How to run only 1 single long running task in separate thread in ASP.NET

How do you run a long running task in ASP.NET in thread and
avoid multiple instances of this task from running?

I saw a solution somewhere but do you have a better one?

[WebMethod]
publicvoid StartTask1()
{
string processKey = this.Context.Re quest.UserHostA ddress + "1";

// Create a lock object to prevent 1 user from running task 1 //
multiple times. string threadLockKey = "thread1" +
this.Context.Re quest.UserHostA ddress;
object threadLock = this.Context.Ca che[threadLockKey];
if (threadLock == null)
{
threadLock = newobject();
this.Context.Ca che[threadLockKey] = threadLock;
}

// Only allow 1 running task per user. if (!
Monitor.TryEnte r(threadLock, 0))
return;

// Simulate a time-consuming task. for (int i = 1; i <= 100; i++)
{
// Update the progress for this task.
this.Context.Ca che[processKey] = i;
Thread.Sleep(10 0);
}

// The task is done. Release the lock. Monitor.Exit(th readLock);
}