sub-thread not returning to main thread

Question

this is my main thread:

private void button1_Click(object sender, EventArgs e)
{
    Thread oThread = new Thread(new ThreadStart(understand));      // create the thread for understand function
    oThread.Start();      // start the thread
    button1.Enabled = false;

    Thread.Sleep(1);      

    if (false == understand_status)
    {
        MessageBox.Show("i am in main thread");
    }
}

this is my sub-thread:

private void understand()
{
    int license_value=0;

    while (understand_status)
    {             
        ..............
        if (license_value < 29)
        {
            understand_status = false;
            ...........
        }
        if (false == understand_status)
        {
            MessageBox.Show("inside while");
            File.Delete("C:\\log.txt");
        }
    }
    MessageBox.Show("outside while");    
}

it is showing message "outside while" but not returning to main thread. where i am showing "i am in main thread". I am new to thread programming any help appreciated

Either your thread takes more than a second to set `understand_status` to `false`, or else `understand_status` is the victim of jitter optimization (in which case marking it `volatile` should make the problem go away, but `volatile` is something you really should not be using at all; read [this](http://stackoverflow.com/questions/72275/when-should-the-volatile-keyword-be-used-in-c)). — Jon, Feb 26 '14 at 09:12
Actually, the thread.Sleep(1) would cause the thread to sleep for a millisecond, not a second.. — Martin Milan, Feb 26 '14 at 09:23

score 0 · Answer 1 · answered Feb 26 '14 at 09:11

0

add oThread.Join() after thread is started

answered Feb 26 '14 at 09:11

Helic

907
1
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25

1

If you are going to start a thread and immediately `Join` it then why bother in the first place? – Jon Feb 26 '14 at 09:13

score 0 · Answer 2 · answered Feb 26 '14 at 09:17

0

Please check that you use "volatile" keyword for declaration of understand_status variable like this:

 volatile bool understand_status = true;

Also try to use Join method insted of Thread.Sleep(1) like this:

 oThread.Join();

answered Feb 26 '14 at 09:17

fastobject

1,372
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my main thread is UI thread if i will use join i won't able to acces UI. – Deepak Rout Feb 26 '14 at 11:29

score 0 · Answer 3 · answered Feb 26 '14 at 09:24

You start the thread which asynchronously starts some work. Your main thread continues it's work, but when checking understand_status, the other thread has not yet reached the point where you have changed the status, thus your if clause is not met and therefore nothing is shown.

score 0 · Answer 4 · answered Feb 26 '14 at 09:34

0

When you main thread gets to

if (false == understand_status)
{
     MessageBox.Show("i am in main thread");
}

'understand_status' is actually true since the other thread is still processing. This is a simple race condition.

answered Feb 26 '14 at 09:34

Georgi-it

3,676
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sub-thread not returning to main thread

4 Answers4