Question

All, I have a generic method called TaskSpin, in this method I launch a Task with an ascociated continutation

public TaskSpin(Func asyncMethod, object[] methodParameters)
{
    ...
    asyncTask = Task.Factory.StartNew<bool>(() => 
        asyncMethod(uiScheduler, methodParameters));

    asyncTask.ContinueWith(task =>
    {
        // Finish the processing update UI etc.
    }
    ...
}

The problem is now that I want to run multiple methods using TaskSpin, but I need to restrict the methods to run one-at-a-time. So foreach row in some DataGridView I want to do something like

foreach (DataGridViewRow row in this.DataGridViewUrg.Rows)
    TaskSpin(Run(DrgDataRowInfo(row.Index)));

However, in the above the TaskSpin method will exit immediately causing TaskSpin to spin off the next method on yet another thread. This is no good as the Run method write to a common set of files. What is the best way to queue these jobs?

Answer 1

You could implement your own task queue and just keep processing the queue after each task is complete until it’s empty e.g.

using TaskPair = KeyValuePair<Func, object[]>;
...

private Queue<TaskPair> taskQueue;
...

// generate the queue of tasks
this.taskQueue = new Queue<TaskPair>(this.DataGridViewUrg.Rows);
foreach (DataGridViewRow row in this.DataGridViewUrg.Rows)
{
    var task = new TaskPair(Run(DrgDataRowInfo(row.Index)), /* params */);
    this.taskQueue.Enqueue(task);
}
// initiate queue processing
ProcessNextTask();

....
private void ProcessNextTask()
{
    try
    {
        var item = this.taskQueue.Dequeue();
        TaskSpin(item.Key, item.Value);
    }
    catch(InvalidOperationException)
    {
        // queue is empty
    }   
}

....
// Execute task and process next in queue (if applicable)
public TaskSpin(Func asyncMethod, object[] methodParameters)           
{            
    ...           
    asyncTask = Task.Factory.StartNew<bool>(() =>            
        asyncMethod(uiScheduler, methodParameters));           

    asyncTask.ContinueWith(task =>           
    {           
        // Finish the processing update UI etc.
        ProcessNextTask();           
    }  
    ...                 
}