Python Parallel Programming Cookbook

Thread synchronization with semaphores

Invented by E. Dijkstra and used for the first time in the operating system, a semaphore is an abstract data type managed by the operating system, used to synchronize the access by multiple threads to shared resources and data. Essentially, a semaphore is constituted of an internal variable that identifies the number of concurrent access to a resource to which it is associated.

Also, in the threading module, the operation of a semaphore is based on the two functions acquire() and release(), as explained:

• Whenever a thread wants to access a resource that is associated with a semaphore, it must invoke the acquire() operation, which decreases the internal variable of the semaphore and allows access to the resource ...