void SingletonVault::scheduleDestroyInstances() {
// Add a dependency on folly::ThreadLocal to make sure all its static
// singletons are initalized first.
- threadlocal_detail::StaticMeta<void>::instance();
+ threadlocal_detail::StaticMeta<void, void>::instance();
class SingletonVaultDestructor {
public:
// Reads the current value plus all the cached increments. Requires grabbing
// a lock, so this is significantly slower than readFast().
IntT readFull() const {
+ // This could race with thread destruction and so the access lock should be
+ // acquired before reading the current value
+ auto accessor = cache_.accessAllThreads();
IntT ret = readFast();
- for (const auto& cache : cache_.accessAllThreads()) {
+ for (const auto& cache : accessor) {
if (!cache.reset_.load(std::memory_order_acquire)) {
ret += cache.val_.load(std::memory_order_relaxed);
}
// little off, however, but it should be much better than calling readFull()
// and set(0) sequentially.
IntT readFullAndReset() {
+ // This could race with thread destruction and so the access lock should be
+ // acquired before reading the current value
+ auto accessor = cache_.accessAllThreads();
IntT ret = readFastAndReset();
- for (auto& cache : cache_.accessAllThreads()) {
+ for (auto& cache : accessor) {
if (!cache.reset_.load(std::memory_order_acquire)) {
ret += cache.val_.load(std::memory_order_relaxed);
cache.reset_.store(true, std::memory_order_release);
private:
std::atomic<IntT> target_;
std::atomic<uint32_t> cacheSize_;
- ThreadLocalPtr<IntCache,Tag> cache_; // Must be last for dtor ordering
+ ThreadLocalPtr<IntCache, Tag, AccessModeStrict>
+ cache_; // Must be last for dtor ordering
// This should only ever be modified by one thread
struct IntCache {
* objects of a parent. accessAllThreads() initializes an accessor which holds
* a global lock *that blocks all creation and destruction of ThreadLocal
* objects with the same Tag* and can be used as an iterable container.
+ * accessAllThreads() can race with destruction of thread-local elements. We
+ * provide a strict mode which is dangerous because it requires the access lock
+ * to be held while destroying thread-local elements which could cause
+ * deadlocks. We gate this mode behind the AccessModeStrict template parameter.
*
* Intended use is for frequent write, infrequent read data access patterns such
* as counters.
#pragma once
+#include <boost/iterator/iterator_facade.hpp>
#include <folly/Likely.h>
#include <folly/Portability.h>
#include <folly/ScopeGuard.h>
-#include <boost/iterator/iterator_facade.hpp>
+#include <folly/SharedMutex.h>
#include <type_traits>
#include <utility>
THIS_THREAD,
ALL_THREADS
};
+struct AccessModeStrict {};
} // namespace
#include <folly/detail/ThreadLocalDetail.h>
namespace folly {
-template<class T, class Tag> class ThreadLocalPtr;
+template <class T, class Tag, class AccessMode>
+class ThreadLocalPtr;
-template<class T, class Tag=void>
+template <class T, class Tag = void, class AccessMode = void>
class ThreadLocal {
public:
constexpr ThreadLocal() : constructor_([]() {
tlp_.reset(newPtr);
}
- typedef typename ThreadLocalPtr<T,Tag>::Accessor Accessor;
+ typedef typename ThreadLocalPtr<T, Tag, AccessMode>::Accessor Accessor;
Accessor accessAllThreads() const {
return tlp_.accessAllThreads();
}
return ptr;
}
- mutable ThreadLocalPtr<T,Tag> tlp_;
+ mutable ThreadLocalPtr<T, Tag, AccessMode> tlp_;
std::function<T*()> constructor_;
};
* with __declspec(thread)
*/
-template<class T, class Tag=void>
+template <class T, class Tag = void, class AccessMode = void>
class ThreadLocalPtr {
private:
- typedef threadlocal_detail::StaticMeta<Tag> StaticMeta;
+ typedef threadlocal_detail::StaticMeta<Tag, AccessMode> StaticMeta;
+
public:
constexpr ThreadLocalPtr() : id_() {}
// Can be used as an iterable container.
