进程间通信_有名管道与无名管道

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本文链接： https://blog.csdn.net/qq_42948022/article/details/102557613

进程间通信----无名管道

/*无名管道
    int filedes[2];char a[100],b[100];
    pipe(filedes);
    write( filedes[1],a,sizeof(a));close( filedes[0] );close( filedes[1] );
    read( filedes[0], b,sizeof(b));close( filedes[0] );close( filedes[1] );
*/
#include <unistd.h>
#include <stdio.h>

int main(void)
{
    int fd[2];		//fd[]必须父子进程共有。
    pid_t pid;
    
    pipe(fd);
    pid=fork();    
    if(pid < 0){
        printf("pid error\n");
        return 0;
    }
    else if(pid > 0){
        printf("父进程写：\n");
        char a[100];
        sprintf(a,"asdfg\n");

        write( fd[1],a,sizeof(a));
        close( fd[0] );
        close( fd[1] );
    }
    else
    {
        sleep(7);
        printf("This is child process.\n");
        char b[100];
        read( fd[0], b, sizeof(b));
        printf( "read pipe: %s\n", b );
        close( fd[0] );
        close( fd[1] );
    }

    waitpid( pid, NULL, 0 );
    return 0;
}

进程间通信----有名管道

mkfifo()本质是将普通文件定义为管道文件。
已存在时error会被置为EEXIST。
格式：
if((mkfifo(FIFO_NAME,0777)<0)&&(errno!=EEXIST))
{
	fd=open(FIFO_NAME,O_RDONLY);
    write(fd,buf,length-1); //read(fd,r_buf,50);
    unlink(FIFO_NAME);
    close(fd);
}

#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h> 
#define FIFO_NAME "/tmp/myfifo"       //建的管道文件名
main()
{
    int fd,length,running=1;
    char w_buf[50],buf[50];
    int w_num;
    while(running)
	{
	    if((mkfifo(FIFO_NAME,0777)<0)&&(errno!=EEXIST))
	    {
		printf("cannot create fifo...\n");
		exit(1);
	    }
	 
	    fd=open(FIFO_NAME,O_WRONLY);
	    printf("pls input something\n");
	    fgets(buf,50,stdin);
	    if(strcmp(buf,"end\n")==0)
		running=0;
	    length=strlen(buf);
	    w_num=write(fd,buf,length-1);
	    printf("length is %d\n",w_num);
	}
    sleep(2);
}


read.c   
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>

//#define FIFO_NAME "/tmp/myfifo" 
#define FIFO_NAME "123"
main()
{
    char r_buf[50];
    int  fd,running=1;
    int  r_num;
    while(running)
	{
	    if((mkfifo(FIFO_NAME,0777)<0)&&(errno!=EEXIST))
	    {
		printf("cannot create fifo...\n");
		exit(1);
	    }

	    fd=open(FIFO_NAME,O_RDONLY);
	    if(fd==-1)
	    {
		    printf("open %s for read error\n");
		    exit(1);
	    }
	 

	    r_num=read(fd,r_buf,50);
	    r_buf[r_num]='\0';
	    if(strcmp(r_buf,"end")==0)
		running=0;
	    printf(" %d bytes read:%s\n",r_num,r_buf);
	}
    unlink(FIFO_NAME);
}

信号（内核发给进程的通知）

#include <unistd.h>  
#include <sys/types.h>  
#include <stdlib.h>  
#include <stdio.h>  
#include <signal.h>  
  
static int alarm_fired = 0;  
  
void ouch(int sig)  
{  
    alarm_fired = 1;  
}  
  
int main()  
{  
    //关联信号处理函数  
    signal(SIGALRM, ouch);  
    alarm(5);  //设置信号传送闹钟,即用来设置信号SIGALRM在经过参数seconds秒数后发送给目前的进程。
    pause();  //使当前进程处于挂起状态，直到捕捉到一个信号，恢复正常执行 
    if(alarm_fired == 1)  
        printf("Receive a signal %d\n", SIGALRM);  
    exit(0);  
}