Question

我正在尝试使用命名管道在进程之间进行通信。它没有按预期运行，它一次又一次地读取相同的消息。

进程1 :(创建一个管道，开始读取直到它读完或读取100条消息）

    char* myfifo = "/tmp/omgfifo"; 
    if ( feature_head == NULL ) {
        vty_out(vty,"%s%s", ERR_STR ,VTY_NEWLINE);
        return  CMD_WARNING ;
    }
    vtysh_diag_list_features(feature_head,vty);
    /* Create UDS connection for ovs-appctl. */
    rc = mkfifo(myfifo,0777);
    if(rc == -1)
    {
        vty_out(vty,"mkfifo errorno  : %d %s",errno,VTY_NEWLINE);
    }
    fd = open(myfifo, O_RDONLY);
    if(fcntl(fd, F_GETFL ) & O_NONBLOCK)
    {
        vty_out(vty,"non block is enabled %s",VTY_NEWLINE);  
    }
    if(fd == -1)
    {
        vty_out(vty,"fd errorno  : %d %s",errno,VTY_NEWLINE);
    }
    else
    {
    while(flag)
    {
        retval ++;
        buf[0] = "\0"
        rc = read(fd,buf,MAX_BUF);
        if(retval > 100)
        {
            flag = 0;
            break;
        }
        if(rc == -1)
        {
            flag = 0;
            vty_out(vty,"read errorno  : %d %s",errno,VTY_NEWLINE);
        }
        else
        {
        if(strlen(buf) > 3 && strcmp(buf,"over"))
        {
            vty_out(vty,"gone case %s",VTY_NEWLINE);
            flag = 0;
        }
        vty_out(vty,"%3d:%s %s",retval,buf,VTY_NEWLINE);
        }
    }
    close(fd);
    }
    unlink(myfifo);
    vty_out(vty,"SIGN : done");
    return CMD_SUCCESS;

进程2（写入同一个管道）

int fd;
char * myfifo = "/tmp/omgfifo";

fd = open(myfifo, O_WRONLY);
if(fd == -1)
{
    vty_out(vty,"fd errorno  : %d %s",errno,VTY_NEWLINE);
}
else
{
    if(fcntl(fd, F_GETFL ) & O_NONBLOCK)
{
    vty_out(vty,"non block is enabled %s",VTY_NEWLINE);  
}
    if(write(fd, "Hi", sizeof("Hi"))== -1)
    {
        vty_out(vty,"write h errorno  : %d %s",errno,VTY_NEWLINE);
        }
if(write(fd, "Hi1", sizeof("Hi1"))== -1)
    {
        vty_out(vty,"write h1 errorno  : %d %s",errno,VTY_NEWLINE);
        }

if(write(fd, "over", sizeof("over")) == -1)
    {
        vty_out(vty,"write o errorno  : %d %s",errno,VTY_NEWLINE);
        }
if(write(fd, "Hi2", sizeof("Hi2")) == -1)
    {
        vty_out(vty,"write h2 errorno  : %d %s",errno,VTY_NEWLINE);
        }

if(write(fd, "Hi3", sizeof("Hi3")) == -1)
    {
        vty_out(vty,"write h3 errorno  : %d %s",errno,VTY_NEWLINE);
        }
if(close(fd)!=0)
{
    vty_out(vty,"close errorno  : %d %s",errno,VTY_NEWLINE);
}
}

    return 0;

过程1的输出（有时它是Hi1，有时它已经结束了

  1:Hi 
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100: 
SIGN : done

这两个进程的fd都是阻塞的。有人可以解释为什么prcoess 1会一次又一次地阅读某些消息

Answer 1

当你关闭写入部分的fd时，read接收到一个文件结尾并返回0（并且缓冲区没有改变，因此它保持包含＆＃34; Hi＆＃34;）。你至少应该检查这个条件（通常你应该使用read＆＃39; s返回值作为实际读取的字节数）。通常，不能保证读写之间存在完美匹配。＆＃34;写＆＃34;只是将字符排入队列，然后阅读＆＃34;最多接收您传递的数字作为第三个参数（MAX_BUF）。所以发生的事情是你在一次读取操作中收到整个字符集，然后在进一步读取时得到EOF。您可以拆分缓冲区并查找部件。

命名管道未按预期工作。正在反复阅读同一条消息

1 个答案: