From: MenTaLguY <mental@...>
Date: 2008-03-26T09:06:02+09:00
Subject: Re: thread.rb

On Wed, 26 Mar 2008 07:32:27 +0900, "Adam Bender" <abender@gmail.com> wrote:
> I couldn't find the Scheduler gem

 gem install scheduler

> I didn't understand the point of the Reader class in your code, since
> only one thread at a time can acquire the lock in pop.

The lock is released (by ConditionVariable#wait) while a reader is
waiting (and re-acquired before ConditionVariable#wait returns).
Otherwise writers couldn't get in to write.

Conceptually, a Queue is actually two queues:  a queue of "pushes" which
holds pushed values, and a queue of "pops" which holds threads waiting
for new values to be pushed.

If there have been more pushes than pops, the "pushes" queue will have
entries in it, and if there have been more pops than pushes, the "pops"
queue will have entries in it.  Each push tries to take an entry from
the "pops" queue and vice-versa, so that when there have been an equal
number of pushes and pops, both queues will be empty.

Readers are just used to represent entries in the "pops" queue.

-mental