The max-connections slot is initially set to f, which disables connection limiting, but can be set to an integer specifying the maximum number of simultaneous connections.
Another method to limit connections is to set the semaphore slot to a semaphore. The server will hold the semaphore while servicing the client connection.
Setting the max-connections slot is equivalent to storing a semaphore with this initial count in the semaphore slot. The semaphore slot is useful for enforcing a maximum connection count shared between multiple threaded servers. See Counting semaphores for details.