Gazebo 8 crashes if a model containing a gazebo_yarp_controlboard plugin is removed

[traversaro]

Gazebo crashes with no further information.
Currently verified in Gazebo 8 on macOS Sierra by me and @nunoguedelha .
Model removal seems to work fine on Gazebo 7 on Ubuntu 16.04 .
We still need to test on Gazebo 8 on Ubuntu 16.04 .

[traversaro]

Sometimes, on crash Gazeb outputs the following error:

gzserver(11133,0x700002e0d000) malloc: *** error for object 0x7febd0a73560: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug

[traversaro]

After half an hour of simulation:

[INFO]created device <gazebo_controlboard>. See C++ class GazeboYarpControlBoardDriver for documentation.
gzserver(11159,0x70000d6e5000) malloc: *** error for object 0x7f9d74d699f0: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug
gzclient(11160,0x7fffa82af3c0) malloc: *** error for object 0x7f9dbcf64080: incorrect checksum for freed object - object was probably modified after being freed.
*** set a breakpoint in malloc_error_break to debug

[traversaro]

I think it is due to this change:
https://bitbucket.org/osrf/gazebo/src/cd526975bc8bdf3813e0600e3ece180870602471/Migration.md?at=default&fileviewer=file-view-default#Migration.md-631 .

[traversaro]

More in detail, it seems that in Gazebo 8 the Disconnect methods are deprecated:

Deprecation: public: void Event::Disconnect(ConnectionPtr);
Deprecation: public: void EventT::Disconnect(ConnectionPtr);
Replacement: Delete the Connection object, perhaps by calling reset() on its smart pointer.

An easy fix for this can be to just called the reset() method on the connection after the call to the Disconnect method (this will continue to work for all Gazebo versions). The fact that the method is deprecated and not removed means that it should still work, and the fact that is not working I think is a Gazebo 8 bug. However I will not take the time to properly open a Gazebo bug because it is a transient behavior that only affect Gazebo 8 .

[traversaro]

Migrating away from the Disconnect function in #285 actually solved this issue. While I can't investigate further the problem with the Disconnect* functions in Gazebo 8 (that should be just deprecated, and hence continue to work) perhaps it is worth to at least notify this strange behavior to @scpeters .