Enhance PendingSend for multiple sends and add support for objgroup

[lifflander]

What Needs to be Done?

We need support for multiple sends. It should push/pop also. We can cleanup much to the manual PendingSend creation code (like in sendMsgUntypedHandler in the VRT collection manager) if that becomes the case.

[PhilMiller]

There's several requests kinda bundled up here. I generally see how they fit together, but if you have more elaborated thoughts on your vision, it would be useful to have them written down.

[PhilMiller]

For the multiple-message use case, what do you think of the approach of adding a method along these lines:

template <typename MsgT>
void PendingSend::addMessage(MsgSharedPtr<MsgT> in_msg, SendActionType const& in_action)
{
  send_action_ = [=, old_msg = msg_, old_size_ = msg_size_, old_action = send_action_]
            (MsgVirtualPtr<BaseMsgType> &msg) {
    old_action(old_msg);
    in_action(in_msg);
  };
}

With a suitable overload for a simple sized message, assertions about the epochs matching , etc.

[nmm0]

@lifflander @PhilMiller I can split objgroup support into a separate issue, and would be up for working on it now that I finally have some time. I need it for some of my contact code

[PhilMiller]

The use case for multiple sends in EMPIRE has become moot.

…

On Wed, Feb 19, 2020, 12:07 Nicolas Morales ***@***.***> wrote: @lifflander <https://github.com/lifflander> @PhilMiller <https://github.com/PhilMiller> I can split objgroup support into a separate issue, and would be up for working on it now that I finally have some time. I need it for some of my contact code — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#688?email_source=notifications&email_token=AAA64ABXS2PEJ7VNPDIU5WDRDVRL5A5CNFSM4KUHSH6KYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEMITRRI#issuecomment-588331205>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAA64ADR4Q7F2SXY44ARBI3RDVRL5ANCNFSM4KUHSH6A> .

[lifflander]

The use case for multiple sends in EMPIRE has become moot.
…

In that case, let's leave this issue open until we are sure, but let development continue on #702 for the required use cases, headed up by @nmm0

[lifflander]

This is done.