rcl: rcl_wait() returns early when a timer awakes

Bug report

Required Info:

• Operating System:
  • Windows 10
• Installation type:
  • From source
• Version or commit hash:
  • master
• DDS implementation:
  • RTI Connext

Steps to reproduce issue

Run timer tests using rmw_connext_cpp.

Expected behavior

Tests pass.

Actual behavior

Often, tests fail when rcl_wait() returns early when a timer awakes.

Additional information

For one, even though a clock is specified for timers, how rmw_wait() abides to the given timeout is not specified. This issue persists for both steady time and system time timers.

This issue does not occur when using rmw_fastrtps*_cpp or rmw_cyclonedds_cpp, as these return at the right time or (most often) past it.

Suspecting a bug in rmw_connext_cpp, I could confirm that the expected timeout is passed to RTI Connext’s WaitSet::wait() API which nonetheless returns early for both steady time and system time clocks. However, I believe this is less of a bug in RTI Connext than a misuse of rmw_wait() for rcl timers’ implementation, considering time resolution. The closest achievable timeout on a given OS is not necessarily greater than or equal than any one specified.