/*
* Copyright (c) Meta Platforms, Inc. and affiliates.
*
* 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.
*/
#pragma once
#include <algorithm>
#include <condition_variable>
#include <functional>
#include <map>
#include <random>
#include <thread>
#include <vector>
#include <glog/logging.h>
#include <folly/Random.h>
#include <folly/Synchronized.h>
#include <folly/container/Foreach.h>
#include <folly/portability/GTest.h>
namespace folly {
namespace sync_tests {
void randomSleep(std::chrono::milliseconds min, std::chrono::milliseconds max) {
std::uniform_int_distribution<> range(min.count(), max.count());
folly::ThreadLocalPRNG prng;
std::chrono::milliseconds duration(range(prng));
/* sleep override */
std::this_thread::sleep_for(duration);
}
/*
* Run a functon simultaneously in a number of different threads.
*
* The function will be passed the index number of the thread it is running in.
* This function makes an attempt to synchronize the start of the threads as
* best as possible. It waits for all threads to be allocated and started
* before invoking the function.
*/
template <class Function>
void runParallel(size_t numThreads, const Function& function) {
std::vector<std::thread> threads;
threads.reserve(numThreads);
// Variables used to synchronize all threads to try and start them
// as close to the same time as possible
folly::Synchronized<size_t, std::mutex> threadsReady(0);
std::condition_variable readyCV;
folly::Synchronized<bool, std::mutex> go(false);
std::condition_variable goCV;
auto worker = [&](size_t threadIndex) {
// Signal that we are ready
++(*threadsReady.lock());
readyCV.notify_one();
// Wait until we are given the signal to start
// The purpose of this is to try and make sure all threads start
// as close to the same time as possible.
{
auto lockedGo = go.lock();
goCV.wait(lockedGo.as_lock(), [&] { return *lockedGo; });
}
function(threadIndex);
};
// Start all of the threads
for (size_t threadIndex = 0; threadIndex < numThreads; ++threadIndex) {
threads.emplace_back([threadIndex, &worker]() { worker(threadIndex); });
}
// Wait for all threads to become ready
{
auto readyLocked = threadsReady.lock();
readyCV.wait(
readyLocked.as_lock(), [&] { return *readyLocked == numThreads; });
}
// Now signal the threads that they can go
go = true;
goCV.notify_all();
// Wait for all threads to finish
for (auto& thread : threads) {
thread.join();
}
}
// testBasic() version for shared lock types
template <class Mutex>
std::enable_if_t<folly::detail::kSynchronizedMutexIsShared<void, Mutex>>
testBasicImpl() {
folly::Synchronized<std::vector<int>, Mutex> obj;
const auto& constObj = obj;
obj.wlock()->resize(1000);
folly::Synchronized<std::vector<int>, Mutex> obj2{*obj.wlock()};
EXPECT_EQ(1000, obj2.rlock()->size());
{
auto lockedObj = obj.wlock();
lockedObj->push_back(10);
EXPECT_EQ(1001, lockedObj->size());
EXPECT_EQ(10, lockedObj->back());
EXPECT_EQ(1000, obj2.wlock()->size());
EXPECT_EQ(1000, obj2.rlock()->size());
{
auto unlocker = lockedObj.scopedUnlock();
EXPECT_EQ(1001, obj.wlock()->size());
}
}
{
auto lockedObj = obj.rlock();
EXPECT_EQ(1001, lockedObj->size());
EXPECT_EQ(1001, obj.rlock()->size());
{
