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javamultithreadingconcurrencyreentrantlock

Is using ReentrantLock reliable as synchronized?

I searched a lot but was confused with the process of 'ReentrantLock' and normal 'synchronized' .

For example(1):

Object obj = new Object();

synchronized(obj){
//lock is guaranteed to be acquired 
}

example(2)

Lock lock = new ReentrantLock();
lock.lock(); //problem here
try{
//dostuff
}
finally{
lock.unlock();
}

My question is:

In example 1: it is guaranteed to acquire a lock on the object using the synchronized keyword.

But

In example 2: is it guaranteed that the lock will be acquired using the lock.lock() method?? or will the thread proceed to the next line for the execution?? without acquiring the lock.

I doubt it because, using threads had resulted in unexpected outcomes for me many times.

Solution

  • Only one thread will acquire the lock: this is the contract of ReentrantLock.

    Therefore your example 2 is perfectly thread safe.