Cover by Javier Fernández González

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

O'Reilly logo

Controlling concurrent access to a resource

In this recipe, you will learn how to use the semaphore mechanism provided by the Java language. A semaphore is a counter that protects the access to one or more shared resources.

Note

The concept of a semaphore was introduced by Edsger Dijkstra in 1965 and was used for the first time in the THEOS operating system.

When a thread wants to access one of these shared resources, first, it must acquire the semaphore. If the internal counter of the semaphore is greater than 0, the semaphore decrements the counter and allows access to the shared resource. A counter bigger than 0 means there are free resources that can be used, so the thread can access and use one of them.

Otherwise, if the counter of the semaphore ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required