auto unlocker = lockedObj.scopedUnlock();
EXPECT_EQ(1001, obj.wlock()->size());
}
}
obj.wlock()->front() = 2;
{
// contextualLock() on a const reference should grab a shared lock
auto lockedObj = constObj.contextualLock();
EXPECT_EQ(2, lockedObj->front());
EXPECT_EQ(2, constObj.rlock()->front());
EXPECT_EQ(2, obj.rlock()->front());
}
EXPECT_EQ(1001, obj.rlock()->size());
EXPECT_EQ(2, obj.rlock()->front());
EXPECT_EQ(10, obj.rlock()->back());
EXPECT_EQ(1000, obj2.rlock()->size());
}
// testBasic() version for non-shared lock types
template <class Mutex>
std::enable_if_t<!folly::detail::kSynchronizedMutexIsShared<void, Mutex>>
testBasicImpl() {
folly::Synchronized<std::vector<int>, Mutex> obj;
const auto& constObj = obj;
obj.lock()->resize(1000);
folly::Synchronized<std::vector<int>, Mutex> obj2{*obj.lock()};
EXPECT_EQ(1000, obj2.lock()->size());
{
auto lockedObj = obj.lock();
lockedObj->push_back(10);
EXPECT_EQ(1001, lockedObj->size());
EXPECT_EQ(10, lockedObj->back());
EXPECT_EQ(1000, obj2.lock()->size());
{
auto unlocker = lockedObj.scopedUnlock();
EXPECT_EQ(1001, obj.lock()->size());
}
}
{
auto lockedObj = constObj.lock();
EXPECT_EQ(1001, lockedObj->size());
EXPECT_EQ(10, lockedObj->back());
EXPECT_EQ(1000, obj2.lock()->size());
}
obj.lock()->front() = 2;
EXPECT_EQ(1001, obj.lock()->size());
EXPECT_EQ(2, obj.lock()->front());
EXPECT_EQ(2, obj.contextualLock()->front());
EXPECT_EQ(10, obj.lock()->back());
EXPECT_EQ(1000, obj2.lock()->size());
}
template <class Mutex>
void testBasic() {
testBasicImpl<Mutex>();
}
// testWithLock() version for shared lock types
template <class Mutex>
std::enable_if_t<folly::detail::kSynchronizedMutexIsShared<void, Mutex>>
testWithLock() {
folly::Synchronized<std::vector<int>, Mutex> obj;
const auto& constObj = obj;
// Test withWLock() and withRLock()
obj.withWLock([](std::vector<int>& lockedObj) {
lockedObj.resize(1000);
lockedObj.push_back(10);
lockedObj.push_back(11);
});
obj.withWLock([](const std::vector<int>& lockedObj) {
EXPECT_EQ(1002, lockedObj.size());
});
constObj.withWLock([](const std::vector<int>& lockedObj) {
EXPECT_EQ(1002, lockedObj.size());
EXPECT_EQ(11, lockedObj.back());
});
obj.withRLock([](const std::vector<int>& lockedObj) {
EXPECT_EQ(1002, lockedObj.size());
EXPECT_EQ(11, lockedObj.back());
});
constObj.withRLock([](const std::vector<int>& lockedObj) {
EXPECT_EQ(1002, lockedObj.size());
});
obj.withWLock([](auto& lockedObj) { lockedObj.push_back(12); });
obj.withWLock(
[](const auto& lockedObj) { EXPECT_EQ(1003, lockedObj.size()); });
constObj.withWLock([](const auto& lockedObj) {
EXPECT_EQ(1003, lockedObj.size());
EXPECT_EQ(12, lockedObj.back());
});
obj.withRLock([](const auto& lockedObj) {
EXPECT_EQ(1003, lockedObj.size());
EXPECT_EQ(12, lockedObj.back());
});
constObj.withRLock(
[](const auto& lockedObj) { EXPECT_EQ(1003, lockedObj.size()); });
obj.withWLock([](auto& lockedObj) { lockedObj.pop_back(); });
// Test withWLockPtr() and withRLockPtr()
using SynchType = folly::Synchronized<std::vector<int>, Mutex>;
obj.withWLockPtr([](auto&& lockedObj) { lockedObj->push_back(13); });
obj.withRLockPtr([](auto&& lockedObj) {
EXPECT_EQ(1003, lockedObj->size());
EXPECT_EQ(13, lockedObj->back());
