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From Sathwik B P <sathwik...@gmail.com>
Subject Re: Dynamically invoke a child process
Date Wed, 02 Nov 2016 13:16:04 GMT
Response Inline

On Wed, Nov 2, 2016 at 4:50 PM, Jit K <jkfrm8@gmail.com> wrote:

> Hi Sathwik,
>
> Thank you for taking time to suggest these ideas.
>
> I was thinking on the same line but did not implement because I was not
> sure about calling <receive /> in a loop.
> Since <receive /> is a blocking activity, I thought the loop will stop
> during the first iteration when it executes the first <receive /> activity
> and will not not complete.
>
> I have few queries.
>
> 1) Iterative forEach parallel='yes'
> In my case I would like to collate the result of all sub-processes in the
> main process. So in the first approach (forEach) do you think I can add a
> <receive /> after <invoke /> as shown below
>
> <bpel:forEach parallel='yes' ...>
>         initialize the counter here
>         <scope>
>                <partnerlink .. /> access the EPR array using the index
> counter and assign it to the partnerlink.
>                <invoke .../>
>                <receive .../> to receive the response from above invoke
>          </scope>
> </bpel:forEach>
>
>
In BPEL a sub-process is implemented by using a <SCOPE /> within the
<PROCESS />. Just to clarify your sub process definition is actually a full
blown process. Am I right?
Yes, you can add a <RECEIVE /> after <INVOKE />, make sure you use
correlations. Also, any variables defined within the <SCOPE /> is a local
variable and cannot be accessed outside of it.

Example forEach Parallel:
https://github.com/apache/ode/blob/master/bpel-scripts/src/main/resources/2.0/good/foreach/ForEach2-2.0.bpel


> 2) While loop with async communication and explicit correlation
> ‚ÄčIn case of while loop, the execution is sequential. This is ok for <invoke
> /> activities. But may not work for <receive /> activities because there is
> no guarantee that the responses will be received in the same order of
> invoke.
> Or putting <receive /> in <while> will create an implicit <flow> like
> <forEach> loop?
>
> Thank you once again.
>
> JK
>

There is no guarantee of order of message processing. But, if you can make
a unique correlated value relate for every invoke-receive then you can know
which receive relates to the invoke. So, it doesn't matter in which order
the receive has arrived.

<FOREACH> creates an implicit <FLOW> as per the bpel specification:
http://docs.oasis-open.org/wsbpel/2.0/OS/wsbpel-v2.0-OS.html#_Toc164738521
<WHILE> does not create any implicit <FLOW>.

regards,
sathwik

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