What are Intrinsic locks and how they are used for synchronization in Java ?

Every Java object can implicitly acts as a lock for providing synchronization.

These built-in lock are called intrinsic locks / monitor locks and acts as mutexes / mutual exclusion locks in Java.

When thread A attempts to acquire a lock held by thread B, A must wait / block, until B releases it.

Java provide build-in locking mechanism using :

1. Synchronized block

    a. takes Object reference acts as a lock

    b. works on block of code

2. Synchronized method

    a. uses Object reference on which method is invoked as a lock

    b. spans entire method

   

Note : static + synchronized method uses Class object as the lock

Intrinsic locks are re-entrant , means same thread can acquire the lock again.

  - Java Concurrency In Practice