1 | /* |
2 | * Copyright (c) Facebook, Inc. and its affiliates. |
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 | #pragma once |
18 | |
19 | #include <future> |
20 | |
21 | #include <glog/logging.h> |
22 | |
23 | #include <folly/Executor.h> |
24 | #include <folly/synchronization/Baton.h> |
25 | |
26 | namespace folly { |
27 | |
28 | /// An Executor accepts units of work with add(), which should be |
29 | /// threadsafe. |
30 | class DefaultKeepAliveExecutor : public virtual Executor { |
31 | public: |
32 | virtual ~DefaultKeepAliveExecutor() { |
33 | DCHECK(!keepAlive_); |
34 | } |
35 | |
36 | folly::Executor::KeepAlive<> weakRef() { |
37 | return WeakRef::create(controlBlock_, this); |
38 | } |
39 | |
40 | protected: |
41 | void joinKeepAlive() { |
42 | DCHECK(keepAlive_); |
43 | keepAlive_.reset(); |
44 | keepAliveReleaseBaton_.wait(); |
45 | } |
46 | |
47 | void joinAndResetKeepAlive() { |
48 | joinKeepAlive(); |
49 | auto keepAliveCount = |
50 | controlBlock_->keepAliveCount_.exchange(1, std::memory_order_relaxed); |
51 | DCHECK_EQ(keepAliveCount, 0); |
52 | keepAliveReleaseBaton_.reset(); |
53 | keepAlive_ = makeKeepAlive(this); |
54 | } |
55 | |
56 | private: |
57 | struct ControlBlock { |
58 | std::atomic<ssize_t> keepAliveCount_{1}; |
59 | }; |
60 | |
61 | class WeakRef : public Executor { |
62 | public: |
63 | static folly::Executor::KeepAlive<> create( |
64 | std::shared_ptr<ControlBlock> controlBlock, |
65 | Executor* executor) { |
66 | return makeKeepAlive(new WeakRef(std::move(controlBlock), executor)); |
67 | } |
68 | |
69 | void add(Func f) override { |
70 | if (auto executor = lock()) { |
71 | executor->add(std::move(f)); |
72 | } |
73 | } |
74 | |
75 | void addWithPriority(Func f, int8_t priority) override { |
76 | if (auto executor = lock()) { |
77 | executor->addWithPriority(std::move(f), priority); |
78 | } |
79 | } |
80 | |
81 | virtual uint8_t getNumPriorities() const override { |
82 | return numPriorities_; |
83 | } |
84 | |
85 | private: |
86 | WeakRef(std::shared_ptr<ControlBlock> controlBlock, Executor* executor) |
87 | : controlBlock_(std::move(controlBlock)), |
88 | executor_(executor), |
89 | numPriorities_(executor->getNumPriorities()) {} |
90 | |
91 | bool keepAliveAcquire() override { |
92 | auto keepAliveCount = |
93 | keepAliveCount_.fetch_add(1, std::memory_order_relaxed); |
94 | // We should never increment from 0 |
95 | DCHECK(keepAliveCount > 0); |
96 | return true; |
97 | } |
98 | |
99 | void keepAliveRelease() override { |
100 | auto keepAliveCount = |
101 | keepAliveCount_.fetch_sub(1, std::memory_order_acq_rel); |
102 | DCHECK(keepAliveCount >= 1); |
103 | |
104 | if (keepAliveCount == 1) { |
105 | delete this; |
106 | } |
107 | } |
108 | |
109 | folly::Executor::KeepAlive<> lock() { |
110 | auto controlBlock = |
111 | controlBlock_->keepAliveCount_.load(std::memory_order_relaxed); |
112 | do { |
113 | if (controlBlock == 0) { |
114 | return {}; |
115 | } |
116 | } while (!controlBlock_->keepAliveCount_.compare_exchange_weak( |
117 | controlBlock, |
118 | controlBlock + 1, |
119 | std::memory_order_release, |
120 | std::memory_order_relaxed)); |
121 | |
122 | return makeKeepAlive(executor_); |
123 | } |
124 | |
125 | std::atomic<size_t> keepAliveCount_{1}; |
126 | |
127 | std::shared_ptr<ControlBlock> controlBlock_; |
128 | Executor* executor_; |
129 | |
130 | uint8_t numPriorities_; |
131 | }; |
132 | |
133 | bool keepAliveAcquire() override { |
134 | auto keepAliveCount = |
135 | controlBlock_->keepAliveCount_.fetch_add(1, std::memory_order_relaxed); |
136 | // We should never increment from 0 |
137 | DCHECK(keepAliveCount > 0); |
138 | return true; |
139 | } |
140 | |
141 | void keepAliveRelease() override { |
142 | auto keepAliveCount = |
143 | controlBlock_->keepAliveCount_.fetch_sub(1, std::memory_order_acquire); |
144 | DCHECK(keepAliveCount >= 1); |
145 | |
146 | if (keepAliveCount == 1) { |
147 | keepAliveReleaseBaton_.post(); // std::memory_order_release |
148 | } |
149 | } |
150 | |
151 | std::shared_ptr<ControlBlock> controlBlock_{std::make_shared<ControlBlock>()}; |
152 | Baton<> keepAliveReleaseBaton_; |
153 | KeepAlive<DefaultKeepAliveExecutor> keepAlive_{makeKeepAlive(this)}; |
154 | }; |
155 | |
156 | } // namespace folly |
157 | |