bvanalderweireldt/concurrent-unique-queue

Java Concurrent Unique Queue

concurrent-unique-queue

A Java concurrent unique queue backed by a Set (LinkedHashSet), for when you need to have a Queue with unique elements. The ConcurrentSetBlockingQueue will behave the same way if the queue is full or if a duplicate entry already exists in the Queue.

Your element needs to have a proper hash and equals implementations !

<dependency>
  <groupId>com.hybhub</groupId>
  <artifactId>concurrent-util</artifactId>
  <version>0.3.0</version>
</dependency>

Usage

#ConcurrentSetBlockingQueue implements BlockingQueue
BlockingQueue<Integer> queue = new ConcurrentSetBlockingQueue<>();

queue.offer(1); # True
queue.offer(2); # True
queue.offer(2); # False

concurrent-unique-queue's Issues

ConcurrentSetBlockingQueue.offer() should return true when element already exists

BlockingQueue documentation for offer() method says it should return true upon success and false if no space is currently available.
I think this block in ConcurrentSetBlockingQueue should return true instead of false:

if (set.contains(e)) {
    return false;
}

Feature request. Ability to add predifined number of each element in queue

Please,
extend functionality to be possible to add predifined number of each element in queue (i.e. not more than "given number"). HashMap maybe?
Thank you.

poll() calls spliterator()

ConcurrentSetQueue#poll() contains a call to set.spliterator() whose results is not used, so I suspect it can be removed.

ConcurrentModifications exceptions

Hi,

I'm getting ConcurrentModificationExceptions while attempting to use two threads to put/take from the queue. I do have a question around locking. There are takeLock's and putLock's... But I don't see how the locking preventing the LinkedHashSet from having these concurrent since they put doesn't check takeLock and viceVersa.