the number of file descriptors when using POSIX semaphore

in src/template/darwin:

# Select appropriate semaphore support. Darwin 6.0 (Mac OS X 10.2) and up

# support System V semaphores; before that we have to use POSIX semaphores,

# which are less good for our purposes because they eat a file descriptor

# per backend per max_connection slot.

To my understanding, the number of descriptors created by POSIX semaphores would be # of actual clients times max_connection. 

However, I monitor the number of open files using sysctl, and I find that kern.num_files doesn't match the result calculated by the formula that is inferred by me...

So, what would the number of file descriptors be, when using POSIX semaphore?  

Thanks!