Java™ How To Program (Early Objects), Tenth Edition

23.4.3 Unsynchronized Mutable Data Sharing

First, we illustrate the dangers of sharing an object across threads without proper synchronization. In this example (Figs. 23.5–23.7), two Runnables maintain references to a single integer array. Each Runnable writes three values to the array, then terminates. This may seem harmless, but we’ll see that it can result in errors if the array is manipulated without synchronization.

Class SimpleArray

A SimpleArray object (Fig. 23.5) will be shared across multiple threads. SimpleArray will enable those threads to place int values into array (declared at line 9). Line 10 initializes variable writeIndex, which will be used to determine the array element that should be written to next. The constructor (lines ...