From: Joel VanderWerf <vjoel@...>
Date: 2003-10-09T14:03:13+09:00
Subject: Re: Standard Queue Implementation and Thread Safety

nobu.nokada@softhome.net wrote:
> Hi,
> 
> At Thu, 9 Oct 2003 03:49:48 +0900,
> Pete Kazmier wrote:
> 
>>The implementation is essentially backed by an Array.  Queue provides
>>synchronized push and pop methods (using Thread.critical), but methods
>>such as clear, length, and empty? are not synchronized.  What happens
>>if one thread is in the middle of clearing the queue and then another
>>comes along to add/remove something from the queue?  Why don't these
>>other methods need synchronization?  Is Array thread-safe by default?
> 
> 
> Yes.  Builtin methods (more accurately, not written in Ruby)
> are thread-safe, unless GC runs.  Since Array#empty? and
> Array#length don't modify anything, and Array#clear just
> releases but requires no memory, GC doesn't get run.

So Array#push is not thread-safe, but Queue#push is, right?

I understand that Array#push could provoke a GC, but why would GC cause 
a context-switch?