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Re: emulating no-senders notifications in L4?

From: Espen Skoglund
Subject: Re: emulating no-senders notifications in L4?
Date: Fri, 21 Dec 2001 20:37:57 +0100

[Niels Möller]
>> And a task can not die violently since if it raises an exception
>> this exception is delivered to an exception handler thread which
>> can handle this situation.

> Is this thread running inside the task in question or in some other
> task?

Either inside the task or in some other task.  It's all a question of
implementation.  One could for instance have an external entity
handling the exception and killing the task if it that was bahaving
incorrectly/maliciously.  One could also let some handler inside the
task handle the exception.  This would make for faster exception
handling in many cases (in particular on x86 and ARM) since one only
need to do context switches inside the task.  It also enables the
handler to directly access intra task memory, e.g., code casuing the
exception.  If the intra task exception handler fails to handle the
exception it should contact some external entity to take some
appropriate measurre like killing the task.  If the handler doesn't do
so the task will merely loop on generating exception, but this is not
much different from a task going into an endless programmed loop.


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