});
constObj.withRLockPtr([](auto&& lockedObj) {
EXPECT_EQ(1003, lockedObj->size());
EXPECT_EQ(13, lockedObj->back());
});
obj.withWLockPtr([&](auto&& lockedObj) {
lockedObj->push_back(14);
{
auto unlocker = lockedObj.scopedUnlock();
obj.wlock()->push_back(15);
}
EXPECT_EQ(15, lockedObj->back());
});
constObj.withWLockPtr([](auto&& lockedObj) {
EXPECT_EQ(1005, lockedObj->size());
EXPECT_EQ(15, lockedObj->back());
});
obj.withWLockPtr([](typename SynchType::LockedPtr&& lockedObj) {
lockedObj->push_back(16);
EXPECT_EQ(1006, lockedObj->size());
});
constObj.withWLockPtr([](typename SynchType::ConstWLockedPtr&& lockedObj) {
EXPECT_EQ(1006, lockedObj->size());
EXPECT_EQ(16, lockedObj->back());
});
obj.withRLockPtr([](typename SynchType::RLockedPtr&& lockedObj) {
EXPECT_TRUE(
(std::is_const<std::remove_reference_t<decltype(*lockedObj)>>{}));
EXPECT_EQ(1006, lockedObj->size());
EXPECT_EQ(16, lockedObj->back());
});
constObj.withRLockPtr([](typename SynchType::ConstRLockedPtr&& lockedObj) {
EXPECT_TRUE(
(std::is_const<std::remove_reference_t<decltype(*lockedObj)>>{}));
EXPECT_EQ(1006, lockedObj->size());
EXPECT_EQ(16, lockedObj->back());
});
}
// testWithLock() version for non-shared lock types
template <class Mutex>
std::enable_if_t<!folly::detail::kSynchronizedMutexIsShared<void, Mutex>>
testWithLock() {
folly::Synchronized<std::vector<int>, Mutex> obj;
// Test withLock()
obj.withLock([](std::vector<int>& lockedObj) {
lockedObj.resize(1000);
lockedObj.push_back(10);
lockedObj.push_back(11);
});
obj.withLock([](const std::vector<int>& lockedObj) {
EXPECT_EQ(1002, lockedObj.size());
});
obj.withLock([](auto& lockedObj) { lockedObj.push_back(12); });
obj.withLock(
[](const auto& lockedObj) { EXPECT_EQ(1003, lockedObj.size()); });
obj.withLock([](auto& lockedObj) { lockedObj.pop_back(); });
// Test withLockPtr()
using SynchType = folly::Synchronized<std::vector<int>, Mutex>;
obj.withLockPtr([](auto&& lockedObj) { lockedObj->push_back(13); });
obj.withLockPtr([](auto&& lockedObj) {
EXPECT_EQ(1003, lockedObj->size());
EXPECT_EQ(13, lockedObj->back());
});
obj.withLockPtr([&](auto&& lockedObj) {
lockedObj->push_back(14);
{
auto unlocker = lockedObj.scopedUnlock();
obj.lock()->push_back(15);
}
EXPECT_EQ(1005, lockedObj->size());
EXPECT_EQ(15, lockedObj->back());
});
obj.withLockPtr([](typename SynchType::LockedPtr&& lockedObj) {
lockedObj->push_back(16);
EXPECT_EQ(1006, lockedObj->size());
});
const auto& constObj = obj;
constObj.withLockPtr([](typename SynchType::ConstLockedPtr&& lockedObj) {
EXPECT_EQ(1006, lockedObj->size());
EXPECT_EQ(16, lockedObj->back());
});
}
template <class Mutex>
void testUnlockCommon() {
folly::Synchronized<int, Mutex> value{7};
const auto& cv = value;
{
auto lv = value.contextualLock();
EXPECT_EQ(7, *lv);
*lv = 5;
lv.unlock();
EXPECT_TRUE(lv.isNull());
EXPECT_FALSE(lv);
auto rlv = cv.contextualLock();
EXPECT_EQ(5, *rlv);
rlv.unlock();
EXPECT_TRUE(rlv.isNull());
EXPECT_FALSE(rlv);
auto rlv2 = cv.contextualRLock();
EXPECT_EQ(5, *rlv2);
rlv2.unlock();
lv = value.contextualLock();
EXPECT_EQ(5, *lv);
*lv = 9;
}
EXPECT_EQ(9, *value.contextualRLock());
}
// testUnlock() version for shared lock types
