Is there a library in Java that does the following? A thread
should repeatedly sleep
for x milliseconds until a condition becomes true or the max time is reached.
This situation mostly occurs when a test waits for some condition to become true. The condition is influenced by another thread
.
[EDIT]Just to make it clearer, I want the test to wait for only X ms before it fails. It cannot wait forever for a condition to become true. I am adding a contrived example.
class StateHolder{
boolean active = false;
StateHolder(){
new Thread(new Runnable(){
public void run(){
active = true;
}
}, "State-Changer").start()
}
boolean isActive(){
return active;
}
}
class StateHolderTest{
@Test
public void shouldTurnActive(){
StateHolder holder = new StateHolder();
assertTrue(holder.isActive); // i want this call not to fail
}
}
EDIT
Most answers focus on the low level API with waits and notifies or Conditions (which work more or less the same way): it is difficult to get right when you are not used to it. Proof: 2 of these answers don't use wait correctly.
java.util.concurrent
offers you a high level API where all those intricacies have been hidden.
IMHO, there is no point using a wait/notify pattern when there is a built-in class in the concurrent package that achieves the same.
A CountDownLatch with an initial count of 1 does exactly that:
latch.countdown();
boolean ok = latch.await(1, TimeUnit.SECONDS);
Contrived example:
final CountDownLatch done = new CountDownLatch(1);
new Thread(new Runnable() {
@Override
public void run() {
longProcessing();
done.countDown();
}
}).start();
//in your waiting thread:
boolean processingCompleteWithin1Second = done.await(1, TimeUnit.SECONDS);
Note: CountDownLatches are thread safe.