From: Carlos Rica <jasampler@gmail.com>
Date: Sat, 28 Jul 2007 18:02:09 GMT
Subject: Re: [PATCH] Make verify-tag a builtin.
Message-ID: <1b46aba20707281102j6d519125y176fd11e3ab53fab@mail.gmail.com>
In-Reply-To: <7vtzrpwo44.fsf@assigned-by-dhcp.cox.net>

Your explanation about the I/O in parallel sounds much better to me,
now I understand, thank you Junio.

2007/7/27, Junio C Hamano <gitster@pobox.com>:
> What is happening is:
>
>  1. Your process prepares the whole thing in vtag-tmp, to hand
>     to gpg;
>
>  2. You make a pipe and start gpg with the above file telling it
>     "here is a detached signature file, the payload will be fed
>     through your stdin";
>
>  3-a. You feed the payload to the pipe, expecting gpg to read it.
>
>  3-b. gpg reads the detached signature file, finds no signature in
>     the vtag-tmp file because the tag in question is not signed,
>     and exits without reading a single byte from the pipe;
>
> Now, 3-a and 3-b run in parallel.  If 3-a is scheduled before
> 3-b happens, because payload is very often much smaller than the
> in-kernel pipe buffer, your write(2) succeeds before gpg gives up
> and exits without reading from the pipe.  If 3-b is scheduled
> before 3-a, then gpg exits and when 3-a gets around to write(2)
> to the pipe, write notices that there is nobody on the other end
> of the pipe, and you get SIGPIPE.