template <class Mutex>
std::enable_if_t<folly::detail::kSynchronizedMutexIsShared<void, Mutex>>
testUnlock() {
folly::Synchronized<int, Mutex> value{10};
{
auto lv = value.wlock();
EXPECT_EQ(10, *lv);
*lv = 5;
lv.unlock();
EXPECT_FALSE(lv);
EXPECT_TRUE(lv.isNull());
auto rlv = value.rlock();
EXPECT_EQ(5, *rlv);
rlv.unlock();
EXPECT_FALSE(rlv);
EXPECT_TRUE(rlv.isNull());
auto lv2 = value.wlock();
EXPECT_EQ(5, *lv2);
*lv2 = 7;
lv = std::move(lv2);
EXPECT_FALSE(lv2);
EXPECT_TRUE(lv2.isNull());
EXPECT_FALSE(lv.isNull());
EXPECT_EQ(7, *lv);
}
testUnlockCommon<Mutex>();
}
// testUnlock() version for non-shared lock types
template <class Mutex>
std::enable_if_t<!folly::detail::kSynchronizedMutexIsShared<void, Mutex>>
testUnlock() {
folly::Synchronized<int, Mutex> value{10};
{
auto lv = value.lock();
EXPECT_EQ(10, *lv);
*lv = 5;
lv.unlock();
EXPECT_TRUE(lv.isNull());
EXPECT_FALSE(lv);
auto lv2 = value.lock();
EXPECT_EQ(5, *lv2);
*lv2 = 6;
lv2.unlock();
EXPECT_TRUE(lv2.isNull());
EXPECT_FALSE(lv2);
lv = value.lock();
EXPECT_EQ(6, *lv);
*lv = 7;
lv2 = std::move(lv);
EXPECT_TRUE(lv.isNull());
EXPECT_FALSE(lv);
EXPECT_FALSE(lv2.isNull());
EXPECT_EQ(7, *lv2);
}
testUnlockCommon<Mutex>();
}
// Testing the deprecated SYNCHRONIZED and SYNCHRONIZED_CONST APIs
template <class Mutex>
[[deprecated]] void testDeprecated() {
folly::Synchronized<std::vector<int>, Mutex> obj;
obj.contextualLock()->resize(1000);
auto obj2 = obj;
EXPECT_EQ(1000, obj2.contextualLock()->size());
SYNCHRONIZED(obj) {
obj.push_back(10);
EXPECT_EQ(1001, obj.size());
EXPECT_EQ(10, obj.back());
EXPECT_EQ(1000, obj2.contextualLock()->size());
}
SYNCHRONIZED_CONST(obj) {
EXPECT_EQ(1001, obj.size());
}
SYNCHRONIZED(lockedObj, *&obj) {
lockedObj.front() = 2;
}
EXPECT_EQ(1001, obj.contextualLock()->size());
EXPECT_EQ(10, obj.contextualLock()->back());
EXPECT_EQ(1000, obj2.contextualLock()->size());
EXPECT_EQ(FB_ARG_2_OR_1(1, 2), 2);
EXPECT_EQ(FB_ARG_2_OR_1(1), 1);
}
template <class Mutex>
void testConcurrency() {
folly::Synchronized<std::vector<int>, Mutex> v;
static const size_t numThreads = 100;
// Note: I initially tried using itersPerThread = 1000,
// which works fine for most lock types, but std::shared_timed_mutex
// appears to be extraordinarily slow. It could take around 30 seconds
// to run this test with 1000 iterations per thread using shared_timed_mutex.
static const size_t itersPerThread = 100;
auto pushNumbers = [&](size_t threadIdx) {
// Test lock()
for (size_t n = 0; n < itersPerThread; ++n) {
v.contextualLock()->push_back((itersPerThread * threadIdx) + n);
std::this_thread::yield();
}
};
runParallel(numThreads, pushNumbers);
std::vector<int> result;
v.swap(result);
EXPECT_EQ(numThreads * itersPerThread, result.size());
sort(result.begin(), result.end());
for (size_t i = 0; i < itersPerThread * numThreads; ++i) {
EXPECT_EQ(i, result[i]);
}
}
template <class Mutex>
void testAcquireLocked() {
folly::Synchronized<std::vector<int>, Mutex> v;
folly::Synchronized<std::map<int, int>, Mutex> m;
auto dualLockWorker = [&](size_t threadIdx) {
// Note: this will be less awkward with C++ 17's structured
// binding functionality, which will make it easier to use the returned
// std::tuple.
