Monday, 12 October 2015

How to check if a thread holds lock on a particular object in Java

Think about a scenario where you would have to find at run time that whether a java thread has lock on a particular object e.g. find out whether thread News Reader has lock on News Paper object or not ?

How to check if a thread holds lock in Java If this questions came in any core java interview then I would automatically assume that there could be at least two answer one is hard earned raw answer which programmer would like to figure out based on fundamentals and other could be some rarely used API calls which is available in java , by the way this is actually asked to me in an interview of one of the biggest global bank.

2 ways to find if thread holds lock on object in Java


Here I am giving my answer and what I had discovered after interview

1)I thought about IllegalMonitorStateException which wait() and notify() methods throw when they get called from non-synchronized context so I said I would call newspaper.wait() and if this call throws exception it means thread in java is not holding lock, otherwise thread holds lock.

2)Later I discovered that thread is a static method called holdsLock(Object obj) which returns true or false based on whether threads holds lock on object passed.

Comments, Suggestions ,innovative better answers are always welcome.

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