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From: skrenta@amix.commodore.com (Rich Skrenta)
Newsgroups: comp.os.misc
Subject: More questions about Amoeba and Capabilities
Message-ID: <2623@amix.commodore.com>
Date: 14 Jun 91 16:55:33 GMT
Organization: Commodore-Amiga Unix Development
Lines: 51

Two questions for fans of Amoeba or other capability-based systems.

Question #1:

An Amoeba server is only listening on a port if it is blocked in a
get_request(port, ...) call.  Does this mean that if the server runs
out of threads executing get_requests that the service appears to vanish
to prospective clients?  A client trying to locate the service port might
fail just because the service is busy.  How is this dealt with in Amoeba?

    client does:
	do_operation(port, ...);

    server does:
	spawn_lightweight_threads(10);
	for (;;) {
		get_request(port, ...);
		process_request();
		put_reply(...);
	}

If all 10 lightweight threads are tied up in process_request(), the server
won't be executing any get_requests on its port, and the client's do_operation
will fail.


Question #2:

The bullet file server returns a capability when you ask it to create a
file.  The capability must be presented to perform operations on the file
such as read, write and delete.

	capability = create_file(...);

Presumably you're supposed to add this capability to a directory or otherwise
responsibly manage it.  But what if you "lose" it?

	capability = 0;

The capability is not stored anywhere, but the bullet file server doesn't
know this.  There is an unreferenced file on the file server with no
way to "garbage collect" it.

It seems that during the development of even a simple program there would
be potential to lose references to many files.  Not even the programmer
whose errant program had created these files could reclaim them.
Is there a solution?

Rich
--
skrenta@amix.commodore.com