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What is the advantage of new Lock interface over synchronized block in Java? You need to implement a high performance cache which allows multiple reader but single writer to keep the integrity how will you implement it?
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Only one thread is allowed to access only one method at any given point of time using a synchronized block. This is a very expensive operation. Locks avoid this by allowing the configuration of various locks for different purpose.
Major difference between lock and synchronized: with locks, you can release and acquire the locks in any order. with synchronized, you can release the locks only in the order it was acquired.
Lock interface handles it. No timeout − Synchronized block has no option of timeout if lock is not granted. Lock interface provides such option. Single method − Synchronized block must be fully contained within a single method whereas a lock interface's methods lock() and unlock() can be called in different methods.
Synchronized blocks provide granular control over a lock, as you can use arbitrary any lock to provide mutual exclusion to critical section code. On the other hand, the synchronized method always locks either on the current object represented by this keyword or class level lock, if it's a static synchronized method.
The advantages of a lock are
Note that this is explained in the javadoc of Lock and its subclasses.
A high performant cache could be implemented using a ConcurrentMap.
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The various advantages of lock interface over synchronisation are listed below
Synchronisation is the only culprit that leads to the problem of deadlock unlike lock which is free of deadlock issue.
In synchronisation , we don’t know after how much time a thread will get a chance after a previous thread has released the lock. This can lead to problem of starvation whereas incase of lock we have its implementing class reentrant lock which has one of its constructor which lets you pass fairness property as one of its argument that leta longest waiting thread get the chance to acquire the lock.
In synchronisation, if a thread is waiting for another thread, then the waiting thread won’t do any other activity which doesn’t require lock access but with lock interface there is a trylock() method with which you can try for access the lock and if you don’t get the lock you can perform other alternate tasks. This helps to improve the performance of the application .
There is no api to check how many threads are waiting for a particular lock whereas this is possible with lock interface implementation class ReentrantLock methods.
One can get better control of locks using lock interface with holdCount() method which is not found with synchronization.
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