Jan 10, 2026 · Semaphores are a powerful and flexible primitive for writing concur-rent programs. Some programmers use them exclusively, shunning locks and condition variables, due to their simplicity …

INTRODUCING Semaphores Condition variables have no state (other than waiting queue) – Programmer must track additional state Semaphores have state: track integer value – State cannot …

Producer/Consumer: Semaphores #1 Single producer thread, single consumer thread Single shared buffer between producer and consumer Use 2 semaphores

Concurrency abstractions How can semaphores help with producer-consumer? How to implement semaphores?

Semaphores can be used for things other than simple mutual exclusion. For example, resource allocation: P = allocate resource, V = return resource. More on this later. Semaphore Example: …

Interestingly, this paper that introduced semaphores actually was an early paper on the art and science of operating system design. Semaphores, which Dijkstra developed to aid in the process of writing …

Semaphores Agenda Definition of Semaphore Using Semaphores instead of locks and condition variables Producer/Consumer Problem Reader-Writer locks Dining Philosophers Building Zemaphores

INTRODUCING Semaphores Condition variables have no state (other than waiting queue) – Programmer must track additional state Semaphores have state: track integer value – State cannot …

Definition of Semaphores Synchronization variable introduced by Dijkstra in 1960s • Mutual exclusion and scheduling control Variable contains non-negative integer values • Cannot read or write value …

Thus semaphores must be built up in software using some lower-level synchronization primitive provided by hardware. Need a simple way of doing mutual exclusion in order to implement P's and V's. We …