Exception Save_Occurence Usage

Exception Save_Occurence Usage

[John J Cupak Jr]

[-- Attachment #1: Type: text/plain, Size: 325 bytes --]

Oh, Ada Gurus:

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.

Neither the RM95 or the Ada 95 Rationale are really helpful in this
area.

Thanks in advance,
John



[-- Attachment #2: Card for John J Cupak Jr --]
[-- Type: text/x-vcard, Size: 364 bytes --]

begin:vcard 
n:Cupak Jr;John J
tel;fax:978.858.4336
tel;work:978.858.1222
x-mozilla-html:TRUE
org:Raytheon Company;Northeast Software Training
version:2.1
email;internet:John_J_Cupak@res.raytheon.com
title:Software Engineering Instructor
adr;quoted-printable:;;50 Apple Hill Road=0D=0AT3MN35;Tewksbury;MA;01876;USA
x-mozilla-cpt:;9904
fn:John J Cupak Jr
end:vcard

Re: Exception Save_Occurence Usage

[Jim Rogers]

This issue is explained on page 652 of "Ada as a Second Language".

Procedure Save_Occurrence is used to make a copy of an
Exception_Occurrence so that the occurrence can be referred to later,
possibly at some other place in the program, even after the original
exception occurrence is no longer active.

--
Jim Rogers
Colorado Springs, Colorado USA


Sent via Deja.com http://www.deja.com/
Before you buy.

Re: Exception Save_Occurence Usage

[John J Cupak Jr]

[-- Attachment #1: Type: text/plain, Size: 574 bytes --]

Jim,

I looked at the example in the book, but was hoping for an actual usage
example,
which Florian provided.

Thanks.
John

Jim Rogers wrote:

> This issue is explained on page 652 of "Ada as a Second Language".
>
> Procedure Save_Occurrence is used to make a copy of an
> Exception_Occurrence so that the occurrence can be referred to later,
> possibly at some other place in the program, even after the original
> exception occurrence is no longer active.
>
> --
> Jim Rogers
> Colorado Springs, Colorado USA
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.

[-- Attachment #2: Card for John J Cupak Jr --]
[-- Type: text/x-vcard, Size: 364 bytes --]

begin:vcard 
n:Cupak Jr;John J
tel;fax:978.858.4336
tel;work:978.858.1222
x-mozilla-html:TRUE
org:Raytheon Company;Northeast Software Training
version:2.1
email;internet:John_J_Cupak@res.raytheon.com
title:Software Engineering Instructor
adr;quoted-printable:;;50 Apple Hill Road=0D=0AT3MN35;Tewksbury;MA;01876;USA
x-mozilla-cpt:;9904
fn:John J Cupak Jr
end:vcard

Re: Exception Save_Occurence Usage

[Florian Weimer]

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;