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Date: Wed, 09 Oct 2013 12:05:43 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/2] rfifolock: add recursive FIFO lock
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, xiawenc@linux.vnet.ibm.com, qemu-devel@nongnu.org, Michael Roth <mdroth@linux.vnet.ibm.com>

Il 09/10/2013 11:55, Stefan Hajnoczi ha scritto:
> +    /* Take a ticket */
> +    unsigned int ticket = r->tail++;
> +
> +    if (r->nesting > 0) {
> +        if (qemu_thread_is_self(&r->owner_thread)) {
> +            r->tail--; /* put ticket back, we're nesting */
> +        } else {

ticket is dead in the "nested" path, why not move it (and the increment)
directly after the else?

Otherwise, the code is very nice.  It's very interesting that no pthread
mutex is held in the rfifolock critical section, so that the thread that
holds the next ticket has a chance to be woken up.

Paolo