Michael ＆Scott 无锁队列 C++ 实现

http://www.cnblogs.com/napoleon_liu/archive/2010/08/07/1794566.html

最近在研究无锁算法， 参照Michael and Scott的伪码，实现了个c++版本。

参考 http://www.cs.rochester.edu/research/synchronization/pseudocode/queues.html

伪代码是：

structure pointer_t {ptr: pointer to node_t, count: unsigned integer}

structure node_t {value: data type, next: pointer_t}

structure queue_t {Head: pointer_t, Tail: pointer_t}

initialize(Q: pointer to queue_t)

node = new_node() // Allocate a free node

node->next.ptr = NULL // Make it the only node in the linked list

Q->Head.ptr = Q->Tail.ptr = node // Both Head and Tail point to it

enqueue(Q: pointer to queue_t, value: data type)

E1: node = new_node() // Allocate a new node from the free list

E2: node->value = value // Copy enqueued value into node

E3: node->next.ptr = NULL // Set next pointer of node to NULL

E4: loop // Keep trying until Enqueue is done

E5: tail = Q->Tail // Read Tail.ptr and Tail.count together

E6: next = tail.ptr->next // Read next ptr and count fields together

E7: if tail == Q->Tail // Are tail and next consistent?

// Was Tail pointing to the last node?

E8: if next.ptr == NULL

// Try to link node at the end of the linked list

E9: if CAS(&tail.ptr->next, next, <node, next.count+1>)

E10: break // Enqueue is done. Exit loop

E11: endif

E12: else // Tail was not pointing to the last node

// Try to swing Tail to the next node

E13: CAS(&Q->Tail, tail, <next.ptr, tail.count+1>)

E14: endif

E15: endif

E16: endloop

// Enqueue is done. Try to swing Tail to the inserted node

E17: CAS(&Q->Tail, tail, <node, tail.count+1>)

dequeue(Q: pointer to queue_t, pvalue: pointer to data type): boolean

D1: loop // Keep trying until Dequeue is done

D2: head = Q->Head // Read Head

D3: tail = Q->Tail // Read Tail

D4: next = head.ptr->next // Read Head.ptr->next

D5: if head == Q->Head // Are head, tail, and next consistent?

D6: if head.ptr == tail.ptr // Is queue empty or Tail falling behind?

D7: if next.ptr == NULL // Is queue empty?

D8: return FALSE // Queue is empty, couldn't dequeue

D9: endif

// Tail is falling behind. Try to advance it

D10: CAS(&Q->Tail, tail, <next.ptr, tail.count+1>)

D11: else // No need to deal with Tail

// Read value before CAS

// Otherwise, another dequeue might free the next node

D12: *pvalue = next.ptr->value

// Try to swing Head to the next node

D13: if CAS(&Q->Head, head, <next.ptr, head.count+1>)

D14: break // Dequeue is done. Exit loop

D15: endif

D16: endif

D17: endif

D18: endloop

D19: free(head.ptr) // It is safe now to free the old node

D20: return TRUE // Queue was not empty, dequeue succeeded

我的 C++实现：

　　

gcc 4.1.2 编译， Linux下 经过框架测试没有问题。