1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
|
/*
==============================================================================
LockFreeQueue.h
Created: 1 Apr 2014 6:27:32pm
Author: Tom Maisey
==============================================================================
*/
#pragma once
/**
* A simple single producer & consumer lock free queue, based on Herb Sutter's code:
* http://www.drdobbs.com/parallel/writing-lock-free-code-a-corrected-queue/
*
* This is a linked list, which can expand arbitrarily without losing old data,
* but which has poor cache locality (I plan to write a ring buffer version soon).
*/
template <typename T>
class LockFreeQueue
{
public:
LockFreeQueue()
{
first = new Node(T()); // Dummy seperator.
last.set(first);
divider.set(first);
}
~LockFreeQueue()
{
while (first != nullptr)
{
Node* toDel = first;
first = toDel->next;
delete toDel;
}
}
/**
* Add an item to the queue. Obviously, should only be called from producer's thread.
*/
void produce(const T& t)
{
last.get()->next = new Node(t);
last.set(last.get()->next);
while (first != divider.get())
{ // trim unused nodes
Node* tmp = first;
first = first->next;
delete tmp;
}
}
/**
* Consume an item in the queue. Returns false if no items left to consume.
*/
bool consume(T& result)
{
Node* div = divider.get();
if (div != last.get())
{ // if queue is nonempty
result = div->next->value; // copy requested value
divider.set(div->next); // publish that we took it
return true;
}
return false;
}
private:
struct Node
{
Node(const T& val)
: value(val)
{}
T value;
Node* next{ nullptr };
};
Node* first{ nullptr };
Atomic<Node*> divider, last;
};
|
