What is Java reentrant lock?

As the name says, ReentrantLock allows threads to enter into the lock on a resource more than once. When the thread first enters into the lock, a hold count is set to one. Before unlocking the thread can re-enter into lock again and every time hold count is incremented by one.

Which is reentrant and lock type?

As per Javadoc, ReentrantLock is a mutual exclusive lock, similar to implicit locking provided by synchronized keyword in Java, with extended features like fairness, which can be used to provide lock to longest waiting thread.

Is reentrant lock thread safe?

ReentrantLock. The class ReentrantLock is a mutual exclusion lock with the same basic behavior as the implicit monitors accessed via the synchronized keyword but with extended capabilities. This method is thread-safe just like the synchronized counterpart.

Why are reentrant locks useful?

A reentrant lock is one where a process can claim the lock multiple times without blocking on itself. It’s useful in situations where it’s not easy to keep track of whether you’ve already grabbed a lock.

What is lock in multithreading?

Locks are one synchronization technique. A lock is an abstraction that allows at most one thread to own it at a time. Locks have two operations: acquire allows a thread to take ownership of a lock. If a thread tries to acquire a lock currently owned by another thread, it blocks until the other thread releases the lock.

How do Java locks work?

Each object in Java is associated with a monitor, which a thread can lock or unlock. Only one thread at a time may hold a lock on a monitor. Any other threads attempting to lock that monitor are blocked until they can obtain a lock on that monitor.

Why is it called reentrant lock?

It is called ReentrantLock as there is an acquisition count associated with the lock which means when you use lock() method to acquire a lock and you get it then the acquisition count is 1. Whichever thread acquires the lock will also be able to access methodA() critical section as it already holds the lock.

What is class level lock and object lock?

Object Level Locks − It can be used when you want non-static method or non-static block of the code should be accessed by only one thread. Class Level locks − It can be used when we want to prevent multiple threads to enter the synchronized block in any of all available instances on runtime.

What are the different types of locks in Java?

1. Types of Java locks

• Optimistic lock / pessimistic lock.
• Exclusive / shared lock.
• Mutex / read / write lock.
• Reentrant lock.
• Fair lock / unfair lock.
• Sectional lock.
• Bias lock / lightweight lock / heavyweight lock.
• Spinlock.

Is synchronized reentrant?

Synchronized blocks in Java are reentrant. This means, that if a Java thread enters a synchronized block of code, and thereby take the lock on the monitor object the block is synchronized on, the thread can enter other Java code blocks synchronized on the same monitor object.

What is the difference between lock and ReentrantLock?

Lock is an interface. It defines a set of methods that all locks should have. ReentrantLock is a concrete class that implements the Lock interface. It implements all the methods defined in Lock , plus much more.

How many types of locks are there in Java?

there is two type of lock in java….