From: Brian Candler <b.candler@...>
Date: 2008-12-24T18:28:18+09:00
Subject: Re: Are all Ruby built-in objects thread safe?

Just Another Victim wrote:
>     I don't think this is relevant.  Concurrency isn't about how many
> processors you use.  Multitasking systems existed long before SMP 
> hardware
> existed.  Concurrency is about doing tasks concurrently.  If you have 
> one
> method running and it may be preempted by another method then they are
> running concurrently.  If the two methods share data then they may 
> corrupt
> that data for each other.  This is true regardless of how these
> concurrencies, or threads, are implemented.  It doesn't matter if 
> they're
> hardware supported system threads or if they're Ruby green threads...

Not exactly. Ruby green threads aren't fully pre-emptive; they will only
pre-empt at the boundaries between execution steps, not within an
execution step.

Hence the single operations @array.pop and @array.push(...) are safe
against preemption. You could consider each method call to be wrapped
implicitly by Thread.critical { ... }
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