CODEWITHSUNDEEP
javamultithreadingwaitsynchronized
DeepanshuJ
DeepanshuJ

Reputation: 159

Synchronized a single method between two threads

I want to update a file within thread. I have created a separate method for updateXML();. Thread1 and Thread2 both are calling the same method. I want only one method to call the method, the other shall wait.

Upvotes: 1

Views: 118

Answers (2)

Phoen-X
Phoen-X

Reputation: 46

extract updateXML() method to separate class, not in the Runnable implemenation. Make this method a synchronized one. Something like this:

public class XmlUpdater {
public synchronized void updateXml() {
    // do something. I imitate work :)
    try {
        System.out.println(Thread.currentThread().getName() + ". Updating XML");
        Thread.sleep(10000);
        System.out.println(Thread.currentThread().getName() + ". Updated successfully");
    }
    catch (InterruptedException e) {
        e.printStackTrace();
    }
}
}

now, create your threads or runnables, giving them (!!!important) the same instance of your xml updating class. Use it :) Example of main class:

public class ThreadTest {


static class TestRunnable implements Runnable {

    private XmlUpdater updater;

    TestRunnable(XmlUpdater updater) {
        this.updater = updater;
    }

    public void run() {
        updater.updateXml();
    }
}
public static void main(String[] args) throws InterruptedException {
    XmlUpdater updater = new XmlUpdater();

    //NOTE the updater object is same for two runnables
    Runnable runnable1 = new TestRunnable(updater);
    Runnable runnable2 = new TestRunnable(updater);
    Thread t1 = new Thread(runnable1);
    Thread t2 = new Thread(runnable2);
    System.out.println("Threads started");
    t1.start();
    t2.start();
    t1.join();
    t2.join();

    System.out.println("Program ended");
}
}

My output is: 

Threads started
Thread-0. Updating XML
Thread-0. Updated successfully
Thread-1. Updating XML
Thread-1. Updated successfully

Program ended

Upvotes: 0

Tobias
Tobias

Reputation: 7771

synchronized void updateXML() {
    /* ... */
}

This, however, also locks other synchronized methods of the class. You could use a lock object if necessary:

private final Object updateXmlLock = new Object();

void updateXML() {
    synchronized(updateXmlLock) {
        /* ... */
    }
}

You can read more about intrinsic locks and synchronized methods in the Java tutorial.

Upvotes: 1

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