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.
17 #include <folly/Singleton.h>
25 #include <folly/FileUtil.h>
26 #include <folly/ScopeGuard.h>
32 [[noreturn]] void singletonWarnDoubleRegistrationAndAbort(
33 const TypeDescriptor& type) {
34 // Not using LOG(FATAL) or std::cerr because they may not be initialized yet.
36 o << "Double registration of singletons of the same "
37 << "underlying type; check for multiple definitions "
38 << "of type folly::Singleton<" << type.name() << ">" << std::endl;
40 writeFull(STDERR_FILENO, s.data(), s.size());
49 if (!leakedSingletons_.empty()) {
50 std::string leakedTypes;
51 for (const auto& singleton : leakedSingletons_) {
52 leakedTypes += "\t" + singleton.name() + "\n";
54 LOG(DFATAL) << "Singletons of the following types had living references "
55 << "after destroyInstances was finished:\n" << leakedTypes
56 << "beware! It is very likely that those singleton instances "
61 std::vector<detail::TypeDescriptor> leakedSingletons_;
64 #if defined(__APPLE__) || defined(_MSC_VER)
65 // OS X doesn't support constructor priorities.
66 FatalHelper fatalHelper;
68 FatalHelper __attribute__ ((__init_priority__ (101))) fatalHelper;
73 SingletonVault::~SingletonVault() { destroyInstances(); }
75 void SingletonVault::registerSingleton(detail::SingletonHolderBase* entry) {
76 RWSpinLock::ReadHolder rh(&stateMutex_);
78 stateCheck(SingletonVaultState::Running);
80 if (UNLIKELY(registrationComplete_)) {
81 throw std::logic_error(
82 "Registering singleton after registrationComplete().");
85 RWSpinLock::ReadHolder rhMutex(&mutex_);
86 CHECK_THROW(singletons_.find(entry->type()) == singletons_.end(),
89 RWSpinLock::UpgradedHolder wh(&mutex_);
90 singletons_[entry->type()] = entry;
93 void SingletonVault::addEagerInitSingleton(detail::SingletonHolderBase* entry) {
94 RWSpinLock::ReadHolder rh(&stateMutex_);
96 stateCheck(SingletonVaultState::Running);
98 if (UNLIKELY(registrationComplete_)) {
99 throw std::logic_error(
100 "Registering for eager-load after registrationComplete().");
103 RWSpinLock::ReadHolder rhMutex(&mutex_);
104 CHECK_THROW(singletons_.find(entry->type()) != singletons_.end(),
107 RWSpinLock::UpgradedHolder wh(&mutex_);
108 eagerInitSingletons_.insert(entry);
111 void SingletonVault::registrationComplete() {
112 std::atexit([](){ SingletonVault::singleton()->destroyInstances(); });
114 RWSpinLock::WriteHolder wh(&stateMutex_);
116 stateCheck(SingletonVaultState::Running);
118 if (type_ == Type::Strict) {
119 for (const auto& p : singletons_) {
120 if (p.second->hasLiveInstance()) {
121 throw std::runtime_error(
122 "Singleton created before registration was complete.");
127 registrationComplete_ = true;
130 void SingletonVault::doEagerInit() {
131 std::unordered_set<detail::SingletonHolderBase*> singletonSet;
133 RWSpinLock::ReadHolder rh(&stateMutex_);
134 stateCheck(SingletonVaultState::Running);
135 if (UNLIKELY(!registrationComplete_)) {
136 throw std::logic_error("registrationComplete() not yet called");
138 singletonSet = eagerInitSingletons_; // copy set of pointers
141 for (auto *single : singletonSet) {
142 single->createInstance();
146 void SingletonVault::doEagerInitVia(Executor& exe, folly::Baton<>* done) {
147 std::unordered_set<detail::SingletonHolderBase*> singletonSet;
149 RWSpinLock::ReadHolder rh(&stateMutex_);
150 stateCheck(SingletonVaultState::Running);
151 if (UNLIKELY(!registrationComplete_)) {
152 throw std::logic_error("registrationComplete() not yet called");
154 singletonSet = eagerInitSingletons_; // copy set of pointers
157 auto countdown = std::make_shared<std::atomic<size_t>>(singletonSet.size());
158 for (auto* single : singletonSet) {
159 // countdown is retained by shared_ptr, and will be alive until last lambda
160 // is done. notifyBaton is provided by the caller, and expected to remain
161 // present (if it's non-nullptr). singletonSet can go out of scope but
162 // its values, which are SingletonHolderBase pointers, are alive as long as
163 // SingletonVault is not being destroyed.
165 // decrement counter and notify if requested, whether initialization
166 // was successful, was skipped (already initialized), or exception thrown.
168 if (--(*countdown) == 0) {
169 if (done != nullptr) {
174 // if initialization is in progress in another thread, don't try to init
175 // here. Otherwise the current thread will block on 'createInstance'.
176 if (!single->creationStarted()) {
177 single->createInstance();
183 void SingletonVault::destroyInstances() {
184 RWSpinLock::WriteHolder state_wh(&stateMutex_);
186 if (state_ == SingletonVaultState::Quiescing) {
189 state_ = SingletonVaultState::Quiescing;
191 RWSpinLock::ReadHolder state_rh(std::move(state_wh));
194 RWSpinLock::ReadHolder rh(&mutex_);
196 CHECK_GE(singletons_.size(), creation_order_.size());
198 for (auto type_iter = creation_order_.rbegin();
199 type_iter != creation_order_.rend();
201 singletons_[*type_iter]->destroyInstance();
204 for (auto& singleton_type: creation_order_) {
205 auto singleton = singletons_[singleton_type];
206 if (!singleton->hasLiveInstance()) {
210 fatalHelper.leakedSingletons_.push_back(singleton->type());
215 RWSpinLock::WriteHolder wh(&mutex_);
216 creation_order_.clear();
220 void SingletonVault::reenableInstances() {
221 RWSpinLock::WriteHolder state_wh(&stateMutex_);
223 stateCheck(SingletonVaultState::Quiescing);
225 state_ = SingletonVaultState::Running;
228 void SingletonVault::scheduleDestroyInstances() {
229 // Add a dependency on folly::ThreadLocal to make sure all its static
230 // singletons are initalized first.
231 threadlocal_detail::StaticMeta<void>::instance();
233 class SingletonVaultDestructor {
235 ~SingletonVaultDestructor() {
236 SingletonVault::singleton()->destroyInstances();
240 // Here we intialize a singleton, which calls destroyInstances in its
241 // destructor. Because of singleton destruction order - it will be destroyed
242 // before all the singletons, which were initialized before it and after all
243 // the singletons initialized after it.
244 static SingletonVaultDestructor singletonVaultDestructor;