The document discusses several concurrent package classes in Java: CountDownLatch, CyclicBarrier, Phaser, Exchanger, and Semaphore. CountDownLatch is used to wait for a set of tasks to complete. CyclicBarrier allows threads to wait for each other to reach a common barrier point. Phaser tracks the progress of participant threads and blocks until a certain phase is reached. Exchanger is used to exchange objects between threads. Semaphore controls access to a set of resources by acquiring and releasing permits. Examples are provided for how each class can be used.

1. concurrent package classes

2. CountDownLatch Example
How to use?
1. new CountDownLatch with count
number
2. Pass CountDownLatch instance to
many threads for doing something
and counting down
3. Pass CountDownLatch instance to
one or many threads to wait for
counting down to zero
4. Thread will keep running after
counting down to zero

3. CountDownLatch Example

4. CylicBarrier
● Call await after work finished
● Thread will wait until all
thread finished

5. CylicBarrier example

6. Phaser
1. Register for each threads
2. Call arrive if job of current phase
finish
3. Call arriveAndAwaitAdvance if
you need wait for everyone
finished
4. Whenever all registered Phaser
arrived, phase will advance and
onAdvance method will be
called

7. Phaser example

8. Exchanger
Only one concept in Exchanger ⇒ exchange.
Used to exchange object between threads.

9. Exchanger Example
Reference: ExchangerMain.java

10. Semaphore
Number of permits to be acquired or released.
1. acquire: grab permit(s), wait until all available
2. tryAcquire: grab permit(s) until given timeout
3. release: release permit(s)
4. drainPermits: grab ALL permits
5. availablePermits: get current available permits count
Reference: Semaphore.java

11. Semaphore Example - TicketPool

12. Semaphore Example - TicketGrabber

13. Semaphore Example - TicketSellPoint and Main