// Use accessAllThreads() to obtain one.
class Accessor {
- friend class ThreadLocalPtr<T,Tag>;
+ friend class ThreadLocalPtr<T, Tag, AccessMode>;
threadlocal_detail::StaticMetaBase& meta_;
+ SharedMutex* accessAllThreadsLock_;
std::mutex* lock_;
uint32_t id_;
Accessor& operator=(const Accessor&) = delete;
Accessor(Accessor&& other) noexcept
- : meta_(other.meta_),
- lock_(other.lock_),
- id_(other.id_) {
+ : meta_(other.meta_),
+ accessAllThreadsLock_(other.accessAllThreadsLock_),
+ lock_(other.lock_),
+ id_(other.id_) {
other.id_ = 0;
+ other.accessAllThreadsLock_ = nullptr;
other.lock_ = nullptr;
}
assert(&meta_ == &other.meta_);
assert(lock_ == nullptr);
using std::swap;
+ swap(accessAllThreadsLock_, other.accessAllThreadsLock_);
swap(lock_, other.lock_);
swap(id_, other.id_);
}
Accessor()
- : meta_(threadlocal_detail::StaticMeta<Tag>::instance()),
- lock_(nullptr),
- id_(0) {
- }
+ : meta_(threadlocal_detail::StaticMeta<Tag, AccessMode>::instance()),
+ accessAllThreadsLock_(nullptr),
+ lock_(nullptr),
+ id_(0) {}
private:
explicit Accessor(uint32_t id)
- : meta_(threadlocal_detail::StaticMeta<Tag>::instance()),
- lock_(&meta_.lock_) {
+ : meta_(threadlocal_detail::StaticMeta<Tag, AccessMode>::instance()),
+ accessAllThreadsLock_(&meta_.accessAllThreadsLock_),
+ lock_(&meta_.lock_) {
+ accessAllThreadsLock_->lock();
lock_->lock();
id_ = id;
}
void release() {
if (lock_) {
lock_->unlock();
+ DCHECK(accessAllThreadsLock_ != nullptr);
+ accessAllThreadsLock_->unlock();
id_ = 0;
lock_ = nullptr;
+ accessAllThreadsLock_ = nullptr;
}
}
};
namespace folly { namespace threadlocal_detail {
-StaticMetaBase::StaticMetaBase(ThreadEntry* (*threadEntry)())
- : nextId_(1), threadEntry_(threadEntry) {
+StaticMetaBase::StaticMetaBase(ThreadEntry* (*threadEntry)(), bool strict)
+ : nextId_(1), threadEntry_(threadEntry), strict_(strict) {
head_.next = head_.prev = &head_;
int ret = pthread_key_create(&pthreadKey_, &onThreadExit);
checkPosixError(ret, "pthread_key_create failed");
};
{
- std::lock_guard<std::mutex> g(meta.lock_);
- meta.erase(&(*threadEntry));
- // No need to hold the lock any longer; the ThreadEntry is private to this
- // thread now that it's been removed from meta.
- }
- // NOTE: User-provided deleter / object dtor itself may be using ThreadLocal
- // with the same Tag, so dispose() calls below may (re)create some of the
- // elements or even increase elementsCapacity, thus multiple cleanup rounds
- // may be required.
- for (bool shouldRun = true; shouldRun;) {
- shouldRun = false;
- FOR_EACH_RANGE (i, 0, threadEntry->elementsCapacity) {
- if (threadEntry->elements[i].dispose(TLPDestructionMode::THIS_THREAD)) {
- shouldRun = true;
+ SharedMutex::ReadHolder rlock;
+ if (meta.strict_) {
+ rlock = SharedMutex::ReadHolder(meta.accessAllThreadsLock_);
+ }
+ {
+ std::lock_guard<std::mutex> g(meta.lock_);
+ meta.erase(&(*threadEntry));
+ // No need to hold the lock any longer; the ThreadEntry is private to this
+ // thread now that it's been removed from meta.
+ }
+ // NOTE: User-provided deleter / object dtor itself may be using ThreadLocal
+ // with the same Tag, so dispose() calls below may (re)create some of the
+ // elements or even increase elementsCapacity, thus multiple cleanup rounds
+ // may be required.
