5 有名管道

1. mkfifo

函数形式：int mkfifo(const char * filename, mode_t mode);

功能：创建管道文件

参数：管道文件名；权限，文件权限仍然和umask有关

返回：成功返回0，失败返回-1

2. mkfifo调用内核，内核在文件系统中生成文件名，并没有在内核中生成管道。

只有在调用open代开有名管道时，才会在内核中创建管道。

3. 创建有名管道mkfifo，打开open，读read，写write，关闭close。

4. 举例：使用有名管道在非父子进程间通信

第一个进程：

#include "unistd.h"
#include "stdio.h"
#include "sys/types.h"
#include "stdlib.h"
#include "fcntl.h"
int main()
{
 int fd;
 int i;
 char process_inter=0;
 fd=open("./myfifo",O_WRONLY);
 if(fd <0)
 {
   printf("open myfifo failure\n");
   return -1;
 }
 printf("open myfifo sucess\n");

 for(i=0;i<5;i++)
 {
   printf("this is first process i=%d\n",i);
   usleep(100);
 }
 process_inter=1;
 sleep(5);
 write(fd,&process_inter,1);
 while(1);
 return 0;  
}

第二个进程：

#include "unistd.h"
#include "stdio.h"
#include "sys/types.h"
#include "stdlib.h"
#include "fcntl.h"
int main()
{
 int fd;
 int i;
 int process_inter=0;
 fd=open("./myfifo",O_RDONLY);
 if(fd <0)
 {
   printf("open myfifo failure\n");
   return -1;
 }
 printf("open myfifo sucess\n");

 read(fd,&process_inter,1);
 while(process_inter == 0);

 for(i=0;i<5;i++)
 {
   printf("this is second process i=%d\n",i);
   usleep(100);
 }
 while(1);
 return 0;  
}

执行结果：

alex@alex-virtual-machine:/extra/process/005$ ls
a.out  first  first.c  mkfifo.c  second  second.c
alex@alex-virtual-machine:/extra/process/005$ ./a.out
creat myfifo sucess
alex@alex-virtual-machine:/extra/process/005$ ls
a.out  first  first.c  mkfifo.c  myfifo  second  second.c
alex@alex-virtual-machine:/extra/process/005$ ./first
open myfifo sucess
this is first process i=0
this is first process i=1
this is first process i=2
this is first process i=3
this is first process i=4

alex@alex-virtual-machine:/extra/process/005$ ls
a.out  first  first.c  mkfifo.c  myfifo  second  second.c
alex@alex-virtual-machine:/extra/process/005$ ./second
open myfifo sucess
this is second process i=0
this is second process i=1
this is second process i=2
this is second process i=3
this is second process i=4

两个进程操作有名管道时，一个读，一个写。当读RD，WR写都open时，程序才会运行，不然会阻塞。