MULTITHREADING AND PARALLEL PROGRAMMING - Introduction to Java Programming: Comprehensive Version - page 1122

96 finally {

97 lock.unlock(); // Release the lock

release the lock

98 return value;

99 }
100 }
101 }
102 }

A sample run of the program is shown in Figure 30.19.

F IGURE 30.19

Locks and conditions are used for communications between the Producer and
Consumer threads.

30.25

✓ ✓

Can the read and write methods in the Buffer class be executed concurrently?

Check

30.26

When invoking the read method, what happens if the queue is empty?

Point

30.27

When invoking the write method, what happens if the queue is full?

30.11 Blocking Queues
Java Collections Framework provides ArrayBlockingQueue , LinkedBlockingQueue ,
and PriorityBlockingQueue for supporting blocking queues.

Key
Point

Queues and priority queues are introduced in Section 20.9. A blocking queue causes a thread
to block when you try to add an element to a full queue or to remove an element from an
empty queue. The BlockingQueue interface extends java.util.Queue and provides the
synchronized put and take methods for adding an element to the tail of the queue and for
removing an element from the head of the queue, as shown in Figure 30.20.

blocking queue

«interface»
java.util.Collection<E>

«interface»
java.util.Queue<E>

«interface»
java.util.concurrent.BlockingQueue<E>

+ put(element: E): void

Inserts an element to the tail of the queue.
Waits if the queue is full.
Retrieves and removes the head of this
queue. Waits if the queue is empty.

+ take(): E

F IGURE 30.20

BlockingQueue is a subinterface of Queue .