Posted by Joachim Geidel on Jan 05, 2011; 7:13pm
URL: https://forum.world.st/Alien-and-callbacks-from-foreign-threads-tp3175989p3176215.html

Igor,

Igor Stasenko wrote

So, unless you running RoarVM, i don't see that it is reasonable to
support cross-thread callbacks.

VisualWorks and Dolphin both support foreign callbacks, using two very different implementations. Yes, it's not easy, as there are lots of ways to create deadlocks and faults etc. Chris Uppal's implementation of JNIPort for Dolphin came with a highly complicated mechanism for deadlock prevention which is now also part of the ports of JNIPort to VisualWorks, Pharo and Squeak.

However, there are situations where foreign callbacks are needed simply because the external libraries which are used have a multithreaded implementation. E.g., the callbacks for monitoring a Java VM (to monitor class loading, garbage collection etc.) will always come from a foreign thread, and this has nothing to do with performance. It's just the way it is. Another example (see screenshot at the end of the page): http://metagnostic.dolphinmap.net/JNIPort/callback-example-1.html

Best regards,
Joachim Geidel