1/*
2 * Copyright 2016-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#include <folly/detail/StaticSingletonManager.h>
18
19#include <mutex>
20#include <typeindex>
21#include <unordered_map>
22
23namespace folly {
24namespace detail {
25
26namespace {
27
28class StaticSingletonManagerImpl {
29 public:
30 using Make = void*();
31 using Cache = std::atomic<void*>;
32
33 void* create(std::type_info const& key, Make& make, Cache& cache) {
34 auto const ptr = entry(key).get(make);
35 cache.store(ptr, std::memory_order_release);
36 return ptr;
37 }
38
39 private:
40 struct Entry {
41 void* ptr{};
42 std::mutex mutex;
43
44 void* get(Make& make) {
45 std::lock_guard<std::mutex> lock(mutex);
46 return ptr ? ptr : (ptr = make());
47 }
48 };
49
50 Entry& entry(std::type_info const& key) {
51 std::lock_guard<std::mutex> lock(mutex_);
52 auto& e = map_[key];
53 return e ? *e : *(e = new Entry());
54 }
55
56 std::unordered_map<std::type_index, Entry*> map_;
57 std::mutex mutex_;
58};
59
60} // namespace
61
62void* StaticSingletonManager::create_(
63 Key const& key,
64 Make& make,
65 Cache& cache) {
66 // This Leaky Meyers Singleton must always live in the .cpp file.
67 static auto& instance = *new StaticSingletonManagerImpl();
68 return instance.create(key, make, cache);
69}
70
71} // namespace detail
72} // namespace folly
73