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: "
75 auto creationOrder = vault_.creationOrder_.wlock();
77 auto it = std::find(creationOrder->begin(), creationOrder->end(), type());
78 if (it != creationOrder->end()) {
79 creationOrder->erase(it);
83 std::lock_guard<std::mutex> entry_lock(mutex_);
85 create_ = std::move(c);
86 teardown_ = std::move(t);
90 T* SingletonHolder<T>::get() {
91 if (LIKELY(state_.load(std::memory_order_acquire) ==
92 SingletonHolderState::Living)) {
97 if (instance_weak_.expired()) {
98 throw std::runtime_error(
99 "Raw pointer to a singleton requested after its destruction."
100 " Singleton type is: " +
104 return instance_ptr_;
107 template <typename T>
108 std::weak_ptr<T> SingletonHolder<T>::get_weak() {
109 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
110 SingletonHolderState::Living)) {
114 return instance_weak_;
117 template <typename T>
118 std::shared_ptr<T> SingletonHolder<T>::try_get() {
119 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
120 SingletonHolderState::Living)) {
124 return instance_weak_.lock();
127 template <typename T>
128 folly::ReadMostlySharedPtr<T> SingletonHolder<T>::try_get_fast() {
129 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
130 SingletonHolderState::Living)) {
134 return instance_weak_fast_.lock();
137 template <typename T>
138 bool SingletonHolder<T>::hasLiveInstance() {
139 return !instance_weak_.expired();
142 template <typename T>
143 void SingletonHolder<T>::preDestroyInstance(
144 ReadMostlyMainPtrDeleter<>& deleter) {
145 instance_copy_ = instance_;
146 deleter.add(std::move(instance_));
149 template <typename T>
150 void SingletonHolder<T>::destroyInstance() {
151 state_ = SingletonHolderState::Dead;
153 instance_copy_.reset();
154 if (destroy_baton_) {
155 constexpr std::chrono::seconds kDestroyWaitTime{5};
156 auto wait_result = destroy_baton_->timed_wait(
157 std::chrono::steady_clock::now() + kDestroyWaitTime);
159 print_destructor_stack_trace_->store(true);
160 LOG(ERROR) << "Singleton of type " << type().name() << " has a "
161 << "living reference at destroyInstances time; beware! Raw "
162 << "pointer is " << instance_ptr_ << ". It is very likely "
163 << "that some other singleton is holding a shared_ptr to it. "
164 << "Make sure dependencies between these singletons are "
165 << "properly defined.";
170 template <typename T>
171 SingletonHolder<T>::SingletonHolder(
172 TypeDescriptor typeDesc,
173 SingletonVault& vault)
174 : SingletonHolderBase(typeDesc), vault_(vault) {}
176 template <typename T>
177 bool SingletonHolder<T>::creationStarted() {
178 // If alive, then creation was of course started.
179 // This is flipped after creating_thread_ was set, and before it was reset.
180 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
184 // Not yet built. Is it currently in progress?
185 if (creating_thread_.load(std::memory_order_acquire) != std::thread::id()) {
192 template <typename T>
193 void SingletonHolder<T>::createInstance() {
194 if (creating_thread_.load(std::memory_order_acquire) ==
195 std::this_thread::get_id()) {
196 LOG(FATAL) << "circular singleton dependency: " << type().name();
199 std::lock_guard<std::mutex> entry_lock(mutex_);
200 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
203 if (state_.load(std::memory_order_acquire) ==
204 SingletonHolderState::NotRegistered) {
205 auto ptr = SingletonVault::stackTraceGetter().load();
206 LOG(FATAL) << "Creating instance for unregistered singleton: "
207 << type().name() << "\n"
210 << (ptr ? (*ptr)() : "(not available)");
213 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
218 // Clean up creator thread when complete, and also, in case of errors here,
219 // so that subsequent attempts don't think this is still in the process of
221 creating_thread_.store(std::thread::id(), std::memory_order_release);
224 creating_thread_.store(std::this_thread::get_id(), std::memory_order_release);
226 auto state = vault_.state_.rlock();
227 if (state->state == SingletonVault::SingletonVaultState::Quiescing) {
231 auto destroy_baton = std::make_shared<folly::Baton<>>();
232 auto print_destructor_stack_trace =
233 std::make_shared<std::atomic<bool>>(false);
234 auto teardown = teardown_;
236 // Can't use make_shared -- no support for a custom deleter, sadly.
237 std::shared_ptr<T> instance(
239 [destroy_baton, print_destructor_stack_trace, teardown, type = type()]
240 (T* instance_ptr) mutable {
241 teardown(instance_ptr);
242 destroy_baton->post();
243 if (print_destructor_stack_trace->load()) {
244 std::string output = "Singleton " + type.name() + " was destroyed.\n";
246 auto stack_trace_getter = SingletonVault::stackTraceGetter().load();
247 auto stack_trace = stack_trace_getter ? stack_trace_getter() : "";
248 if (stack_trace.empty()) {
249 output += "Failed to get destructor stack trace.";
251 output += "Destructor stack trace:\n";
252 output += stack_trace;
255 LOG(ERROR) << output;
259 // We should schedule destroyInstances() only after the singleton was
260 // created. This will ensure it will be destroyed before singletons,
261 // not managed by folly::Singleton, which were initialized in its
263 SingletonVault::scheduleDestroyInstances();
265 instance_weak_ = instance;
266 instance_ptr_ = instance.get();
267 instance_.reset(std::move(instance));
268 instance_weak_fast_ = instance_;
270 destroy_baton_ = std::move(destroy_baton);
271 print_destructor_stack_trace_ = std::move(print_destructor_stack_trace);
273 // This has to be the last step, because once state is Living other threads
274 // may access instance and instance_weak w/o synchronization.
275 state_.store(SingletonHolderState::Living, std::memory_order_release);
277 vault_.creationOrder_.wlock()->push_back(type());