2 * Copyright 2017 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
22 template <typename Tag, typename VaultTag>
23 SingletonHolder<T>& SingletonHolder<T>::singleton() {
24 /* library-local */ static auto entry =
25 createGlobal<SingletonHolder<T>, std::pair<Tag, VaultTag>>([]() {
26 return new SingletonHolder<T>({typeid(T), typeid(Tag)},
27 *SingletonVault::singleton<VaultTag>());
32 [[noreturn]] void singletonWarnDoubleRegistrationAndAbort(
33 const TypeDescriptor& type);
36 void SingletonHolder<T>::registerSingleton(CreateFunc c, TeardownFunc t) {
37 std::lock_guard<std::mutex> entry_lock(mutex_);
39 if (state_ != SingletonHolderState::NotRegistered) {
42 * You have two instances of the same
43 * folly::Singleton<Class>. Probably because you define the
44 * singleton in a header included in multiple places? In general,
45 * folly::Singleton shouldn't be in the header, only off in some
46 * anonymous namespace in a cpp file. Code needing the singleton
47 * will find it when that code references folly::Singleton<Class>.
49 * Alternatively, you could have 2 singletons with the same type
50 * defined with a different name in a .cpp (source) file. For
53 * Singleton<int> a([] { return new int(3); });
54 * Singleton<int> b([] { return new int(4); });
57 singletonWarnDoubleRegistrationAndAbort(type());
60 create_ = std::move(c);
61 teardown_ = std::move(t);
63 state_ = SingletonHolderState::Dead;
67 void SingletonHolder<T>::registerSingletonMock(CreateFunc c, TeardownFunc t) {
68 if (state_ == SingletonHolderState::NotRegistered) {
69 LOG(FATAL) << "Registering mock before singleton was registered: "
72 if (state_ == SingletonHolderState::Living) {
77 auto creationOrder = vault_.creationOrder_.wlock();
79 auto it = std::find(creationOrder->begin(), creationOrder->end(), type());
80 if (it != creationOrder->end()) {
81 creationOrder->erase(it);
85 std::lock_guard<std::mutex> entry_lock(mutex_);
87 create_ = std::move(c);
88 teardown_ = std::move(t);
92 T* SingletonHolder<T>::get() {
93 if (LIKELY(state_.load(std::memory_order_acquire) ==
94 SingletonHolderState::Living)) {
99 if (instance_weak_.expired()) {
100 throw std::runtime_error(
101 "Raw pointer to a singleton requested after its destruction."
102 " Singleton type is: " +
106 return instance_ptr_;
109 template <typename T>
110 std::weak_ptr<T> SingletonHolder<T>::get_weak() {
111 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
112 SingletonHolderState::Living)) {
116 return instance_weak_;
119 template <typename T>
120 std::shared_ptr<T> SingletonHolder<T>::try_get() {
121 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
122 SingletonHolderState::Living)) {
126 return instance_weak_.lock();
129 template <typename T>
130 folly::ReadMostlySharedPtr<T> SingletonHolder<T>::try_get_fast() {
131 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
132 SingletonHolderState::Living)) {
136 return instance_weak_fast_.lock();
139 template <typename T>
140 bool SingletonHolder<T>::hasLiveInstance() {
141 return !instance_weak_.expired();
144 template <typename T>
145 void SingletonHolder<T>::preDestroyInstance(
146 ReadMostlyMainPtrDeleter<>& deleter) {
147 instance_copy_ = instance_;
148 deleter.add(std::move(instance_));
151 template <typename T>
152 void SingletonHolder<T>::destroyInstance() {
153 state_ = SingletonHolderState::Dead;
155 instance_copy_.reset();
156 if (destroy_baton_) {
157 constexpr std::chrono::seconds kDestroyWaitTime{5};
158 auto last_reference_released = destroy_baton_->timed_wait(
159 std::chrono::steady_clock::now() + kDestroyWaitTime);
160 if (last_reference_released) {
161 teardown_(instance_ptr_);
163 print_destructor_stack_trace_->store(true);
164 LOG(ERROR) << "Singleton of type " << type().name() << " has a "
165 << "living reference at destroyInstances time; beware! Raw "
166 << "pointer is " << instance_ptr_ << ". It is very likely "
167 << "that some other singleton is holding a shared_ptr to it. "
168 << "This singleton will be leaked (even if a shared_ptr to it "
169 << "is eventually released)."
