illegal fseek/ftell

raedbenz · 07-17-2010, 06:33 PM

could u plz specify an example code ?
cheers

Sergei Steshenko · 07-17-2010, 06:37 PM

Quote:

Originally Posted by raedbenz

could u plz specify an example code ?
cheers

No. That's for you to learn. Start from here: https://computing.llnl.gov/tutorials/pthreads/ .

wje_lq · 07-17-2010, 07:23 PM

Any time I want to write a program which doesn't hang waiting for input, but rather is free to do other things if input is not available, I use select(). I highly recommend that you investigate it.

Sergei Steshenko · 07-17-2010, 07:44 PM

Quote:

Originally Posted by wje_lq

Any time I want to write a program which doesn't hang waiting for input, but rather is free to do other things if input is not available, I use select(). I highly recommend that you investigate it.

You still need to see somehow that the input you want is there. I.e. you will have to organize some polling. So that's why I'm suggesting threads - using them one thread just polls a flag signifying the input is ready; the flag is set by the thread stuck in waiting for input.

Looks like a more generic solution to me, and the percentage of CPU time needed to poll the flag can be set by the corresponding thread priority.

raedbenz · 07-18-2010, 02:35 AM

Quote:

Originally Posted by wje_lq

Any time I want to write a program which doesn't hang waiting for input, but rather is free to do other things if input is not available, I use select(). I highly recommend that you investigate it.

hello,
i have already used select() with open,, read and write, and i tried to used it with fopen, fwrite, fread an it didn't work, like that:

Code:

    fd_set rfds;
    struct timeval tv;
    int retval, nfd;

    nfd = fileno( rfcomm ); //converts the FILE pointer to integer
    FD_ZERO(&rfds);
    FD_SET(nfd, &rfds);
    tv.tv_sec = 1;
    tv.tv_usec = 0;
    retval = select(1+nfd, &rfds, NULL, NULL, &tv);

    if (retval == -1)
        perror("select()");
    else if (retval)
        printf("Data is available now.\n");
    else
        printf("No data within 1 seconds.\n");

an ii kept getting No data available.
cheers

PTrenholme · 07-19-2010, 01:41 PM

Quote:

Originally Posted by raedbenz

could u plz specify an example code ?

Have you looked at the standard method for setting up interrupt driven systems? Specifically, the use of call-back functions triggered by hardware events. Examples abound, and shouldn't be hard to find. (Do recall that almost all GUI systems use interrupt-driven call-back functions.)

The analogy between what you're trying to accomplish and what the OS does to read the keyboard made, above, by Sergei Steshenko should, I believe, have suggested using event-driven call-back functions. (Which, as Sergei also noted, can be implemented as a thread processing asynchronous events. Did you look at the tutorial on POSIX threads to which he pointed you?)