+ for (bool shouldRun = true; shouldRun;) {
+ shouldRun = false;
+ FOR_EACH_RANGE (i, 0, threadEntry->elementsCapacity) {
+ if (threadEntry->elements[i].dispose(TLPDestructionMode::THIS_THREAD)) {
+ shouldRun = true;
+ }
}
}
}
}
};
- explicit StaticMetaBase(ThreadEntry* (*threadEntry)());
+ StaticMetaBase(ThreadEntry* (*threadEntry)(), bool strict);
~StaticMetaBase() {
LOG(FATAL) << "StaticMeta lives forever!";
uint32_t nextId_;
std::vector<uint32_t> freeIds_;
std::mutex lock_;
+ SharedMutex accessAllThreadsLock_;
pthread_key_t pthreadKey_;
ThreadEntry head_;
ThreadEntry* (*threadEntry_)();
+ bool strict_;
};
// Held in a singleton to track our global instances.
// Creating and destroying ThreadLocalPtr objects, as well as thread exit
// for threads that use ThreadLocalPtr objects collide on a lock inside
// StaticMeta; you can specify multiple Tag types to break that lock.
-template <class Tag>
+template <class Tag, class AccessMode>
struct StaticMeta : StaticMetaBase {
- StaticMeta() : StaticMetaBase(&StaticMeta::getThreadEntrySlow) {
+ StaticMeta()
+ : StaticMetaBase(
+ &StaticMeta::getThreadEntrySlow,
+ std::is_same<AccessMode, AccessModeStrict>::value) {
registerAtFork(
/*prepare*/ &StaticMeta::preFork,
/*parent*/ &StaticMeta::onForkParent,
/*child*/ &StaticMeta::onForkChild);
}
- static StaticMeta<Tag>& instance() {
+ static StaticMeta<Tag, AccessMode>& instance() {
// Leak it on exit, there's only one per process and we don't have to
// worry about synchronization with exiting threads.
- static auto instance = detail::createGlobal<StaticMeta<Tag>, void>();
+ static auto instance =
+ detail::createGlobal<StaticMeta<Tag, AccessMode>, void>();
return *instance;
}
#include <folly/ThreadCachedInt.h>
#include <atomic>
+#include <condition_variable>
#include <thread>
#include <glog/logging.h>
using namespace folly;
+using std::unique_ptr;
+using std::vector;
+
+using Counter = ThreadCachedInt<int64_t>;
+
+class ThreadCachedIntTest : public testing::Test {
+ public:
+ uint32_t GetDeadThreadsTotal(const Counter& counter) {
+ return counter.readFast();
+ }
+};
+
+// Multithreaded tests. Creates a specified number of threads each of
+// which iterates a different amount and dies.
+
+namespace {
+// Set cacheSize to be large so cached data moves to target_ only when
+// thread dies.
+Counter g_counter_for_mt_slow(0, UINT32_MAX);
+Counter g_counter_for_mt_fast(0, UINT32_MAX);
+
+// Used to sync between threads. The value of this variable is the
+// maximum iteration index upto which Runner() is allowed to go.
+uint32_t g_sync_for_mt(0);
+std::condition_variable cv;
+std::mutex cv_m;
+
+// Performs the specified number of iterations. Within each
+// iteration, it increments counter 10 times. At the beginning of
+// each iteration it checks g_sync_for_mt to see if it can proceed,
+// otherwise goes into a loop sleeping and rechecking.
+void Runner(Counter* counter, uint32_t iterations) {
+ for (uint32_t i = 0; i < iterations; ++i) {
+ std::unique_lock<std::mutex> lk(cv_m);
+ cv.wait(lk, [i] { return i < g_sync_for_mt; });
+ for (uint32_t j = 0; j < 10; ++j) {
+ counter->increment(1);
+ }
+ }
+}
+}
+
+// Slow test with fewer threads where there are more busy waits and
+// many calls to readFull(). This attempts to test as many of the
+// code paths in Counter as possible to ensure that counter values are
+// properly passed from thread local state, both at calls to
+// readFull() and at thread death.
