SJF.py

from processes import Process


def SJF(processes):

    not_done = len(processes)
    waiting_sum = 0
    time = 0
    queue = []
    executing = None
    burst = None

    # Simulating working processor
    while not_done > 0:

        # Checking whether any process arrived
        for process in processes:
            if process.arrival == time:

                # Adding to queue if processor occupied
                queue.append(process)

                # Sorting queue by burst time
                queue.sort(key=lambda x: x.burst)

        # Starting to execute another process from queue if there are any
        if not executing and queue:
            executing = queue.pop(0)
            burst = executing.burst

        #  Finishing a process when it's done
        if burst == 0:
            not_done -= 1
            executing.set_finish(time)
            waiting_sum += executing.waiting
            executing = None
            burst = None

            # If there are any processes in queue, starting to execute the first one
            if queue:
                executing = queue.pop(0)
                burst = executing.burst

        if burst:
            burst -= 1

        time += 1

    # Returning average time of waiting
    return waiting_sum/len(processes)