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Re: [libvirt] [PATCH 2/2] Fix updating of haveTheBuck in RPC client to be race-free

On 12/07/2011 03:46 PM, Daniel P. Berrange wrote:
From: "Daniel P. Berrange"<berrange redhat com>

When one thread passes the buck to another thread, it uses
virCondSignal to wake up the target thread. The variable
'haveTheBuck' is not updated in a race-free manner when
this occurs. The current thread sets it to false, and the
woken up thread sets it to true. There is a window where
a 3rd thread can come in and grab the buck.

Even if this didn't lead to crashes&  deadlocks, this would
still result in unfairness in the buckpassing algorithm.

A better solution is to *never* set haveTheBuck to false
when we're passing the buck. Only set it to false when there
is no further thread waiting for the buck.

* src/rpc/virnetclient.c: Only set haveTheBuck to false
   if no thread is waiting
I've tested it with virt-manager and also the trheaded test. Works fine to me and looks good.



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