<html xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta name=Title content=""><meta name=Keywords content=""><meta http-equiv=Content-Type content="text/html; charset=utf-8"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><style></style></head><body bgcolor=white lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1>Hello!<o:p></o:p> <o:p></o:p>I have been playing around and writing my own DBus bindings for IPC using C++ to communicate using DBus signals to mimic “socket like” communications on top of the libdbus C API.<o:p></o:p> <o:p></o:p>This is the situation I am running into that I would like to see if there is some rules or exceptions I can use to work around some functionality:<o:p></o:p> <o:p></o:p>1. I have 2 processes attached to a session bus named “test.echo” on an object / interface named “pingpong” with a signal called “pingpong”.<o:p></o:p>2. Each process can read and write to that signal to act as a pipe.<o:p></o:p>3. Using synchronous reading and writing, process 2 reads the data and echo’s the data back for a ping pong demo.<o:p></o:p>4. After process 1 sends data, process 2 then reads the data and echo’s it back, in which process 1 waits to read the data.<o:p></o:p> <o:p></o:p>Eventually, I would like to attach multiple processes to the same signal for broadcasting.<o:p></o:p> <o:p></o:p>Here is some sudo code<o:p></o:p> <o:p></o:p>Process 1:<o:p></o:p> writeSignalData(“pingpong”)<o:p></o:p> print(“Wrote pingpong”)<o:p></o:p> while (true) {<o:p></o:p> message = readSignalData()<o:p></o:p> if (message.size()) {<o:p></o:p> print(“Echo received:” + message)<o:p></o:p> }<o:p></o:p> }<o:p></o:p> <o:p></o:p>Process 2:<o:p></o:p> while (true) {<o:p></o:p> message = readSignalData()<o:p></o:p> if (message.size()) {<o:p></o:p> print(“Echoing: “ + message)<o:p></o:p> writeSignalData(message)<o:p></o:p> }<o:p></o:p> }<o:p></o:p> <o:p></o:p>The problem that I am running into is that in the echoing process 2 is receiving its own signal after process 2 calls “writeSignalData()” since it is also technically subscribed to the signal…<o:p></o:p> <o:p></o:p>For example, the output of the sudo code would be:<o:p></o:p> <o:p></o:p>Process 1 – Wrote pingpong<o:p></o:p>Process 2 – Echoing: pingpong<o:p></o:p>Process 1 – Echo received: pingpong<o:p></o:p>Process 2 – Echoing: pingpong<o:p></o:p>Process 2 – Echoing: pingpong<o:p></o:p>Process 2 – Echoing: pingpong<o:p></o:p>Process 2 – Echoing: pingpong<o:p></o:p>Process 2 – Echoing: pingpong<o:p></o:p>Process 2 – Echoing: pingpong<o:p></o:p>Process 2 – Echoing: pingpong<o:p></o:p>Process 2 – Echoing: pingpong<o:p></o:p>…<o:p></o:p> <o:p></o:p>One way I can think of getting around this is to add a randomly generated serial (the serial functionality in a libdbus message) to each message sent and keep an internal list of ignored serials after echoing. If the serial from the message received is a part of the blacklisted serials, then pop the message, ignore it, and move on.<o:p></o:p> <o:p></o:p>I didn’t know if there was a better way to do this using rules, or possibly using two signals for bi-directional communications so that I don’t get my own sent data. I found very little for examples on the net for this way of using DBus.<o:p></o:p> <o:p></o:p>I know I may not be using the DBus the way it was intended… I just like the fact that all of the TCP packet parsing is already done and grouped, also the fact that it is typed data transactions.<o:p></o:p> <o:p></o:p><o:p> </o:p><o:p> </o:p>Derrill Vezina, PE <a href="mailto:vezinadj@gmail.com">vezinadj@gmail.com</a> 207-251-9072<o:p></o:p></div></body></html>