2 * Copyright 2015 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 static auto entry = new SingletonHolder<T>(
25 {typeid(T), typeid(Tag)},
26 *SingletonVault::singleton<VaultTag>());
31 void SingletonHolder<T>::registerSingleton(CreateFunc c, TeardownFunc t) {
32 std::lock_guard<std::mutex> entry_lock(mutex_);
34 if (state_ != SingletonHolderState::NotRegistered) {
37 * You have two instances of the same
38 * folly::Singleton<Class>. Probably because you define the
39 * singleton in a header included in multiple places? In general,
40 * folly::Singleton shouldn't be in the header, only off in some
41 * anonymous namespace in a cpp file. Code needing the singleton
42 * will find it when that code references folly::Singleton<Class>.
44 * Alternatively, you could have 2 singletons with the same type
45 * defined with a different name in a .cpp (source) file. For
48 * Singleton<int> a([] { return new int(3); });
49 * Singleton<int> b([] { return new int(4); });
52 LOG(FATAL) << "Double registration of singletons of the same "
53 << "underlying type; check for multiple definitions "
54 << "of type folly::Singleton<" + type_.name() + ">";
57 create_ = std::move(c);
58 teardown_ = std::move(t);
60 state_ = SingletonHolderState::Dead;
64 void SingletonHolder<T>::registerSingletonMock(CreateFunc c, TeardownFunc t) {
65 if (state_ == SingletonHolderState::NotRegistered) {
67 << "Registering mock before singleton was registered: " << type_.name();
71 std::lock_guard<std::mutex> entry_lock(mutex_);
73 create_ = std::move(c);
74 teardown_ = std::move(t);
78 T* SingletonHolder<T>::get() {
79 if (LIKELY(state_ == SingletonHolderState::Living)) {
84 if (instance_weak_.expired()) {
85 throw std::runtime_error(
86 "Raw pointer to a singleton requested after its destruction."
87 " Singleton type is: " +
95 std::weak_ptr<T> SingletonHolder<T>::get_weak() {
96 if (UNLIKELY(state_ != SingletonHolderState::Living)) {
100 return instance_weak_;
103 template <typename T>
104 TypeDescriptor SingletonHolder<T>::type() {
108 template <typename T>
109 bool SingletonHolder<T>::hasLiveInstance() {
110 return !instance_weak_.expired();
113 template <typename T>
114 void SingletonHolder<T>::destroyInstance() {
115 state_ = SingletonHolderState::Dead;
117 if (destroy_baton_) {
118 auto wait_result = destroy_baton_->timed_wait(
119 std::chrono::steady_clock::now() + kDestroyWaitTime);
121 print_destructor_stack_trace_->store(true);
122 LOG(ERROR) << "Singleton of type " << type_.name() << " has a "
123 << "living reference at destroyInstances time; beware! Raw "
124 << "pointer is " << instance_ptr_ << ". It is very likely "
125 << "that some other singleton is holding a shared_ptr to it. "
126 << "Make sure dependencies between these singletons are "
127 << "properly defined.";
132 template <typename T>
133 SingletonHolder<T>::SingletonHolder(TypeDescriptor type__,
134 SingletonVault& vault) :
135 type_(type__), vault_(vault) {
138 template <typename T>
139 void SingletonHolder<T>::createInstance() {
140 // There's no synchronization here, so we may not see the current value
141 // for creating_thread if it was set by other thread, but we only care about
142 // it if it was set by current thread anyways.
143 if (creating_thread_ == std::this_thread::get_id()) {
144 LOG(FATAL) << "circular singleton dependency: " << type_.name();
147 std::lock_guard<std::mutex> entry_lock(mutex_);
148 if (state_ == SingletonHolderState::Living) {
151 if (state_ == SingletonHolderState::NotRegistered) {
152 auto ptr = SingletonVault::stackTraceGetter().load();
153 LOG(FATAL) << "Creating instance for unregistered singleton: "
154 << type_.name() << "\n"
156 << "\n" << (ptr ? (*ptr)() : "(not available)");
159 if (state_ == SingletonHolderState::Living) {
164 // Clean up creator thread when complete, and also, in case of errors here,
165 // so that subsequent attempts don't think this is still in the process of
167 creating_thread_ = std::thread::id();
170 creating_thread_ = std::this_thread::get_id();
172 RWSpinLock::ReadHolder rh(&vault_.stateMutex_);
173 if (vault_.state_ == SingletonVault::SingletonVaultState::Quiescing) {
177 auto destroy_baton = std::make_shared<folly::Baton<>>();
178 auto print_destructor_stack_trace =
179 std::make_shared<std::atomic<bool>>(false);
180 auto teardown = teardown_;
181 auto type_name = type_.name();
183 // Can't use make_shared -- no support for a custom deleter, sadly.
184 instance_ = std::shared_ptr<T>(
186 [destroy_baton, print_destructor_stack_trace, teardown, type_name]
187 (T* instance_ptr) mutable {
188 teardown(instance_ptr);
189 destroy_baton->post();
190 if (print_destructor_stack_trace->load()) {
191 std::string output = "Singleton " + type_name + " was destroyed.\n";
193 auto stack_trace_getter = SingletonVault::stackTraceGetter().load();
194 auto stack_trace = stack_trace_getter ? stack_trace_getter() : "";
195 if (stack_trace.empty()) {
196 output += "Failed to get destructor stack trace.";
198 output += "Destructor stack trace:\n";
199 output += stack_trace;
202 LOG(ERROR) << output;
206 // We should schedule destroyInstances() only after the singleton was
207 // created. This will ensure it will be destroyed before singletons,
208 // not managed by folly::Singleton, which were initialized in its
210 SingletonVault::scheduleDestroyInstances();
212 instance_weak_ = instance_;
213 instance_ptr_ = instance_.get();
214 destroy_baton_ = std::move(destroy_baton);
215 print_destructor_stack_trace_ = std::move(print_destructor_stack_trace);
217 // This has to be the last step, because once state is Living other threads
218 // may access instance and instance_weak w/o synchronization.
219 state_.store(SingletonHolderState::Living);
222 RWSpinLock::WriteHolder wh(&vault_.mutex_);
223 vault_.creation_order_.push_back(type_);