8tracks - use it!

Well this is not software engineering related, but if you read my blog than you probably aware that I really like good music. Lately I discovered a website that I wasn't aware of before. It goes by the name 8tracks and it's an internet radio.

Yep, I know - there are lots of those lately... Pandora, Last.fm, Grooveshark, Jango, Deezer, Serendip - there are so many more. Some of them free, some of them not.

Those online music services suggest you music to listen to and some of the algorithms that are responsible for that are very interesting. While Pandora, Jango and Grooveshark are based on the resemblance of the music parameters, Last.fm and Serendip based on the social networking approach.

To my opinion, while some of these site provide pretty good playlists for you to listen, they are not focusing enough on the mood of the listener and rely on the assumption that if you listen to a certain music style, you probably would like to listen to songs in the same style over and over again. This assumption is right for, let's say, 85% of the time - "I'm in a mood for some Jazz', you'll say for yourself, "I'll use Jango and ask it to play some good old Brazilian Jazz".

Stan Getz, Bossa nova anyone?

But what about the other 15% of the time when you are interested, for example, to listen to music when you are drinking you morning coffee? You don't care if this is Stan Getz, the Red Hot Chili Peppers or Bob Marley as long as it is in the right mood to fit in the scene of you drinking your morning coffee, right?

The best job, up until I discovered 8tracks, was done by Serendip. Serendip is pretty new in the scene of the online music radio websites. The idea of it is so simple, yet very smart. It connects to your Facebook and Twitter friends and plays the music that your friends shared on their walls. The trick is that this is done almost in real time and therefore the stream consists of tracks that create "the music of now". The music that your friends shared in the morning might fit your morning as well right? The music that you want to hear on a cold winter day, might as well be shared by a friend in the same mood, isn't it?

Nevertheless, what I found so special about 8tracks is that they don't fight for the spot of who has the best algorithm to match the music for your personal taste. It is based on the idea of a simple radio show - meaning that the users themselves create the playlists. The websites provides a very nice and easy to use interface to create a playlist, name it, say a few words about it, and the most important - tag it.

The tag cloud of 8tracks is a vast list of moods, music styles, state of minds and more: "sleep", "love", "workout", "cozy", "party", "rock"... there are so many. One might create a playlist that has a nice acoustic tunes that can fit a gloomy Saturday morning nap, the other can create a playlist that is the best for jogging. This is so simple, yet genius.

Although we are living in the era of technology. Sometimes algorithms, formulas and calculations simply cannot provide what I think is best described by the term "a human touch". Until we would be able to describe a machine what is "a gloomy Saturday morning nap mood" the algorithms based websites will stay on that 85%.

Try 8tracks.com guys.

Gloomy Saturday Morning from emptyskiesabove on 8tracks Radio.

What is DCOM? (Part 2)

After discussing COM and DCOM in the previous posts, I would like to dig into the way DCOM is transmitted over the wire. As I already mentioned, DCOM needs to execute procedures and receive their output via the network. To achieve that it has to use a standard protocol that is implemented on multiple platforms, be security aware and provide a suitable interface that will not harm the advantage of DCOM.

DCE/RPC protocol was chosen for those reasons and it is used as the wire-protocol for DCOM. DCE/RPC stands for Distributed Computing Environment / Remote Procedure Calls and it defines a standard for converting objects and structures into a format that can be split into packets and sent over the network in a platform independent way. Let's dig a little more into details.

The Challenge

It can be said that the goal is set up a "conversation" between a user and the service provider in a way that that the interface that is defined by the service provider could be called by the user from far away, the service provider will process the request and return an answer. When this happens within a local machine, both client and server will usually share the same memory address space so the interface calls, the arguments passed and the return values can be passed and accessed on the process's stack.

When the whole things goes remote and the client and server are not on the same machine/system, the interface calls including the arguments and return values must have a Network Data Representation (NDR) to be sent over the network. The cool thing that RPC mechanism managed to achieve is that it makes the process look to the programmer almost as the interface he uses is just a regular local procedure call. That is why using DCE/RPC was chosen from DCOM.

The IDL

The Interface Definition Language and its compiler. DCE/RPC uses a language to define the procedures, the parameters to these procedures and the data types and objects that the interface will use. An IDL interface will have the following structure:

<interface> ::= <interface_header> { <interface_body> }

For a detailed explanation regarding the definition for the interface header and body, please refer to the DCE/RPC opengroup.org document here.

RPC runtime library

The RPC runtime library is used by both client and server side to implement the communication between them. The runtime library is responsible for finding the server over the network, manage the connection, sending messages, receiving answers, manage and handle errors and more. To keep it simple let's just look at the diagram below.

RPC flow (Source: MSDN)

The client application calls a client stub that is responsible on calling the runtime library interface with the parameter the client application has passed to it. The client RPC runtime library converts the request into a standard NDR and sends the message to the server. The server receives the requests, the runtime library translates it back from NDR into objects and structures that the server understands, queries the server application for and answers and transmits it back to the client.

Every DCE enables machine runs a daemon application called DCE Host Daemon (DCED) and a DCE control program (DCECP) to administrate it. The DCED is listening to the DCE requests and manage them.

DCE/RPC development process

When it comes to the development of a DCE/RPC client/server application the process is pretty straightforward. It comprises of defining the interfaces using DCE IDL, running the IDL compiler to create the client and the server stubs and implement them on the client and server machines.

The IDL interface, like every other interface in computer science, is a set of procedures that the server can execute. On the client side, the client application is linked with the client-stub created by the IDL compiler. The client-stub hides all the network communication with the server. On the server side, the server-stub is linked with the server application, converts the client's calls from NDR and calls the server application that the client requested.

Conclusion

After this discussion I feel that now you should have a pretty good idea what is DCOM, why do we need it and how it works. I didn't go into many details as I think that this blog should be a more-or-less easy read for those of you who want to have a general idea of the subjects that I'm dealing with. Please comment and write me your remarks or requests.

It's a rainy day today so let me finish with a song on that subject. Enjoy!