http://www.yourworldoftext.com/FileObjects
NicoleWillson
from http://www.merlintec.com/old-self-interest/msg00676.html
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On Wed, 26 Apr 95 10:03:17 METDST Reto Kramer <kramer@al.esec.ch> wrote:
- .... The notion of active vs. passive objects has proved to be an advantage in our project because the application developers are shielded from low level process/semaphore/queue related synchronization issues and can work on the a higher abstraction level provided by asynchronous/synchronous/future and balking message passing sematics.
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That is what I think too. BTW, what is a "balking" message send?
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- Is there any attempt to bring the notion of active/passive objects, and multiple message passing sematics into self ?
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I am working on it, but I don't think it will be ready in time to be of use to you. My ( mythical ) TinySelf interpreter has only active objects. Every message send returns a future object immediately as the result, while the message gets queued at the receiver for later processing ( if it is already doing something else, each object executes a single method at a time ). If you try to send a message to the future object, however, you block. When the receiver finishes executing the message and returns the real answer, the future "become:"s that answer and unblocks any waiting objects ( threads ). In code like "x mess1 + y mess2", mess1 will block while mess2 won't ( it will inside the + method, of course, but that doesn't matter here ).
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So messages are synchronous or asynchronous depending on how they are used, no matter what the sender or the receiver. This might prove to be *too* simple for serious applications, but I hope it will be enough. Of course, the way I have described it so far this model would make recursive methods deadlock and an object like the number 2 would be a serious bottleneck in the system. But I won't go into these details here.
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- Is it considered to be a good idea to build these features into the language or should they always be provided by an add on system (if so, things like the CLOS "around/before/after" functions are useful and make the doesNotUnderstand trick obsolete in certain cases).
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In some systems this might be done using some metaobject protocol, but I feel that Self's "message passing at the bottom" approach makes it better to have a built-in concurrency model.
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Regards,
- -- Jecel Mattos de Assumpcao Jr
- Laboratorio de Sistemas Integraveis - University of Sao Paulo - Brazil -- jecel@lsi.usp.br
- http://www.lsi.usp.br/~jecel/jecel.html
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