wait(long timeout) in a while loop?

But if you don't put it in a loop then how can you ensure that it won't be woken up early?

This is a deficiency in Java IMO although maybe it's a deficiency with the underlying thread support in various OS varients. I suspect Java knows whether the wait timed out or not but there is no way for the caller to figure it out without re-testing the condition and specifically testing the time. Ugly.

So you will need to put the wait(long timeout) in a while loop as well and also test to see if the time is past the timeout period. I know of no other way to accomplish this.

long timeoutExpiredMs = System.currentTimeMillis() + timeoutMs;while (!condition) {    long waitMillis = timeoutExpiredMs - System.currentTimeMillis();    if (waitMillis <= 0) {       // timeout expired       break;    }    // we assume we are in a synchronized (object) here    object.wait(waitMillis);    // we might be improperly awoken here so we loop around to see if the    // condition is still true or if we timed out}

long deadline = now() + timeout;synchronized(lock)    while( !condition() && now()<deadline )        lock.wait( deadline - now() );    if(condition())        ...    else // timeout        ...

it is because java has Mesa style monitors instead of Hoare style monitors. So you need to put wait in a while loop.Please search the string "For this reason, it is usually necessary to enclose each wait operation in a loop like this" on the follwing web page,

http://en.wikipedia.org/wiki/Monitor_(synchronization)#Nonblocking_condition_variables

.if it had been a Hoare style monitors then you could have put your wait in if. I will soon add details of Mesa monitors. This is not deficiency in Java. Both types of monitors have advantages and disadvantages.