeSpinLock) {
SpinLock spinlock(base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL);
ThreadedTest(&spinlock);
}
TEST(SpinLockWithThreads, StackNonCooperativeSpinLock) {
SpinLock spinlock(base_internal::SCHEDULE_KERNEL_ONLY);
ThreadedTest(&spinlock);
}
TEST(SpinLockWithThreads, StaticCooperativeSpinLock) {
ThreadedTest(&static_cooperative_spinlock);
}
TEST(SpinLockWithThreads, StaticNonCooperativeSpinLock) {
ThreadedTest(&static_noncooperative_spinlock);
}
TEST(SpinLockWithThreads, DoesNotDeadlock) {
struct Helper {
static void NotifyThenLock(Notification* locked, SpinLock* spinlock,
BlockingCounter* b) {
locked->WaitForNotification(); // Wait for LockThenWait() to hold "s".
b->DecrementCount();
SpinLockHolder l(spinlock);
}
static void LockThenWait(Notification* locked, SpinLock* spinlock,
BlockingCounter* b) {
SpinLockHolder l(spinlock);
locked->Notify();
b->Wait();
}
static void DeadlockTest(SpinLock* spinlock, int num_spinners) {
Notification locked;
BlockingCounter counter(num_spinners);
std::vector<std::thread> threads;
threads.push_back(
std::thread(Helper::LockThenWait, &locked, spinlock, &counter));
for (int i = 0; i < num_spinners; ++i) {
threads.push_back(
std::thread(Helper::NotifyThenLock, &locked, spinlock, &counter));
}
for (auto& thread : threads) {
thread.join();
}
}
};
SpinLock stack_cooperative_spinlock(
base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL);
SpinLock stack_noncooperative_spinlock(base_internal::SCHEDULE_KERNEL_ONLY);
Helper::DeadlockTest(&stack_cooperative_spinlock,
base_internal::NumCPUs() * 2);
Helper::DeadlockTest(&stack_noncooperative_spinlock,
base_internal::NumCPUs() * 2);
Helper::DeadlockTest(&static_cooperative_spinlock,
base_internal::NumCPUs() * 2);
Helper::DeadlockTest(&static_noncooperative_spinlock,
base_internal::NumCPUs() * 2);
}
} // namespace
} // namespace base_internal
} // namespace absl