A lock is
a thread synchronization mechanism like synchronized blocks except
locks can be more sophisticated than Java’s synchronized blocks. Locks (and other more advanced synchronization mechanisms) are created using synchronized blocks, so it is not like we can get totally rid of the synchronized keyword.
What is the java locks lock interface?
Simply put, a lock is a more flexible and sophisticated thread synchronization mechanism than the standard synchronized block. The Lock interface has been around since Java 1.5. It’s defined
inside the
java.
What is a lock in programming?
In computer science, a lock or mutex (from mutual exclusion) is
a synchronization primitive: a mechanism that enforces limits on access to a resource when there are many threads of execution
.
How do you release a lock in java?
Thread inside the synchronized method is set as the owner of the lock and is in RUNNABLE state. Any thread that attempts to enter the locked method becomes BLOCKED.
When thread calls wait it
releases the current object lock (it keeps all locks from other objects) and than goes to WAITING state.
What are different types of locks in java?
- 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.
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 do you acquire locked objects?
If a
thread wants to execute then synchronized method
on the given object. First, it has to get a lock-in that object. Once the thread got the lock then it is allowed to execute any synchronized method on that object. Once method execution completes automatically thread releases the lock.
What is object lock and when it is required?
An object-level lock is a
mechanism when we want to synchronize a non-static method or non-static code block
such that only one thread will be able to execute the code block on a given instance of the class.
What is the difference between lock and semaphore?
A lock (or mutex) has
two states
(0 or 1). It can be either unlocked or locked. They’re often used to ensure only one thread enters a critical section at a time. A semaphore has many states (0, 1, 2, …).
How can deadlock be prevented?
- 7.4.1 Mutual Exclusion. Shared resources such as read-only files do not lead to deadlocks. …
- 2 Hold and Wait. …
- 3 No Preemption. …
- 4 Circular Wait.
Does notify Release lock?
8 Answers. No — notify / notifyAll
don’t release locks like wait does
. The awakened thread can’t run until the code which called notify releases its lock. … The thread then waits until it can re-obtain ownership of the monitor and resumes execution.
Does sleep release lock?
Sleep()
method does not release the lock on object during Synchronization
. Wait() should be called only from Synchronized context.
What is the point of a reentrant lock?
Reentrant Locks are provided in Java to provide synchronization with greater flexibility. What are Reentrant Locks? The ReentrantLock class
implements the Lock interface and provides synchronization to methods while accessing shared resources
.
What is class level lock?
Class level lock
prevents multiple threads to enter a synchronized block in any of all available instances of the class on runtime
. This means if in runtime there are 10 instances of a class, only one thread will be able to access only one method or block of any one instance at a time.
What is race condition in Java?
Race condition in Java occurs
in a multi-threaded environment when more than one thread try to access a shared resource (modify, write) at the same time
. Since multiple threads try to race each other to finish executing a method thus the name race condition.
How does ConcurrentHashMap works in Java?
ConcurrentHashMap class is thread-safe i.e. multiple threads can operate on a single object without any complications. … In ConcurrentHashMap, the
Object is divided into a number of segments according to the concurrency level
. The default concurrency-level of ConcurrentHashMap is 16.
