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Thread: Java strange thread behavior

  1. #1
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    Default Java strange thread behavior

    I've got a thread with a loop, here's my code:

    public class UpdateThread extends Thread
    {
    	public void run()
    	{
     
    		while (Game.isActive)
    		{
     
    		}
    		System.out.println("Thread stopped");
    	}
    }

    The Game.isActive is a static boolean that's true while the game is running. It's false when the game stopped.

    The code above doesn't work. But why does this code work?

    public class UpdateThread extends Thread
    {
    	public void run()
    	{
     
    		while (Game.isActive)
    		{
                            System.out.println("Thread running");
    		}
    		System.out.println("Thread stopped");
    	}
    }

    It's very strange. But it would be very inefficient and annoyoing to output something while running the thread, please help!


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    Default Re: Java strange thread behavior

    There's probably a better option than a while( true ) loop to begin with, but the reason the first version isn't doing anything is because of the magic optimizing done by the Java compiler (I think that's where it's done). You can learn more about it by searching 'java empty while loop' or similar search about code that really doesn't do anything.

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    Default Re: Java strange thread behavior

    Actually, this isn't my real code it's just an example. My real code has lots of object updating stuff in it but without an output it doesn't seem to stop.

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    Default Re: Java strange thread behavior

    The code above doesn't work. But why does this code work?
    Define doesn't work. Does the while loop get executed? Does the while loop continue indefinitely? Is the field Game.isActive declared as volatile? In situations such as this, it helps to provide an SSCCE which can be run and tested by others so that everyone is on the same page.

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    Default Re: Java strange thread behavior

    I don't want to show all my code just for this problem. But the while loop continues indefinitely.

    --- Update ---

    But strangely when in debug mode in eclipse and suspending the program and stepping over or into the code, it will stop.

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    Super Moderator copeg's Avatar
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    Default Re: Java strange thread behavior

    I don't want to show all my code just for this problem.
    I didn't ask for all your code, I asked for an SSCCE

    But the while loop continues indefinitely.
    I'll ask again, is Game.isActive declared as volatile? If not, please try it

  7. The Following User Says Thank You to copeg For This Useful Post:

    Bingo90 (October 19th, 2013)

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    Default Re: Java strange thread behavior

    Ah thanks, the volatile worked

  9. #8
    Super Moderator copeg's Avatar
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    Default Re: Java strange thread behavior

    Glad you got it working

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