if (threadIdx & 1) {
auto ret = acquireLocked(v, m);
std::get<0>(ret)->push_back(threadIdx);
(*std::get<1>(ret))[threadIdx] = threadIdx + 1;
} else {
auto ret = acquireLocked(m, v);
std::get<1>(ret)->push_back(threadIdx);
(*std::get<0>(ret))[threadIdx] = threadIdx + 1;
}
};
static const size_t numThreads = 100;
runParallel(numThreads, dualLockWorker);
std::vector<int> result;
v.swap(result);
EXPECT_EQ(numThreads, result.size());
sort(result.begin(), result.end());
for (size_t i = 0; i < numThreads; ++i) {
EXPECT_EQ(i, result[i]);
}
}
template <class Mutex>
void testAcquireLockedWithConst() {
folly::Synchronized<std::vector<int>, Mutex> v;
folly::Synchronized<std::map<int, int>, Mutex> m;
auto dualLockWorker = [&](size_t threadIdx) {
const auto& cm = m;
if (threadIdx & 1) {
auto ret = acquireLocked(v, cm);
(void)std::get<1>(ret)->size();
std::get<0>(ret)->push_back(threadIdx);
} else {
auto ret = acquireLocked(cm, v);
(void)std::get<0>(ret)->size();
std::get<1>(ret)->push_back(threadIdx);
}
};
static const size_t numThreads = 100;
runParallel(numThreads, dualLockWorker);
std::vector<int> result;
v.swap(result);
EXPECT_EQ(numThreads, result.size());
sort(result.begin(), result.end());
for (size_t i = 0; i < numThreads; ++i) {
EXPECT_EQ(i, result[i]);
}
}
// Testing the deprecated SYNCHRONIZED_DUAL API
template <class Mutex>
[[deprecated]] void testDualLocking() {
folly::Synchronized<std::vector<int>, Mutex> v;
folly::Synchronized<std::map<int, int>, Mutex> m;
auto dualLockWorker = [&](size_t threadIdx) {
if (threadIdx & 1) {
SYNCHRONIZED_DUAL(lv, v, lm, m) {
lv.push_back(threadIdx);
lm[threadIdx] = threadIdx + 1;
}
} else {
SYNCHRONIZED_DUAL(lm, m, lv, v) {
lv.push_back(threadIdx);
lm[threadIdx] = threadIdx + 1;
}
}
};
static const size_t numThreads = 100;
runParallel(numThreads, dualLockWorker);
std::vector<int> result;
v.swap(result);
EXPECT_EQ(numThreads, result.size());
sort(result.begin(), result.end());
for (size_t i = 0; i < numThreads; ++i) {
EXPECT_EQ(i, result[i]);
}
}
// Testing the deprecated SYNCHRONIZED_DUAL API
template <class Mutex>
[[deprecated]] void testDualLockingWithConst() {
folly::Synchronized<std::vector<int>, Mutex> v;
folly::Synchronized<std::map<int, int>, Mutex> m;
auto dualLockWorker = [&](size_t threadIdx) {
const auto& cm = m;
if (threadIdx & 1) {
SYNCHRONIZED_DUAL(lv, v, lm, cm) {
(void)lm.size();
lv.push_back(threadIdx);
}
} else {
SYNCHRONIZED_DUAL(lm, cm, lv, v) {
(void)lm.size();
lv.push_back(threadIdx);
}
}
};
static const size_t numThreads = 100;
runParallel(numThreads, dualLockWorker);
std::vector<int> result;
v.swap(result);
EXPECT_EQ(numThreads, result.size());
sort(result.begin(), result.end());
for (size_t i = 0; i < numThreads; ++i) {
EXPECT_EQ(i, result[i]);
}
}
template <class Mutex>
void testTimed() {
folly::Synchronized<std::vector<int>, Mutex> v;
folly::Synchronized<uint64_t, Mutex> numTimeouts{0};
auto worker = [&](size_t threadIdx) {
// Test directly using operator-> on the lock result
v.contextualLock()->push_back(2 * threadIdx);
// Test using lock with a timeout
for (;;) {
auto lv = v.contextualLock(std::chrono::milliseconds(5));
if (!lv) {
++(*numTimeouts.contextualLock());
continue;
}
// Sleep for a random time to ensure we trigger timeouts
// in other threads
randomSleep(std::chrono::milliseconds(5), std::chrono::milliseconds(15));
lv->push_back(2 * threadIdx + 1);
break;
}
};
static const size_t numThreads = 100;
runParallel(numThreads, worker);
std::vector<int> result;
v.swap(result);
EXPECT_EQ(2 * numThreads, result.size());
sort(result.begin(), result.end());
for (size_t i = 0; i < 2 * numThreads; ++i) {
EXPECT_EQ(i, result[i]);
}
// We generally expect a large number of number timeouts here.
