CODEWITHSUNDEEP
javamultithreadinglockingthread-synchronization
Felipe
Felipe

Reputation: 29

Holding locks on two objects

I have a question about locks and synchronization.

I have a method that locks object 1, and other method that locks object 2:

private void a(){
    synchronized(obj1){
        System.out.println("Object 1 being used");
    }
        System.out.println("Object 1 finished");

}

private void b(){
    synchronized(obj2){
        System.out.println("Object 2 being used");
    }
        System.out.println("Object 2 finished");

}

Also I have a third method:

private void c(){
for(int i=0;i<=0;i++){
        a();
        b();
        Thread.sleep(2000);
    }
}

I want to hold the lock on both objects, 1 and 2 while the method c is running, after c is done, both locks can be released. How can I achieve this? I tried putting them into a for loop, but the methods a and b just start and finish.

Upvotes: 2

Views: 321

Answers (1)

Nathan Hughes
Nathan Hughes

Reputation: 96385

Have the c method acquire both locks in nested blocks:

synchronized (obj1) {
    synchronized (obj2) {
         // c method logic here
    }
}

Intrinsic locks are re-entrant so it doesn't matter that methods a and b already acquire them.

If you make more than one method that does this, make sure they acquire the locks in the same order, to avoid deadlocks.

Upvotes: 1

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