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Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!xanth!ukma!husc6!bbn!inmet!ishmael!inmet!ada-uts!stt
From: stt@ada-uts
Newsgroups: comp.lang.ada
Subject: Re: Two questions
Message-ID: <57900091@ada-uts>
Date: 31 Mar 89 13:10:00 GMT
References: <674@uva.UUCP>
Nf-ID: #R:uva.UUCP:-67400:ada-uts:57900091:000:1457
Nf-From: ada-uts!stt    Mar 31 09:10:00 1989
List-Id: <comp.lang.ada>


1. The concept of "trace-back" is a compiler/run-time-system
feature.  It is certainly possible to convince a compiler
vendor to create some sort of debugging output on this
kind of task termination.  Alternatively, and more portably,
you can create an "exception when others=>" in all task bodies
to report appropriately the unexpected demise of a task.

2. It is certainly true that "masters" must wait for their
dependent tasks to terminate.  If you have a large number
of completed tasks all with the same master, this suggests
that perhaps your tasks should be structured so that they
are reusable.  That is, enclose the main operation of
a task in a large loop headed by an entry call (to some kind of
job manager, presumably) which receives the next job to do.
This saves repeatedly creating and terminating tasks,
both of which are frequently slow operations.
(The job manager may indicate the next job for the task is
to terminate itself, if it decides that there are more
server tasks than needed.)

It is possible to have the creator of the task *not* be
the master by using access types.  For tasks within objects
designated by access types, the master is the block/unit enclosing
the declaration of the access type.  In most cases, unchecked
deallocation of such objects-containing-tasks will reclaim
the storage associated with the task as soon as the task completes.

S. Tucker Taft
Intermetrics, Inc.
733 Concord Avenue
Cambridge, MA  02138