Is this thread safe for two threads share on queue in java?

Question

I got a Queue in my Server class:

public class Server{

    Queue<Input> inputQueue; 

    public void start() {
      inThread = new InThread(inputQueue);
      outThread = new OutThread(inputQueue);

      inThread.start();
      outThread.start();
    }
}

The inThread will responsible for fill in data in the inputQueue, and the outThread will responsible for take out data from the outputQueue. InThread and OutThread will execute concurrently. Will there a chance that the data will not thread safe? If so, I did some study, it have synchronized variable and synchronized method. Which one should I use? Thanks.

score 0 · Answer 1 · answered Aug 15 '13 at 12:39

0

As the queue is shared between threads so it is not thread safe without sunchronizing your read and write methods.

If you want a thread safe queue readymade then you may consider using ConcurrentLinkedQueue:

http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/ConcurrentLinkedQueue.html

answered Aug 15 '13 at 12:39

Juned Ahsan

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I would use a Java 7 javadoc, if providing a link. – Peter Lawrey Aug 15 '13 at 12:42

score 0 · Answer 2 · answered Aug 15 '13 at 12:40

There isn't much of a need for hand-synchronization, although your existing approach is not threadsafe.

java.util.concurrent.ArrayBlockingQueue<E> can work for you. Its constructor allows one to pass in a collection, so you can do:

ArrayBlockingQueue<Input>blockingQueue=new ArrayBlockingQueue<>(128, false, inputQueue);

changing 128 as the capacity and the boolean as specifying whether queueing after blocks should be fair.

You can also use ConcurrentLinkedQueue. Its constructor is just:

ConcurrentLinkedQueue<Input> clq=new ConcurrentLinkedQueue<>(inputQueue);

I would use a Java 7 javadoc, if providing a link. – Peter Lawrey Aug 15 '13 at 12:42 — Peter Lawrey, Aug 15 '13 at 12:42

score 0 · Answer 3 · answered Aug 15 '13 at 12:41

I would use an ExecutorService which wraps a thread pool and a Queue and is thread safe/tested/is written for you.

You are right that some Queues require external synchronization but if you use a thread safe collection like ConcurrentLinkedQueue you don't need synchronized, though it won't hurt much if you do.

score 0 · Answer 4 · answered Aug 15 '13 at 12:42

0

To me Your question seems to be the case of standard producer consumer case with Wait and Notify .

Just google producer consumer example in java , you will get thousands of examples.Hope it helps.

answered Aug 15 '13 at 12:42

M Sach

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I wouldn't use notify/wait unless you have to use Java 1.3 or older. For Java 1.4+ I would use the concurrency library – Peter Lawrey Aug 15 '13 at 12:43
Not a good idea for this, and also link-only answers are discouraged. – nanofarad Aug 15 '13 at 12:44

Is this thread safe for two threads share on queue in java?

4 Answers4