Let’s see what does it take to send a message to Coral8. The latest available version on the website is 5.5 and I have 5.1 installed, so it is time for an upgrade.
The upgrade (installation) went smooth. There is a good "getting started guide" available too. Coral8 Server is the engine of the application and Coral8 Studio is a developer’s GUI. I have installed both on a Windows Server 2003 for Small Business — 2.53GHz, 2.5GB RAM — which also runs a developer version of MS SQL Server 2005. The average CPU usage seems to be below 5% when idle, not bad.
Coral8 has quite a few adapters included, but none of them seems to fit my GPS example; I will have to find another way. There is a SDK for several languages — including Python — so this seems a way to go. Now I can sketch a road map:
- Create a simple Coral8 project;
- Study the Python SDK and figure out how to send a message to Coral8;
- If it works, continue with the GPS example.
Step 1 – a simple Coral8 project
Coral8 CCL (Continuous Computation Language) is SQL like, so I have created two streams (think one-row tables) with just two columns: Entity and Val. Imagine a measurement device (Entity) sending a number (Val) each measurement. Streams are connected by a query which copies data from the input to the output.
-- Input CREATE INPUT STREAM StreamIn SCHEMA ( Entity STRING ,Val INTEGER ); -- Output CREATE OUTPUT STREAM StreamOut SCHEMA ( Entity STRING ,Val INTEGER ); -- Pass Through INSERT INTO StreamOut SELECT * FROM StreamIn;
This is how it looks in the Coral8 Flow View.
If I manage to insert data into the input stream, the same data should show up in the output stream.
Step 2 – the Python SDK
The SDK has an example which sends and receives data, and also includes Python multitasking. After some tinkering I have decided to simplify it a bit:
""" c8_test_1.py Test sending data to Coral8 """ import time from coral8 import Coral8 uri = 'ccl://damir5:6789/Stream/Default/' uri += 'TestPythonInAdapter/StreamIn' col_names = ['Entity','Val'] def send_to_c8(j): pb = Coral8.Publisher(uri) tp = Coral8.Tuple(col_names) tp.setvalue('Entity', 'DS_1') tp.setvalue('Val', j) pb.write_tuple(tp) if __name__ == '__main__': for j in range(10): send_to_c8(j) time.sleep(0.2)
The program is supposed to send ten numbers (0-9) to Coral8 Server. Note the uri variable, I got that one by inspecting the StreamIn properties and substituting “localhost” with the server name (damir5).
Step 3 – Test
Guess what, it works; just like that. Here is a screen capture of both stream viewers.
Step 4 – Continue
Now I can add service and template modules for Coral8 to my GPS Event example. I still have to figure out what to do with events inside the server. Maybe I can use it to write events to a database and send notifications when the GPS starts loosing satellite signals — we’ll see.
To be continued.
Everything I write about Coral8 is my own opinion and experience.
There is no contract nor any kind of active business relationship between Coral8 and me (Damir Systems Inc).