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Re: [perl #118059] race condition+fail indist\IO\t\cachepropagate-tcp.t

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From:
Tony Cook
Date:
June 28, 2013 06:49
Subject:
Re: [perl #118059] race condition+fail indist\IO\t\cachepropagate-tcp.t
Message ID:
20130628064936.GA20986@mars.tony.develop-help.com
On Thu, Jun 27, 2013 at 04:34:17PM -0700, bulk88 via RT wrote:
> On Mon May 20 02:10:13 2013, tonyc wrote:
> > 
> > I see this failure maybe 1 in 20 runs (Windows 7 x64, Core i7).
> > 
> > I suspect the problem is that winsock is invalidating the accept socket 
> > once the child socket goes out of scope, causing a race in the accept()
> > implementation.
> > 
> > I changes the code so the child reads a line from the socket, and 
> > the parent closes the socket.  With that I had 2700 successful runs
> > before I stopped testing.
> > 
> > I'll try a smoke-me to see if it breaks anywhere else.
> > 
> > Tony
> 
> Any updates TonyC?

It smoked ok, but I don't trust that it fixes the underlying problem
(which may not be fixable, leaving us with the work-around.)

My theory above, as written, is hopefully nonsense - Windows returning
a socket and suddenly making it not-a-socket, rather than return an
end-of-file or EPIPE on the next operation would be even more broken
than I expect from Microsoft.

For a Realâ„¢ fork() any open file handles or sockets are cloned in the
child - the child can exit or explicitly cose their socket handle, but
it won't have an effect on the socket handle the parent has.

Under Win32 we emulate that, which I suspect is the real cause of the
problem here - when a thread is created fp_dup() calls
PerlIO_fdupopen() which does reasonable things on Unix, but on Win32
that leaves all the work to win32_fdupopen().

win32_fdupopen() calls win32_dup() a trivial wrapper around dup() -
and I don't see how that works for a socket fd unless the CRT dup() is
tolerant of errors from DuplicateHandle().

Tony

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