What is a reentrant lock?

Summary:

Lock is an interface that defines a set of methods that all locks should have. ReentrantLock is a concrete class that implements the Lock interface and provides additional features.

Java’s answer to the traditional mutex is the reentrant lock. It is similar to the implicit monitor lock accessed when using synchronized methods or blocks, but with more flexibility. You can lock and unlock a reentrant lock in different methods, but not with different threads.

ReentrantLock performs better than synchronized in high concurrency scenarios. It also provides a more convenient way of inter-thread communication through the Condition API.

The reentrant lock is a type of mutual exclusion (mutex) device that can be locked multiple times by the same process/thread without causing a deadlock.

ReentrantLock provides a tryLock() method that acquires the lock only if it’s available, reducing the blocking of threads waiting for lock-in Java applications.

The four basic types of locks are padlocks, deadbolts, knob locks, and levers.

A semaphore is a variable used to control access to a shared resource within the operating system, while a mutex is a lock acquired before entering a critical section. Semaphores are better for multiple instances of a resource, while a mutex is better for a single shared resource.

ReentrantLock is a better choice when we need reentrant mutual exclusion or a simple mutex.

The major difference between lock and synchronized is that with locks, you can release and acquire the locks in any order, while with synchronized, you can only release the locks in the order they were acquired.

Binary semaphores are non-reentrant by nature, which means that the same thread can’t re-acquire a critical section without leading to a deadlock. On the other hand, a reentrant lock allows a thread to re-enter the same lock multiple times.

A mutex is an object, while a semaphore is an integer variable. Mutex allows multiple program threads to access a single resource but not simultaneously, while semaphore allows multiple program threads to access a finite instance of resources.

Questions:

1. What is the difference between lock and reentrant lock?
   Lock is an interface that defines a set of methods that all locks should have. ReentrantLock is a concrete class that implements the Lock interface and provides additional features.
2. What is the difference between mutex and reentrant lock?
   The reentrant lock is Java’s answer to the traditional mutex. It can be locked and unlocked in different methods but not with different threads.
3. What is the difference between synchronized and reentrant lock?
   ReentrantLock performs better in high concurrency scenarios and provides a more convenient way of inter-thread communication through the Condition API.
4. Is reentrant lock a mutex?
   Reentrant lock is a type of mutual exclusion (mutex) device that can be locked multiple times by the same process/thread without causing a deadlock.
5. What’s the reason we need a reentrant lock?
   ReentrantLock provides a tryLock() method that acquires the lock only if it’s available, reducing the blocking of threads waiting for lock-in Java applications.
6. What are the four basic types of locks?
   The four basic types of locks are padlocks, deadbolts, knob locks, and levers.
7. What is semaphore vs mutex locks and which is better?
   A semaphore is used to control access to a shared resource within the operating system, while a mutex is a lock acquired before entering a critical section. Semaphores are better for multiple instances of a resource, while a mutex is better for a single shared resource.
8. What is the difference between semaphore and ReentrantLock?
   Semaphores are blind to which thread calls acquire() and release() methods, while ReentrantLock provides reentrant mutual exclusion or a simple mutex.
9. Why use lock instead of synchronized?
   The major difference between lock and synchronized is that with locks, you can release and acquire the locks in any order, while with synchronized, you can only release the locks in the order they were acquired.
10. What is the difference between semaphore and ReentrantLock?
    Binary semaphores are non-reentrant by nature, which means the same thread can’t re-acquire a critical section without causing a deadlock. However, a reentrant lock allows a thread to re-enter the same lock multiple times.
11. What is the difference between a mutex and a semaphore?
    A mutex is an object, while a semaphore is an integer variable. Mutex allows multiple program threads to access a single resource but not simultaneously, while semaphore allows multiple program threads to access a finite instance of resources.