Linux 多线程学习 .

一、多线程 VS 多进程

和进程相比，线程有很多优势。在Linux系统下，启动一个新的进程必须分配给它独立的地址空间，建立众多的数据表来维护代码段和数据。而运行于一个进程中的多个线程，他们之间使用相同的地址空间。正是这样，同一进程下的线程之间共享数据空间，数据可以相互使用，并且线程间切换也要更快些，可以更有效的利用CPU。

二、程序设计

[注] 头文件<pthread.h> 编译时要加载动态库 libpthread.a，使用 -lpthread

1、创建线程

2、等待线程

3、关闭线程

4、退出清除

1、创建线程

         int pthread_create(pthread_t *tidp, const pthread_attr_t *attr, void *(*start_rtn)(void), void *arg)

tidp为线程id，是函数分配的值，所以要传一个 pthread_t 的地址。

attr线程属性，通常为空。

start_rtn为线程要执行的函数，返回值为空指针，参数为后面的*arg

若成功则返回0，否则返回出错编号。

例：

[cpp] view plain copy print ?

#include<stdio.h>
#include<pthread.h>

void *func1(void *arg){        //原函数声明
        int i;
        for(i=0;i<5;i++){
                printf("this is func1! The num is %d\n",*(int*)arg);    //将空指针转换为int型指针
                sleep(1);
        }
}

void *func2(int *m){ //自定义类型声明，也可以定义非指针类型，但是在create时会有警告，因为非地址并不能改变传入的值
        int i;
        for(i=0;i<5;i++){
                printf("this is func2! The num is %d\n",*m);
                (*m)++;
                sleep(1);
        }
}

int main(){
        pthread_t id1,id2;
        int num = 5;
        int *p = &num;
        if(pthread_create(&id1,NULL,(void *)func1,(void *)p) != 0){
                printf("thread1 create error!\n");
                return -1;
        }
        if(pthread_create(&id2,NULL,(void *)func2,&num) != 0){
                printf("thread2 create error!\n");
                return -1;
        }
        pthread_join(id1,NULL);     //等待线程结束
        pthread_join(id2,NULL);
        printf("Running complete!\n");
        return 0;


}
#include<stdio.h>
#include<pthread.h>

void *func1(void *arg){        //原函数声明
        int i;
        for(i=0;i<5;i++){
                printf("this is func1! The num is %d\n",*(int*)arg);    //将空指针转换为int型指针
                sleep(1);
        }
}

void *func2(int *m){ //自定义类型声明，也可以定义非指针类型，但是在create时会有警告，因为非地址并不能改变传入的值
        int i;
        for(i=0;i<5;i++){
                printf("this is func2! The num is %d\n",*m);
                (*m)++;
                sleep(1);
        }
}

int main(){
        pthread_t id1,id2;
        int num = 5;
        int *p = &num;
        if(pthread_create(&id1,NULL,(void *)func1,(void *)p) != 0){
                printf("thread1 create error!\n");
                return -1;
        }
        if(pthread_create(&id2,NULL,(void *)func2,&num) != 0){
                printf("thread2 create error!\n");
                return -1;
        }
        pthread_join(id1,NULL);     //等待线程结束   
        pthread_join(id2,NULL);
        printf("Running complete!\n");
        return 0;


}
运行结果：

[plain] view plain copy print ?

[fsy@localhost process]$ gcc thC.c -o thC -lpthread -g
[fsy@localhost process]$ ./thC
this is func2! The num is 5
this is func1! The num is 6
this is func2! The num is 6
this is func1! The num is 7
this is func2! The num is 7
this is func1! The num is 8
this is func2! The num is 8
this is func1! The num is 9
this is func2! The num is 9
this is func1! The num is 10
Running complete!
[fsy@localhost process]$
[fsy@localhost process]$ gcc thC.c -o thC -lpthread -g
[fsy@localhost process]$ ./thC
this is func2! The num is 5
this is func1! The num is 6
this is func2! The num is 6
this is func1! The num is 7
this is func2! The num is 7
this is func1! The num is 8
this is func2! The num is 8
this is func1! The num is 9
this is func2! The num is 9
this is func1! The num is 10
Running complete!
[fsy@localhost process]$
2、等待线程

[注]当调用pthread_create函数时，线程并没有开始执行，主进程应有等待，比如用sleep，或者用更专业的函数：pthread_join

    int pthread_join(pthread_t tid, void **rval_ptr)

调用函数可以阻塞调用线程，直到指定的线程终止。

tid为等待退出线程的id，rval_ptr为函数的返回值。是指向指针的指针，可以置空。

例：

[cpp] view plain copy print ?

