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From: Florian Weimer <fw@deneb.cygnus.argh.org>
Subject: Re: Exception Save_Occurence Usage
Date: 2000/02/15
Message-ID: <87zot2c07u.fsf@deneb.cygnus.argh.org>#1/1
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References: <38A83769.13E22D48@res.raytheon.com>
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Reply-To: Florian Weimer <fw-usenet@deneb.cygnus.argh.org>
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Date: 2000-02-15T08:57:09+00:00
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John J Cupak Jr <John_J_Cupak@res.raytheon.com> writes:

> Does anyone have an example of  how to use the
> Ada.Exceptions.Save_Occurence function/procedure and the corresponding
> Reraise_Occurence procedure? Syntax is easy to understand, semantics
> takes a bit longer.

You can use them to promote exceptions across tasks.  (Disclaimer: I
don't know whether this is politically correct usage of this
subprograms or brutal abuse.)

      task type Feeder is
         ...
         entry Get_Exception (E     : out Exception_Occurrence;
                              Error : out POSIX.Error_Code);
         --  Retrieves information about the error status of the task. 
         --  ...                            If no exception was raised, E is
         --  Null_Occurrence.  If no POSIX_Error exception was raised, Error is
         --  POSIX.No_Error.
      end Feeder;

      task body Feeder is
         ...
         Excep : Exception_Occurrence;
         Err   : POSIX.Error_Code := POSIX.No_Error;
      begin
         ...
         begin
            ...
         exception
            when E : others =>
               if Exception_Identity (E) = POSIX.POSIX_Error'Identity then
                  Err := POSIX.Get_Error_Code;
               end if;
               Save_Occurrence (Target => Excep, Source => E);
         end;
         select
            accept Get_Exception (E     : out Exception_Occurrence;
                                  Error : out POSIX.Error_Code) do
               Save_Occurrence (Target => E, Source => Excep);
               Error := Err;
            end Get_Exception;
         or
            terminate;
         end select;
      end Feeder;

      Feeders : array (Streams'Range) of Feeder;

      EO    : Exception_Occurrence;
      Error : POSIX.Error_Code;

   begin
      ...
      for I in Feeders'Range loop
         Feeders (I).Get_Exception (EO, Error);
         --  The following operations do nothing if no exception occured in the
         --  task.
         if Error /= POSIX.No_Error then
            POSIX.Set_Error_Code (Error);
         end if;
         Reraise_Occurrence (EO);
      end loop;
   end Feed;