This issue which can be found as;

http://trac.nginx.org/nginx/ticket/714
http://trac.nginx.org/nginx/ticket/626
http://trac.nginx.org/nginx/ticket/346

Still exists in 1.7.12, 1.8 and 1.9

We've isolated this between SPDY and (file)caching such as fastcgi_cache and proxy_cache, where exactly is not yet known, should you have this issue either disable file caching or spdy.

You often need to run debug logging for days to get anything useful, should you have a worker with a de-attached port state then attempt to core-dump this worker.

This issue is OS independent.

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nginx for Windows http://nginx-win.ecsds.eu/