Add statistics for handle_loaned_message

[Barry-Xu-2018]

Add statistics for handle_loaned_message().
If loan message is enabled, some tests in test_subscription_topic_statistics fail. This issue is found in ros2/rmw_fastrtps#568 (comment)

[wjwwood]

Need to resolve the question about double delivery and the interaction with intra-process.

[Barry-Xu-2018]

(Edit: Progress -> Process)

@fujitatomoya @wjwwood

This is a case of double delivery.
The topic is '/number' for Pub1/Pub2 and Sub1/Sub2.
Message is Int32 (Pod)
RMW: FastDDS (with ros2/rmw_fastrtps#568 )

• Process A
  • Pub1 (use_intra_process)
  • Sub 1 (use_intra_process)
• Process B
  • Pub2

At this time, Sub1 receives messages from Pub1 via dispatch_intra_process(). Sub1 receives messages from Pub2 via handle_loaned_message().

Now start a new subscriber

• Process C
  • Sub2

In order to send message to Sub2, Pub1 will send message via RMW.
At this time, for the message from Pub1, Sub1 can receive messages via handle_loaned_message() and via dispatch_intra_process().
This is double delivery.

So below code is necessary for handle_loaned_message()

    if (matches_any_intra_process_publishers(&message_info.get_rmw_message_info().publisher_gid)) {
      // In this case, the message will be delivered via intra process and
      // we should ignore this copy of the message.
      return;
    }

[fujitatomoya]

@Barry-Xu-2018

thanks for checking!

At this time, Sub1 receives messages from Pub1 via dispatch_intra_process().

• Process A
  • Pub1 (use_intra_process, cannot use LoanedMessage)
  • Sub1 (use_intra_process)

in this situation, How Sub1 avoid to call handle_loaned_message?

my expectation is, Sub1 recognizes can_loan_messages is true since data type is PoD. So Sub1 would call handle_loaned_message instead of handle_message? currently (w/o this PR), handle_loaned_message does not call matches_any_intra_process_publishers, so i was thinking that there might be double delivery.

i mean there seems to be a double delivery problem in intra-process communication.

[Barry-Xu-2018]

@fujitatomoya

my expectation is, Sub1 recognizes can_loan_messages is true since data type is PoD. So Sub1 would call handle_loaned_message instead of handle_message? currently (w/o this PR), handle_loaned_message does not call matches_any_intra_process_publishers, so i was thinking that there might be double delivery.

Right.
I forgot to mention ros2/rmw_fastrtps#568 is applied in my test environment. So even if data-sharing is OFF, can_loan_message is true once message is PoD.
If not apply ros2/rmw_fastrtps#568, handle_message is called instead of handle_loaned_message.

[fujitatomoya]

@Barry-Xu-2018 yeah, that means we have an unexpected double delivery problem if we enable data sharing for rmw_fastfrpt with current code.

anyway, solution can be applied on this PR.

[fujitatomoya]

we need to backport this to humble, galactic and foxy.

[fujitatomoya]

@wjwwood @ivanpauno could you take a look when you have time? I will start the CI.

[fujitatomoya]

CI:

• Linux
• Linux-aarch64
• Windows

[wjwwood]

lgtm

[fujitatomoya]

@mergify backport humble galactic foxy

[mergify]

backport humble galactic foxy

✅ Backports have been created

• #1932 Add statistics for handle_loaned_message (backport #1927) has been created for branch humble
• #1933 Add statistics for handle_loaned_message (backport #1927) has been created for branch galactic
• #1934 Add statistics for handle_loaned_message (backport #1927) has been created for branch foxy