Fix deadlock when publishing performance metrics

Currently the PublishPerformanceMetrics function is called within
SensorManager.cc by each SensorContainer with protection by the
mutex of each SensorContainer. This leads to a deadlock when a
world has sensors in more than one container (i.e. more than one
category of sensors) as described in #2902.

Since the PublishPerformanceMetrics function is not a member
function of SensorContainer and uses only global variables,
the function can be called by the SensorManager thread instead
of by each SensorContainer thread. This change will avoid the
deadlock.

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

Author: scpeters

gazebo/sensors/SensorManager.cc

@@ -371,6 +371,8 @@ void SensorManager::Update(bool _force)
   // Only update if there are sensors
   if (this->sensorContainers[sensors::IMAGE]->sensors.size() > 0)
     this->sensorContainers[sensors::IMAGE]->Update(_force);
+
+  PublishPerformanceMetrics();
 }
 
 //////////////////////////////////////////////////
@@ -853,8 +855,6 @@ void SensorManager::SensorContainer::Update(bool _force)
 {
   boost::recursive_mutex::scoped_lock lock(this->mutex);
 
-  PublishPerformanceMetrics();
-
   if (this->sensors.empty())
     gzlog << "Updating a sensor container without any sensors.\n";