Posted by Schwab,Wilhelm K on Jan 05, 2011; 5:45pm
URL: https://forum.world.st/Alien-and-callbacks-from-foreign-threads-tp3175989p3176039.html

Not really an answer to your question, but Dale Rogerson's Inside COM is an excellent book (a must-have on its own) that might help with such topics.  I suspect what Alien will need to do is something similar to Apartment Threading - maybe it already does.  It has (thankfully??) been a long time, but I vaguely recall mutterings about sequencing calls through the message queue, and even marshaling data and interface pointers across thread boundaries.  Maybe Hydra holds some helpful answers??  If you have truly free threaded Java, it would probably be possible to get into situations where an Apartment threaded server would deadlock due to the synchronization of calls - I know enough to ask the question but not enough to answer it.

I await an interesting discussion among the experts.


________________________________________
From: [hidden email] [[hidden email]] On Behalf Of Joachim Geidel [[hidden email]]
Sent: Wednesday, January 05, 2011 12:22 PM
To: [hidden email]
Subject: [Pharo-project] Alien and callbacks from "foreign" threads?

Hi everybody,

I am close to releasing JNIPort (http://jniport.wikispaces.com) for Pharo
and Squeak. Almost everything works on both Mac OS X and Windows with one
exception. I can attach a Java VM to Pharo/Squeak, I can send messages to
Java objects and get results back, and even callbacks from Java to Smalltalk
seem to work.

The exception is that a callback from Java to Smalltalk which comes from a
different thread leads to a crash of the Squeak VM. I have not been able to
figure out what the problem is. There is a similar problem with a hook of
the Java VM: one can register a callback function which is called whenever
the Java VM produces output for stdout/stderr. With Pharo 1.1.1 on Mac OS X,
using this hook works when the hook contains a "nil halt", and if I simply
proceed in each of the notifiers. When I remove the halt or replace it by a
Delay, the image freezes. In Squeak 4.1 on Windows, the behavior is
different: the VM crashes.

Does Alien support callbacks coming from a "foreign" thread? Or is this a
limitation of Alien?

Thanks in advance for any help,
Joachim Geidel

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