As a premise I must say I am very inexperienced with ROS.
I am trying to publish several ros messages but for every publish that I make I get the "publishing and latching message for 3.0 seconds", which looks like it is blocking for 3 seconds.
I'll leave you with an example of how I am publishing one single message:
rostopic pub -1 /heifu0/mavros/adsb/send mavros_msgs/ADSBVehicle "header: // then the rest of the message
I've also tried to use the following argument: -r 10, which sets the message frequency to 10Hz (which it does indeed) but only for the first message I.e. it keeps re-sending the first message 10 times a second.
Basically i want to publish a message without latching, if possible, so i can publish multiple messages a second. I have a constant stream of messages coming and i need to publish them all as fast as i can.
Part of the issue is that rostopic CLI tools are really meant to be helpers for debugging/testing. It has certain limitations that you're seeing now. Unfortunately, you cannot remove that latching for 3 seconds message, even for 1-shot publications. Instead this is a job for an actual ROS node. It can be done in a couple of lines of Python like so:
import rospy
from mavros_msgs.msg import ADSBVehicle
class MyNode:
def __init__(self):
rospy.init_node('my_relay_node')
self.rate = rospy.Rate(10.0) #10Hz
self.status_pub = rospy.Publisher('/heifu0/mavros/adsb/send', ADSBVehicle, queue_size=10)
def check_and_send(self):
#Check for some condition here
if some_condition:
output_msg = ADSBVehicle()
#Fill in message fields here
self.status_pub.publish(output_msg)
def run_node(self):
while not rospy.is_shutdown():
self.check_and_send()
self.rate.sleep() #Run at 10Hz
if __name__ == '__main__':
node = myNode()
node.run_node()
Related
i have a simple python application without any framework and API calls.
how i will monitor python application on instana kubernates.
i want code snippet to add with python application ,which trace application
and display on instana
how i will monitor python application on instana kubernates
There is publicly available guide, that should help you setting up the kubernetes agent.
i have a simple python application without any framework and API calls
Well, instana is for distributed tracing, meaning distributed components calling each other, each other's APIs predominantly by using known frameworks (with registered spans).
Nevertheless, you could make use of SDKSpan, here is a super simple example:
import os
os.environ["INSTANA_TEST"] = "true"
import instana
import opentracing.ext.tags as ext
from instana.singletons import get_tracer
from instana.util.traceutils import get_active_tracer
def foo():
tracer = get_active_tracer()
with tracer.start_active_span(
operation_name="foo_op",
child_of=tracer.active_span
) as foo_scope:
foo_scope.span.set_tag(ext.SPAN_KIND, "exit")
result = 20 + 1
foo_scope.span.set_tag("result", result)
return result
def main():
tracer = get_tracer()
with tracer.start_active_span(operation_name="main_op") as main_scope:
main_scope.span.set_tag(ext.SPAN_KIND, "entry")
answer = foo() + 21
main_scope.span.set_tag("answer", answer)
if __name__ == '__main__':
main()
spans = get_tracer().recorder.queued_spans()
print('\nRecorded Spans and their IDs:',
*[(index,
span.s,
span.data['sdk']['name'],
dict(span.data['sdk']['custom']['tags']),
) for index, span in enumerate(spans)],
sep='\n')
This should work in any environment, even without an agent and should give you an output like this:
Recorded Spans and their IDs:
(0, 'ab3af60079f3ca57', 'foo_op', {'span.kind': 'exit', 'result': 21})
(1, '53b67f7298684cb7', 'main_op', {'span.kind': 'entry', 'answer': 42})
Of course in a production, you wouldn't want to print the recorded spans, but send it to the well configured agent, so you should remove setting the INSTANA_TEST.
I am using dask in jupyter notebook on a linux server to run python functions on multiple CPUs. The python functions have standard print statement. I would like the output of the print to be shown in the jupyter notebook right below the cell. However, the print out were all shown in the console. Can anyone explain why this happens and how to make dask.function.print output to the notebook, or both the console and the notebook.
The following is a simplified version of the problem:
import dask
import functools
from dask import compute, delayed
iter_list=[0,1]
def iFunc(item):
print('Meme',item)
# call this function itself will print normally to the
# notebook below the cell, desired.
with dask.config.set(scheduler='processes',num_workers=2):
func1=functools.partial(iFunc)
ret=compute([delayed(func1)(item) for item in iter_list])
# surprisingly, Meme 0, Meme 1 only print out to the console,
# not the notebook, Not desired, hard to debug. Any clue?
The whole point of dask is leveraging multiple threads, processes, or nodes/machines to distribute work. The workers you create are therefore not on the same thread as your client, and may not be on the same process, or even the same machine (or like, in the same country) as your client, depending on how you set up your cluster.
