According to the documentation of the Java Condition
interface:
When waiting upon a
Condition
, a "spurious wakeup" is permitted to occur, in general, as a concession to the underlying platform semantics. This has little practical impact on most application programs as a Condition should always be waited upon in a loop, testing the state predicate that is being waited for. An implementation is free to remove the possibility of spurious wakeups but it is recommended that applications programmers always assume that they can occur and so always wait in a loop.
The same advice is also found for the Object.wait(...)
method:
waits should always occur in loops, like this one:
synchronized (obj) { while (<condition does not hold>){ obj.wait(timeout); } ... // Perform action appropriate to condition }
synchronized (obj) { if (!suitableCondition()){ obj.wait(timeout); //the thread can wake up even if the condition is still false } ... // Perform action appropriate to condition }
synchronized (obj) { while (!suitableCondition()){ obj.wait(timeout); } ... // Perform action appropriate to condition }