Thread: A fifo file and select() problem

Basically I have a server running an almost infinite, select controlled, mini webserver. I have created a fifo file with mkfifo called "pipe" which is opened in read only mode. My select is suppose to wait for something to happen in that file (which talks to a java GUI using JNI but not important) or if a client connects asking for a website. The GUI has pause, unpause and shutdown options so I figured I would have a variable "paused" in my server which if paused would stop the "FD_SET(s_sock, &fs)" with an if statement. The server will wait perfectly until I send it something along the pipe (the first time) then the select picks it out my "readGUI()" function reads the message and returns; 1, if there was nothing in the pipe or an unpaused call; 0, if there was a pause call; and -1, if there was a shutdown call. My problem is that after it goes back and initializes the select variables again the select automatically calls my readGUI again, says theres nothing in there, returns a 1 and continues this loop indefinetly.

This would have to be a problem with my select I would assume because it proves my pipe is empty.

Heres the code:

Code:

...
shutter_down = 1;
paused = 1;

while(shutter_down)
{
     T.tv_sec = 1;
     T.tv_usec = 0;
     FD_ZERO(&fs);
     FD_SET(fd, &fs);
     if (paused)
          FD_SET(s_sock, &fs);

     r = select(FD_SETSIZE, &fs, NULL, NULL, &T);

     if (r < 0)
          exit (-1)
     else if (r > 0)
     {
          if (FD_ISSET(fd, &fs))
          {
               paused = readGUI();
               if (paused == -1)
                    shutter_down = 0;
          }
          else if (FD_ISSET(s_sock, &fs))
          {
               /*Accept incoming socket and do stuff*/
          }
     }
}

int readGUI()
{
     char buf[100];
     int ret_val;

     ret_val = read(fd, buf, sizeof(buf));

     if (ret_val < 1)
          return 1;  /*Nothings there, big problem*/

     buf[ret_val] = '\0';

     printf ("buf: %s\n", buf); /*This only gets printed the first time*/
                                             /*Its how I know theres nothing in the pipe*/

     if (!(strcasecmp(buf, "1")))
          return 1;
     if (!(strcasecmp(buf, "0")))
          return 0;
     if (!(strcasecmp(buf, "-1")))
          return -1;

     return 1;
}

Let me know if you need more code. Only posted the problem.
Thanks in advance.

This might be your problem

Code:

...
shutter_down = 1;
paused = 1;

while(shutter_down)
{
     T.tv_sec = 1;
     T.tv_usec = 0;
     FD_ZERO(&fs);
     FD_SET(fd, &fs);
     if (paused)
          FD_SET(s_sock, &fs);

     r = select(FD_SETSIZE, &fs, NULL, NULL, &T);

     if (r < 0)
          exit (-1)
     else if (r > 0)
     {
          if (FD_ISSET(fd, &fs))
          {
               paused = readGUI();
               if (paused == -1)
                    shutter_down = 0;
          }
          else if (FD_ISSET(s_sock, &fs))
          {
               /*Accept incoming socket and do stuff*/
          }
          else
          {
              /* Does Nothing */
          }
      } /* you didn't close the "else if (r >0)" so there isn't a closing brace on the while statement*/

int readGUI()
{
     char buf[100];
     int ret_val;

     ret_val = read(fd, buf, sizeof(buf));

     if (ret_val < 1)
          return 1;  /*Nothings there, big problem*/

     buf[ret_val] = '\0';

     printf ("buf: %s\n", buf); /*This only gets printed the first time*/
                                             /*Its how I know theres nothing in the pipe*/

     if (!(strcasecmp(buf, "1")))
          return 1;
     if (!(strcasecmp(buf, "0")))
          return 0;
     if (!(strcasecmp(buf, "-1")))
          return -1;

     return 1;
}

If you're not going to use the else statement then I don't see any reason in putting it there