When some connection was reset Tornado started to use 100% of CPU. That was caused by not closed socket which constantly generated socket.error with errno.ECONNRESET code instead handled errno.ECONNABORTED.
Platform the error detected: windows. However other platforms probably affected too.
Fix ssl socket error handling.
Can you reproduce this with a simple test case? It's always good to get more test cases for platform-specific behavior, but if it's difficult to reproduce don't worry about it.