How to parallelize file reading and writing

Question

I have a program which reads data from 2 text files and then save the result to another file. Since there are many data to be read and written which cause a performance hit,

Answer 1

This isn't really an answer to your question but rather a re-design (which we all hate but can't help doing). As already mentioned, trying to speed up I/O on a hard disk with multiple threads probably won't help.

However, it might be possible to use another approach depending on data sensitivity, throughput needs, data size, etc. It would not be difficult to create a structure in memory that maintains a picture of the data and allows easy/fast updates of the lines of text anywhere in the data. You could then use a dedicated thread that simply monitors that structure and whose job it is to write the data to disk. Writing data sequentially to disk can be extremely fast; it can be much faster than seeking randomly to different sections and writing it in pieces.