CSCI 241 Systems Programming Labs

Part 4. Execution times (15 points)

You’re nearly finished with ps. Two tasks remain. The first is making the execution time of a process print out in the [DD-]hh:mm:ss format. Meaning that if the process has been running for less than a day, the hours, minutes, and seconds are printed out (two digits each) and if the process has been running for longer than a day, the number of days are printed out followed by a dash and then hours, minutes, and seconds. For example, 00:05:23 for a process that has been running for 5 minutes and 23 seconds and 03-15:59:21 for a process that has been running for 3 days, 15 hours, 59 minutes, and 21 seconds.

The process for computing the execution time has two parts: getting the execution time (in seconds), and converting that into days, hours, minutes, and seconds format.

Computers keep track of time in terms of ticks, however the number of ticks per second will vary depending on the system. To figure out the number of ticks per second for your OS, you can use this libc function:

/// Returns the number of clock ticks per second.
fn ticks_per_second() -> Result<i64> {
    let ret = unsafe { libc::sysconf(libc::_SC_CLK_TCK) };

    if ret == -1 {
        return Err(io::Error::last_os_error().into());
    }
    Ok(ret)
}

Your task

In your ps’s run(), call ticks_per_second(). To compute the execution time of a process in seconds, use the execution_time field of the Process struct and divide it by the result of ticks_per_second().

Convert this time to days, hours, minutes, and seconds, and when printing the execution time, use the appropriate format.