On Feb 4, 2008, at 6:21 PM, Igor Stasenko wrote:

> On 04/02/2008, Andreas Raab <andreas.raab at gmx.de> wrote:
>> Hi -
>>
>> In my never-ending quest for questionable behavior in multi-threaded
>> situations just today I ran into a pattern which is dangerously  
>> common
>> in our code. It basically goes like this:
>>
>
> Hmm, IMO, you wanting to kill two rabbits in one shot..
>
> Why not write like following:
>
> MyClass>>startWorkerProcess
>         "worker is an instance variable"
>        running := true.
>        worker := [self runWorkerProcess] fork.
>
> MyClass>>runWorkerProcess
>         "Run the worker process"
>         [running] whileTrue:[
>                 "...do the work..."
>         ].
>
> MyClass>>stopWorkerProcess
>         "Stop the worker process"
>        running := false. "let it terminate itself"

This doesn't work either (and is actually the reason that the  
original, broken pattern described by Andreas was used).  Consider the  
following:

inst := MyClass new.
inst startWorkerProcess; stopWorkerProcess; startWorkerProcess

If the first worker process happens not to notice that 'running' was  
set to false for a moment, then you will have two processes running.   
By comparing against the worker process, you avoid this problem.

Josh



>
>
> Yes, you will need an additional inst var - 'running', but i think
> it's reasonable: controlling a process in context of scheduler
> operations, where you need it's handle, and controlling when it's
> should terminate graciously (by setting running flag to false), is
> different things.
>
> -- 
> Best regards,
> Igor Stasenko AKA sig.
>