Programming with YARP

Programming in C++ with YARP

• We usually derive our base classes from yarp::os::RFModule, thus inheriting a configure(yarp::os::ResourceFinder& rf) method that receives a map (rf) passed from main(), a close() that gets called by CRTL+C, and a updateModule() which is invoked with a periodicity measured in seconds given by getPeriod(). In case you need a function that gets called more often, you may inherit the run() method from yarp::os::PeriodicThread and obtain a periodicity given in seconds wih double precision, to be specified in the constructor.
• Implement your device as a class, and ideally as a YARP device (tutorial (Spanish)).

Regarding close()

If there exists a close method that needs to release unmanaged resources (dynamically allocated memory) or terminate stuff in an ordered manner (if using PolyDriver class members, e.g. close device A before device B), always define a class destructor that calls close, be it a DeviceDriver or an RFModule derived class. Also, make sure nothing bad happens if this close method is called several times (i.e. set dangling pointers to nullptr). Why is that:

• PolyDriver::open may fail to initialize a subdevice, but it does not call the subdevice's close method; instead, it is immediately destructed via delete (ref).
• If RFModule::configure returns false, as explained in the above comments, close will never be called, hence we also want to use a destructor here.
• PolyDriver::close will never close a wrapped device twice, but callers of RFModule can do that inadvertently because of the previous point: once after a successful RFModule::configure and a CTRL+C signal (it just stops execution flow and calls close before leaving runModule), and one more time on class destruction.
• Despite those two mechanisms being relatively different, this policy ensures we treat both RFModule and DeviceDriver constructs in a similar manner: close() on destruction, avoid dangling pointers.

Similar and Related

• Appendix: YARP Tricks
• Install YARP (perma)
  • Install YARP: Similar and Related (perma)

If you have any doubts or comments

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