// I'm not adding a check for it since it's theoretically possible that
// we might get 0 timeouts depending on the CPU scheduling if our threads
// don't get to run very often.
LOG(INFO) << "testTimed: " << *numTimeouts.contextualRLock() << " timeouts";
// Make sure we can lock with various timeout duration units
{
auto lv = v.contextualLock(std::chrono::milliseconds(5));
EXPECT_TRUE(bool(lv));
EXPECT_FALSE(lv.isNull());
auto lv2 = v.contextualLock(std::chrono::microseconds(5));
// We may or may not acquire lv2 successfully, depending on whether
// or not this is a recursive mutex type.
}
{
auto lv = v.contextualLock(std::chrono::seconds(1));
EXPECT_TRUE(bool(lv));
}
}
template <class Mutex>
void testTimedShared() {
folly::Synchronized<std::vector<int>, Mutex> v;
folly::Synchronized<uint64_t, Mutex> numTimeouts{0};
auto worker = [&](size_t threadIdx) {
// Test directly using operator-> on the lock result
v.wlock()->push_back(threadIdx);
// Test lock() with a timeout
for (;;) {
auto lv = v.rlock(std::chrono::milliseconds(10));
if (!lv) {
++(*numTimeouts.contextualLock());
continue;
}
// Sleep while holding the lock.
//
// This will block other threads from acquiring the write lock to add
// their thread index to v, but it won't block threads that have entered
// the for loop and are trying to acquire a read lock.
//
// For lock types that give preference to readers rather than writers,
// this will tend to serialize all threads on the wlock() above.
randomSleep(std::chrono::milliseconds(5), std::chrono::milliseconds(15));
auto found = std::find(lv->begin(), lv->end(), threadIdx);
CHECK(found != lv->end());
break;
}
};
static const size_t numThreads = 100;
runParallel(numThreads, worker);
std::vector<int> result;
v.swap(result);
EXPECT_EQ(numThreads, result.size());
sort(result.begin(), result.end());
for (size_t i = 0; i < numThreads; ++i) {
EXPECT_EQ(i, result[i]);
}
// We generally expect a small number of timeouts here.
// For locks that give readers preference over writers this should usually
// be 0. With locks that give writers preference we do see a small-ish
// number of read timeouts.
LOG(INFO) << "testTimedShared: " << *numTimeouts.contextualRLock()
<< " timeouts";
}
template <class Mutex>
void testConstCopy() {
std::vector<int> input = {1, 2, 3};
const folly::Synchronized<std::vector<int>, Mutex> v(input);
std::vector<int> result;
v.copyInto(result);
EXPECT_EQ(input, result);
result = v.copy();
EXPECT_EQ(input, result);
}
struct NotCopiableNotMovable {
NotCopiableNotMovable(int, const char*) {}
NotCopiableNotMovable(const NotCopiableNotMovable&) = delete;
NotCopiableNotMovable& operator=(const NotCopiableNotMovable&) = delete;
NotCopiableNotMovable(NotCopiableNotMovable&&) = delete;
NotCopiableNotMovable& operator=(NotCopiableNotMovable&&) = delete;
};
template <class Mutex>
void testInPlaceConstruction() {
// This won't compile without std::in_place
folly::Synchronized<NotCopiableNotMovable> a(std::in_place, 5, "a");
}
template <class Mutex>
void testExchange() {
std::vector<int> input = {1, 2, 3};
folly::Synchronized<std::vector<int>, Mutex> v(input);
std::vector<int> next = {4, 5, 6};
auto prev = v.exchange(std::move(next));
EXPECT_EQ((std::vector<int>{{1, 2, 3}}), prev);
EXPECT_EQ((std::vector<int>{{4, 5, 6}}), v.copy());
}
} // namespace sync_tests
} // namespace folly
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