UWP background tasks: Does it run indefinitely? How to check if it is already running?

From a UWP app I start the following UWP background task using BackgroundTaskBuilder:

namespace Background.UWP
{
    public sealed class BackgroundTask : IBackgroundTask
    {
        private WatchLoop _watchLoop;

        public void Run(IBackgroundTaskInstance taskInstance)
        {
            ApplicationTriggerDetails details = taskInstance.TriggerDetails as ApplicationTriggerDetails;
            var arg = details.Arguments["MyArg"].ToString();

            // Start an infinite loop that periodically does some checks 
            _watchLoop = new WatchLoop(arg, new ToastNotification());
            _watchLoop.Start();    
        }    
    }
}

First question: Does this background task run indefinitely if not cancelled by certain check conditions?

Second question: In my UWP app, how can I check if this background task is already running? I want to avoid starting a second background task. Is there a global handle of this task that I can store (serialized) in global storage (e.g. database) and use in the next instance of the UWP app?

I solved this problem as follows:

Before registering and starting my background task I do a check like in Junjie Zhu's example. I register and start the background task only if it is not yet registered.

I then put a try ... finally around my _watchLoop.Start() loop and in the finally block I put some code to unregister the background task.

This should work in normal operation. However, if I stop all processes in VS Debugger, the background task stops immediately without reaching the finally block. For this purpose I declare a compile switch that during development always unregisters my background task before starting.