170 << "Make sure dependencies between these singletons are "
171 << "properly defined.";
176 template <typename T>
177 SingletonHolder<T>::SingletonHolder(
178 TypeDescriptor typeDesc,
179 SingletonVault& vault)
180 : SingletonHolderBase(typeDesc), vault_(vault) {}
182 template <typename T>
183 bool SingletonHolder<T>::creationStarted() {
184 // If alive, then creation was of course started.
185 // This is flipped after creating_thread_ was set, and before it was reset.
186 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
190 // Not yet built. Is it currently in progress?
191 if (creating_thread_.load(std::memory_order_acquire) != std::thread::id()) {
198 template <typename T>
199 void SingletonHolder<T>::createInstance() {
200 if (creating_thread_.load(std::memory_order_acquire) ==
201 std::this_thread::get_id()) {
202 LOG(FATAL) << "circular singleton dependency: " << type().name();
205 std::lock_guard<std::mutex> entry_lock(mutex_);
206 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
209 if (state_.load(std::memory_order_acquire) ==
210 SingletonHolderState::NotRegistered) {
211 auto ptr = SingletonVault::stackTraceGetter().load();
212 LOG(FATAL) << "Creating instance for unregistered singleton: "
213 << type().name() << "\n"
216 << (ptr ? (*ptr)() : "(not available)");
219 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
224 // Clean up creator thread when complete, and also, in case of errors here,
225 // so that subsequent attempts don't think this is still in the process of
227 creating_thread_.store(std::thread::id(), std::memory_order_release);
230 creating_thread_.store(std::this_thread::get_id(), std::memory_order_release);
232 auto state = vault_.state_.rlock();
233 if (vault_.type_ != SingletonVault::Type::Relaxed &&
234 !state->registrationComplete) {
235 auto stack_trace_getter = SingletonVault::stackTraceGetter().load();
236 auto stack_trace = stack_trace_getter ? stack_trace_getter() : "";
237 if (!stack_trace.empty()) {
238 stack_trace = "Stack trace:\n" + stack_trace;
241 LOG(FATAL) << "Singleton " << type().name() << " requested before "
242 << "registrationComplete() call.\n"
243 << "This usually means that either main() never called "
244 << "folly::init, or singleton was requested before main() "
245 << "(which is not allowed).\n"
248 if (state->state == SingletonVault::SingletonVaultState::Quiescing) {
252 auto destroy_baton = std::make_shared<folly::Baton<>>();
253 auto print_destructor_stack_trace =
254 std::make_shared<std::atomic<bool>>(false);
256 // Can't use make_shared -- no support for a custom deleter, sadly.
257 std::shared_ptr<T> instance(
259 [ destroy_baton, print_destructor_stack_trace, type = type() ](
261 destroy_baton->post();
262 if (print_destructor_stack_trace->load()) {
263 std::string output = "Singleton " + type.name() + " was released.\n";
265 auto stack_trace_getter = SingletonVault::stackTraceGetter().load();
266 auto stack_trace = stack_trace_getter ? stack_trace_getter() : "";
267 if (stack_trace.empty()) {
268 output += "Failed to get release stack trace.";
270 output += "Release stack trace:\n";
271 output += stack_trace;
274 LOG(ERROR) << output;
278 // We should schedule destroyInstances() only after the singleton was
279 // created. This will ensure it will be destroyed before singletons,
280 // not managed by folly::Singleton, which were initialized in its
282 SingletonVault::scheduleDestroyInstances();
284 instance_weak_ = instance;
285 instance_ptr_ = instance.get();
286 instance_.reset(std::move(instance));
287 instance_weak_fast_ = instance_;
289 destroy_baton_ = std::move(destroy_baton);
290 print_destructor_stack_trace_ = std::move(print_destructor_stack_trace);
292 // This has to be the last step, because once state is Living other threads
293 // may access instance and instance_weak w/o synchronization.
294 state_.store(SingletonHolderState::Living, std::memory_order_release);
296 vault_.creationOrder_.wlock()->push_back(type());
299 } // namespace detail