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The Object.wait() method temporarily cedes possession of a lock so that other threads that may be requesting the lock can proceed. Object.wait() must always be called from a synchronized block or method. The waiting thread resumes execution only after it has been notified, generally due to invocation of the notify() or notifyAll() method by some other thread. The wait() method must be invoked from a loop that checks whether a condition predicate holds. Note that a condition predicate is the negation of the condition expression in the loop. For example, the condition predicate for removing an element from a vector is !isEmpty(), whereas the condition expression for the while loop condition is isEmpty(). The correct way to invoke the wait() method when the vector is empty is shown below.

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New code should use the java.util.concurrent.locks concurrency utilities in place of the wait/notify mechanism. However, legacy code that complies with the other requirements of this rule is permitted to depend upon the wait/notify mechanism.

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synchronized (object) {
  while (<condition does not hold>) {
    object.wait();
  }
  // Proceed when condition holds
}

Invocations of the await() method of the java.util.concurrent.locks.Condition interface .await() method must also be enclosed in a similar loop.

Risk Assessment

To guarantee liveness and safety, Failure to encase the wait() and or await() methods must always be invoked inside a while loop can lead to indefinite blocking and denial of service.

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