1/*
2 * Copyright 2017-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/AtFork.h>
18
19#include <list>
20#include <mutex>
21
22#include <folly/lang/Exception.h>
23#include <folly/portability/PThread.h>
24
25namespace folly {
26
27namespace detail {
28
29namespace {
30
31struct AtForkTask {
32 void* object;
33 folly::Function<bool()> prepare;
34 folly::Function<void()> parent;
35 folly::Function<void()> child;
36};
37
38class AtForkList {
39 public:
40 static AtForkList& instance() {
41 static auto instance = new AtForkList();
42 return *instance;
43 }
44
45 static void prepare() noexcept {
46 instance().tasksLock.lock();
47 while (true) {
48 auto& tasks = instance().tasks;
49 auto task = tasks.rbegin();
50 for (; task != tasks.rend(); ++task) {
51 if (!task->prepare()) {
52 break;
53 }
54 }
55 if (task == tasks.rend()) {
56 return;
57 }
58 for (auto untask = tasks.rbegin(); untask != task; ++untask) {
59 untask->parent();
60 }
61 }
62 }
63
64 static void parent() noexcept {
65 auto& tasks = instance().tasks;
66 for (auto& task : tasks) {
67 task.parent();
68 }
69 instance().tasksLock.unlock();
70 }
71
72 static void child() noexcept {
73 auto& tasks = instance().tasks;
74 for (auto& task : tasks) {
75 task.child();
76 }
77 instance().tasksLock.unlock();
78 }
79
80 std::mutex tasksLock;
81 std::list<AtForkTask> tasks;
82
83 private:
84 AtForkList() {
85#if FOLLY_HAVE_PTHREAD_ATFORK
86 int ret = pthread_atfork(
87 &AtForkList::prepare, &AtForkList::parent, &AtForkList::child);
88 if (ret != 0) {
89 throw_exception<std::system_error>(
90 ret, std::generic_category(), "pthread_atfork failed");
91 }
92#elif !__ANDROID__ && !defined(_MSC_VER)
93// pthread_atfork is not part of the Android NDK at least as of n9d. If
94// something is trying to call native fork() directly at all with Android's
95// process management model, this is probably the least of the problems.
96//
97// But otherwise, this is a problem.
98#warning pthread_atfork unavailable
99#endif
100 }
101};
102} // namespace
103
104void AtFork::init() {
105 AtForkList::instance();
106}
107
108void AtFork::registerHandler(
109 void* object,
110 folly::Function<bool()> prepare,
111 folly::Function<void()> parent,
112 folly::Function<void()> child) {
113 std::lock_guard<std::mutex> lg(AtForkList::instance().tasksLock);
114 AtForkList::instance().tasks.push_back(
115 {object, std::move(prepare), std::move(parent), std::move(child)});
116}
117
118void AtFork::unregisterHandler(void* object) {
119 auto& list = AtForkList::instance();
120 std::lock_guard<std::mutex> lg(list.tasksLock);
121 for (auto it = list.tasks.begin(); it != list.tasks.end(); ++it) {
122 if (it->object == object) {
123 list.tasks.erase(it);
124 return;
125 }
126 }
127}
128
129} // namespace detail
130} // namespace folly
131