Synchronization of processes in a multiprogramming/multiprocessing system is provided by P and V instructions that are executed during execution of processes and operate on data structures known as semaphores which represent processes and events. A process that performs P instruction requests data. The...http://www.google.com.hk/patents/US4374409?utm_source=gb-gplus-share專利 US4374409 - Method of and system using P and V instructions on semaphores for transferring data among processes in a multiprocessing system
