队列
需要队列是出于两个原因。首先，需要队列来保存工作作业。还需要可用于跟踪已终止线程的数据结构。还记得前几篇文章（请参阅本文结尾处的 参考资料）中，我曾提到过需要使用带有特定进程标识的 pthread_join 吗？使用“清除队列”（称作 "cq"）可以解决无法等待 任何已终止线程的问题（稍后将详细讨论这个问题）。以下是标准队列代码。将此代码保存到文件 queue.h 和 queue.c：
queue.h
/* queue.h
** Copyright 2000 Daniel Robbins, Gentoo Technologies, Inc.
** Author: Daniel Robbins
** Date: 16 Jun 2000
*/
typedef struct node {
struct node *next;
} node;
typedef struct queue {
node *head, *tail;
} queue;
void queue_init(queue *myroot);
void queue_put(queue *myroot, node *mynode);
node *queue_get(queue *myroot);
|
queue.c
/* queue.c
** Copyright 2000 Daniel Robbins, Gentoo Technologies, Inc.
** Author: Daniel Robbins
** Date: 16 Jun 2000
**
** This set of queue functions was originally thread-aware. I
** redesigned the code to make this set of queue routines
** thread-ignorant (just a generic, boring yet very fast set of queue
** routines). Why the change? Because it makes more sense to have
** the thread support as an optional add-on. Consider a situation
** where you want to add 5 nodes to the queue. With the
** thread-enabled version, each call to queue_put() would
** automatically lock and unlock the queue mutex 5 times -- that's a
** lot of unnecessary overhead. However, by moving the thread stuff
** out of the queue routines, the caller can lock the mutex once at
** the beginning, then insert 5 items, and then unlock at the end.
** Moving the lock/unlock code out of the queue functions allows for
** optimizations that aren't possible otherwise. It also makes this
** code useful for non-threaded applications.
**
** We can easily thread-enable this data structure by using the
** data_control type defined in control.c and control.h. */
#include <stdio.h>
#include "queue.h"
void queue_init(queue *myroot) {
myroot->head=NULL;
myroot->tail=NULL;
}
void queue_put(queue *myroot,node *mynode) {
mynode->next=NULL;
if (myroot->tail!=NULL)
myroot->tail->next=mynode;
myroot->tail=mynode;
if (myroot->:head==NULL)
myroot->head=mynode;
}
node *queue_get(queue *myroot) {
//get from root
node *mynode;
mynode=myroot->head;
if (myroot->head!=NULL)
myroot->head=myroot->head->next;
return mynode;
}
|