线程

1.什么是线程？


定义：在一个程序中多个执行路线就是线程。线程是一个进程内部的一个控制序列。所有进程都有一个执行线程。
      区别：当进程执行fork调用时，将创建出该进程的一个副本，新进程由自己的PID，时间调度也是独立的，执行几乎完全独立于父进程。
  当创建一个新线程时，新线程拥有自己的栈，但它与创建者共享全局变量，文件描述符，信号处理函数和当前目录状态。


2.第一个线程程序。


创建线程
#include <pthread.h>


int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine) (void *), void *arg);


成功返回0失败返回错误代码








终止线程


#include <pthread.h>void pthread_exit(void *retval);终止线程并且返回某个对象的指针。


#include <pthread.h>int pthread_join(pthread_t thread, void **retval);


retval返回线程的返回值。   成功返回0失败返回错误代码


thread1.c:两个线程共享变量，主线程获取另外一个线程的返回值$ vi thread1.c


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




char message[] = "hello world";


void *thread_function(void *arg)
{
    printf("thread_function massage : %s\n",(char*)arg);


    sleep(1);
    strcpy(message,"OK OK OK");
    pthread_exit("thread_function gameover");
}


int main()
{
    pthread_t thread;
    void *thread_result;


    int res = pthread_create(&thread,NULL,thread_function,(void *)message);
    if(res != 0)
    {
        perror("thread create error");
        exit(EXIT_FAILURE);
    }


    res = pthread_join(thread,&thread_result);
    if(res != 0)
    {
        perror("thread_join error");
        exit(EXIT_FAILURE);
    }


    printf("thread was runed\n");


    printf("thread_jion  returned is %s\n",(char *)thread_result);
    printf("now massege is %s\n",message);


    exit(EXIT_SUCCESS);


}






$ gcc -o thread1 thread1.c -lpthread


$ ./thread1 


thread_function massage : hello world
thread was runed
thread_jion  returned is thread_function gameover
now massege is OK OK OK


thread2.c:两个线程同时执行（在两个线程中使用轮询技术）
#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
#include<string.h>
#include<unistd.h>
int run_now = 1;
void *thread_function(void *arg)
{
int count1 = 0;
while(count1<10)
{
if(run_now == 2)
{
printf("thread_function running\n");
run_now = 1;
}
else
{
sleep(1);
}
count1++;
}
pthread_exit("thread_function gameover");
}


int main()
{
pthread_t thread;
void *thread_result;
int res =pthread_create(&thread,NULL,thread_function,(void *)0);
if(res != 0)
{
perror("thread create error");
exit(EXIT_FAILURE);
}


int count2 = 0;
while(count2<10)
{
if(run_now == 1)
{
printf("main running\n");
run_now = 2;
}
else
{
sleep(1);
}
count2++;
}
res = pthread_join(thread,&thread_result);


if(res != 0)
{
perror("thread_join error");
exit(EXIT_FAILURE);
}
printf("thread_jion returned is %s\n",(char *)thread_result);
exit(EXIT_SUCCESS);
}


$ gcc -o thread2 thread2.c -lpthread


$ ./thread2


main running
thread_function running
main running
thread_function running
main running
thread_function running
main running
thread_function running
main running
thread_function running
thread_jion  returned is thread_function gameover




thread3.c:一个线程信号量（用信号量进行同步，主线程写，另外一个线程读字符串的长度）
#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
#include<string.h>
#include<unistd.h>
#include<semaphore.h>
#define  BUFF_SIZE 1024
char Buff[BUFF_SIZE];
sem_t sem;


void *thread_function(void *arg)
{
    while(strncmp(Buff,"end", 3) != 0)
    {
        sem_wait(&sem);
        printf("You input %d characters\n",strlen(Buff)-1);
    }
    pthread_exit("thread_function gameover");
}


int main()
{
    pthread_t thread;
    void *thread_result;


    int res = sem_init(&sem,0,0);
    if(res != 0)
    {
        perror("sem_init error");
        exit(EXIT_FAILURE);
    }


    res = pthread_create(&thread,NULL,thread_function,(void *)0);
    if(res != 0)
    {
        perror("thread create error");
        exit(EXIT_FAILURE);
    }
    
    printf("input end to finish\n");
    while(strncmp(Buff,"end",3) != 0)
    {
        fgets(Buff,BUFF_SIZE,stdin);
        sem_post(&sem);
    }


    res = pthread_join(thread,&thread_result);
   
    if(res != 0)
    {
        perror("thread_join error");
        exit(EXIT_FAILURE);
    }


    printf("thread was runed\n");


    printf("thread_jion  returned is %s\n",(char *)thread_result);
 
    sem_destroy(&sem);


    exit(EXIT_SUCCESS);


}




$ gcc -o thread3 thread3.c -lpthread
$ ./thread3
input end to finish
ni
You input 2 characters
hao
You input 3 characters
meimeida
You input 8 characters
woaini
You input 6 characters
dniejdiejd
You input 10 characters
wo aini chentong
You input 16 characters
end
You input 3 characters
thread was runed
thread_jion  returned is thread_function gameover


thread4.c:用互斥量进行同步（一个线程输入数据，一个线程计算数据的大小）


#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
#include<string.h>
#include<unistd.h>
#define BUFF_SIZE 1024
int time_to_exit = 1;
char buff[BUFF_SIZE];
pthread_mutex_t mutex;


void *thread_function(void *arg)
{
    sleep(1);
    pthread_mutex_lock(&mutex);
    while(strncmp(buff,"end",3) != 0)
    {
        printf("You input %d charcters\n",strlen(buff)-1);
        buff[0] = '\0';
        pthread_mutex_unlock(&mutex);
        sleep(1);
        pthread_mutex_lock(&mutex);
        while(buff[0] == '\0')
        {
             pthread_mutex_unlock(&mutex);
             sleep(1);
             pthread_mutex_lock(&mutex);
           
        }
    }
    time_to_exit = 0;
    buff[0] ='\0';
    pthread_mutex_unlock(&mutex);
    pthread_exit("thread_function gameover");
}


int main()
{
    pthread_t thread;
    void *thread_result;


    int res = pthread_mutex_init(&mutex,NULL);
    if(res != 0)
    {
        perror("pthread_mutex_init error");
        exit(EXIT_FAILURE);
    }


    res = pthread_create(&thread,NULL,thread_function,(void *)0);
    if(res != 0)
    {
        perror("thread create error");
        exit(EXIT_FAILURE);
    }
    
    pthread_mutex_lock(&mutex);
    while(time_to_exit)
    {
        fgets(buff,BUFF_SIZE,stdin);


        pthread_mutex_unlock(&mutex);
        while(1)
        {
            pthread_mutex_lock(&mutex);
            if(buff[0] != 0)
            {
                pthread_mutex_unlock(&mutex);
                sleep(1);
            }
            else
            {
                break;
            }
        }


    }


    pthread_mutex_unlock(&mutex);
    printf("thread is finished...\n");
    res = pthread_join(thread,&thread_result);
    if(res != 0)
    {
        printf("ppthread_join() error\n");
        exit(EXIT_FAILURE);
    }


    pthread_mutex_destroy(&mutex);




    printf("thread_jion  returned is %s\n",(char *)thread_result);


    exit(EXIT_SUCCESS);


}






 

 
 
  
  
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