1 /*
2 * Copyright 2015-present Facebook, Inc.
3 *
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
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
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.
15 */
16
17 namespace folly {
18
19 namespace detail {
20
21 template <typename T>
22 template <typename Tag, typename VaultTag>
singleton()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>(
27 {typeid(T), typeid(Tag)}, *SingletonVault::singleton<VaultTag>());
28 });
29 return *entry;
30 }
31
32 [[noreturn]] void singletonWarnDoubleRegistrationAndAbort(
33 const TypeDescriptor& type);
34
35 template <typename T>
registerSingleton(CreateFunc c,TeardownFunc t)36 void SingletonHolder<T>::registerSingleton(CreateFunc c, TeardownFunc t) {
37 std::lock_guard<std::mutex> entry_lock(mutex_);
38
39 if (state_ != SingletonHolderState::NotRegistered) {
40 /* Possible causes:
41 *
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>.
48 *
49 * Alternatively, you could have 2 singletons with the same type
50 * defined with a different name in a .cpp (source) file. For
51 * example:
52 *
53 * Singleton<int> a([] { return new int(3); });
54 * Singleton<int> b([] { return new int(4); });
55 *
56 */
57 singletonWarnDoubleRegistrationAndAbort(type());
58 }
59
60 create_ = std::move(c);
61 teardown_ = std::move(t);
62
63 state_ = SingletonHolderState::Dead;
64 }
65
66 template <typename T>
registerSingletonMock(CreateFunc c,TeardownFunc t)67 void SingletonHolder<T>::registerSingletonMock(CreateFunc c, TeardownFunc t) {
68 if (state_ == SingletonHolderState::NotRegistered) {
69 detail::singletonWarnRegisterMockEarlyAndAbort(type());
70 }
71 if (state_ == SingletonHolderState::Living) {
72 destroyInstance();
73 }
74
75 {
76 auto creationOrder = vault_.creationOrder_.wlock();
77
78 auto it = std::find(creationOrder->begin(), creationOrder->end(), type());
79 if (it != creationOrder->end()) {
80 creationOrder->erase(it);
81 }
82 }
83
84 std::lock_guard<std::mutex> entry_lock(mutex_);
85
86 create_ = std::move(c);
87 teardown_ = std::move(t);
88 }
89
90 template <typename T>
get()91 T* SingletonHolder<T>::get() {
92 if (LIKELY(
93 state_.load(std::memory_order_acquire) ==
94 SingletonHolderState::Living)) {
95 return instance_ptr_;
96 }
97 createInstance();
98
99 if (instance_weak_.expired()) {
100 detail::singletonThrowGetInvokedAfterDestruction(type());
101 }
102
103 return instance_ptr_;
104 }
105
106 template <typename T>
get_weak()107 std::weak_ptr<T> SingletonHolder<T>::get_weak() {
108 if (UNLIKELY(
109 state_.load(std::memory_order_acquire) !=
110 SingletonHolderState::Living)) {
111 createInstance();
112 }
113
114 return instance_weak_;
115 }
116
117 template <typename T>
try_get()118 std::shared_ptr<T> SingletonHolder<T>::try_get() {
119 if (UNLIKELY(
120 state_.load(std::memory_order_acquire) !=
121 SingletonHolderState::Living)) {
122 createInstance();
123 }
124
125 return instance_weak_.lock();
126 }
127
128 template <typename T>
try_get_fast()129 folly::ReadMostlySharedPtr<T> SingletonHolder<T>::try_get_fast() {
130 if (UNLIKELY(
131 state_.load(std::memory_order_acquire) !=
132 SingletonHolderState::Living)) {
133 createInstance();
134 }
135
136 return instance_weak_fast_.lock();
137 }
138
139 template <typename T>
vivify()140 void SingletonHolder<T>::vivify() {
141 if (UNLIKELY(
142 state_.load(std::memory_order_relaxed) !=
143 SingletonHolderState::Living)) {
144 createInstance();
145 }
146 }
147
148 template <typename T>
hasLiveInstance()149 bool SingletonHolder<T>::hasLiveInstance() {
150 return !instance_weak_.expired();
151 }
152
153 template <typename T>
preDestroyInstance(ReadMostlyMainPtrDeleter<> & deleter)154 void SingletonHolder<T>::preDestroyInstance(
155 ReadMostlyMainPtrDeleter<>& deleter) {
156 instance_copy_ = instance_;
157 deleter.add(std::move(instance_));
158 }
159
160 template <typename T>
destroyInstance()161 void SingletonHolder<T>::destroyInstance() {
162 state_ = SingletonHolderState::Dead;
163 instance_.reset();
164 instance_copy_.reset();
165 if (destroy_baton_) {
166 constexpr std::chrono::seconds kDestroyWaitTime{5};
167 auto last_reference_released =
168 destroy_baton_->try_wait_for(kDestroyWaitTime);
169 if (last_reference_released) {
170 teardown_(instance_ptr_);
171 } else {
172 print_destructor_stack_trace_->store(true);
173 detail::singletonWarnDestroyInstanceLeak(type(), instance_ptr_);
174 }
175 }
176 }
177
178 template <typename T>
SingletonHolder(TypeDescriptor typeDesc,SingletonVault & vault)179 SingletonHolder<T>::SingletonHolder(
180 TypeDescriptor typeDesc,
181 SingletonVault& vault)
182 : SingletonHolderBase(typeDesc), vault_(vault) {}
183
184 template <typename T>
creationStarted()185 bool SingletonHolder<T>::creationStarted() {
186 // If alive, then creation was of course started.