If you start a LocalCluster from your jupyter notebook, whether you're using threads or processes, you should see printed output appearing as output in the cells which execute jobs on the workers:
In [1]: import dask.distributed as dd
In [2]: client = dd.Client(processes=4)
In [3]: def job():
...: print("hello from a worker!")
In [4]: client.submit(job).result()
hello from a worker!
However, if a different process is spinning up your workers, it is up to that process to decide how to handle stdout. So if you're spinning up workers using the jupyterlab terminal, stdout will appear there. If you're spinning up workers in a kubernetes pod, stdout will appear in the worker logs. Dask doesn't actively manage standard out, so it's up to you to handle this. Note that this also applies to logging - neither stdout nor logs are captured by dask. This is actually a really important design feature - many distributed systems have their own systems for managing the standard out & logging of nodes, and dask does not want to impose its own parallel/conflicting system for handling output. The main focus of dask is executing the tasks, not managing a distributed logging system.
That said, dask does have the infrastructure for passing around messages, and this is something the package could support. There is an open issue and pull request attempting to add this ability as a feature, but it looks like there are a lot of open design questions that would need to be resolved before this could be added. Many of them revolve around the issues I raised above - how to add a clean distributed logging feature without overburdening the scheduler, complicating the already complex set of configuration options, or overriding the important, existing logging systems users rely on. The dask core team seems to agree that this is a good idea, if the tough design questions can be resolved.
You certainly always have the option of returning messages. For example, the following would work:
In [10]: def job():
...: return_blob = {"diagnostics": {}, "messages": [], "return_val": None}
...: start = time.time()
...: return_blob["diagnostics"]["start"] = start
...:
...: try:
...: return_blob["messages"].append("raising error")
...: # this causes a DivideByZeroError
...: return_blob["return_val"] = 1 / 0
...: except Exception as e:
...: return_blob["diagnostics"]["error"] = e
...:
...: return_blob["diagnostics"]["end"] = time.time()
...: return return_blob
...:
In [11]: client.submit(job).result()
Out[11]:
{'diagnostics': {'start': 1644091274.738912,
'error': ZeroDivisionError('division by zero'),
'end': 1644091274.7389162},
'messages': ['raising error'],
'return_val': None}
I need some sort of schedule thing to schedule a task to happen at x:y (12:00 for example) in Tcl.
The scenario is a router using Openwrt with Tcl 8.6.10 with limited RAM and storage where I have some sort of IRC client "bot" (using socket to connect). The "bot" was just a barebone that I modify to suit my needs. Most of the things work fine, except that I don't have way to schedule easily things. I wanted something like how eggdrop has "bind time" where the bind thing is "bind time flag "cron-style string" caller".
The "bot" scheme is like:
Main Tcl script:
<info+code to connect to IRC>
<while loop>
<some code in case of IRC disconnection>
<list of files with tcl code aka sub-scripts>
<usage of source based from a list of the filenames>
<code for error handling>
<end of while loop>
The list of files is source filelist.tcl, where filelist.tcl is a set var {filename1.tcl filename2.tcl...}. The filenamex.tcl has some basic code to respond to IRC server or IRC input from channels and reply to channels.
I can make some sort of schedule if I base a execution like if {[clock format [clock seconds] -format "%H:%M"]=="12:00"} {code to execute} and hopefully wait for a server ping/pong but that can lead to repeated code inside of the if body.
I been looking around and found a package called cron but I don't know how to use it correctly because there are not many examples and I don't know to use vwait properly and I don't want vwait to hang the bot waiting for a value to change. I also read about tcl threads for maybe parallel execution.
So I need some code inside of a sub-script that looks like (a package cron style):
#beginning of file
#add a task specifying hour and minute
task-at "12:00" proccaller
proc procname {optional} {
<some code to be executed at specific hour+time>
}
#end of file
I also don't know how to use after command to use it.
How can I accomplish I want?
Thanks for the replies and yes, it would help if I study event loops and coroutine, which probably comes next.
Some time has passed since I posted the question and kinda sorted the thing by creating a sub-script in a folder named scripts with the following structure:
#beginning of the script
if {![file exists executed]} {set executed "no"}
#the following clock instruction returns for example: Tuesday 22:14
switch -glob -- [clock format [clock seconds] -format "%A %H:%M"] {
"*12:00" - "*12:01" {
#Basic example of sending a message to the irc channel when it's midday
if {$executed=="no"} {
puts $fd "PRIVMSG #CODE :It's midday right now."
flush $fd
set executed "yes"
}
}
#...more time comparisions and code
default {set executed "no"}
}
#end of script
And the script is almost the top of the list of scripts to be loaded so if I wish to send some command down stream at giving time, the command can be executed.
There is double timings because the "bot" reacts, at least at minimum, to the irc server's ping which happens each 90 seconds and it may skip some minutes.
This is not an answer but an unproper workaround.
