2 * Copyright 2016 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() {
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 RWSpinLock::WriteHolder wh(&vault_.mutex_);
78 vault_.creation_order_.begin(), vault_.creation_order_.end(), type());
79 if (it != vault_.creation_order_.end()) {
80 vault_.creation_order_.erase(it);
84 std::lock_guard<std::mutex> entry_lock(mutex_);
86 create_ = std::move(c);
87 teardown_ = std::move(t);
91 T* SingletonHolder<T>::get() {
92 if (LIKELY(state_.load(std::memory_order_acquire) ==
93 SingletonHolderState::Living)) {
98 if (instance_weak_.expired()) {
99 throw std::runtime_error(
100 "Raw pointer to a singleton requested after its destruction."
101 " Singleton type is: " +
105 return instance_ptr_;
108 template <typename T>
109 std::weak_ptr<T> SingletonHolder<T>::get_weak() {
110 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
111 SingletonHolderState::Living)) {
115 return instance_weak_;
118 template <typename T>
119 std::shared_ptr<T> SingletonHolder<T>::try_get() {
120 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
121 SingletonHolderState::Living)) {
125 return instance_weak_.lock();
128 template <typename T>
129 folly::ReadMostlySharedPtr<T> SingletonHolder<T>::try_get_fast() {
130 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
131 SingletonHolderState::Living)) {
135 return instance_weak_fast_.lock();
138 template <typename T>
139 bool SingletonHolder<T>::hasLiveInstance() {
140 return !instance_weak_.expired();
143 template <typename T>
144 void SingletonHolder<T>::destroyInstance() {
145 state_ = SingletonHolderState::Dead;
147 if (destroy_baton_) {
148 constexpr std::chrono::seconds kDestroyWaitTime{5};
149 auto wait_result = destroy_baton_->timed_wait(
150 std::chrono::steady_clock::now() + kDestroyWaitTime);
152 print_destructor_stack_trace_->store(true);
153 LOG(ERROR) << "Singleton of type " << type().name() << " has a "
154 << "living reference at destroyInstances time; beware! Raw "
155 << "pointer is " << instance_ptr_ << ". It is very likely "
156 << "that some other singleton is holding a shared_ptr to it. "
157 << "Make sure dependencies between these singletons are "
158 << "properly defined.";
163 template <typename T>
164 SingletonHolder<T>::SingletonHolder(
165 TypeDescriptor typeDesc,
166 SingletonVault& vault)
167 : SingletonHolderBase(typeDesc), vault_(vault) {}
169 template <typename T>
170 bool SingletonHolder<T>::creationStarted() {
171 // If alive, then creation was of course started.
172 // This is flipped after creating_thread_ was set, and before it was reset.
173 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
177 // Not yet built. Is it currently in progress?
178 if (creating_thread_.load(std::memory_order_acquire) != std::thread::id()) {
185 template <typename T>
186 void SingletonHolder<T>::createInstance() {
187 if (creating_thread_.load(std::memory_order_acquire) ==
188 std::this_thread::get_id()) {
189 LOG(FATAL) << "circular singleton dependency: " << type().name();
192 std::lock_guard<std::mutex> entry_lock(mutex_);
193 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
196 if (state_.load(std::memory_order_acquire) ==
197 SingletonHolderState::NotRegistered) {
198 auto ptr = SingletonVault::stackTraceGetter().load();
199 LOG(FATAL) << "Creating instance for unregistered singleton: "
200 << type().name() << "\n"
203 << (ptr ? (*ptr)() : "(not available)");
206 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
211 // Clean up creator thread when complete, and also, in case of errors here,
212 // so that subsequent attempts don't think this is still in the process of
214 creating_thread_.store(std::thread::id(), std::memory_order_release);
217 creating_thread_.store(std::this_thread::get_id(), std::memory_order_release);
219 RWSpinLock::ReadHolder rh(&vault_.stateMutex_);
220 if (vault_.state_ == SingletonVault::SingletonVaultState::Quiescing) {
224 auto destroy_baton = std::make_shared<folly::Baton<>>();
225 auto print_destructor_stack_trace =
226 std::make_shared<std::atomic<bool>>(false);
227 auto teardown = teardown_;
228 auto type_name = type().name();
230 // Can't use make_shared -- no support for a custom deleter, sadly.
231 std::shared_ptr<T> instance(
233 [destroy_baton, print_destructor_stack_trace, teardown, type_name]
234 (T* instance_ptr) mutable {
235 teardown(instance_ptr);
236 destroy_baton->post();
237 if (print_destructor_stack_trace->load()) {
238 std::string output = "Singleton " + type_name + " was destroyed.\n";
240 auto stack_trace_getter = SingletonVault::stackTraceGetter().load();
241 auto stack_trace = stack_trace_getter ? stack_trace_getter() : "";
242 if (stack_trace.empty()) {
243 output += "Failed to get destructor stack trace.";
245 output += "Destructor stack trace:\n";
246 output += stack_trace;
249 LOG(ERROR) << output;
253 // We should schedule destroyInstances() only after the singleton was
254 // created. This will ensure it will be destroyed before singletons,
255 // not managed by folly::Singleton, which were initialized in its
257 SingletonVault::scheduleDestroyInstances();
259 instance_weak_ = instance;
260 instance_ptr_ = instance.get();
261 instance_.reset(std::move(instance));
262 instance_weak_fast_ = instance_;
264 destroy_baton_ = std::move(destroy_baton);
265 print_destructor_stack_trace_ = std::move(print_destructor_stack_trace);
267 // This has to be the last step, because once state is Living other threads
268 // may access instance and instance_weak w/o synchronization.
269 state_.store(SingletonHolderState::Living, std::memory_order_release);
272 RWSpinLock::WriteHolder wh(&vault_.mutex_);
273 vault_.creation_order_.push_back(type());