> This will make sure that #fork has (for the purpose of resumption) the 
> same semantics as forking at a lower priority has.
> 
> What do people think about this?

Curiously, I prefer to have the *opposite* behavior in #fork, i.e. 
always resume the forked process if the priority is equal.  Note that 
this wouldn't be an ultimate fix, because it could lead to an equally 
wrong idiom,

     MyClass>>startWorkerProcess
         "worker is an instance variable"
         [self runWorkerProcess] fork.

     MyClass>>runWorkerProcess
         "Run the worker process"
         worker := Processor activeProcess.
         [Processor activeProcess == worker] whileTrue:[
             "...do the work..."
         ].

     MyClass>>stopWorkerProcess
         "Stop the worker process"
         worker := nil. "let it terminate itself"

I'm with Terry on the correct idiom to use, i.e.

     workerProcess := [self runWorkerProcess] newProcess.
     workerProcess resume.

if you really do not want to use a separate instance variable.  Another 
possibility is to signal a Notification:

        | running |
        [running := true.
        [running] whileTrue: [ ... ]]
	   on: StopRunning
	   do: [ :ex | running := false. ex resume ].

Paolo