I'm using mysql-proxy 0.8.3 on a Windows 7 system.
Sometimes, I get the following debug message in the log :
(debug) .\chassis-event-thread.c:254: recv() from event-notify-fd failed: Unknown error
and mysql-proxy process starts to use 25% of the CPU (on a quad-core) until I kill it. It continues to handle queries properly while it overloads the system.
The same queries/scripts doesn't always trigger the problem. I have very no idea of how to fix it.
I don't have experience with mysql proxy and windows but I did some investigation. I found mysql-proxy source and your error is logged from here: http://bazaar.launchpad.net/~mysql-proxy-developers/mysql-proxy/0.8/view/head:/src/chassis-event-thread.c#L252 (I guess 2 line difference is from source code formatting). It looks like recv from line 238 returns E_NET_WOULDBLOCK value. On line 57 there is definition (you said you are on windows)
#define E_NET_WOULDBLOCK WSAEWOULDBLOCK
So real error is WSAEWOULDBLOCK. Searching for it I found: https://stackoverflow.com/a/14549541
WSAEWOULDBLOCK is not really an error but simply tells you that your send buffers are full. This can happen if you saturate the network or if the other side simply doesn't acknowledge the received data.
I guess it is an error in mysql proxy. It is probably falling to infinite loop trying to recv from socket which is busy/empty/dead (and that's why 100% cpu usage). Maybe you could try with version from master (I don't know if there is a windows build)?
