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This noncompliant code example declares a nonvolatile {{Boolean}} flag. "The compiler is free to read the field {{this.done}} just once, and reuse the cached value in each execution of the loop. This would mean that the loop would never terminate, even if another thread changed the value of {{this.done}}." \[[JLS 05|AA. Java References#JLS 05]\]. This occurs because there is no {BB. Definitions#happens-before order|happens-before relation] offered by {{Thread.sleep()}}. |
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private Boolean done;
while (!this.done) {
Thread.sleep(1000);
}
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This compliant solution declares the flag volatile to ensure that updates to it are seen immediately across multiple threads. The volatile flag provides a {BB. Definitions#happens-before order|happens-before relation] between this thread and any thread that sets done.
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private volatile Boolean done;
while (!this.done) {
Thread.sleep(1000);
}
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