CODEWITHSUNDEEP
c#multithreading
Eric
Eric

Reputation: 186

Thread doesn't stop when calling timer thread returns

I created this test program to find out what happens when a timer callback thread returns but a newly created thread is still running. I will see "In Work" 10 times below, even though the local thread variable should no longer be in scope when timer_Elapsed returns. Setting the thread's "IsBackground" property to true had no effect.

Is this happening because the GC has not run yet? Is it therefore dangerous to assume that a thread created in this manner will complete, since the GC may run at any time and clean up the thread?

I'm aware this is a silly example, but I'm mostly interested in just understanding what's going on here so I know what to avoid. Thanks!

public class Program
{
    static void Main(string[] args)
    {
        var timer = new Timer(500);
        timer.Elapsed += new ElapsedEventHandler(timer_Elapsed);
        timer.AutoReset = false;
        timer.Start();
        Console.ReadLine();
    }

    static void timer_Elapsed(object sender, ElapsedEventArgs e)
    {
        Console.WriteLine("In timer elapsed.  Kicking off a thread in new local thread and then immediately exiting.");
        var thread = new Thread(Work);
        thread.Start(); // but...this doesn't stop when the current thread exits!  
        Console.WriteLine("About to exit timer elapsed.");
    }

    static void Work()
    {
        for (int i = 0; i < 10; i++)
        {
            Console.WriteLine("In Work");
            Thread.Sleep(1000);
        }
    }
}

Upvotes: 1

Views: 256

Answers (2)

paquetp
paquetp

Reputation: 1651

MSDN says that once a thread is started, it is not neccessary to retain the reference to the Thread object.

Upvotes: 2

Dark Falcon
Dark Falcon

Reputation: 44181

An executing thread holds a reference to itself. The GC will never terminate a thread which has gone out of scope elsewhere.

Upvotes: 3

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