Optimized algorithm to schedule tasks with dependency?

Question

There are tasks that read from a file, do some processing and write to a file. These tasks are to be scheduled based on the dependency. Also tasks can be run in parallel, so the

Answer 1

Without considering the serial/parallel aspect of the problem, this code can at least determine the overall serial solution:

def order_tasks(num_tasks, task_pair_list):
    task_deps= []
    #initialize the list
    for i in range(0, num_tasks):
        task_deps[i] = {}

    #store the dependencies
    for pair in task_pair_list:
        task = pair.task
        dep = pair.dependency

        task_deps[task].update({dep:1})

    #loop through list to determine order
    while(len(task_pair_list) > 0):
        delete_task = None

        #find a task with no dependencies
        for task in task_deps:
            if len(task_deps[task]) == 0:
                delete_task = task
                print task
                task_deps.pop(task)
                break

        if delete_task == None:
            return -1

        #check each task's hash of dependencies for delete_task
        for task in task_deps:
            if delete_key in task_deps[task]:
                del task_deps[task][delete_key]

    return 0

If you update the loop that checks for dependencies that have been fully satisfied to loop through the entire list and execute/remove tasks that no longer have any dependencies all at the same time, that should also allow you to take advantage of completing the tasks in parallel.