What are instance-level locking and class-level locking in java?

By | March 5, 2023

In Java, instance-level locking and class-level locking refer to two different ways of synchronizing access to shared resources among multiple threads.

Instance level locking is a mechanism that ensures that only one thread at a time can access an instance of a class. When a thread acquires the lock on an object’s monitor, no other thread can access the object’s synchronized methods or blocks until the first thread releases the lock. This is achieved using the synchronized keyword on a method or block.

For example:

public class MyClass {
private int count = 0;

public synchronized void increment() {
count++;
}
}

In this example, the increment() method is synchronized at the instance level. This means that when a thread calls the increment() method on an instance of MyClass, it must acquire the lock on that instance’s monitor before executing the method. No other thread can access the increment() method on the same instance until the lock is released.

Class-level locking, on the other hand, is a mechanism that ensures that only one thread at a time can access a class’s static synchronized methods or blocks. When a thread acquires the lock on a class’s monitor, no other thread can access the class’s static synchronized methods or blocks until the first thread releases the lock. This is also achieved using the synchronized keyword but on a static method or block.

For example:

public class MyClass {
private static int count = 0;

public static synchronized void increment() {
count++;
}
}

In this example, the increment() method is synchronized at the class level. This means that when a thread calls the increment() method on the MyClass class, it must acquire the lock on the class’s monitor before executing the method. No other thread can access the increment() method on the MyClass class until the lock is released.

It’s important to note that while instance-level locking and class-level locking provides a way to synchronize access to shared resources, they can also cause contention and reduce performance if not used properly. Therefore, it’s important to carefully consider the synchronization needs of your application and choose the appropriate synchronization mechanism accordingly.

 

 

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