c# - How to ensure just one instance of a Task is running? -


i have "long running function" needs triggered on timer, , able triggered button click. while task running, button switch 'cancel' button. want single instance of task running @ time. i've made task private variable timer can check iscompleted status of task. created private variable

private task sync;

i have function task

private async task syncusers() {     // }

right now, on button click, have variable assigned function

sync = syncusers(); await sync;

it seems when task completed, that's it. how restart task/function? tried using task factory , async delegate , did not work. 

sync = task.factory.startnew(async delegate { await syncstudents(); }); await sync;

i have feeling i'm going wrong not sure start.

private task sync; private readonly object synclock = new object(); private task syncusers() {     lock (synclock)     {         if (this.sync == null || this.sync.iscompleted)         {             this.sync = ...         }     }      return this.sync; }

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