Add async support for subscribing messages

[Ryanf55]

This is an alternative to #356, used for discussion. It doesn't pass because the wait blocks.

[Ryanf55]

@LastStarDust FYI, here is another approach without using callbacks. Note how I also create a publisher in the test python code rather than calling the CI, which is more conducive to an application where you want to set specific fields in the test.

[LastStarDust]

@Ryanf55 Thank you for letting me know. I have some comments about the code, but before I invest any time in this I want to hear the opinion of the maintainers.

[Ryanf55]

@Ryanf55 Thank you for letting me know. I have some comments about the code, but before I invest any time in this I want to hear the opinion of the maintainers.

Looks like there are not really any active maintainers who have time to discuss this support. Are you still interested in getting better subscriber testing on humble?

[LastStarDust]

@Ryanf55 for sure I am still interested in getting better subscriber testing on humble.

@project owners
If there are no active maintainers or if they have no time for this feature, would you let us take care of this? In other words, would you give @Ryanf55 and @LastStarDust temporary maintainer role?

[clalancette]

If there are no active maintainers or if they have no time for this feature, would you let us take care of this? In other words, would you give @Ryanf55 and @LastStarDust temporary maintainer role?

There are active maintainers of this repository. In general, this is very core ROS 2 stuff, so I don't think giving temporary maintainer role is suitable here.

That said, at the very least a new feature needs to target rolling first. Once this is targeted at rolling, I'll try to get a maintainer to look at it.

[LastStarDust]

If there are no active maintainers or if they have no time for this feature, would you let us take care of this? In other words, would you give @Ryanf55 and @LastStarDust temporary maintainer role?

There are active maintainers of this repository. In general, this is very core ROS 2 stuff, so I don't think giving temporary maintainer role is suitable here.

That said, at the very least a new feature needs to target rolling first. Once this is targeted at rolling, I'll try to get a maintainer to look at it.

Fair enough. BTW my PR is already targeting rolling.