This approach will indeed hit bottleneck even in SSD. Thus, file can be read into RAM line by line in thread 0, then once specified amount of lines was gathered, schedule thread 1 to process them, while thread 0 still reads new lines. Once another chunk is ready, give to thread 2 and so on. This way you can start processing data in asynchronous regime in the fastest way possible. Slightly slower but more convenient approach is to firstly read all the file into RAM and only then assign parts of it to each thread at the same time.