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Re: [PATCH] Universally-unique gensyms

From: Mark H Weaver
Subject: Re: [PATCH] Universally-unique gensyms
Date: Wed, 18 Jan 2012 23:50:04 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.92 (gnu/linux)

David Kastrup <address@hidden> writes:

> Mark H Weaver <address@hidden> writes:
>> Andy Wingo <address@hidden> writes:
>>> Sorry for asking a stupid question, but why is it that we want the
>>> gensym counter to be thread-local?  Just to avoid the mutex?  TBH I
>>> don't think it's that big of a point of contention.  This risks
>>> devolution into bike-shed-landia tho...
>> It's a reasonable question.  I don't feel strongly about it, but I
>> prefer lock-free programming where practical, and in this case there's
>> really no need for coordination between threads.  Indeed, these UUIDs
>> are already designed to avoid collisions between multiple _sessions_
>> without coordination.  So why bother with the lock?
> To avoid both threads reading the same seed value before generating the
> same number?  I have not looked at the code, but that could be a reason
> for serializing.

Hence the _thread-local_ gensym counters, which is what we're
discussing.  Please read before you post.


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