A Simple Text Editor

A parallel world has many doors,
With lots to explore and lots to find.
Knock knock and thee shall ask for more,
With fork and join, to blow your mind.

Enough with the theatricals? Yes, I understand.

So, for my second adventure in the parallel world, I set out to inspect parallelism in Java. Don't worry - this is not going to be the nine hundred and ninety ninth post that you are reading, explaining Java's incredible journey from threads to executor service! Contrarily, this is about my experience in putting the same into use.

I found this cute, simple text editor written in Java on GitHub, that I thought had some scope for improvement. It had most of the features of a typical text editor, except for scroll pane (which I thought was pretty necessary). After sufficient twiddling, I happened to notice that it had no "find all" feature and there was my light-bulb moment - implementing a parallel search for a word in a document.


Implementing a parallel search for a word in a document

If you think about it, it is piece of cake - You have some jumbo text, in which you have to find the occurrence of a word. All you java lovers are probably wondering why all this hue and cry for a simple String.indexOf() function call. Well, I was also in agreement till I discovered that the indexOf function is, in reality, implemented as O(mn) algorithm.  (If you are fortunate enough to have not come across this notation, you can either refer here or take my word for "We can do better".)

A simple parallel approach to the same problem is to divide the search among threads i.e break up the jumbo text into smaller chunks and make each thread return occurrences of the search string. But wait, what if the word is spread across the chunks? Yes, we have to handle that case separately.

A screenshot of the find all implementation

All said and done, with a few lines of code, this new feature was added to the text editor. It seemed to perform pretty well with a running time of 2 milliseconds for 237 occurrences in a text of about 20000 characters (using the same old O(mn) algorithm). However, there was no significant change in the performance when the number of threads was increased.

Hope you liked this short simple post on Java parallelism. Look forward to more in the upcoming posts. Till such time, happy coding in a parallel world.😊

P.S. All relevant code will be available here.