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From: mab@wdl1.wdl.loral.com (Mark A Biggar)
Subject: Re: Ada.strings.bounded problems?
Message-ID: <1995Feb1.214813.14642@wdl.loral.com>
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Organization: Loral Western Development Labs
References: <Mats.Weber-2701952307410001@mlma11.matrix.ch>
 <EMERY.95Jan30091540@goldfinger.mitre.org> <D3Bqzw.D12@inmet.camb.inmet.com>
Date: Wed, 1 Feb 1995 21:48:13 GMT
Date: 1995-02-01T21:48:13+00:00
List-Id: <comp.lang.ada>

In article <D3Bqzw.D12@inmet.camb.inmet.com> brennan@panther.warm.inmet.com (William Brennan) writes:
>Please, what are "passive tasks"? (Non-periodic ones?)
>Why is it important for the optimizer to recognize them?

A "passive task" is one that does nothing significant outside of any
of its accept statements; such a task doesn't really need a separate
thread of control as it can do all its work piggy backed on the thread of
control of any task that calls one of its entries.  A simple example is:

task foo is 
    entry a;
    entry b;
end foo;

task body foo is
begin
    loop
        select
            accept a do
                -- do task operation a
            end a;
        or
            accept b do
                -- do task operation b
            end b;
        end select;
    end loop;
end foo;

The simple buffer tasks often required by the Ada tasking model a usually
passive tasks.

Recognizing that a task is passive can greatly reduce the amount of code 
necessary to be generated for it and also reduces the run time burden on
the tasking run time system.  That this optimization can be so useful
is one of the reasons that "protected objects" were added to the Ada95
specification.

--
Mark Biggar
mab@wdl.loral.com