通过调用另一个线程来停止执行线程

Question

I have a thread that watches for keyboard and mouse input. When the user clicks a button in my program it activates this thread, and then when the user inputs a specific combination it calls the method test() in the example code below. So obviously the thread cannot watch for my input while it is in this test() method so spacePressed will never become true because this thread cannot call another one of its methods until this has finished.

 public void test()
{
    spacePressed = false; 
    while(!spacePressed)
    {
        pasteAtCursorLocation("Test");
        sleepy(1000);
    }
}

So could I create another thread that also watches for input and when the space is pressed it return true to a specific function call. So that it does do what I desire?

public void test()
{
    SpaceWatcher sw = new SpaceWatcher();
    sw.start();
    while(!sw.SpacePressed())
    {
        pasteAtCursorLocation("Test");
        sleepy(1000);
    }
}

But will this call SpaceWatcher to often to be effective? That is will space watch ever have enough time to watch for input between the calls to it for the space input?

EDIT: pasteAtCursorLocation does just as it says, and sleepy calls Thread.sleep(ms)

Answer 1

Maybe you should move the test() method to a new thread and manipulate the shared field spacePressed from the event handler.

That way, you would have a background thread which does some magic until the variable becomes false and the event handler is driven by the OS.

Note that it's usually not a good idea to use a thread to watch keyboard and mouse; the events sent to you by the OS are already asynchronous. Waiting for them in a special thread is like doing the same thing twice.

Instead use worker threads which respond to "events" sent by the event handler. Look into queues .

Event handler:

if( spaceWasPressed( keyboardEvent ) ) {
    queue.put( new SpaceWasPressed() );
}

Worker thread:

while( queue.poll( 1, TimeUnit.SECONDS ) == null ) {
    pasteAtCursorLocation("Test");
}

Answer 2

Sleeping for 1000 ms is a very very long time for a computer, so there is plenty of time to do other stuff in between. The SpacePressed() function will only return a boolean, this is a really cheap thing to do.

Your way is a correct way (there are many others when things get more complex than what you are doing) to have threads react to others. But you must bear in mind synchronization when sharing data (in this case spacePressed ) between threads. They need to be synchronized. This can be done by using the synchronized keyword. Another option is to declare spacePressed volatile , this can only be used in very particular cases (such as a single flag that is changed only once or if you don't care if you miss a true-false-true change).