APUE学习笔记——11 线程基础

深藏阁楼爱情的钟 2022-08-12 00:09 11阅读 0赞

# 线程标识 #

线程由线程号进行标识。线程号仅在线程所属的进程环境中有效。也就是说属于不同进程的两个线程可能线程号一样。

线程标识用结构体pthread\_t tid表示。与线程Id相关的函数如下：

**比较两个线程ID：**

#include <pthread.h>
    int pthread_equal(pthread_t tid1,pthread_t tid2);
                                  Returns: nonzero if equal, 0 otherwise

**获取自身线程ID：**

#include <pthread.h>
    pthread_t pthread_self(void);
                             Returns: the thread ID of the calling thread

# 创建和终止进程： #

## 创建线程： ##

#include <pthread.h>
    int pthread_create(pthread_t *restrict tidp, const pthread_attr_t *restrict attr,
                        void *(*start_rtn)(void *), void *restrict arg);
                                    Returns: 0 if OK, error number on failure

tidp： 线程ID

attr：定制线程属性

start\_rtn：新线程从start\_rtn指向的函数开始执行

arg：传入start\_rtn指向函数的参数

## 线程终止： ##

线程有三种终止方式：

1）从启动例程返回（return），返回值为线程退出码 
        
         2）被同进程的其他线程取消 
        
         3）调用pthread_exit

**1）调用pthread\_exit**

#include <pthread.h>
    void pthread_exit(void *rval_ptr);

启动例程调用 pthread\_exit  可以退出线程。rval\_ptr可以被其他线程通过 pthread\_join 访问到

#include <pthread.h>
    int pthread_join(pthread_t thread,void **rval_ptr);
                                 Returns: 0 if OK, error number on failure

pthread\_join 使线程发生阻塞，知道thread指向的线程终止，rval\_ptr用于获取终止线程的返回值。如果线程是通过被取消的方式结束，则返回值被置为PTHREAD\_CANCELED。

**2）被同进程其他线程取消**

#include <pthread.h>
    int pthread_cancel(pthread_t tid);
    Returns: 0 if OK, error number on failure

**3）线程的清理**

线程可以构建线程清理程序栈来自定义线程清理程序。（栈：后进先出）

#include <pthread.h>
    void pthread_cleanup_push(void (*rtn)(void *), void *arg);
    void pthread_cleanup_pop(int execute);

在三种情况之一，线程清理程序栈被调用

a .线程调用pthread_exit 
        
         b.应答其他线程的cancellation请求 
        
         c. execute参数非0

具体使用见后面的example

#include "apue.h"
    #include "myerr.h"
    #include <pthread.h>
    void
    cleanup(void *arg)
    {
            printf("cleanup: %s\n", (char *)arg);
    }
    void *
    thr_fn1(void *arg)
    {
            printf("thread 1 start\n");
            pthread_cleanup_push(cleanup, "thread 1 first handler");
            pthread_cleanup_push(cleanup, "thread 1 second handler");
            printf("thread 1 push complete\n");
            if (arg)
                    return((void *)1);
            pthread_cleanup_pop(0);
            pthread_cleanup_pop(0);
            return((void *)1);
    }
    void *
    thr_fn2(void *arg)
    {
            printf("thread 2 start\n");
            pthread_cleanup_push(cleanup, "thread 2 first handler");
            pthread_cleanup_push(cleanup, "thread 2 second handler");
            printf("thread 2 push complete\n");
            if (arg)
                    pthread_exit((void *)2);
            pthread_cleanup_pop(0);
            pthread_cleanup_pop(0);
            pthread_exit((void *)2);
    }
    int
    main(void)
    {
            int  err;
            pthread_t  tid1, tid2;
            void  *tret;
            err = pthread_create(&tid1, NULL, thr_fn1, (void *)1);
            if (err != 0)
                    err_exit(err, "can’t create thread 1");
            err = pthread_create(&tid2, NULL, thr_fn2, (void *)1);
            if (err != 0)
                    err_exit(err, "can’t create thread 2");
            err = pthread_join(tid1, &tret);
            if (err != 0)
                    err_exit(err, "can’t join with thread 1");
            printf("thread 1 exit code %ld\n", (long)tret);
            err = pthread_join(tid2, &tret);
            if (err != 0)
                    err_exit(err, "can’t join with thread 2");
            printf("thread 2 exit code %ld\n", (long)tret);
            exit(0);
    }

执行结果

windeal@ubuntu:~/Windeal/apue$ ./exe 
    thread 2 start
    thread 2 push complete
    cleanup: thread 2 second handler
    cleanup: thread 2 first handler
    thread 1 start
    thread 1 push complete
    cleanup: thread 1 second handler
    thread 1 exit code 1
    thread 2 exit code 2
    windeal@ubuntu:~/Windeal/apue$