How to differentiate when wait(long timeout) exit for notify or timeout?

Question

Having this wait declaration:

public final native void wait(long timeout) throws InterruptedException;

It could exit by InterruptedException, or by timeout, or because Notify/NotifyAll method was called in another thread, Exception is easy to catch but...

There is any way to know if the exits cause was timeout or notify?

EDIT:

This is a tricky way that could work, (although I don't like it)

          long tBefore=System.currentTimeMillis();
          wait(TIMEOUT);
          if ((System.currentTimeMillis() - tBefore) > TIMEOUT) 
            { 
               //timeout
            }

I had a similar need and in my case it turned out that a Semaphore was better suited; Semaphore.tryAcquire(long timeout, TimeUnit unit) returns false if the timeout has elapsed. — Santosh
Semaphore would work unless you need to have the ability to wait, which is not supported by the Semaphore public contract. — Victor Grazi
need to change condition to (>=): if ((System.currentTimeMillis() - tBefore) >= TIMEOUT) — Filomat
Your solution is not correct. After a notify event, the scheduler resume the thread when other thread with higher priority are not running. This mean that, after the notify, an interval of time occurs before thread resuming, if it's enough to make true your condition, your code manage a timeout instead of the correct behaviour. — Rudy Barbieri

Darron Darron · Accepted Answer · 2010-08-03T15:11:14

There is one more reason that notify can return: spurious wakeup. This is an unlikely but possible thing, because preventing spurious wakeups is very expensive on some hardware/OS combinations.

Because of this you always have to call wait() in a loop and re-check the condition that you are waiting for. During this work it's easy to check for timeout at the same time.

For details I recommend the book "Java Concurrency In Practice". And using higher level constructs that will get this all correct for you.

How to differentiate when wait(long timeout) exit for notify or timeout?

7 Answers