help on task types

help on task types

[coxaw]

If I declare a task type that reads input from a file and prints to
screen

Then instantiate 3 copies of this type

can i tell each one to read from a different file ?

and how is it done ?

ie

task type reader_type is
blah
blah
blah
end reader;

read1:reader_type;
read2:reader_type;

but read1 is to read from inFile1
and read2 from inFile2

Re: help on task types

[Steve Folly]

coxaw wrote in message <36DD8EBF.EAA@rmcs.cranfield.ac.uk>...
>If I declare a task type that reads input from a file and prints to
>screen
>
>Then instantiate 3 copies of this type
>can i tell each one to read from a different file ?
>and how is it done ?
>


1. Why not create an entry point with a parameter specifying the file?

2. Or make it a discriminated task type, where the discriminant is an access
string type which identifies the file - that way you don't need to
explicitly call an entry point; just declaring it would start the task and
it could read the discriminant.

Steve Folly
mailto:steve@follysplace.demon.co.uk

Re: help on task types

[dennison]

In article <36DD8EBF.EAA@rmcs.cranfield.ac.uk>,
  coxaw@rmcs.cranfield.ac.uk wrote:
> If I declare a task type that reads input from a file and prints to
> screen
>
> Then instantiate 3 copies of this type
>
> can i tell each one to read from a different file ?
>
> and how is it done ?

Hmmm. This sounds suspiciously like a homework problem.

I know of 3 ways to pass task specific info to such a task.

   o  Make the object a discriminant in the task type declaration.
   o  Pass the object to the task via a rendezvous.
   o  Use a generic package w/ a task instead of a task type, and instantiate
w/ the object.

There are probably more.

T.E.D.

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Re: help on task types

[Stephen Leake]

coxaw <coxaw@rmcs.cranfield.ac.uk> writes:

> If I declare a task type that reads input from a file and prints to
> screen
> 
> Then instantiate 3 copies of this type
> 
> can i tell each one to read from a different file ?
> 
> and how is it done ?
> 
> ie
> 
> task type reader_type is
> blah
> blah
> blah
> end reader;
> 
> read1:reader_type;
> read2:reader_type;
> 
> but read1 is to read from inFile1
> and read2 from inFile2

One way is to use a discriminant:

task type reader_type (File_Name : access String) is
...
end reader_type;

File_Name_1 : aliased constant String := "inFile1";
read1 : reader_type (File_Name_1'access);

Discriminants must be scalars, so you can't put a string there directly.

Another way is to pass the file name to the task via an Initialize
entry:

task type reader_type is
    entry Initialize (File_Name : in String);
end reader_type;

This requires the user to call Initialize, which is usually a pain. But
you can pass more complex stuff that way, than with a discriminant.

-- Stephe