[Libguestfs] [nbdkit PATCH 1/2] plugins: Add .thread_model callback

[Eric Blake]

On 5/20/19 9:18 AM, Eric Blake wrote:

>> (2) Shouldn't it be an error if the thread model returns a more
>> parallel thread model than the constant?
> 
> I thought about that, but my initial idea was to instead just declare
> that attempts at a more parallel model are just silently ignored (with
> at most a debug message visible during -fv).

I hit send too soon. My biggest reasoning for this? Consider the python
plugin. If we allow a python script to request PARALLEL now (but
silently ignore it, because our C glue code currently defines the
constant to SERIALIZE_ALL_REQUESTS), then that script will instantly
gain parallel support if a future nbdkit version manages to get the C
glue code rewritten to use better re-entrancy to the point of redefining
THREAD_MODEL to PARALLEL after all. (Based on code comments, it may be
doable with some effort for python, although I have less hopes for Ruby).

> 
>>
>> Anyway patch series generally looks fine to me.

Thanks; I'll push shortly.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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