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The wait() method is used to temporarily cede possession of a lock so that another requesting thread can proceed. It must always be used inside a synchronized block or method. To resume activity, the requesting thread must notify the waiting thread. Moreover, the wait() method should be invoked in a loop that checks if a condition predicate holds.

The invocation of notify() or notifyAll() in another thread cannot pin point which waiting thread must be resumed. A condition predicate statement is used so that the correct thread is notified. Another use is that sometimes A condition predicate also helps when a thread is required to block until a condition becomes true, for instance, when it cannot proceed without obtaining some data from a an input stream.

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

  // Proceed when condition holds
}

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To guarantee liveness, the while loop condition should be tested before invoking the wait() method. This is because the condition might already be true which indicates that a notify signal may have already been sent from the other thread. Invoking the wait() method after the notify signal has been sent invites is futile and results in an infinitely blocked state.

To guarantee _safety_, the {{while}} loop condition must be tested even after the call to {{wait()}}. While {{wait()}} is meant to block indefinitely till a notification is received, this practice is toutedrecommended because: \[[Bloch 01|AA. Java References#Bloch 01]\] 

• Thread in the middle: A third thread can acquire the lock on the shared object during the interval between a notification being sent and the receiving thread actually resuming execution. This thread can change the state of the object leaving it inconsistent. This is akin to the "time of check, time of use" (TOCTOU) condition.
• Malicious notifications: There is no guarantee that a notification will not be sent when the condition does not hold. This means that the invocation of wait() is nullified by the notification.
• Mis-delivered notification: Sometimes on receipt of a notifyAll() signal, an unrelated thread can start executing and it is possible for its condition predicate to be true.
• Spurious wakeups: Certain JVM implementations are vulnerable to spurious wakeups that result in waiting threads waking up even without a notification.

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Likewise, if the await() method of the {java.util.concurrent.locks.Condition}} interface is implemented, it should be enclosed in a loop.

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