Timing function in C

Discussion in 'C Programming' started by ericunfuk, Mar 9, 2007.

  1. ericunfuk

    ericunfuk Guest

    Dear All...............

    In the following java imp of stop-and-wait protocol, it creates a
    timer, are there any similar functions in C that allows me to do this?


    Thanks in advance.

    //waiting for the ACK message, stop-and-wait , waiting for 10sec
    t = new ACK_timer(10);
    while (true)
    {
    if ( t.timer_out == true )break;

    p_rcv = port_default.recv(false);

    if ( p_rcv == null ) continue;

    len_rcvd = (int)
    p_rcv.getPropertyLong("HEADER_CONTENT_LENGTH", l);
    message_rcv_id = p_rcv. getPropertyLong ("MESSAGE_ID", k);
    //Verify the ACK message
    if
    ( p_rcv.getProperty("HEADER_CONTENT_TYPE","EEE") == "ACK" &&
    message_rcv_id == last_send_msg_id )
    {
    last_ack_msg_id = message_rcv_id ;
    t.del_ACK_timer();
    break;
    }
    }

    next_send_msg_id = last_ack_msg_id + 1;

    } while (true);
    }



    }
     
    ericunfuk, Mar 9, 2007
    #1
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  2. ericunfuk

    user923005 Guest

    >From the C-FAQ:
    19.37: How can I implement a delay, or time a user's response, with
    sub-
    second resolution?

    A: Unfortunately, there is no portable way. V7 Unix, and derived
    systems, provided a fairly useful ftime() function with
    resolution up to a millisecond, but it has disappeared from
    System V and POSIX. Other routines you might look for on your
    system include clock(), delay(), gettimeofday(), msleep(),
    nap(), napms(), nanosleep(), setitimer(), sleep(), times(), and
    usleep(). (A function called wait(), however, is at least under
    Unix *not* what you want.) The select() and poll() calls (if
    available) can be pressed into service to implement simple
    delays. On MS-DOS machines, it is possible to reprogram the
    system timer and timer interrupts.

    Of these, only clock() is part of the ANSI Standard. The
    difference between two calls to clock() gives elapsed execution
    time, and may even have subsecond resolution, if CLOCKS_PER_SEC
    is greater than 1. However, clock() gives elapsed processor time
    used by the current program, which on a multitasking system may
    differ considerably from real time.

    If you're trying to implement a delay and all you have available
    is a time-reporting function, you can implement a CPU-intensive
    busy-wait, but this is only an option on a single-user, single-
    tasking machine as it is terribly antisocial to any other
    processes. Under a multitasking operating system, be sure to
    use a call which puts your process to sleep for the duration,
    such as sleep() or select(), or pause() in conjunction with
    alarm() or setitimer().

    For really brief delays, it's tempting to use a do-nothing loop
    like

    long int i;
    for(i = 0; i < 1000000; i++)
    ;

    but resist this temptation if at all possible! For one thing,
    your carefully-calculated delay loops will stop working properly
    next month when a faster processor comes out. Perhaps worse, a
    clever compiler may notice that the loop does nothing and
    optimize it away completely.

    References: H&S Sec. 18.1 pp. 398-9; PCS Sec. 12 pp. 197-8,215-
    6; POSIX Sec. 4.5.2.
     
    user923005, Mar 9, 2007
    #2
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