Handle Leak in Apple’s mDNSResponder.exe

A while ago, I noticed a handle leak in Apple's "Bonjour Service" (yeah, that sounds like something I want running on my system...) - mDNSResponder.exe. I knew right away that that was the executable for the "Bonjour Service" because the name is so helpful. (Joking. Even if it was named after the service, how the heck would I even guess what the "Bonjour Service" did. But I digress...)

The service description is:

Bonjour allows applications like iTunes and Safari to advertise and discover services on the local network. Having Bonjour running enables you to connect to hardware devices like Apple TV and software services like iTunes sharing and AirTunes. If you disable Bonjour, any network service that explicitly depends on it will fail to start.

I put up with the leak for a while, from time to time stopping the service when I thought of it after booting. Most of the time I didn't think of it and the leak did not appear to be having any kind of performance impact on my system (I never saw it get above 80,000 handles). An update (or two?) later, I thought it would be fixed. So I was surprised to find mDNSResponder.exe had more than 55,000 handles when I checked recently with Sysinternals' Process Explorer.

I tried to use Process Explorer's handle pane to see the handles in mDNSResponder.exe, but with that many handles to display, and with Process Explorer running with its default High priority and refreshing every second, the system became rather sluggish. I dropped the priority of Process Explorer with Task Manager, hid the lower-pane view, and gave Handle.exe a shot with handle.exe -a -p mdnsresponder.exe.

I found that the handles being leaked are handles to registry keys - specifically, HKLM\SYSTEM\ControlSet001\Services\Tcpip\Parameters. (ControlSet001 is the current control set on my system.)

Since there's not much I can do about the handle leak, I'll disable the service, and hope the next update fixes the problem as surely the next update will set the service to Automatic start. Wonder why the installer doesn't at least set a service such as this as "Delayed Start" in Vista...

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