互斥锁概念使用

news2024/9/23 7:18:05

互斥锁的创建两种方式

1.动态方式

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
FILE *fp;
void *func2(void *arg)
{
    pthread_detach(pthread_self());
    printf("this is func2 thread\n");
    char str2[]="i write func2 line\n";
    char c;
    int i=0;
    while(1)
    {
    while(i<strlen(str2))
    {
        c=str2[i];
        fputc(c,fp);
        usleep(1);
        i++;
       
    }
    i=0;
    usleep(1);
    }
    pthread_exit("func2 exit");
}
void *func(void *arg)
{
    pthread_detach(pthread_self());
    printf("this is func thread\n");
    char str[]="i write func line\n";
    char c;
    int i=0;
    while(1)
    {
    while(i<strlen(str))
    {
        c=str[i];
        fputc(c,fp);
        i++;
        usleep(1);
        
    }
    i=0;
    usleep(1);
    }
    pthread_exit("func exit");
}

int main(int argc, char **argv)
{
    pthread_t tid,tid2;
    void *retv;
    int i;
    fp=fopen("2.txt","a+");
    if(fp==NULL) 
    {
        printf("Error opening");
        return 0;
    }

    pthread_create(&tid, NULL,func,NULL);
    pthread_create(&tid2, NULL,func2,NULL);
    while(1)
    {
        sleep(1);
    }
}

从结果2.txt可以看出写入文件的内容是乱的，因为文件是临界资源，两个线程同时写入会乱套，因此引入了互斥锁的概念

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

pthread_mutex_t mutex =PTHREAD_MUTEX_INITIALIZER;
FILE *fp;
void *func2(void *arg)
{
    pthread_detach(pthread_self());
    printf("this is func2 thread\n");
    char str2[]="i write func2 line\n";
    char c;
    int i=0;
    while(1)
    {
    pthread_mutex_lock(&mutex); //上锁
    while(i<strlen(str2))
    {
        c=str2[i];
        fputc(c,fp);
        usleep(1);
        i++;
       
    }
 pthread_mutex_unlock(&mutex); //解锁
    i=0;
    usleep(1);
    }
    pthread_exit("func2 exit");
}
void *func(void *arg)
{
    pthread_detach(pthread_self());
    printf("this is func thread\n");
    char str[]="i write func line\n";
    char c;
    int i=0;
    while(1)
    {
        pthread_mutex_lock(&mutex); //上锁
    while(i<strlen(str))
    {
        c=str[i];
        fputc(c,fp);
        i++;
        usleep(1);
        
    }
    pthread_mutex_unlock(&mutex); //解锁
    i=0;
    usleep(1);
    }
    pthread_exit("func exit");
}

int main(int argc, char **argv)
{
    pthread_t tid,tid2;
    void *retv;
    int i;
    fp=fopen("2.txt","a+");
    if(fp==NULL) 
    {
        printf("Error opening");
        return 0;
    }

    pthread_create(&tid, NULL,func,NULL);
    pthread_create(&tid2, NULL,func2,NULL);
    while(1)
    {
        sleep(1);
    }
}

写入之前上锁，写入之后解锁

可以看出文件中的写入内容是完整的。