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Re: cygwin source-patch fixing deadlock while writing to serial port
- From: Christopher Faylor <cgf-no-personal-reply-please at cygwin dot com>
- To: cygwin at cygwin dot com
- Date: Mon, 19 Jan 2004 16:14:40 -0500
- Subject: Re: cygwin source-patch fixing deadlock while writing to serial port
- References: <400C4757.email@example.com>
- Reply-to: cygwin at cygwin dot com
On Mon, Jan 19, 2004 at 10:08:39PM +0100, H. Henning Schmidt wrote:
>I found a potential deadlock while writing to a serial port (e.g.
>/dev/com1) that has been opened as O_RDWR. The deadlock occurs from time
>to time (not sure about exact conditions) when I write to that port,
>while there is data coming in (e.g. from an external device) and I do
>not read away that data fast enough from the port.
>I did provide a test case a while ago in
>http://sources.redhat.com/ml/cygwin/2003-03/msg01529.html. I digged into
>the issue some more now and found that the executing thread got
>sometimes deadlocked in fhandler_serial::raw_write(). It basically ends
>up in a for(;;) loop and just never hits the break;
>The applied patch adds a safety exit to that for(;;) loop.
>This fixes the testcase referenced above.
>This might not be the last problem lingering in the serial access code
>(there are some FIXME tokens still around ...), but it is definitely an
>improvement for me. I thought I'd share that with you.
Can you convince me that this isn't just a band-aid? I don't understand
why cygwin *shouldn't* hang in a situation like this. There are
certainly similar situations where this happens on linux.
Perhaps we need a low_priority_sleep (10) in the loop in that situation
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