The Acceptor Threads property for the Transport service specifies how many threads you want in accept mode on a listen socket at any time. It is a good practice to set this to less than or equal to the number of CPUs in your system.
In the GlassFish Server, acceptor threads on an HTTP Listener accept connections and put them onto a connection queue. Session threads then pick up connections from the queue and service the requests. The server posts more session threads if required at the end of the request.
See Administering HTTP Network Listeners in Oracle GlassFish Server 3.1 Administration Guide for instructions on modifying the Acceptor Threads property. If using the Administration Console, the Acceptor Threads property is available on the Configurations->configuration-name->Network Config->Transports->tcp page.