187 // This is flipped after creating_thread_ was set, and before it was reset.
188 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
189 return true;
190 }
191
192 // Not yet built. Is it currently in progress?
193 if (creating_thread_.load(std::memory_order_acquire) != std::thread::id()) {
194 return true;
195 }
196
197 return false;
198 }
199
200 template <typename T>
createInstance()201 void SingletonHolder<T>::createInstance() {
202 if (creating_thread_.load(std::memory_order_acquire) ==
203 std::this_thread::get_id()) {
204 detail::singletonWarnCreateCircularDependencyAndAbort(type());
205 }
206
207 std::lock_guard<std::mutex> entry_lock(mutex_);
208 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
209 return;
210 }
211 if (state_.load(std::memory_order_acquire) ==
212 SingletonHolderState::NotRegistered) {
213 detail::singletonWarnCreateUnregisteredAndAbort(type());
214 }
215
216 if (state_.load(std::memory_order_acquire) == SingletonHolderState::Living) {
217 return;
218 }
219
220 SCOPE_EXIT {
221 // Clean up creator thread when complete, and also, in case of errors here,
222 // so that subsequent attempts don't think this is still in the process of
223 // being built.
224 creating_thread_.store(std::thread::id(), std::memory_order_release);
225 };
226
227 creating_thread_.store(std::this_thread::get_id(), std::memory_order_release);
228
229 auto state = vault_.state_.rlock();
230 if (vault_.type_ != SingletonVault::Type::Relaxed &&
231 !state->registrationComplete) {
232 detail::singletonWarnCreateBeforeRegistrationCompleteAndAbort(type());
233 }
234 if (state->state == detail::SingletonVaultState::Type::Quiescing) {
235 return;
236 }
237
238 auto destroy_baton = std::make_shared<folly::Baton<>>();
239 auto print_destructor_stack_trace =
240 std::make_shared<std::atomic<bool>>(false);
241
242 // Can't use make_shared -- no support for a custom deleter, sadly.
243 std::shared_ptr<T> instance(
244 create_(),
245 [destroy_baton, print_destructor_stack_trace, type = type()](T*) mutable {
246 destroy_baton->post();
247 if (print_destructor_stack_trace->load()) {
248 detail::singletonPrintDestructionStackTrace(type);
249 }
250 });
251
252 // We should schedule destroyInstances() only after the singleton was
253 // created. This will ensure it will be destroyed before singletons,
254 // not managed by folly::Singleton, which were initialized in its
255 // constructor
256 SingletonVault::scheduleDestroyInstances();
257
258 instance_weak_ = instance;
259 instance_ptr_ = instance.get();
260 instance_.reset(std::move(instance));
261 instance_weak_fast_ = instance_;
262
263 destroy_baton_ = std::move(destroy_baton);
264 print_destructor_stack_trace_ = std::move(print_destructor_stack_trace);
265
266 // This has to be the last step, because once state is Living other threads
267 // may access instance and instance_weak w/o synchronization.
268 state_.store(SingletonHolderState::Living, std::memory_order_release);
269
270 vault_.creationOrder_.wlock()->push_back(type());
271 }
272
273 } // namespace detail
274
275 } // namespace folly
276