3_linux多线程编程

基本概念

程序执行的最小单位

进程是线程的容器，不是基本执行单位，是线程容器

线程是进程中的不同执行路径， 有独立的堆栈、局部变量（因为线程需要线程函数）

进程有自己的内存空间，线程在进程内，所以多进程程序比多线程健壮，但是进程切换开销大于线程切换。

基本api

需要-lpthred 编译选项，因为需要pthread库

线程开发基本概念有3个： 线程、互斥锁、条件

• 线程操作： 创建，退出和等待3种状态。

//创建线程
	int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine) (void *), void *arg);
	参数一：线程id
	参数二：线程属性，默认可置为NULL，表示线程属性取缺省值
	参数三：线程入口函数
	参数四：*线程入口函数的参数

//线程退出
	void pthread_exit(void *retval);
	参数：线程退出时的返回值，也可为NULL

//线程等待
	int pthread_join(pthread_t thread, void **retval);
	参数二：收回线程的退出状态线程的返回值不感兴趣，可以把rval_ptr置为NULL

 //获取线程ID
	pthread_t pthread_self(void);

• demo

#include <stdio.h>
#include <pthread.h>
void *func(void *arg)
{
        static char *p = "xiaobian henshuai";
        printf("this is t1 thread pid=%ld\n",(unsigned long)pthread_self());
        printf("deliver param is %d\n",*(int *)arg);
        pthread_exit((void *)p);
        //退出时返回退出时的状态，返回一个字符串
}
int main()
{
        pthread_t t1;
        char *p =NULL;
        int param = 10;
        pthread_create(&t1,NULL,func,(void*)&param);
        //创建线程时，传递了一个param参数
        pthread_join(t1,(void **)&p);
        //等待t1线程的退出，用p收集，t1线程退出时的状态
        printf("return value is %s\n",p);
        return 0;
}

• 互斥锁操作：创建，销毁，加锁，解锁 4种操作

#include <pthread.h>
//互斥锁的初始化
int pthread_mutex_init(pthread_mutex_t *restrict mutex, const pthread_mutexattr_t *restrict attr);
参数一：互斥锁变量mutex
参数二：通常为NULL，为默认参数
//销毁互斥锁
int pthread_mutex_destroy(pthread_mutex_t *mutex);
//加锁
int pthread_mutex_lock(pthread_mutex_t *mutex);
//解锁
int pthread_mutex_unlock(pthread_mutex_t *mutex);

-demo

#include <stdio.h>
#include <pthread.h>
int data = 0;//定义一个全局变量验证线程是共享内存空间的
pthread_mutex_t mutex;
void *func1(void *arg)
{
         static char *p = "xiaobian henshuai";
         printf("t1:this is t1 thread pid=%ld\n",(unsigned long)pthread_self());
         printf("t1:deliver param is %d\n",*(int *)arg);
         int i=3;
         pthread_mutex_lock(&mutex);//加锁的目的是在执行以下代码的过程中不会被其他的进程打断
         while(i--)
         {
                 printf("t1:data=%d\n",data++);
                 sleep(1);
         }
         pthread_mutex_unlock(&mutex);
         pthread_exit((void *)p);
}

void *func2(void *arg)
{
        pthread_mutex_lock(&mutex);
        static char *p = "xiaobian henshuai";
        printf("t2:this is t2 thread pid=%ld\n",(unsigned long)pthread_self());
        printf("t2:deliver param is %d\n",*(int *)arg);
        while(1)
        {
                printf("t2:data=%d\n",data++);
                sleep(1);
        }
        pthread_mutex_unlock(&mutex);
        pthread_exit((void *)p);
}
int main()
{
        pthread_t t1;
        pthread_t t2;
        char *p =NULL;
        int param = 10;
        pthread_create(&t1,NULL,func1,(void*)&param);
        pthread_create(&t2,NULL,func2,(void*)&param);
        pthread_mutex_init(&mutex,NULL);
        pthread_join(t1,(void **)&p);
        pthread_join(t2,(void **)&p);
        pthread_mutex_destroy(&mutex);
        printf("main:return value is %s\n",p);
        return 0;
        }

死锁是怎么产生的：前提是有两个锁，线程一获得锁一的同时，又想获得锁二，线程二获得锁二的同时，又想获得锁一，线程一和二都想拿到对方的锁，导致线程停滞不前。

• 条件操作: 创建，销毁，触发，广播，等待 5种操作

#include <pthread.h>
//创建条件变量
int pthread_cond_init(pthread_cond_t *restrict cond, const pthread_condattr_t *restrict attr);
//销毁条件变量
int pthread_cond_destroy(pthread_cond_t* cond);
//等待
int pthread_cond_wait(pthread_cond_t *restrict cond, pthread_mutex_t *restrict mutex);
//触发
int pthread_cond_signal(pthread_cond_t c*ond)
//广播
int pthread_cond_broadcast(pthread_cond_t cond);

• demo

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
int data = 0;
pthread_mutex_t mutex;
pthread_cond_t cond;
void *func1(void *arg)
{
        printf("t1:this is t1 thread pid=%ld\n",(unsigned long)pthread_self());
        printf("t1:deliver param is %d\n",*(int *)arg);
        while(1)
        {
                pthread_cond_wait(&cond,&mutex);//等待某个条件的唤醒
                printf("t1 run========\n");
                data=0;
        }
}
void *func2(void *arg)
{
        printf("t2:this is t2 thread pid=%ld\n",(unsigned long)pthread_self());
        printf("t2:deliver param is %d\n",*(int *)arg);
        while(1)
        {
                printf("t2:data=%d\n",data);
                pthread_mutex_lock(&mutex);
                data++;
                if(data==3)
 		{
                        pthread_cond_signal(&cond);//唤醒条件执行线程t1
                }
                pthread_mutex_unlock(&mutex);
                sleep(1);
        }
}
int main()
{
        pthread_t t1;
        pthread_t t2;
        char *p =NULL;
        int param = 10;
        pthread_create(&t1,NULL,func1,(void*)&param);
        pthread_create(&t2,NULL,func2,(void*)&param);
        pthread_mutex_init(&mutex,NULL);
        pthread_cond_init(&cond,NULL);
        pthread_join(t1,(void **)&p);
        pthread_join(t2,(void **)&p);
        pthread_mutex_destroy(&mutex);
        pthread_cond_destroy(&cond);
        printf("main:return value is %s\n",p);
        return 0;