I want you to consider the following program and think about the output logged in the console,
Is it 11 or 21? As most of you would guess correctly, the answer would be 11. That’s because, once the value of b is computed, it is no longer dependent on the value of a. As a result, changing the value of a does not change the value of b.
Suppose the value of a changes over time, e.g., it may be a user input from a webpage that can be modified by the user anytime. And we want b to be calculated as soon as a is changed. A new programming paradigm called Reactive Programming is used for such problems.
An example of Reactive Programming would be a spreadsheet. If you have used it before, you know that when you write a formula for a cell like “=A1+B1″, the value of the cell gets modified as soon as the value in either cell A1 or cell B1 is modified.
Let us now modify our example using Reactive Programming. The value of a is going to change every 3 sec, and as soon as it does, b will be modified. The resulting reactive program is following:
- Jafar Husain (from Netflix) explains Reactive Programming based on known design patterns and how it is being used in Netflix. [video]
- Why do we care about reactive systems – The Reactive Manifesto. [link]
[Prereq: Windows, Visual Studio, Eclipse]
[Project link: https://github.com/rfaisal/ThriftStarterCSharpServerJavaClient]
How it started:
Recently I have been introduced with a very cool technology called Apache Thrift. It is originally developed by Facebook and later open-sourced in Apache Software Foundation. It is one of the core building block of the Facebook technology. The technical paper introducing Thrift can be found here.
What is it:
In layman’s terms, Thrift allows an application written in one language (e.g., Java) to exchange data with an application written another language (e.g., C#). Probably the most popular technology in this area is SOAP. Although SOAP is more general, but Thrift has less overhead. In technical terms, Thrift is a Remote Procedure Call (RPC) framework that can be used to develop scalable cross-language services. Thrift is an interface definition language, i.e., you can only write interfaces or pure abstract classes by Thrift. The Thrift compiler can generate corresponding classes and interfaces for any particular language (e.g., C#) from the Thrift interface. The server (e.g., C#) should implement these interfaces and start a service, and the client (e.g., Java) can call the functions of these interfaces by communicating with the service.
Dynamic Programming is a discrete optimization technique. It means, the variables we want to calculate using this method are discrete. As an example, if x is one such variable then is acceptable, but ‘x is a real number between 0 and 1′ is NOT acceptable since there are infinitely many real numbers between 0 and 1. In math terms, we can say that the domain of the variable x is a countable set.
Problems that are solved by dynamic programming are recursive nature. Let’s look at the problem that ask us to calculate the sum up to a number, i.e., if is such a function then . The recursive definition (assuming i is non negative) is following:
Few years back, I wrote a simple logging library in ActionScript3 using the Chain of Responsibility pattern. Recently, I dug up the old codes, made some modifications, and put it in github for other people to use and contribute. In this post, I will mainly focus on how to use the library and do some project specific modifications, but I will also briefly discuss my reasons for using the Chain Of Responsibility and the Singleton Pattern. I started writing this library with the following 4 goals in mind:
- It should be easily accessible to all of the classes of a project.
- It should be able to write logging information to different output sources, i.e., file, database, console, etc., and additional output sources can be added easily.
- It should be able to handle different levels of logging like FATAL_ERROR or INFO (as different actions may be needed for handling different levels), and additional levels can be added easily.
- It should require minimal setup.
When people ask me what my first language is, I sometimes playfully answer, “C”. C taught me what it meant to be a programmer. Few days back when I decided to start hacking the linux kernel again, I realized how much I miss programming in C. Playing with the pointers was undoubtedly the best part! So, I thought I would write this post.
If you have irrational fear of pointers or preparing for a C interview or just want to have fun, you should read this post! I am assuming you know the basics of pointers, but just cannot get a total hold on them.
I will start by stating a quote by Joel Spolsky:
I don’t care how much you know about continuations and closures and exception handling: if you can’t explain why
while(*s++ = *t++); copies a string, or if that isn’t the most natural thing in the world to you, well, you’re programming based on superstition, as far as I’m concerned: a medical doctor who doesn’t know basic anatomy, passing out prescriptions based on what the pharma sales babe said would work.
“I don’t believe in Computer Science.”~ Richard Feynman at Bell Labs (1985).
Feynman argued that science is the study of the behavior of the nature. He pointed out the limitations of classical computers for simulating the nature, which is very difficult because nature is quantum mechanical. At his lectures at Caltech, Feynman talked about the limitations of computation due to mathematics, noise, thermodynamics, reversible computing (where it is possible to compute and un-compute), and quantum mechanics. He predicted a new type of computer that is not a Turing machine, which he called a quantum computer. Continue reading
“There has not been a king since the first brethren court, and that is not likely to change!”, Captain Chevalle sighed. Elizabeth Swann wondered, “Why not?”. “Because the pirate king is elected by popular vote…”, as Mr. Gibbs started to explain, Captain Barbossa finished the sentence, “…and each pirate only votes for himself.”~Pirates of the Caribbean.
Yesterday I was having lunch with my friends Jocelyn, Johnson, and Adrian. One thing lead to another, we started talking about pirates. In one of her interviews, Jocelyn came across a question about how a senior pirate would divide some gold coins among 4 other pirates so that they would not vote to kill him. It was immediately apparent that the senior pirate would not give any gold to 2 of the pirates, but how much he should give the other 2 pirates was not obvious to me. It was stuck in my mind. I concluded that there must be some missing pieces of the question. It turns out that this problem is of a significant theoretical interest to many people. Let’s define the problem first.
There are 5 pirates of different ranks in a ship and they have a treasure of 100 gold coins. The current highest ranking pirate will divide the coins, and all 5 pirates will vote for or against it. If half or more of the pirates vote for it, then the coins will be divided that way. Otherwise, the pirate proposing the scheme will be killed, and the process is repeated with the pirates that remain. The most important thing for a pirate is his life. After that he wants to get as much coins as possible. As every pirate is bloodthirsty, if voting for or against will give him the same number of coins, he will vote against so that the pirate who proposed the plan will be killed. All 5 pirates are intelligent, rational, and good at math. How will the highest ranking pirate divide the coins?