进程间通信___命名管道(FIFO)
命名管道(FIFO)
基本概念
命名管道和一般的管道基本相同,但也有一些显著的不同:
管道只能由相关进程使用,它们共同的祖先进程创建了管道。但是,通过FIFO,不相关的进程也能交换数据。
命名管道创建和操作::
#include
#include
int mkfifo(const char *pathname, mode_t mode);
返回:若成功则为0,若出错则为-1
一旦已经用mkfifo创建了一个FIFO,就可用open打开它。确实,一般的文件I/O函数(close、read、write、unlink等)都可用于FIFO。
当打开一个FIFO时,非阻塞标志(O_NONBLOCK)产生下列影响:
(1)
(2)
类似于管道,若写一个尚无进程为读而打开的FIFO,则产生信号SIGPIPE。若某个FIFO的最后一个写进程关闭了该FIFO,则将为该FIFO的读进程产生一个文件结束标志。
FIFO相关出错信息:
EACCES
EEXIST
ENAMETOOLONG
ENOENT
ENOSPC
ENOTDIR
EROFS
fifo_read.c文件内容如下:
#include
#include
#include
#include
#define FIFO “/tmp/myfifo”
main(int argc, char **argv)
{
if((mkfifo(FIFO,O_CREAT|O_EXCL)<0)&&(errno!=EEXIST))
printf(“cannot create fifoserver\n”);
printf(“Preparing for reading bytes…\n”);
memset(buf_r, 0, sizeof(buf_r);
fd=open(FIFO, O_RDONLY|O_NONBLOCK,0);
if(fd==-1)
{
}
while(1)
{
}
}
pause();
unlink(FIFO);
}
fifo_write.c文件内容如下:
#include
#include
#include
#include
#include
#include
#define FIFO_SERVER “/tmp/myfifo”
main(int argc, char **argv)
{
char w_buf[100];
if(error==ENXIO)
fd=open(FIFO_SERVER, O_WRONLY|O_NONBLOCK,0);
if(argc==1)
strcpy(w_buf, argv[1]);
if((nwrite==write(fd,w_buf,100))==-1)
{
if(errno==EAGAIN)
printf(“The FIFO has not been read yet. Please try later\n”);
}
else
{
}
gcc –o fifo_read fifo_read.c
gcc –o fifo_write fifo_write.c
运行结果:
读管道:
./fifo_read
Preparing for reading bytes…
read from FIFO
read from FIFO
read from FIFO
read from FIFO
read from FIFO
read from FIFO
写管道:
./fifo_write ccccccccccc
write ccccccccccc to the FIFO
读管道:
read from FIFO
read from FIFO
read from FIFO
read from FIFO
read ccccccccccc from FIFO
read from FIFO
read from FIFO
read from FIFO