On Synchronizing Readers and Writers with Semaphores

A weakness in the reader priority solution proposed by Curtois, Heymans and Paraas for the problem of synchronizing concurrent readers and writers is described and an improvement is explained. The difficulties of solving complex synchronizing problems by using standard semaphore primitives, as illustrated by this example, lead us to propose that special-purpose synchronization techniques should be supported by a judicious combination of hardware/microcode and software routines. We then describe an efficient solution for the reader/writer problem which is easy to understand, to implement and to use