inter-process signaling

Stephen Pair stephen at
Fri Sep 19 21:17:58 UTC 2003

Ned Konz wrote:

>On Friday 19 September 2003 11:56 am, Stephen Pair wrote:
>>One of the things that crossed my mind not too long ago is that it
>>would be nice if we could signal exceptions in another process. 
>>For example:
>>  Error new messageText: 'some error message'; signalProcess:
>>  someProcess signal: (Error new messageText: 'some error message';
>>This could be useful for graceful termination of processes (among
>>many other things)...unwind actions could always happen in the
>>process where they were defined.  The default action of a Terminate
>>exception would be to terminate the active process.  Here's the
>>method that seems to do the trick:
>>Process>>signal: anException
>>    Processor activeProcess == self ifTrue: [^anException signal].
>>    suspendedContext := MethodContext
>>        sender: suspendedContext
>>        receiver: self
>>        method: thisContext method
>>        arguments: (Array with: anException).
>I've asked for this several times and no one has come up with it yet.
>One obvious use of this is to provide Semaphore>>wait methods that 
>raise an exception on a timeout.

Of course, if your process happens to be waiting on a Semaphore, sending 
#signal: to the process will not wake it up (nothing will happen until 
the semaphore gets signaled) could add a line to the end of that 
method to suspend and resume (ie.  "self suspend; resume") and that will 
wake it up...but, what I'd really like is a way of waking it up to 
process the exception and when you resume the exception have the process 
go back into a state where it's still waiting on the original semaphore 
(if it hadn't been signaled in the interim).  I had a solution for that, 
but it seems to have a tendency to crash the VM.  ;)
- Stephen

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