进程间通信

管道：管道是一种半双工的通信方式，数据只能单向流动。

有名管道：可用在同意主机下的任意间的进程通信 — FIFO

无名管道：只能用在具有亲缘关系的进程中通信（同一主机）— PIPE

管道的特点：

1、读阻塞：当读端和写端都存在时，管道中无数据时，read读阻塞
2、read到0：当所有写端关闭时，管道中有数据则读数据，无数据则read不阻塞返回0
3、写阻塞：当读端和写端都存在时，当管道满，则发生写阻塞（管道最大64k）
4、当所有读端都关闭时，向管道中写数据，发生管道破裂（异常）

无名管道

#include <fcntl.h>              /* Obtain O_* constant definitions */
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include<stdio.h>
#include<string.h>
#include <stdlib.h>


int main(void)
{

    int pipefd[2] = {0};
    int ret = pipe(pipefd);
    if(ret < 0)
    {
        perror("fail pipe");
    }
    pid_t pid = fork();


    if(pid > 0)
    {  
        close(pipefd[0]);
        while(1)
        {
            char buff[1024] = {0};  
            scanf("%s",buff);
            getchar();
            //buff[strlen(buff)-1] = '\0';
            write(pipefd[1],buff,strlen(buff));
            if(0 == strcmp(buff,".quit"))
            {
                break;
            }
        }
            wait(NULL);
        
    }else if(0 == pid)
    {   
        close(pipefd[1]);
        while(1)
        {
            char buff[1024] = {0};
            read(pipefd[0],buff,sizeof(buff));
            if(0 == strcmp(buff,".quit"))
            {
                break;
            }
            printf("%s\n",buff);
        }
    }else
    {
        perror("fail fork");
    }

    close(pipefd[0]);
    close(pipefd[1]);
    return 0;
}

有名管道

#include<stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include<string.h>

int main(void)
{
    int fifo = mkfifo("./mkfifo",0664);
    if(fifo < 0 && errno != EEXIST)
    {
        perror("fail mkfifo");
        return -1;
    }

    int fd = open("./mkfifo",O_RDONLY);
    if(fd < 0)
    {
        perror("fail open");
        return -1;
    }


    while(1)
    {
        char buff[1024] = {0};
        read(fd,buff,sizeof(buff));
        if(strcmp(buff,".quit") == 0)
        {
            break;
        }
        printf("%s\n",buff);
    }


    close(fd);

    remove("./mkfifo");
    return 0;
}

----------------------------------------------------------------------------------------

#include<stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>

#include<string.h>

int main(void)
{
    int fifo = mkfifo("./mkfifo",0664);
    if(fifo < 0 && errno != EEXIST)
    {
        perror("fail mkfifo");
        return -1;
    }

    int fd = open("./mkfifo",O_WRONLY);
    if(fd < 0)
    {
        perror("fail open");
        return -1;
    }

    while(1)
    {
        char buff[1024] = {0};
        scanf("%s",buff);
        getchar();
        write(fd,buff,strlen(buff));
        if(strcmp(buff,".quit") == 0)
        {
            break;
        }
    }


    close(fd);
    return 0;
}