Why is ReentrantLock needed?

Summary of the article

ReentrantLock provides several advantages over the traditional wait and notify methods. It is more efficient, more reliable, and more flexible. It also provides a more reliable way to implement thread waiting and wakeup.

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.

A thread can take a lock only once. Synchronized blocks don’t offer any mechanism of a waiting queue and after the exit of one thread, any thread can take the lock. This could lead to starvation of resources for some other thread for a very long period of time.

To prevent data anomalies and conflicts, database systems use locking mechanisms to control the access and modification of data by different transactions.

ReentrantReadWriteLock can provide higher performance when the read operations are more than write operations by controlling the AbstractQueuedSynchronizer$state carefully. If not, the overhead of controlling is higher than ReentrantLock.

Java’s answer to the traditional mutex is the reentrant lock, which comes with additional bells and whistles. It is similar to the implicit monitor lock accessed when using synchronized methods or blocks. With the reentrant lock, you are free to lock and unlock it in different methods but not with different threads.

In computer science, the reentrant mutex (recursive mutex, recursive lock) is a particular type of mutual exclusion (mutex) device that may be locked multiple times by the same process/thread, without causing a deadlock.

A ReentrantLock is owned by the thread last successfully locking, but not yet unlocking it. A thread invoking lock will return, successfully acquiring the lock, when the lock is not owned by another thread. The method will return immediately if the current thread already owns the lock.

The Semaphore, by design, is blind to which thread calls acquire() and release() methods, all it cares about is permit becomes available. If we need reentrant mutual exclusion or a simple mutex then ReentrantLock is the best choice.

Locking systems provide security and control access authorization. Whether in administrative buildings, production plants, public institutions, hospitals, commercial or private buildings, now more than ever security is a top priority in society.

DisadvantagesContention: some threads/processes have to wait until a lock (or a whole set of locks) is released.Overhead: the use of locks adds overhead for each access to a resource, even when the chances for collision are very rare.

Questions and Answers:

1. What would be advantages of using a ReentrantLock?
ReentrantLock provides several advantages over the traditional wait and notify methods. It is more efficient, more reliable, and more flexible. It also provides a more reliable way to implement thread waiting and wakeup.

2. 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.

3. What are the advantages of using a lock instead of synchronization?
A thread can take a lock only once. Synchronized blocks don’t offer any mechanism of a waiting queue and after the exit of one thread, any thread can take the lock. This could lead to starvation of resources for some other thread for a very long period of time.

4. What is the advantage of locking in a database?
To prevent data anomalies and conflicts, database systems use locking mechanisms to control the access and modification of data by different transactions.

5. What is the difference between ReentrantLock and ReentrantReadWriteLock?
ReentrantReadWriteLock can provide higher performance when the read operations are more than write operations by controlling the AbstractQueuedSynchronizer$state carefully. If not, the overhead of controlling is higher than ReentrantLock.

6. What is the difference between mutex and reentrant lock?
Java’s answer to the traditional mutex is the reentrant lock, which comes with additional bells and whistles. It is similar to the implicit monitor lock accessed when using synchronized methods or blocks. With the reentrant lock, you are free to lock and unlock it in different methods but not with different threads.

7. Is Reentrantlock a mutex?
In computer science, the reentrant mutex (recursive mutex, recursive lock) is a particular type of mutual exclusion (mutex) device that may be locked multiple times by the same process/thread, without causing a deadlock.

8. What is reentrant lock?
A ReentrantLock is owned by the thread last successfully locking, but not yet unlocking it. A thread invoking lock will return, successfully acquiring the lock, when the lock is not owned by another thread. The method will return immediately if the current thread already owns the lock.

9. What is the difference between semaphore and ReentrantLock?
The Semaphore, by design, is blind to which thread calls acquire() and release() methods, all it cares about is permit becomes available. If we need reentrant mutual exclusion or a simple mutex then ReentrantLock is the best choice.

10. What is the purpose of locking?
Locking systems provide security and control access authorization. Whether in administrative buildings, production plants, public institutions, hospitals, commercial or private buildings, now more than ever security is a top priority in society.

11. What are the disadvantages of using locks in concurrency?
Contention: some threads/processes have to wait until a lock (or a whole set of locks) is released. Overhead: the use of locks adds overhead for each access to a resource, even when the chances for collision are very rare.