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According to the Java Language Specification [JLS 2011] , §17.3, "Sleep and Yield" [JLS 2011],

It is important to note that neither Thread.sleep nor Thread.yield have any synchronization semantics. In particular, the compiler does not have to flush writes cached in registers out to shared memory before a call to Thread.sleep or Thread.yield, nor does the compiler have to reload values cached in registers after a call to Thread.sleep or Thread.yield.

Code that depends on thread suspension or yielding that yields to

• flush cached registers
• reload any values
• provide any happens-before relationships when execution resumes

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This noncompliant code attempts to use the nonvolatile primitive Boolean member done as a flag to terminate execution of a thread. A separate thread sets done to true by calling the shutdown() method.

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This compliant solution declares the flag field volatile to ensure that updates to its value are made visible across multiple threads.:

final class ControlledStop implements Runnable {
  private volatile boolean done = false;

  // ...
  @Override public void run() {
  //...
  }
}

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Related Guidelines

Bibliography

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