Bluish Coder

Programming Languages, Martials Arts and Computers. The Weblog of Chris Double.


2007-09-12

Distributed Channels in Factor

Following on from my Channels implementation, I've now added 'Remote Channels'. These are distributed channels that allow you to access channels in separate Factor instances, even on different machines on the network. It's based on my Distributed Concurrency work.

A channel can be made accessible by remote Factor nodes using the 'publish' word. Given a channel this will return a long Id value that can be used by remote nodes to use the channel. For example:

<channel> [ sieve ] spawn drop publish .
 => "ID12345678901234567890....."

From a remote node you can create a <remote-channel> which contains the hostname and port of the node containing the channel, and the Id of that channel:

"foo.com" 9000 <node> "ID1234..." <remote-channel>

You can use 'from' and 'to' on the remote channel exactly as you can on normal channels. The data is marshalled over the network using the serialization library. Remote channels are implemented using distributed concurrency so you must start a node on the Factor instance you are using. This is done with 'start-node' giving the hostname and port:

"foo.com" 9000 start-node

Once this is done all published channels become available. Note that the hostname and port must be accessible by the remote machine so it can connect to send the data you request.

As an experiment I published the prime number sieve example mentioned in my last post. It's running on one of my servers. To make it easy to create a <remote-channel> without needing to know the hostname and port I serialized the <remote-channel> instance, saved it in a file and made it available as [...server down sorry...].

You can load this file into Factor, deserialize it and get the <remote-channel> instance. You can then call 'from' on it to get the next prime number in the series. Until they get so big that my Factor instance is DOS'd of course! The code to do this is:

USING: serialization http.client 
       channels.remote concurrency.distributed ;

"yourhostname-or-ip-address.com" 9000 start-server
"[server-down-sorry]/prime.ser" http-get-stream 2nip 
[ deserialize ] with-stream
dup from .
dup from .
...etc...

The '9000' can be any port number openly accessible on your machine. A current Factor bug means you may get an error in 'start-server' about an address already assigned if you run Linux. This is due to an interaction with ipv6 - you can ignore it, the server will start fine. 'start-server' needs to be run whenever you start our Factor instance.

The 'dup from .' duplicates the <remote-channel>, gets the next number from it and prints it. It may not be in sequence as other users may have gotten the next number before you.

There is a lot of room for improvement and additions to the code. Feel free to hack at it and send in patches. Let me know some ideas on how this could be used in 'real world' applications.

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