MULTITHREADING AND PARALLEL PROGRAMMING - Introduction to Java Programming: Comprehensive Version - page 1119

30.19

✓ ✓

How do you create a condition on a lock? What are the await() , signal() , and
signalAll() methods for?

Check

Point

30.20

What would happen if the while loop in line 58 of Listing 30.6 was changed to an
if statement?

Replaced by

while (balance < amount) if (balance < amount)

30.21

Why does the following class have a syntax error?

public class Test implements Runnable {
public static void main(String[] args) {
new Test();

}

public Test() throws InterruptedException {
Thread thread = new Thread( this );
thread.sleep( 1000 );
}

public synchronized void run() {
}
}

30.22 What is a possible cause for IllegalMonitorStateException ?
30.23 Can the wait() , notify() , and notifyAll() be invoked from any object? What
is the purpose of these methods?
30.24 What is wrong in the following code?

synchronized (object1) {
try {
while (!condition) object2.wait();

}
catch (InterruptedException ex) {
}
}

30.10 Case Study: Producer/Consumer
This section gives the classic Consumer/Producer example for demonstrating thread
coordination.

Key
Point

Suppose you use a buffer to store integers and that the buffer size is limited. The buffer pro-
vides the method write(int) to add an int value to the buffer and the method read()
to read and delete an int value from the buffer. To synchronize the operations, use a lock
with two conditions: notEmpty (i.e., the buffer is not empty) and notFull (i.e., the buffer
is not full). When a task adds an int to the buffer, if the buffer is full, the task will wait for
the notFull condition. When a task reads an int from the buffer, if the buffer is empty, the
task will wait for the notEmpty condition. The interaction between the two tasks is shown in
Figure 30.18.
Listing 30.7 presents the complete program. The program contains the Buffer class (lines
50-101) and two tasks for repeatedly adding and consuming numbers to and from the buffer
(lines 16-47). The write(int) method (lines 62-79) adds an integer to the buffer. The
read() method (lines 81-100) deletes and returns an integer from the buffer.