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Re: Re: emulating no-senders notifications in L4?

From: Ondrej Hurt
Subject: Re: Re: emulating no-senders notifications in L4?
Date: Tue, 25 Dec 2001 15:25:03 +0100 (CET)

> > But who tells the user-level that a task is a candidate for
> > slaughter ? The L4 user manuals says that shouldn't an exception be
> > handled, the faulting thread would be blocked forever. Nothing more.

> The user-level (exception handler) tells the user-level.

> Of course,
> if there's no valid exception handler installed it can be pretty hard
> to detect such faulty tasks.  It can be done through other ways of
> monitoring the task, though.  The faulting task can also be given a
> new exception handler at a later point in time, enabling the exception
> to be caught when that happens.
>       eSk

IMHO this is exactly the reason why the exception handler should be
reliable (i.e. reside in some system server like 'exec'). Otherwise
you would have to poll each task to check if it is alive, wouldn't
you ? With exceptions being delivered reliably to some task manager,
the system will be told about all faults.

I think that worse performace (inter-task IPC instead of intra-task
IPC) is not an issue here as exceptions do no occur often and tasks
are killed in response to them.

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