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c#.netparallel-processingtask-parallel-library
Dave New
Dave New

Reputation: 40092

Check if task is already running before starting new

There is a process which is executed in a task. I do not want more than one of these to execute simultaneously.

Is this the correct way to check to see if a task is already running?

private Task task;

public void StartTask()
{
    if (task != null && (task.Status == TaskStatus.Running || task.Status == TaskStatus.WaitingToRun || task.Status == TaskStatus.WaitingForActivation))
    {
        Logger.Log("Task has attempted to start while already running");
    }
    else
    {
        Logger.Log("Task has began");

        task = Task.Factory.StartNew(() =>
        {
            // Stuff                
        });
    }
}

Upvotes: 40

Views: 44881

Answers (5)

Lotan
Lotan

Reputation: 4283

Following @Mohammad Kohanrooz answer, here is my extension method:

/// <summary>
/// Checks if task is running.
/// </summary>
/// <param name="task">Task to evaluate</param>
/// <returns>True if task is not completed or it's value is null</returns>
public static bool IsRunning(this Task task)
{
    return !task?.IsCompleted ?? false;
}

Use it like:

if(myOwnTask.IsRunning())
{
    Logger.Log("Task is already running");  
}
else
{
    Logger.Log("Starting new task");    
    myOwnTask = StartNewTask(); 
}

Upvotes: 0

Mohammad Kohanrooz
Mohammad Kohanrooz

Reputation: 19

Even easier:

if (task?.IsCompleted ?? true)
    task = TaskFunction();

Upvotes: 1

Abdul Saleem
Abdul Saleem

Reputation: 10622

private Task task;

public void StartTask()
{
    if ((task != null) && (task.IsCompleted == false ||
                           task.Status == TaskStatus.Running ||
                           task.Status == TaskStatus.WaitingToRun ||
                           task.Status == TaskStatus.WaitingForActivation))
    {
        Logger.Log("Task is already running");
    }
    else
    {
        task = Task.Factory.StartNew(() =>
        {
            Logger.Log("Task has been started");
            // Do other things here               
        });
    }
}

Upvotes: 15

guest123
guest123

Reputation: 21

You can check it with:

if ((taskX == null) || (taskX.IsCompleted))
{
   // start Task
   taskX.Start();
   //or
   taskX = task.Factory.StartNew(() =>
   {
      //??
   }
}

Upvotes: 2

Dave New
Dave New

Reputation: 40092

As suggested by Jon Skeet, the Task.IsCompleted is the better option.

According to MSDN:

IsCompleted will return true when the task is in one of the three final states: RanToCompletion, Faulted, or Canceled.

But it appears to return true in the TaskStatus.WaitingForActivation state too.

Upvotes: 38

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