Class RWLock

source code

Synchronization object used in a solution of so-called second readers-writers problem. In this problem, many readers can simultaneously access a share, and a writer has an exclusive access to this share. Additionally, the following constraints should be met:

• no reader should be kept waiting if the share is currently opened for reading unless a writer is also waiting for the share,
• no writer should be kept waiting for the share longer than absolutely necessary.

The implementation is based on [1, secs. 4.2.2, 4.2.6, 4.2.7] with a modification -- adding an additional lock (self.__readers_queue) -- in accordance with [2].

Sources:

1. A.B. Downey: "The little book of semaphores", Version 2.1.5, 2008
2. P.J. Courtois, F. Heymans, D.L. Parnas: "Concurrent Control with 'Readers' and 'Writers'", Communications of the ACM, 1971 (via [3])
3. http://en.wikipedia.org/wiki/Readers-writers_problem