Fortsätt till huvudinnehåll

Take a look at the beautiful F# code

I have taken a special interest in parallel and asynchronous data processing in F#. The absolute majority of the really hard to fix bugs that I have come across during the last years all have one thing in common, thread safety. Or rather, the lack of thereof.

It is very easy to write a class in C#, Java, or C++ that is not thread safe. And if you try to make it thread safe it quickly can become quite complex and it is easy to forget to put a lock on a variable or make some subtle mistake that makes the lock useless (locking on a reference to an object that you later make a copy of, which makes locking the old reference useless, is a not so uncommon mistake that can be really hard to spot).

Another thing about thread safety is that it is really hard to test for. All your tests might run perfectly fine, but then when you go into production, things starts crashing in really strange ways.

F#, and other functional languages, addresses these problems and makes it easy to write code that can execute in parallel, safely. More info on the topic can be found here.

Also, I have started to write (well, mostly copy...) code to try out concurrency in F#. See my repo at https://github.com/Backhage/Parallellism for some code samples.

Kommentarer

Skicka en kommentar

Populära inlägg i den här bloggen

Does TDD really improve software quality?

I have asked myself this question several times, and searched for answers, without coming up with any clear answer. Therefore I have decided to go hard core TDD for a longer period of time (at least 6 months) to really evaluate the effects. There are several things that I find confusing when it comes to TDD. One example is what actually defines a unit test. What is a "unit" anyway? After reading a bit about it I found a text claiming that the "unit" is "a unit of work", i.e. something quite small. Like converting a string to UPPERCASE or splitting a string into an ['a','r', 'r', 'a', 'y'] of chars. This work is usually performed by a single call to a single method in a single, isolated, class. So, what does it mean that a class is isolated? Does it mean that it doesn't have any dependencies to other classes? NO! In the context of TDD it means that any dependencies are supplied by the test environment, for exa...
3 kommentarer
Läs mer

Codility tasks - Part I

I was recently faced with two codility tasks when applying for a job as an Embedded Software Engineer. For those of you who arn't familiar with Codility you can check out their website here:  www.codility.com Task one - Dominator The first task was called Dominator. The goal was to, given a std::vector of integers, find an integer that occurs in more than half of the positions in the vector. If no dominator was found -1 should be returned. My approach was to loop through the vector from the first to the last element, using a std::map to count the number of occurences of each integer. If the count ever reached above half the size of the vector I stopped and returned that integer and if I reached the end without finding a dominator I returned -1. So was that a good approach? Well, the reviewer at the company rated the solution as 'pretty ok'. His preferred solution was store the first integer in the array and set a counter to 1. Then loop through the remaining i...
7 kommentarer
Läs mer

Codility tasks - Part II

Now, the second codility task I was faced with was a bit tougher. The goal was to create a function that, given a vector of integers A and an integer K, returned the number of integer pairs in the vector that, when added, sums up to K. Let me give you an example. Assume that you are given a vector A = [0, -1, 3, 2, -5, 7] and K = 2. Possible combinations to get K are (0, 2), (-1, 3), (3, -1), (2, 0),  (-5, 7), and (7, -5). In other words, the function should return 6. Now, how did I solve this task? The first solution that came to mind involved nested for-loops. The outer loop picking one integer at the time from the vector and the inner loop adding the integer to the others one by one to see if the result is K. This solution works, but it does not scale well. Time complexity will be O(N**2) ,   something that for large vectors will result in very long execution times. My second approach was to use my old friend, the integer counter, and count all occurences of each...
2 kommentarer
Läs mer