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Date: Wed, 27 Jun 2012 16:54:00 -0000
From: Eli Zaretskii <eliz@gnu.org>
Subject: Re: [PATCH]Fix that GDB will get hang on Windows when using pipe to get stdout and stderr from stub
In-reply-to: <000001cd5338$ded61b20$9c825160$%guo@arm.com>
To: Terry Guo <terry.guo@arm.com>
Cc: gdb-patches@sourceware.org, Joey.Ye@arm.com, Matthew.Gretton-Dann@arm.com, palves@redhat.com, daniel.jacobowitz@gmail.com
Reply-to: Eli Zaretskii <eliz@gnu.org>
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> From: "Terry Guo" <terry.guo@arm.com>
> Cc: <eliz@gnu.org>,
> 	"Joey Ye" <Joey.Ye@arm.com>,
> 	"Matthew Gretton-Dann" <Matthew.Gretton-Dann@arm.com>,
> 	"'Pedro Alves'" <palves@redhat.com>,
> 	<daniel.jacobowitz@gmail.com>
> Date: Tue, 26 Jun 2012 09:13:14 +0800
> 
> I noticed a cross-built MINGW arm-none-eabi GDB will get hang on Windows
> when use pipe to get stderr and stdout from stub. The command used to start
> stub in GDB is "target extended-remote |
> stub-that-write-stderr-before-stdout". For my case, after send
> "$vFlashDone#ea" to stub, GDB get hang. The GDB source show that GDB will
> keep waiting for ACK message from stdout of stub, after send the packet.
> Unfortunately my stub will write some kind of log information into stderr
> and this action takes place before stub write ACK message to its stdout. So
> the only pipe is occupied by stderr which is waiting for GDB to consume,
> while GDB keep waiting for message from the stdout which hasn't pipe to use.
> We finally end up with a deadlock on pipe between GDB/stderr/stdout.
> 
> The following patch can avoid such deadlock by letting GDB also probe and
> consume stderr when waiting for stdout. Please review and comment.

I only read it superficially, but it looked fine to me.

Thanks.