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From: "Ronald F. Guilmette" <rfg@tristatelogic.com>
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Subject: Re: Is a successful call to write(2) atomic?
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Date: Wed, 16 Jun 2021 16:18:22 -0700
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In message <af9666f4-f327-432e-5b10-100557aa9cf5@panix.com>, 
Kurt Hackenberg <kh@panix.com> wrote:

>Since you only open the file once, you should seek to end of file before 
>each write, as somebody else pointed out. You should do that seek, and 
>the write, while holding the file lock. That is:
>
>   lock file
>   seek to EOF
>   write
>   unlock file
>
>Does your code do that?

Nope.  I'll give it a try.  Thanks!

>The reason, of course, is that some other process could move end of file 
>out from under you while you do not hold the file lock.

Sounds entirely plausible.


Regards,
rfg