----- Original Message ----- 
From: "James Foster" <Smalltalk at JGFoster.net>
To: "The general-purpose Squeak developers list" 
<squeak-dev at lists.squeakfoundation.org>
Sent: Tuesday, October 30, 2007 9:29 AM
Subject: Re: #copyStack on Error


> Rob Withers wrote:
>> Let's say I have a process which is consuming events off of a queue.  I 
>> don't want the process to ever terminate.  If the handling of one of 
>> these events results in an Error, even a Halt, this process will be 
>> opened in the Debugger and the user could choose to abandon or terminate 
>> at will.  Is it possible to copyStack the activeProcess and open that 
>> stack in the Debugger for the user.  This way if the User terminates the 
>> process, it won't affect the main process.
>>
>> I wonder though, if the user resumes, will two proceses be consuming 
>> events from the queue?  Perhaps I can copyStack using copyTo: a specific 
>> context that is above the point of consuming events, such that a resume 
>> will cause the copied stack to go away.
>>
>> Thanks for any assistance,
>> Rob
> One approach would be to have a "monitor" process that forks the "event 
> consumer" process. If the event consumer process terminates, the monitor 
> process would restart another one. The monitoring could be with a 
> semaphore that the event consumer signals in an unwind block. The monitor 
> process could also watch a flag to see if the event consumer should be 
> terminated or restarted.

This works and it avoids problems with copying stacks then trying to resume 
them.  Here is my processing loop:

processSends

    [[pendingSends next value. true] whileTrue]
        ifCurtailed: [self restart].


where restart first terminates the process (redundent perhaps), then starts 
a new one.  It works like a champ.

thanks,
Rob