Question

Should FIFO queue be synchronized if there is only one reader and one writer?

Answer 1

What do you mean by ‘synchronized’? If your reader & writer are in separate threads, you want the FIFO to handle the concurrency ‘correctly’, including such details as:

• proper use of FIFO API should never cause data structures to be corrupted
• proper use of FIFO API should not cause deadlock (although there should be a mechanism for a reader to wait until there is something to read)
• the objects read from the FIFO should be the same objects, in the same order, written to the FIFO (there shouldn’t be missing objects or rearranged order)
• there should be a bounded time (one would hope!) between when the writer puts something into the FIFO, and when it is available to the reader.

In the Java world there’s a good book on this, Java Concurrency In Practice. There are multiple ways to implement a FIFO that handles concurrency correctly. The simplest implementations are blocking, more complex ones use non-blocking algorithms based on compare-and-swap instructions found on most processors these days.