#include<stdio.h>
#include<pthread.h>
#include<stdlib.h>

void *func(int *p){
        int *num=(int *)malloc(sizeof(int));     //必须动态创建，原因可以参考我动态分配内存的博客
        printf("Please input the number: ");
        scanf("%d",num);
        return (void *)num;              //类型是pthread_create的参数规定的
}

int main(){
        pthread_t pth;
        void *a;
        if(pthread_create(&pth,NULL,(void *)func,NULL) != 0){
                printf("create thread error!\n");
                return 1;
        }
        pthread_join(pth,&a);          //指向空指针的指针
        printf("get the num from the thread, it's %d\n",*(int *)a);
        return 0;
}
#include<stdio.h>
#include<pthread.h>
#include<stdlib.h>

void *func(int *p){
        int *num=(int *)malloc(sizeof(int));     //必须动态创建，原因可以参考我动态分配内存的博客
        printf("Please input the number: ");
        scanf("%d",num);
        return (void *)num;              //类型是pthread_create的参数规定的
}

int main(){
        pthread_t pth;
        void *a;
        if(pthread_create(&pth,NULL,(void *)func,NULL) != 0){
                printf("create thread error!\n");
                return 1;
        }
        pthread_join(pth,&a);          //指向空指针的指针
        printf("get the num from the thread, it's %d\n",*(int *)a);
        return 0;
}
3、终止线程

线程终止有以下三种方式：

1、线程从函数中返回

2、线程可以别其他函数终止

3、线程自己调用pthread_exit函数

void pthread_exit(void *rval_ptr)

rval_ptr为线程退出返回值的指针，即函数返回值。

4、退出清除

       void pthread_cleanup_push(void (*rtn)(void*), void *arg)

rtn为清除函数，arg是清除函数的参数

void pthread_cleanup_pop(int execute)

当execute 非0时执行清除函数。为0时不执行。

从pthread_cleanup_push的调用点到pthread_cleanup_pop之间的程序段中，如果有终止进程的动作，如调用pthread_exit或异常终止（不包括return），就会执行pthread_cleanup_push()所指定的清理函数。多个嵌套匹配时，就近匹配。

例：

[cpp] view plain copy print ?

#include<stdio.h>
#include<pthread.h>

void *clean(char *argv){
        printf("clean is called by %s\n",argv);
        return NULL;
}
void *func1(void *argv){
        printf("welcome enter the func1!\n");
        pthread_cleanup_push((void*)clean,"the first time call!");
        pthread_cleanup_push((void*)clean,"the second time call!");
        if(argv){
                return (void *)1;            //第二次运行将此句注掉
        }
        pthread_cleanup_pop(0);
        pthread_cleanup_pop(1);
        return (void *)0;
}

void *func2(void *argv){
        sleep(1);             //两个线程运行先后不确定
        printf("welcome enter the func2!\n");
        pthread_cleanup_push((void*)clean,"the first time call!");
        pthread_cleanup_push((void*)clean,"the second time call!");
        if(argv){
                pthread_exit(NULL);
        }
        pthread_cleanup_pop(0);
        pthread_cleanup_pop(0);
        return (void *)0;
}


int main(){
        pthread_t tid1,tid2;
        if(pthread_create(&tid1,NULL,(void *)func1,(void *)1) != 0){
                printf("thread1 create error!\n");
                return 1;
        }

         if(pthread_create(&tid2,NULL,(void *)func2,(void *)1) != 0){
                printf("thread2 create error!\n");
                return 1;
        }
        pthread_join(tid1,NULL);
        pthread_join(tid2,NULL);
        return 0;
}
#include<stdio.h>
#include<pthread.h>

void *clean(char *argv){
        printf("clean is called by %s\n",argv);
        return NULL;
}
void *func1(void *argv){
        printf("welcome enter the func1!\n");
        pthread_cleanup_push((void*)clean,"the first time call!");
        pthread_cleanup_push((void*)clean,"the second time call!");
        if(argv){
                return (void *)1;            //第二次运行将此句注掉
        }
        pthread_cleanup_pop(0);
        pthread_cleanup_pop(1);
        return (void *)0;
}

void *func2(void *argv){
        sleep(1);             //两个线程运行先后不确定
        printf("welcome enter the func2!\n");
        pthread_cleanup_push((void*)clean,"the first time call!");
        pthread_cleanup_push((void*)clean,"the second time call!");
        if(argv){
                pthread_exit(NULL);
        }
        pthread_cleanup_pop(0);
        pthread_cleanup_pop(0);
        return (void *)0;
}


int main(){
        pthread_t tid1,tid2;
        if(pthread_create(&tid1,NULL,(void *)func1,(void *)1) != 0){
                printf("thread1 create error!\n");
                return 1;
        }

         if(pthread_create(&tid2,NULL,(void *)func2,(void *)1) != 0){
                printf("thread2 create error!\n");
                return 1;
        }
        pthread_join(tid1,NULL);
        pthread_join(tid2,NULL);
        return 0;
}
运行结果：

[plain] view plain copy print ?

[fsy@localhost process]$ gcc thClean.c -o thclean -lpthread
[fsy@localhost process]$ ./thclean
welcome enter the func1!
welcome enter the func2!
clean is called by the second time call!          //此处先2后1
clean is called by the first time call!
[fsy@localhost process]$ vim thClean.c
[fsy@localhost process]$ gcc thClean.c -o thclean -lpthread
[fsy@localhost process]$ ./thclean
welcome enter the func1!
clean is called by the first time call!          //second已经被pop
welcome enter the func2!
clean is called by the second time call!
clean is called by the first time call!
[fsy@localhost process]$