CODEWITHSUNDEEP
java
Sahil
Sahil

Reputation: 96

issue in locking a own object in synchronized block

I have a class and i make synchronized lock in that class for the same class object For ex.

class Demo{
    private Demo obj=new Demo();
    synchronized(obj){
         //some code here
    }
}

then it gives error of stack overflow but i write the same code as

class Demo{
    private static Demo obj=new Demo();
    synchronized(obj){
         //some code here
    }
}

Then it works fine so please any one is there to explain me logically what is happening here.

Upvotes: 2

Views: 108

Answers (1)

Jon Skeet
Jon Skeet

Reputation: 1502196

It's nothing to do with synchronization. You'll have the exact same problem with this code:

class Demo {
    private Demo obj=new Demo();
}

You're saying that in order to create an instance of Demo, you need to create a new instance of Demo - which will create another new instance of Demo etc. In your static version, there's only one static field, initialized once, so you don't get this infinite recursion.

If you want some code to synchronize on itself, you can just use this:

synchronized(this) {
    ...
}

Personally I would recommend synchronizing on a separate object which was never exposed though:

public class Demo {
    private final Object lock = new Object();
    ...
    // In a method
    synchronized(lock) {
        ...
    }
}

It's easier to reason about locks when you know that the only thing which knows about that reference is the Demo object itself.

Upvotes: 9

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