Basically, I have different sensors and each sensor data is available at different ports (as a server)
Two things I need to do:
Write a client to connect to the server to get the data
Publish data to ROS
(I prefer writing my program in C++)
I am trying to searching information on the internet but still have several doubts.
Can one client connect to many different servers? I mean creating many sockets in one main function?
Does client/server and ROS publish/subscribe have to be the main function? or can I write them in normal functions and call these functions in the main function?
I can write the main function which able to get data from the server and publish it to ROS. But it means for each sensor I need to write a main function. Then I need to run many programs. It is certainly not a good solution. Also, each ROS publisher has a while loop, many loops in one main function may be a problem.
If anyone has experience with this please give me some hint on how I can build my program correctly?
Thank you.
Related
I'm integrating orocos with ros, basically i created a component that read data from some input ports and write on output ports that create streams, because i want to public this values on ros topics and then read those values in plotjuggler.
So I created this component without any problem and work perfectly. After that i created used another ssd configured in the same way as the previos ssd in which i build this component that publish data on ROS but on this new ssd when i call the first createStream() it stuck without any error as if it is in an infinite loop. The only thing that i notice different from the other ssd is that i got the following message
[2022-05-06 12:33:28] [connect] WebSocket Connection 192.168.2.13:8081 v-2 "WebSocket++/0.7.0" /socket.io/?EIO=4&transport=websocket&t=1651833208 101
to create the stream I'm using, in the c++ code the following code
port.setName(<port_name>);
port.doc(<doc>);
port.createStream(rtt_roscomm::topic(<topic_name>));
i also tried to create the stream in the ops file, but i get exactly the same result, when it reach that point it stuck.
I repeat again that i have a working version of this component on a similar ssd, so this means that the code inside the component is should be correct
as well as the ops file.
I'm on ubuntu 18.04.06 LTS, I'm using ROS melodic.
Is 1 week that I'm working on this issue without success, so i tried a lot of different things but at the end when i create a stream it stuck.
Ros is working because if i create a topic and i publish something from terminal or a create a simple ros package i can send and receive data, also orocos is working because i have different component running without problem.
I know that with so few information is difficult to solve the problem but why when i create a topic, with createStream, i get stuck in this loop?
There is any known case in which it is possible to remain stacked in this way during the creation of a topic in ros?
Hi I'm working on a c++ project that I'm trying to keep OS independent and I have two processes which need to communicate. I was thinking about setting up a 3rd process (possibly as a service?) to coordinate the other two, asynchronously.
Client 1 will tell the intermediate process when data is ready, and send the data to it. The intermediate process will then hold this data until client 2 tells it that it is ready for the data. If the intermediate process has not received new data from client 1, it will tell client 2 to wait.
Since I am trying to keep this OS independent I don't really know what to use. I have looked into using MPI but it doesn't really seem to fit this purpose. I have also looked into Boost.ASIO, Named Pipes, RPC's and RCF. Im currently programming in Windows but I'd like to avoid using the WIN_API so that the code could potentially be compiled in Linux.
Here's a little more detail on the two processes.
We have a back end process/model (client 1) that will receive initial inputs from a GUI (client 2, written in Qt) via the intermediate process. The model will then proceed to work until the end condition is met, sending data to the server as it becomes ready. The GUI will ask the intermediate process for data on regular intervals and will be told to wait if the model has not updated the data. As the data becomes available from the model we also want to be able to keep any previous data from the current session for exporting to a file if the user chooses to do so (i.e., we'll want the GUI to issue a command to the interface to export (or load) the data).
My modification privleges of the the back end/model are minimal, other than to adhere to the design outlined above. I have a decent amount of c++ experience but not much parallel/asynchronous application experience. Any help or direction is greatly appreciated.
Standard BSD TCP/IP socket are mostly platform independent. They work with some minor differences on both windows and Unices (like linux).
PS windows does not support AF_UNIX sockets.
I'd checkout the boost.interprocess library. If the two processes are on the same machine it has a number of different ways to communicate between processes, and do so in an platform independent manner.
I am not sure if you have considered the messaging system but if you are sending structured data between processes you should consider looking at google protocol buffers.
These related to the content of the messaging (what is passed) rather than how they are passed.
boost::asio is platform independent although it doesn't imply C++ at both ends. Of course, when you are using C++ you can use boost::asio as your form of transport.
I want my server app to be able to send data to be processed by a bunch of various clients, and then have the processed data returned to the server.
Ideally, I'd have some call like some_process = send_to_client_for_calculating(connection, data)
I just need to be able to send a bunch of data to a client, tell the client what to do (preferably in the same message, which can be done with an array [command, data]), and then return the data...
I'm breaking up pieces of a neural network (tis very large), and then assembling them all later.
If I need to be clearer, let me know how.
I'm shocked no one has thrown it out there... how about boost::asio.
Why don't you have a look at using Apache ActiveMQ? It's a Java JMS server, but it has C++ bindings, and does what you want with a minimum of writing networking code. You basically just subscribe to messages, and send responses back. The MQ server takes care of dispatch and message persistence for you.
You could try using beanstalkd, a fast working queue. I don't know if it fits your purposes. There is a client library written in C, which you should be able to use from C++.
I'd suggest looking at gSOAP, which implements SOAP in C++, including networking.
I'm currently working on transitioning a small console application to a TCP server / client application. The client will connect to the server via any Telnet client, and the server will replicate the standard console interface for each Telnet connection.
I started looking into doing this using the techniques I've learned from Beej's guide to network programming -- accepting the connection and then using fork() to separate it into its own process.
However, I would prefer to maintain my use of streaming IO (the original console application uses cin / cout, using similar functions for the networking logic would make the conversion process much simpler).
I've discovered the TCPStream class, hiding within sockets.h (http://www.gnutelephony.org/doxy/bayonne2/a00215.html)
It appears this class will allow me to use the server with streaming IO. However, I can't find a single example of using this class, nor can I find an explanation as to how to use fork() with it.
Any ideas? Thanks in advance for any help.
I think you are confusing the trees for the forest. One socket class is such a small part of what you need to do overall that it is not worth focusing on that.
If your objective is just to get your project working then just use an existing framework rather than trying to pull individual classes out of a large project. POCO has a TCPServer class that will do 90% of the work for you. QT, ACE and others have similar classes. There is not a huge amount of documentation on POCO but they do cover TCPServer pretty well and you can learn a lot from reading the source code if that is really where your interest lies.
I need to create a C++ add-in to Matlab where add-in will listen to packet coming from network and notify Matlab to draw an packet analysis graph. I understood that using a MEX file I can easily call c functions inside Matlab, but I could not find a way to notify Matlab when data is available at C++ end. Is there any way we can pass a user-defined Matlab function pointer into my C++ add-in?
BTW, I found this thread: real-time-data-in-matlab
Unfortunately suggestion is to use ActiveX control, but in my case, I need to create add-in in pure C++.
Have a look at Gurobi. It 'just' prints status information to the command window. Using a mex command like mexCallMATLAB you may access 'any' matlab function.
Would it make your life easier if you could listen for the network data directly from Matlab? I've never tried it, but there are a few submissions on MathWorks' File Exchange site that allow you to create sockets within Matlab. Here's a TCP/IP example that creates both a client and a server, and here's a similar UDP example.