+TEST_F(ThreadCachedIntTest, MultithreadedSlow) {
+ static constexpr uint32_t kNumThreads = 20;
+ g_sync_for_mt = 0;
+ vector<unique_ptr<std::thread>> threads(kNumThreads);
+ // Creates kNumThreads threads. Each thread performs a different
+ // number of iterations in Runner() - threads[0] performs 1
+ // iteration, threads[1] performs 2 iterations, threads[2] performs
+ // 3 iterations, and so on.
+ for (uint32_t i = 0; i < kNumThreads; ++i) {
+ threads[i].reset(new std::thread(Runner, &g_counter_for_mt_slow, i + 1));
+ }
+ // Variable to grab current counter value.
+ int32_t counter_value;
+ // The expected value of the counter.
+ int32_t total = 0;
+ // The expected value of GetDeadThreadsTotal().
+ int32_t dead_total = 0;
+ // Each iteration of the following thread allows one additional
+ // iteration of the threads. Given that the threads perform
+ // different number of iterations from 1 through kNumThreads, one
+ // thread will complete in each of the iterations of the loop below.
+ for (uint32_t i = 0; i < kNumThreads; ++i) {
+ // Allow upto iteration i on all threads.
+ {
+ std::lock_guard<std::mutex> lk(cv_m);
+ g_sync_for_mt = i + 1;
+ }
+ cv.notify_all();
+ total += (kNumThreads - i) * 10;
+ // Loop until the counter reaches its expected value.
+ do {
+ counter_value = g_counter_for_mt_slow.readFull();
+ } while (counter_value < total);
+ // All threads have done what they can until iteration i, now make
+ // sure they don't go further by checking 10 more times in the
+ // following loop.
+ for (uint32_t j = 0; j < 10; ++j) {
+ counter_value = g_counter_for_mt_slow.readFull();
+ EXPECT_EQ(total, counter_value);
+ }
+ dead_total += (i + 1) * 10;
+ EXPECT_GE(dead_total, GetDeadThreadsTotal(g_counter_for_mt_slow));
+ }
+ // All threads are done.
+ for (uint32_t i = 0; i < kNumThreads; ++i) {
+ threads[i]->join();
+ }
+ counter_value = g_counter_for_mt_slow.readFull();
+ EXPECT_EQ(total, counter_value);
+ EXPECT_EQ(total, dead_total);
+ EXPECT_EQ(dead_total, GetDeadThreadsTotal(g_counter_for_mt_slow));
+}
+
+// Fast test with lots of threads and only one call to readFull()
+// at the end.
+TEST_F(ThreadCachedIntTest, MultithreadedFast) {
+ static constexpr uint32_t kNumThreads = 1000;
+ g_sync_for_mt = 0;
+ vector<unique_ptr<std::thread>> threads(kNumThreads);
+ // Creates kNumThreads threads. Each thread performs a different
+ // number of iterations in Runner() - threads[0] performs 1
+ // iteration, threads[1] performs 2 iterations, threads[2] performs
+ // 3 iterations, and so on.
+ for (uint32_t i = 0; i < kNumThreads; ++i) {
+ threads[i].reset(new std::thread(Runner, &g_counter_for_mt_fast, i + 1));
+ }
+ // Let the threads run to completion.
+ {
+ std::lock_guard<std::mutex> lk(cv_m);
+ g_sync_for_mt = kNumThreads;
+ }
+ cv.notify_all();
+ // The expected value of the counter.
+ uint32_t total = 0;
+ for (uint32_t i = 0; i < kNumThreads; ++i) {
+ total += (kNumThreads - i) * 10;
+ }
+ // Wait for all threads to complete.
+ for (uint32_t i = 0; i < kNumThreads; ++i) {
+ threads[i]->join();
+ }
+ int32_t counter_value = g_counter_for_mt_fast.readFull();
+ EXPECT_EQ(total, counter_value);
+ EXPECT_EQ(total, GetDeadThreadsTotal(g_counter_for_mt_fast));
+}
+
TEST(ThreadCachedInt, SingleThreadedNotCached) {
ThreadCachedInt<int64_t> val(0, 0);
EXPECT_EQ(0, val.readFast());
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