Thread safety

[xqms]

This PR addresses some thread safety and race conditions present in the trajectory action server.

The problems/fixes include:

• has_goal_ is accessed from doTraj() and the action server callbacks, so protect it by a mutex.
• goalCB() and cancelCB() also have to be protected against affecting each other, since an async spinner with 3 threads is used - the action server itself does not provide any locking.
• The UrRealtimeCommunication class is not thread-safe. If you call addCommandToQueue() from a different thread (e.g. the trajectory thread in UrDriver::uploadProg()), you can get data corruption.

There are other subtle changes (joining the trajectory thread properly, ...).

@ThomasTimm, we talked briefly at MBZIRC about your driver. If you want, I can spend some more time on separating the changes so that they are easier for you to check. Does that make sense or will you release your new version soon?

[smurray47]

I'm surprised this PR has been sitting for so long! It seems to fix a quite dangerous bug! It seems to have an occasional deadlock problem I tried to investigate, but its going to be a non-obvious one. My guess is that one of the threads must hang after acquiring goal_mutex or something.

[darkdragon-001]

Any progress on this?

[gavanderhoorn]

Not that I'm aware of. This PR is also targeting master, which is deprecated. The refactor in kinetic-devel uses a different architecture so it would need to be seen whether it could also benefit from the changes in this PR (and whether it even needs them).

[jaymwong]

This PR has been merged into this fork of ur_modern_driver but I don't think it's made it back upstream to ros-industrial.

[gavanderhoorn]

@jaymwong wrote:

This PR has been merged into this fork of ur_modern_driver but I don't think it's made it back upstream to ros-industrial.

that fork is also based on the deprecated master.