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From: Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Press Release - Ada 2012 Language Standard Approved by ISO
Date: Thu, 27 Dec 2012 11:48:50 -0700
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Date: 2012-12-27T11:48:50-07:00
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On 12/27/2012 08:30 AM, Dmitry A. Kazakov wrote:
>
>
> And a nice race condition coming with that! Never use File_Exists if you
> can.

Precisely. Multiple processes may access the file system at the same time. The 
idea that you can check the precondition to an operation and have the result 
still hold when you invoke the operation is only valid for sequential 
activities; when you're using a concurrent language like Ada then there are 
often cases when that's a race. The Get operation for a concurrent, non-blocking 
queue has the precondition "not Is_Empty", but between checking that and 
invoking Get another task may have changed the state of the queue.

-- 
Jeff Carter
"He didn't get that nose from playing ping-pong."
Never Give a Sucker an Even Break
110