The function must check that the pointer is valid (if it stay a pointers).
(Actually it should also check all the other pointers coming in.)

Same below and for OpenSplice.

Double posting comment from ros2/rmw_opensplice#55:

As I was writing a test for this, I realized that the existing logic of this loop is not what I thought it was.

Old behavior:

• Get "blocking" or "non-blocking in rclcpp.
• In rmw implementation:
• if non-blocking, call rmw_wait with a timeout of zero, and don't loop if timed out.
• if blocking: while return code is timeout, wait for 1 second. throw if error, continue if retcode was not timeout. The executor will always block indefinitely inside of rmw_wait.

Here's what I think the new behavior should be:

Get timeout from rclcpp.

• If NULL: block indefinitely in rmw_wait, by passing DURATION_INFINITE to WaitSet::Wait.
• If positive: pass the timeout value to WaitSet::wait and return if timed out.
• If non-blocking: same behavior as before.