The Little Book Of Semaphores is available for free in PDF form.

Julia's Semaphore is different from the one described in the book in that it has extra constraints:

• Semaphore(sem_size > 0), i.e. you can't create a Semaphore(0).
• The number of releases (signal) and acquires (wait) must match. For this reason, we cannot implement the examples with Semaphore without further ado.

In Julia, most of the time you don't use a Semaphore directly. Instead, you can use a lock (ReentrantLock), which corresponds to a Semaphore(1), and a Threads.Condition for what is done with "Semaphore(0)" in the book.

• barrier.jl: A simple barrier at which all participating tasks wait for each other before moving on.
• producer_consumer.jl: Producer tasks produce elements (in parallel) and independent consumer tasks process them (in parallel). Can be used/generalized for pipelining.
• readers_writers.jl: "Critical" section with categorical mutual exclusion of reader tasks (non-exclusive access) and writer tasks (exclusive access). The simpler case of a purely exclusive critical section is not covered because it can simply be realized with a lock.
• dining_philosophers.jl: Avoid circular synchronization deadlock appearing in the Dining philosophers problem formulated by Dijkstra.
• h2o.jl: U.C. Berkeley exercise in which two kinds of tasks, hydrogen and oxygen, should pair up such that they can pass a barrier as complete H₂O molecules (2 H + 1 O → H₂O).