94.574 Elements of Computer Systems

SCE 574

211

Semaphores

äSynchronization tool (provided by the OS) that do not require busy waiting

äA semaphore S is an integer variable that, apart from initialization, can only be accessed through 2 atomic and mutually exclusive operations:

äwait(S)

äsignal(S)

äTo avoid busy waiting: when a process has to wait, it will be put in a blocked queue of processes waiting for the same event