FIFO 和普通文件

最新推荐文章于 2025-07-07 11:12:47 发布

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FIFO; a named pipe

[root@localhost ch13]# cat fifo3.c 
/*************write*****/
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/types.h>
#include <sys/stat.h>

#define FIFO_NAME "/tmp/my_fifo"
#define BUFFER_SIZE PIPE_BUF
//PIPE_BUF=4096
#define TEN_MEG (1024 * 1024 * 10)

int main()
{	
    int pipe_fd;
    int res;
    int open_mode = O_WRONLY;
    int bytes_sent = 0;
    char buffer[BUFFER_SIZE + 1]="agds";

    if (access(FIFO_NAME, F_OK) == -1) {
        res = mkfifo(FIFO_NAME, 0777);
        if (res != 0) {
            fprintf(stderr, "Could not create fifo %s\n", FIFO_NAME);
            exit(EXIT_FAILURE);
        }
    }

    printf("Process %d opening FIFO O_WRONLY\n", getpid());
    pipe_fd = open(FIFO_NAME, open_mode);
    printf("Process %d result %d\n", getpid(), pipe_fd);

    if (pipe_fd != -1) {
        while(bytes_sent < TEN_MEG) {
            res = write(pipe_fd, buffer, BUFFER_SIZE);
            if (res == -1) {
                fprintf(stderr, "Write error on pipe\n");
                exit(EXIT_FAILURE);
            }
	printf("%s\n",buffer);
            bytes_sent += res;
        }
        (void)close(pipe_fd); 
    }
    else {
        exit(EXIT_FAILURE);        
    }

    printf("Process %d finished\n", getpid());
    exit(EXIT_SUCCESS);
}
[root@localhost ch13]# 
[root@localhost ch13]# 
[root@localhost ch13]# 
[root@localhost ch13]# cat fifo4.c 
/*************read*****/
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/types.h>
#include <sys/stat.h>

#define FIFO_NAME "/tmp/my_fifo"
#define BUFFER_SIZE PIPE_BUF

int main()
{
    int pipe_fd;
    int res;
    int open_mode = O_RDONLY;
    char buffer[BUFFER_SIZE + 1];
    int bytes_read = 0;

    memset(buffer, '\0', sizeof(buffer));

    
    printf("Process %d opening FIFO O_RDONLY\n", getpid());
    pipe_fd = open(FIFO_NAME, open_mode);
    printf("Process %d result %d\n", getpid(), pipe_fd);

    if (pipe_fd != -1) {
        do {
            res = read(pipe_fd, buffer, BUFFER_SIZE);
		printf("%s\n",buffer);
            bytes_read += res;
        } while (res > 0);
        (void)close(pipe_fd);
    }
    else {
        exit(EXIT_FAILURE);
    }

    printf("Process %d finished, %d bytes read\n", getpid(), bytes_read);
    exit(EXIT_SUCCESS);
}

[root@localhost ch13]#

[root@localhost ch13]# rm /tmp/my_fifo -f
[root@localhost ch13]# ./fifo3 &
[2] 17216
[root@localhost ch13]# Process 17216 opening FIFO O_WRONLY

[root@localhost ch13]# time ./fifo4 
...
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
agds
Process 17220 finished, 10485760 bytes read
real    0m0.610s
user    0m0.002s
sys    0m0.284s
Process 17216 finished
[root@localhost ch13]# 
//FIFO文件是fifo3创建，所以先运行fifo3，如果先运行fifo4则找不到my_fifo而出错

fifo3 is blocked when it opens without NONBLOCK mode until fifo4 also open the same FIFO file

[root@localhost ch13]# ll /tmp/my_fifo 
prwxr-xr-x. 1 root root 0 Aug 26 03:14 /tmp/my_fifo

the FIFO file my_fifo is 0 bytes

如果他们之间读写的不是FIFO文件，而是一个普通文件会是怎么样呢

[root@localhost ch13]# rm /tmp/my_fifo -f
[root@localhost ch13]# touch /tmp/my_fifo 
[root@localhost ch13]# ll /tmp/my_fifo 
-rw-r--r--. 1 root root 0 Aug 26 03:20 /tmp/my_fifo

run fifo3 and fifo4 just as the cmd above,then

Process 17276 finished, 10485760 bytes read

real	0m0.253s
user	0m0.006s
sys	0m0.235s

[root@localhost ch13]# ll /tmp/my_fifo 
-rw-r--r--. 1 root root 10485760 Aug 26 03:23 /tmp/my_fifo

看来,普通文件用于进程间通信也不慢哈
并且还可以从外部查看通信的内容和大小
但是不管open中是否用了O_NONBLOCK,都会O_NONBLOCK的