Multiple readers on FIFO

Question

I've asked a question here before about multiple writers on a FIFO, and I know now that the write is thread safe as long as I write less than the PIPE_BIF, here is the link for that limit.

What about read? what if have two(or more) readers in multiple threads for reading from the same fifo, do I need locks here? or all I need is to read less than the PIPE_BUF?

BTW, I'm talking about Linux FIFO, And I'm using C.

Answer 1

Updated answer

Per the manual, you are NOT guaranteed atomic reads. However, their intent is for reads with FIFOs to be atomic. From paragraphs 2 and 4 of Rationale | Input and output

The standard developers considered adding atomicity requirements to a pipe or FIFO, but
 recognized that due to the nature of pipes and FIFOs there could be no guarantee of 
atomicity of reads of {PIPE_BUF} or any other size that would be an aid to applications 
portability.

I/O is intended to be atomic to ordinary files and pipes and FIFOs.

Until you see evidence otherwise, I would still be willing to say that you are fine.

Original answer

Based upon your previous question, I'm assuming all of your reads will be less than PIPE_BUF as well.

I don't believe you'll need any additional serialization around the reads since your unit of consumption is less than the guaranteed atomic, thread-safe write amount. If you had sequences of objects that needed to be read, then you would need some additional mechanism for serialization.