Interview Questions for Programmers by MK #4

Home

Question #4
You have to implement a very fast, time critical, network communication between nodes of a distributed system. You decided to use good old sockets. However, you haven't decided yet whether to use TCP or UDP protocol. Which one would you choose and why?

Answer #4
If a speed is the only one important factor, I'd choose UDP. UDP is faster than TCP because it has a smaller overhead. In comparison to TCP it is a connection-less, unreliable protocol that doesn't provide features like retransmission, acknowledgment or ordering of messages.

However, it also means that usage of UDP might be more difficult and will require additional coding in some cases. For example, if we have to assure that sent messages have been delivered. In this case, I'd certainly use TCP.

Finally, there is one more thing in favor of UDP. It provides broadcasting and multicasting. So, if it is required I'd also use UDP instead of TCP.

What every blogger should do if using someone else's code #3

Home

Recently, I've written a post about integration with Dropbox. This one is also about integration but this time with Skydrive. I spent some time on investigating how to implement this feature in a desktop application. I was even considering to write what I need from the scratch on my own.

Fortunately, it turned out that someone did it for me. I found a nice piece of code prepared by Microsoft. It includes sample applications showing how to do everything step by step. You can download it from github.

A practical example of using TaskCompletionSource<T>

Home

Recently I've found a question about real life scenarios for using rather unknown TaskCompletionSource<T> class. I started thinking where I would use it and very quickly I found a good practical example.

I have a pet project LanguageTrainer that helps me in learning words in foreign languages. Some time ago I added Dropbox support to it. It allows me to export/import list of words to/from Dropbox. I developed it in synchronous way. Now I prefer an asynchronous approach and I want to take advantages of async/await keywords.

The problem is that DropNet library, that makes communication with Dropbox easy, doesn't use async/await. It has asynchronous API but it is callback based. The really easy solution here is to use TaskCompletionSource<T>. Here is an example (simplified). Let's start with the original code that downloads a given file from Dropbox.

public void ProcessFile(string key, string secret, string path)
{
   var client = new DropNetClient(key, secret);
   // ...
   var bytes = client.GetFile(path)
   //Process bytes
}

The version that uses DropNet asynchronous API looks in the following way:

public void ProcessFileAsync(string key, string secret, string path)
{
   var client = new DropNetClient(key, secret);
   //...
   client.GetFileAsync(path, 
      response => 
      {
         var bytes = response.RawBytes;
         //Process bytes
      }, 
      ex => 
      {
         //Handle exception
      });
}

And finally the asynchronous version with async/await looks in the following way:

public async Task<Stream> ProcessFileAsync(string key, string secret, string path)
{
   var client = new DropNetClient(key, secret);
   //...
   var tcs = new TaskCompletionSource<Stream>();
   client.GetFileAsync(path, response => tcs.SetResult(new MemoryStream(response.RawBytes)), tcs.SetException);
   return tcs.Task;
}
...
var bytes = await ProcessFileAsync(key, secret, path);
//Process bytes

The method ProcessFileAsync is marked as async and returns a task so it can be awaited. Easy. isn't it? A few lines of code and you can use async/await with other types of asynchronous APIs.

Careercon Warszawa 2015 - surveys

Home

I'd like to share with you the results of 2 surveys regarding my last presentation. The first one was prepared by organizers of the conference. The second one was created by me on SurveyMonkey portal. I placed a link to it on each slide in the lower  left corner. It was visible through the whole presentation so anyone with a smartphone could have filled it. The survey was short and consisted of 3 obligatory and 2 voluntary questions.

Let's start with the official survey of the conference. According to it there were ~50 people on my presentation. ~30 said that it was very good, ~18 that it was good and ~2 that it was week. In average it gives 4,56. These are very good results for me, thanks!



My survey looked in the following way:

• Question 1 - What is your overall assessment of my presentation on a scale of 1 to 5 (5 - the highest evaluation)?
• Question 2 - How do you assess the substantive content of my presentation on a scale of 1 to 5 (5 - the highest evaluation)?
• Question 3 - How would you rate my way of presenting on a scale of 1 to 5 (5 - the highest evaluation)?
• Question 4 - Name one thing that you remember from my presentation.
• Question 5 - This is the place for all sorts of comments, applications and complaints. Each comment will be valuable for me.

I received 8 answers for these questions. Much less than for the previous survey but all the answers were extremely valuable to me. Thanks! Here are details:

	1	2	3	4	5	Average
Question 1			1	4	3	4,25
Question 2				4	4	4,50
Question 3				3	5	4,63

I also received a couple of comments that will allow me to be a better speaker in the future:

• The demo should have been a little bit longer.
• The sample code used during a demo could be more complex.
• I should have used a microphone.
• I should have spoken slower.
• Not all terms used by me were understandable for a layman.

It was nice to read that my presentation was useful and that I showed interesting tools.

As a summary I have to say that these results are a boost of energy for me and an encouragement to be a speaker more often.

Careercon Warszawa 2015 - already after the presentation

Home

A couple of hours ago I returned from the conference Carrercon Warszawa 2015 where I had a presentation about historical debuggers. I'm generally happy with my speech. There were dozens of people in the room. I didn't forget to tell about anything important, I wasn't stressed too much and my presentation took as much time as I planned. As always I see a room for improvement but it was a good decision to take part in the conference as a speaker.

In the next post I want to write much more about Careercon Warszawa 2015 and my presentation. Now, I'd like to ask everybody who attended my presentation and who are reading this post for one thing. The thing which is very important to me. I'll be happy if you fill the following short survey:

Click to start a survey

Any feedback will be extremely valuable for me.