BlockingQueue is a thread-safe queue where we can enqueue on one end of queue, and dequeue on another end of queue., All BlockingQueue implementions on array or linked queues are thread-safe implementations. Below is a simple usage of BlockingQueue.



BlockingDeque is an extended implementation of queue where we can enqueue or dequeue on both ends of the queue. All BlockingDeque implementions on array or linked queues are thread-safe implementations. Below is a simple usage of BlockingDeque


Threads (Runnable vs Thread)

1.What is Thread? A thread in Java is nothing but an instance of class which is running independently to complete its job.Thread is created in Java with the help of java.lang.Thread class, and hence it is controlled using the same class. Threads executes parallel without waiting for main program/each other and completes its job, unless … Continue reading “Threads (Runnable vs Thread)”


CountDownLatch is another concurrency class, in which makes one thread wait for other until it reaches the threshold limit mentioned.Reach for the threshold limit, is counted by calling countdown() method present in CountDownLatch class.Every time countdown() method is called, the count is decremented by 1, finally when arrives at zero, the awaiting will stop. Assume … Continue reading “CountdownLatch”


ForkJoinPool is the core of the concurrency frameworks which follows divide and conquer approach in completing the tasks. Fork – Recursively break the single task into multiple smaller tasks till the threshold. Join – Join the multiple smaller tasks results and produce the output recursively. Initialise the maximum number of worker threads.

RecursiveAction class … Continue reading “ForkJoinPool”

Reentrant Lock

The ReentrantLock class is an implementation of Lock Interface, which will lock() the execution block for the thread which calls it.Until the locked thread calls the lock.unlock() method, the code block in between will not be available to other Threads…even when it is idle or sleeping or taking long time.Hence the block after lock.lock() is … Continue reading “Reentrant Lock”

Cyclic Barrier

Assume a the conference call will be opened when 4 users join., Assume until all the users join, that conference call wont be opened even when the less than 4 users join. Below example is a simple illustration of the scenario using Cyclic Barrier.


Executor & Executor Service

Executor and ExecutorService are the utility classes present starting from JDK 1.5 for executing a java process/block parallely in a controlled manner. Executor – Executor is used for creates a thread pool to for fixed number, using the method newFixedThreadPool. e.g., We have a 2 dimensional array where each row needs to be processed or set to … Continue reading “Executor & Executor Service”


A semaphore maintains a fixed number of threads in executions if exceeds lock can be acquired for that semaphore thread. Below method will get the lock of semaphore within semaphore.availablePermits()

If there are more that fixed threads, it will wait to acquire/get the semaphore lock until it has semaphore.availablepermits() greater than ‘0’.A semaphore initialised to … Continue reading “Semaphore”