How to avoid multiple writers in a named pipe?
This would be a typical use for semaphores:
Create 2 semaphores - one for reading processed, the other one for writing processes. set each semaphore to value 1
Reading processes sem_wait(2) on the semaphore for readers until semphore > 0 and lower it to zero if they get it.
Writing processes will do the same with the semaphore intended for them
A controlling process (which may also set up the semaphores initially) could check, if both semaphores are zero and assign the pair
reader/writer release the semaphores (increasing them by 1 again) so next readr or writer will get the semaphore.
For passing informations between reader/writer shared memory may be used...