I have a ROS node that allows you to "publish" a data structure to it, to which it responds by publishing an output. The timestamp of what I published and what it publishes is matched.
Is there a mechanism for a blocking function where I send/publish and output, and it waits until I receive an output?
I think you need the ROS_Services (client/server) pattern instead of the publisher/subscriber.
Here is a simple example to do that in Python:
Client code snippet:
import rospy
from test_service.srv import MySrvFile
rospy.wait_for_service('a_topic')
try:
send_hi = rospy.ServiceProxy('a_topic', MySrvFile)
print('Client: Hi, do you hear me?')
resp = send_hi('Hi, do you hear me?')
print("Server: {}".format(resp.response))
except rospy.ServiceException, e:
print("Service call failed: %s"%e)
Server code snippet:
import rospy
from test_service.srv import MySrvFile, MySrvFileResponse
def callback_function(req):
print(req)
return MySrvFileResponse('Hello client, your message received.')
rospy.init_node('server')
rospy.Service('a_topic', MySrvFile, callback_function)
rospy.spin()
MySrvFile.srv
string request
---
string response
Server out:
request: "Hi, do you hear me?"
Client out:
Client: Hi, do you hear me?
Server: Hello client, your message received.
Learn more in ros-wiki
Project repo on GitHub.
[UPDATE]
If you are looking for fast communication, TCP-ROS communication is not your purpose because it is slower than a broker-less communicator like ZeroMQ (it has low latency and high throughput):
ROS-Service pattern equivalent in ZeroMQ is REQ/REP (client/server)
ROS publisher/subscriber pattern equivalent in ZeroMQ is PUB/SUB
ROS publisher/subscriber with waitformessage equivalent in ZeroMQ is PUSH/PULL
ZeroMQ is available in both Python and C++
Also, to transfer huge amounts of data (e.g. pointcloud), there is a mechanism in ROS called nodelet which is supported only in C++. This communication is based on shared memory on a machine instead of TCP-ROS socket.
What exactly is a nodelet?
Since you want to stick with publish/ subscribers, assuming from your comment, that services are to slow I would have a look at waitForMessage (Documentation).
And for an example on how to use it you can have a look at this ros answers question.
All you need to do is to publish your data and immediately call waitForMessage on the output topic and manually pass the received message to your "callback".
I hope this is what you were looking for.
To get this request/reply behaviour ROS has a mechanism called ROS service.
You can specify the input and output of your service in a service file similar to a ROS message definition. You can then call the service of a node with your input and the call will receive an output when the service is finished.
Here is a tutorial how to use this mechanism in python. If you prefer C++ there is also one, you should find it.
I installed ROS melodic version in Ubuntu 18.04.
I'm running a rosbag in the background to mock cameras in messages rostopics.
I set the camera names in rosparams and iterated through it to capture each camera topics.
I'm using message_filter ApproximateTimeSynchronizer to get time synchronized data as mentioned in the official documentation,
http://wiki.ros.org/message_filters
But most of the time the callback function to ApproximateTimeSynchronizer is not being called/is having delay. The code snippet I'm using is given below:
What am I doing wrong here?
def camera_callback(*args):
pass # Other logic comes here
rospy.init_node('my_listener', anonymous=True)
camera_object_data = []
for camera_name in rospy.get_param('/my/cameras'):
camera_object_data.append(message_filters.Subscriber(
'/{}/hd/camera_info'.format(camera_name), CameraInfo))
camera_object_data.append(message_filters.Subscriber(
'/{}/hd/image_color_rect'.format(camera_name), Image))
camera_object_data.append(message_filters.Subscriber(
'/{}/qhd/image_depth_rect'.format(camera_name), Image))
camera_object_data.append(message_filters.Subscriber(
'/{}/qhd/points'.format(camera_name), PointCloud2)
topic_list = [filter_obj for filter_obj in camera_object_data]
ts = message_filters.ApproximateTimeSynchronizer(topic_list, 10, 1, allow_headerless=True)
ts.registerCallback(camera_callback)
rospy.spin()
Looking at your code, it seems correct. There is, however, a trouble with perhaps bad timestamps and ergo this synchronizer as well, see http://wiki.ros.org/message_filters/ApproximateTime for algorithm assumptions.
My recommendation is to write a corresponding node that publishes empty versions of these four msgs all at the same time. If it's still not working in this perfect scenario, there is an issue with the code above. If it is working just fine, then you need to pay attention to the headers.
Given that you have it as a bag file, you can step through the msgs on the command line and observe the timestamps as well. (Can also step within python).
$ rosbag play --pause recorded1.bag # step through msgs by pressing 's'
On time-noisy msgs with small payloads, I've just written a node to listen to all these msgs, and republish them all with the latest time found on any of them (for sync'd logging to csv). Not optimal, but it should reveal where the issue lies.