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Publish too slow

asked 2014-11-04 13:32:34 -0500

csherstan gravatar image

updated 2014-11-05 09:55:20 -0500

This is for the dynamixel_controllers package ( http://wiki.ros.org/dynamixel_control... ), but I don't think it's specific to this particular package. The package is installed from source in my catkin_workspace, not from binaries.

Ok, I have 5 callbacks (JointController.process_motor_states, 5 instances of JointController) that subscribe to a topic (MotorState.msg) that is being published at 20Hz, so 0.05s. Each of the callbacks also publishes a message (JointState.msg). Now timing the callbacks I see that summing up all 5 takes longer than 0.05 s and is creating a bottleneck. So what is happening is that process_motor_states ends up falling way behind and gets further and further out of sync as time goes on. Further inspection of the process_motor_states shows that the bottleneck is the publishing of the message (JointState.msg), which itself can take up to 0.05s. So in the code snippet below, the issue is the last line.

def process_motor_states(self, state_list):
    if self.running:
        state = filter(lambda state: state.id == self.motor_id, state_list.motor_states)
        if state:
            state = state[0]
            self.joint_state.motor_temps = [state.temperature]
            self.joint_state.goal_pos = self.raw_to_rad(state.goal, self.initial_position_raw, self.flipped, self.RADIANS_PER_ENCODER_TICK)
            self.joint_state.current_pos = self.raw_to_rad(state.position, self.initial_position_raw, self.flipped, self.RADIANS_PER_ENCODER_TICK)
            self.joint_state.error = state.error * self.RADIANS_PER_ENCODER_TICK
            self.joint_state.velocity = state.speed * self.VELOCITY_PER_TICK
            self.joint_state.load = state.load
            self.joint_state.is_moving = state.moving
            self.joint_state.header.stamp = rospy.Time.from_sec(state.timestamp)

            self.joint_state_pub.publish(self.joint_state)

Here's the JointState.msg:

Header header
string name         # joint name
int32[] motor_ids   # motor ids controlling this joint
int32[] motor_temps # motor temperatures, same order as motor_ids

float64 goal_pos    # commanded position (in radians)
float64 current_pos # current joint position (in radians)
float64 error       # error between commanded and current positions (in radians)
float64 velocity    # current joint speed (in radians per second)
float64 load        # current load
bool is_moving      # is joint currently in motion

There is one subscriber for each of the instances of this publisher:

rospy.Subscriber('/%s/state' % controller_name, JointState, self.state_update)

If the subscriber callback for the JointState.msg is simply a pass statement so:

def state_update(self, joint_state):
      pass

Then we still have the bottleneck. If I remove the single subscriber then there is no bottle neck.

Any help is welcome. I don't think I'm doing anything weird here.

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Comments

What message type are you publishing (because size / complexity does matter)? How many subscribers are connected to the publisher?

Dirk Thomas gravatar image Dirk Thomas  ( 2014-11-04 13:56:30 -0500 )edit

I don't think this is a generic problem since numerous other nodes are able to publish way faster then 100 Hz. May be you want to put together a simple example package with a publisher and subscriber and the measurement code. Then others can try running your example,

Dirk Thomas gravatar image Dirk Thomas  ( 2014-11-05 11:49:44 -0500 )edit

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answered 2014-11-05 22:14:12 -0500

csherstan gravatar image

I seem to have gotten it sorted out.

Cause: No idea. Bug in out of date ROS binaries?

Solution:

 sudo apt-get upgrade

The problem is that I'm stuck on Raring, which is end of life and upgrade and update don't work properly any more. I had to figure out which sources to point apt-get at. Once I did that and ran upgrade the issue with serious delays in this particular situation went away.

So either I go back to 12.04 or hope that National Instruments updates their DAQ drivers soon so I can move forward to 14.04.

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Asked: 2014-11-04 13:32:34 -0500

Seen: 1,309 times

Last updated: Nov 05 '14