[rules-dev] IMPORTANT: Time cheat sheet

[Edson Tirelli]

   All,

   This applies to the core engine itself and anyone touching its code.
   As we move to a time-controlled engine in Drools 5, we need to be aware
of a few things when developing our code:

1. We need to have a synchronization clock, and we do: in the
InternalWorkingMemory interface:

    public TimerService getTimerService();

    TimerService has a method to get the current time:

    public long getCurrentTime();

    This means you should NEVER EVER EVER NEVER EVER use
System.currentTimeMillis() again... if you see it in the code, please either
fix it or add a FIXME tag and let me know so that I can fix it. I am
cleaning up things right now.

     The reason is obvious: controlling the synchronization clock means we
control time as the engine sees it, so that we can use real time clocks,
pseudo clocks controlled by the application, heart beat clocks, etc. This is
also a requirement for us to implement clusters and distributed agents.

     We still have a lot to fix on the serialization side of things for
serializing scheduled executions, but lets see how this goes.

2. We need to have a synchronization clock, meaning if you use anything else
as a clock, we need to remove it and make sure it is using the TimerService.
I know Guvnor uses a TimerMachine class... I didn't had the time to look
into this yet, but we will need to make sure it either starts using the
TimerService or is synchronized with it.

3. Thread creation: make sure you don't execute anything assynchronously
with your own created threads. We need to implement a factory based thread
creation for the cases where we have to spawn threads.

   Thanks,
      Edson



-- 
 Edson Tirelli
 JBoss Drools Core Development
 JBoss, a division of Red Hat @ www.jboss.com
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