When I run Thread second time: java.lang.IllegalThreadStateException: Thread already started

Question

I have Thrad and Handler:

Handler handler = new Handler() {
    @Override
    public void handleMessage(android.os.Message msg) {
        super.handleMessage(msg);
        //do somethink
    }
};

Thread thread = new Thread(new Runnable() {
    @Override
    public void run() {
        //do somethink
        msg.obj = 1;
        handler.sendMessage(msg);
        thread.interrupt();
    }
});

When app start, at first time thread.start(); all work fine. But when I try start thread.start(); second time from button I have:

E/MessageQueue-JNI﹕ java.lang.IllegalThreadStateException: Thread already started.

also an ans here http://stackoverflow.com/questions/13538668/stop-thread-and-again-start-giving-illegalthreadstateexception-in-blackberry — dev2d, Apr 11 '14 at 08:39

score 38 · Accepted Answer · answered Apr 11 '14 at 08:38

38

You should check state of that thread before starting it.

if (thread.getState() == Thread.State.NEW)
{
     thread.start();
}

answered Apr 11 '14 at 08:38

Manish Dubey

4,206
8
36
65

it fixes the crash, but the panel is dead... – jim Jul 18 '19 at 05:28

Yuvaraja · Answer 2 · 2014-11-24T05:45:01.123

4

Its not a good Idea to start a Thread more then once. You have to check Whether a Thread is already started or not. if Thread not started yet

if(!thread.isAlive()){
thread.start();
}

The Better Idea is to Create new Thread instance.

edited Nov 24 '14 at 05:45

answered Apr 11 '14 at 08:36

Yuvaraja

715
6
22

6

i think there should be ! in `if(!thread.isAlive())...` but finished thread is not in state `NEW` and not alive at same time, so the exception can still occure – Zavael Nov 22 '14 at 15:58
1

thread.isAlive() is prone to "IllegalThreadStateException: Thread already started" - better use thread.getState(). – Kozuch Jan 26 '18 at 14:01
Tried it, still not working. – mrek May 02 '18 at 13:44

score 0 · Answer 3 · answered Apr 11 '14 at 08:58

At the end of run(), your thread dies. If you want to keep it alive, then add a blocking queue to the thread and make run() a big while loop that reads from the queue. Instead of calling start for each message, just add it to the queue instead.

Of course, you still have to call start() once (when your program initializes).

When I run Thread second time: java.lang.IllegalThreadStateException: Thread already started

3 Answers3

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