An information structure called a semaphore serves as a signalling mechanism in process synchronization. The semaphore is used to relate a process and an event which do not appear simultaneously. In accomplishing this, the semaphore is capable of storing the presence of events or resources waiting for...http://www.google.de/patents/US4395757?utm_source=gb-gplus-sharePatent US4395757 - Process synchronization utilizing semaphores
