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Re: Tag locking change

From: Greg A. Woods
Subject: Re: Tag locking change
Date: Wed, 9 Oct 2002 16:52:29 -0400 (EDT)

[ On Wednesday, October 9, 2002 at 10:13:42 (-0700), Paul Sander wrote: ]
> Subject: Re: Tag locking change
> There are lots of cases where someone demands "tag branch x as of time y".

What the heck does that have to do with tagging the head of a branch?!?!?!?

> As for the instantaneous part:  It takes a while for CVS to apply tags
> using the rtag command.

Well, "Duh!"

>  The proposed change to the locking system opens
> a race condition between rtag and commit, where the head of the branch
> can change while the tag is being applied.

The point is you shouldn't be tagging the head of the branch without
doing so from within a working directory which is up-to-date to the head
of the branch in the first place.  It really doesn't matter whether "cvs
rtag" makes it a safe "atomic" operation or not.

> However, assuming a timestamp of "now" during rtag is a low-overhead and
> lock-free method to remove the race condition.

Well, yes, in the implementation "now" hopefully gets converted to the
time at the start of the command and doesn't change as the procedure
progresses, and so it's a silly cheap trick to still get undefined
results with the tag....

                                                                Greg A. Woods

+1 416 218-0098;            <address@hidden>;           <address@hidden>
Planix, Inc. <address@hidden>; VE3TCP; Secrets of the Weird <address@hidden>

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