Threaded Java - Java - page 888

One caveat is that, in real life, you generally would not want to perform I/O while holding
the monitor lock, because doing so is bad for performance.

Simplifying Producer/Consumer with the Queue Interface

Problem

You need to control producer/consumer implementations involving multiple threads.

Solution

Use the Queue interface or the BlockingQueue subinterface.

Discussion

As an example of the simplifications possible with java.util.Concurrent package, con-
sider the producer/consumer program in Synchronizing Threads the Hard Way with wait( )
and notifyAll( ) . Example 22-14 , ProdCons15.java, uses the java.util.BlockingQueue
(itself a subinterface of the java.util.Queue interface) to reimplement the program
ProdCons2 from Example 22-13 in about two-thirds the number of lines of code. With these
new features, the application need not be concerned with wait() or the vagaries of noti-
fy() and the use of notifyAll() in its place.

The application simply puts items into a queue and takes them from it. In the example, I have
(as before) four producers and only three consumers, so the producers eventually wait. Run-
ning the application on one of my older notebooks, the producers' lead over the consumers
increases to about 350 over the 10 seconds or so of running it.

Example 22-14. ProdCons15.java
public public class class ProdCons15 ProdCons15 {

protected protected volatile volatile boolean boolean done = false false ;

/** Inner class representing the Producer side */
class class Producer Producer implements implements Runnable {

protected protected BlockingQueue < Object > queue ;