nginx异步io

 if (socketpair(AF_UNIX, SOCK_STREAM, 0, ngx_processes[s].channel) == -1) //建立父子进程通信的管道
        {
            ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                          "socketpair() failed while spawning \"%s\"", name);
            return NGX_INVALID_PID;
        }
 on = 1; //打开异步io
        if (ioctl(ngx_processes[s].channel[0], FIOASYNC, &on) == -1) { //设置异步IO
            ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                          "ioctl(FIOASYNC) failed while spawning \"%s\"", name);
            ngx_close_channel(ngx_processes[s].channel, cycle->log);
            return NGX_INVALID_PID;
        }

        //看unix高级网络编程14.6.2BSD异步io
        if (fcntl(ngx_processes[s].channel[0], F_SETOWN, ngx_pid) == -1) { //设置将接收SIGIO和SIGURG信号的进程id或进程组ID，进程组id通过提供负值的arg来说明，否则，arg将被认为所进程id
            //SIGURG网络传来带外数据时产生，也是紧急套接口，SIGIO异步id（设置异步后必须设置），异步io是SIGIO和SIGURG组合
            ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                          "fcntl(F_SETOWN) failed while spawning \"%s\"", name);
            ngx_close_channel(ngx_processes[s].channel, cycle->log);
            return NGX_INVALID_PID;
        }

        if (fcntl(ngx_processes[s].channel[0], F_SETFD, FD_CLOEXEC) == -1) { //设置FD_CLOEXEC标志，在子进程里面没有关闭，在EXEC里面关闭，不拷贝进入
            ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                          "fcntl(FD_CLOEXEC) failed while spawning \"%s\"",
                           name);
            ngx_close_channel(ngx_processes[s].channel, cycle->log);
            return NGX_INVALID_PID;
        }