1/*
2 * Copyright (C) 2017 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
17 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#pragma once
27
28#include <wtf/Atomics.h>
29#include <wtf/Noncopyable.h>
30
31namespace WTF {
32
33// This a simple single consumer, multiple producer Bag data structure.
34
35template<typename T>
36class LocklessBag {
37 WTF_MAKE_NONCOPYABLE(LocklessBag);
38public:
39 struct Node {
40 WTF_MAKE_FAST_ALLOCATED;
41 public:
42 T data;
43 Node* next;
44 };
45
46 LocklessBag()
47 : m_head(nullptr)
48 {
49 }
50
51 enum PushResult { Empty, NonEmpty };
52 PushResult add(T&& element)
53 {
54 Node* newNode = new Node();
55 newNode->data = std::forward<T>(element);
56
57 Node* oldHead;
58 m_head.transaction([&] (Node*& head) {
59 oldHead = head;
60 newNode->next = head;
61 head = newNode;
62 return true;
63 });
64
65 return oldHead == nullptr ? Empty : NonEmpty;
66 }
67
68 // CONSUMER FUNCTIONS: Everything below here is only safe to call from the consumer thread.
69
70 // This function is actually safe to call from more than one thread, but ONLY if no thread can call consumeAll.
71 template<typename Functor>
72 void iterate(const Functor& func)
73 {
74 Node* node = m_head.load();
75 while (node) {
76 const T& data = node->data;
77 func(data);
78 node = node->next;
79 }
80 }
81
82 template<typename Functor>
83 void consumeAll(const Functor& func)
84 {
85 consumeAllWithNode([&] (T&& data, Node* node) {
86 func(WTFMove(data));
87 delete node;
88 });
89 }
90
91 template<typename Functor>
92 void consumeAllWithNode(const Functor& func)
93 {
94 Node* node = m_head.exchange(nullptr);
95 while (node) {
96 Node* oldNode = node;
97 node = node->next;
98 func(WTFMove(oldNode->data), oldNode);
99 }
100 }
101
102 ~LocklessBag()
103 {
104 consumeAll([] (T&&) { });
105 }
106
107private:
108 Atomic<Node*> m_head;
109};
110
111} // namespace WTF
112