Segmentation fault when using TransformControl tool in crowded worlds

[luca-della-vedova]

When using the Transform Control plugin to move objects around, it "often" results in a segmentation fault in https://github.com/ignitionrobotics/ign-gazebo/blob/ign-gazebo4/src/EntityComponentManager.cc#L788 line with the following backtrace:

#0  ignition::gazebo::v4::EntityComponentManagerPrivate::SetRemovedComponentsMsgs (this=0x555555b08f60, _entity=@0x7fffce60b888: 22, _msg=...) at /home/luca/ws_citadel/src/ign-gazebo/src/EntityComponentManager.cc:794
#1  0x00007ffff38a0110 in ignition::gazebo::v4::EntityComponentManager::AddEntityToMessage (this=0x555555891650, _msg=..., _entity=<optimized out>, _types=..., _full=false) at /usr/include/c++/9/bits/unique_ptr.h:360
#2  0x00007ffff38a147e in ignition::gazebo::v4::EntityComponentManager::State (this=this@entry=0x555555891650, _state=..., _entities=std::unordered_set with 0 elements, _types=std::unordered_set with 1 element = {...}, _full=_full@entry=false)
    at /home/luca/ws_citadel/src/ign-gazebo/src/EntityComponentManager.cc:1031
#3  0x00007fffce658bd0 in ignition::gazebo::v4::systems::SceneBroadcaster::PostUpdate (this=0x55555cb2b350, _info=..., _manager=...) at /home/luca/ws_citadel/install/include/ignition/msgs6/ignition/msgs/serialized_map.pb.h:724
#4  0x00007ffff3944505 in ignition::gazebo::v4::SimulationRunner::<lambda()>::operator()(void) const (__closure=0x55555cc108e8) at /home/luca/ws_citadel/src/ign-gazebo/src/SimulationRunner.cc:430
#5  0x00007ffff2fdad84 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#6  0x00007ffff7a20609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#7  0x00007ffff7b5e293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

To reproduce:

• Run a world with many objects (I used actors_population with 100 actors).
• Select an actor and a transform tool (translation)
• Click on an arrow many times in a sequence.

It seems the reason for the crash is that, at least in this world, the mutable_entities() structure is empty, hence the find returns an iterator to end().
I tried a hacky fix by doing early return if the entity is not found but that didn't sound like a sensible solution so I avoided creating a PR.

Here is an example:

I'm not familiar enough with the EntityComponentManager to know why this would happen so any input is welcome!

[iche033]

looks like that function was added recently in Dome in #272