table of Contents
2. Check the size of the pipeline buffer
1.pipe function
#include <unistd.h>
int pipe(int pipefd[2]);
功能：创建一个匿名管道，用来进程间通信
参数：int pipefd[2]，这是数组是一个传出参数
pipefd[0] 对应的是管道的读端
pipefd[1] 对应的是管道的写端
返回值：
成功：0
失败：-1
管道默认是阻塞的：如果管道中没有数据，read阻塞；如果管道满了，write阻塞
注意：匿名进程只能用于具有血缘关系的进程之间的通信（父子进程、兄弟进程等）Program example 1: The child process sends once, the parent process receives once
#include <stdio.h>
#include <unistd.h>
#include <string.h>
//子进程发送数据给父进程，父进程读取到数据后输出
int main()
{
//在fork之前创建管道
int pipefd[2];
int ret=pipe(pipefd);
if(ret==-1)
{
perror("pipe");
return -1;
}
//创建子进程
pid_t pid=fork();
if(pid>0)
{
//父进程 从管道的读取端读取数据
char buf[1024]={0};
int len=read(pipefd[0],buf,sizeof(buf));
printf("parent recv :%s,pid=%d\n",buf,getpid());
}
else if(pid==0)
{
//子进程 向管道的写入端写入数据
//sleep(10); //如果有这句话，子进程会休眠10秒再写入，父进程会一直等待直到子进程将数据写入再读取
char *str="hello,I am the child";
write(pipefd[1],str,strlen(str));
}
return 0;
}
Program example 2: The child process keeps sending, the parent process keeps receiving
#include <stdio.h>
#include <unistd.h>
#include <string.h>
//子进程发送数据给父进程，父进程读取到数据后输出
int main()
{
//在fork之前创建管道
int pipefd[2];
int ret = pipe(pipefd);
if (ret == -1)
{
perror("pipe");
return -1;
}
//创建子进程
pid_t pid = fork();
if (pid > 0)
{
printf("parent process,pid=%d\n", getpid());
//父进程 从管道的读取端读取数据
char buf[1024] = {0};
while (1)
{
int len = read(pipefd[0], buf, sizeof(buf));
printf("parent recv :%s,pid=%d\n", buf, getpid());
}
}
else if (pid == 0)
{
//子进程
printf("child process,pid=%d\n", getpid());
while (1)
{ //向管道的写入端写入数据
char *str = "hello,I am the child";
write(pipefd[1], str, strlen(str));
sleep(1);
}
}
return 0;
}
Program example 3: The child process keeps sending data, and the parent process receives the data; the parent process also keeps sending data, and the child process receives the data
#include <stdio.h>
#include <unistd.h>
#include <string.h>
//子进程发送数据给父进程，父进程读取到数据后输出
int main()
{
//在fork之前创建管道
int pipefd[2];
int ret = pipe(pipefd);
if (ret == -1)
{
perror("pipe");
return -1;
}
//创建子进程
pid_t pid = fork();
if (pid > 0)
{
printf("parent process,pid=%d\n", getpid());
//父进程 从管道的读取端读取数据
char buf[1024] = {0};
while (1)
{
//读取数据
int len = read(pipefd[0], buf, sizeof(buf));
printf("parent recv :%s,pid=%d\n", buf, getpid());
bzero(buf,1024);
//写入数据
char* str="hello,I am parent";
write(pipefd[1],str,strlen(str));
sleep(1);
}
}
else if (pid == 0)
{
//子进程
printf("child process,pid=%d\n", getpid());
char buf[1024]={0};
while (1)
{ //向管道的写入端写入数据
char *str = "hello,I am child";
write(pipefd[1], str, strlen(str));
sleep(1);
//读取数据
read(pipefd[0],buf,sizeof(buf));
printf("child recv :%s,pid=%d\n", buf, getpid());
bzero(buf,1024);
}
}
return 0;
}
//注：父进程和子进程的读写顺序要相反，不然两个都会阻塞，不能运行下去
2. Check the size of the pipeline buffer
Command mode:
As you can see from the picture below, it is 4K
Function method:
#include <stdio.h>
#include <unistd.h>
#include <string.h>
int main()
{
int pipefd[2];
pipe(pipefd);
//获取管道的大小
long ret=fpathconf(pipefd[0],_PC_PIPE_BUF);
printf("管道大小：%ld\n",ret);
ret=fpathconf(pipefd[0],_PC_PIPE_BUF);
printf("管道大小：%ld\n",ret);
return 0;
}
Reference: Niuke.com C++ high-paying job search project "Linux High Concurrency Server Development" 2.12 father and son processes communicate through anonymous channels
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