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Microsoft Windows NT Build 297 06-28-1992

Summary:

This article refers to the file Database.c which is one
variation of the classical synchronization problem
Reader/Writers. The Reader/Writer problem first stated and
solved by Courtois revolves around a shared resource a DataBase
typically. The issue here is to allow both readers and writers
access to the database without corrupting it. Typically one allows
multiple Readers to access the database as long as a Writer is not
in there. However when a Writer is in the database no one else is
allowed in either Reader or Writer. There are several variations
of this problem around the simplest will favor Readers to the
exclusion of Writers or visa versa.

The implementation I used I believe was modeled after Dijkstra;
however I've long since misplaced my operating systems book so can't
verify it. His method would allow as many readers in the database
at one time until a Writer wished entrance in. Then no other Reader
can enter the database until this Writer is finished. All Readers
currently in the database however can finish. This way no starvation
of either the Readers or Writers which is inherent in the simpler
methods will happen.

More Information: 

In order to keep this sample focused, I've left the user interface
simple; to run this sample at the command prompt type

   ReadWrit

What you will see are the values the Readers put on the screen. These
are the running total of the threads that wrote to the database.

Enjoy

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