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>());
33 void SingletonHolder<T>::registerSingleton(CreateFunc c, TeardownFunc t) {
34 std::lock_guard<std::mutex> entry_lock(mutex_);
36 if (state_ != SingletonHolderState::NotRegistered) {
39 * You have two instances of the same
40 * folly::Singleton<Class>. Probably because you define the
41 * singleton in a header included in multiple places? In general,
42 * folly::Singleton shouldn't be in the header, only off in some
43 * anonymous namespace in a cpp file. Code needing the singleton
44 * will find it when that code references folly::Singleton<Class>.
46 * Alternatively, you could have 2 singletons with the same type
47 * defined with a different name in a .cpp (source) file. For
50 * Singleton<int> a([] { return new int(3); });
51 * Singleton<int> b([] { return new int(4); });
54 LOG(FATAL) << "Double registration of singletons of the same "
55 << "underlying type; check for multiple definitions "
56 << "of type folly::Singleton<" + type_.name() + ">";
59 create_ = std::move(c);
60 teardown_ = std::move(t);
62 state_ = SingletonHolderState::Dead;
66 void SingletonHolder<T>::registerSingletonMock(CreateFunc c, TeardownFunc t) {
67 if (state_ == SingletonHolderState::NotRegistered) {
69 << "Registering mock before singleton was registered: " << type_.name();
73 std::lock_guard<std::mutex> entry_lock(mutex_);
75 create_ = std::move(c);
76 teardown_ = std::move(t);
80 T* SingletonHolder<T>::get() {
81 if (LIKELY(state_.load(std::memory_order_acquire) ==
82 SingletonHolderState::Living)) {
87 if (instance_weak_.expired()) {
88 throw std::runtime_error(
89 "Raw pointer to a singleton requested after its destruction."
90 " Singleton type is: " +
98 std::weak_ptr<T> SingletonHolder<T>::get_weak() {
99 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
100 SingletonHolderState::Living)) {
104 return instance_weak_;
107 template <typename T>
108 std::shared_ptr<T> SingletonHolder<T>::try_get() {
109 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
110 SingletonHolderState::Living)) {
114 return instance_weak_.lock();
117 template <typename T>
118 folly::ReadMostlySharedPtr<T> SingletonHolder<T>::try_get_fast() {
119 if (UNLIKELY(state_.load(std::memory_order_acquire) !=
120 SingletonHolderState::Living)) {
124 return instance_weak_fast_.lock();
127 template <typename T>
128 TypeDescriptor SingletonHolder<T>::type() {
132 template <typename T>
133 bool SingletonHolder<T>::hasLiveInstance() {
134 return !instance_weak_.expired();
137 template <typename T>
138 void SingletonHolder<T>::destroyInstance() {
139 state_ = SingletonHolderState::Dead;
141 if (destroy_baton_) {
142 auto wait_result = destroy_baton_->timed_wait(
143 std::chrono::steady_clock::now() + kDestroyWaitTime);
145 print_destructor_stack_trace_->store(true);
146 LOG(ERROR) << "Singleton of type " << type_.name() << " has a "
147 << "living reference at destroyInstances time; beware! Raw "
148 << "pointer is " << instance_ptr_ << ". It is very likely "
149 << "that some other singleton is holding a shared_ptr to it. "
150 << "Make sure dependencies between these singletons are "
151 << "properly defined.";
156 template <typename T>
157 SingletonHolder<T>::SingletonHolder(TypeDescriptor type__,
158 SingletonVault& vault) :
159 type_(type__), vault_(vault) {
162 template <typename T>
163 bool SingletonHolder<T>::creationStarted() {
164 // If alive, then creation was of course started.
165 // This is flipped after creating_thread_ was set, and before it was reset.
166 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
170 // Not yet built. Is it currently in progress?
171 if (creating_thread_.load(std::memory_order_acquire) != std::thread::id()) {
178 template <typename T>
179 void SingletonHolder<T>::createInstance() {
180 if (creating_thread_.load(std::memory_order_acquire) ==
181 std::this_thread::get_id()) {
182 LOG(FATAL) << "circular singleton dependency: " << type_.name();
185 std::lock_guard<std::mutex> entry_lock(mutex_);
186 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
189 if (state_.load(std::memory_order_acquire) ==
190 SingletonHolderState::NotRegistered) {
191 auto ptr = SingletonVault::stackTraceGetter().load();
192 LOG(FATAL) << "Creating instance for unregistered singleton: "
193 << type_.name() << "\n"
195 << "\n" << (ptr ? (*ptr)() : "(not available)");
198 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
203 // Clean up creator thread when complete, and also, in case of errors here,
204 // so that subsequent attempts don't think this is still in the process of
206 creating_thread_.store(std::thread::id(), std::memory_order_release);
209 creating_thread_.store(std::this_thread::get_id(), std::memory_order_release);
211 RWSpinLock::ReadHolder rh(&vault_.stateMutex_);
212 if (vault_.state_ == SingletonVault::SingletonVaultState::Quiescing) {
216 auto destroy_baton = std::make_shared<folly::Baton<>>();
217 auto print_destructor_stack_trace =
218 std::make_shared<std::atomic<bool>>(false);
219 auto teardown = teardown_;
220 auto type_name = type_.name();
222 // Can't use make_shared -- no support for a custom deleter, sadly.
223 std::shared_ptr<T> instance(
225 [destroy_baton, print_destructor_stack_trace, teardown, type_name]
226 (T* instance_ptr) mutable {
227 teardown(instance_ptr);
228 destroy_baton->post();
229 if (print_destructor_stack_trace->load()) {
230 std::string output = "Singleton " + type_name + " was destroyed.\n";
232 auto stack_trace_getter = SingletonVault::stackTraceGetter().load();
233 auto stack_trace = stack_trace_getter ? stack_trace_getter() : "";
234 if (stack_trace.empty()) {
235 output += "Failed to get destructor stack trace.";
237 output += "Destructor stack trace:\n";
238 output += stack_trace;
241 LOG(ERROR) << output;
245 // We should schedule destroyInstances() only after the singleton was
246 // created. This will ensure it will be destroyed before singletons,
247 // not managed by folly::Singleton, which were initialized in its
249 SingletonVault::scheduleDestroyInstances();
251 instance_weak_ = instance;
252 instance_ptr_ = instance.get();
253 instance_.reset(std::move(instance));
254 instance_weak_fast_ = instance_;
256 destroy_baton_ = std::move(destroy_baton);
257 print_destructor_stack_trace_ = std::move(print_destructor_stack_trace);
259 // This has to be the last step, because once state is Living other threads
260 // may access instance and instance_weak w/o synchronization.
261 state_.store(SingletonHolderState::Living, std::memory_order_release);
264 RWSpinLock::WriteHolder wh(&vault_.mutex_);
265 vault_.creation_order_.push_back(type_);