virThread: why no return values permitted in thread API?

[Daniel P. Berrangé]

On Wed, Apr 20, 2022 at 02:33:19PM +0200, Peter Krempa wrote:
> On Wed, Apr 20, 2022 at 14:24:39 +0200, Claudio Fontana wrote:
> > Hi,
> > 
> > I noticed that in the virThread API return values from threads are explicitly excluded from the API.
> > 
> > The "virThreadHelper" sits in the middle between the caller of virThreadCreate and pthread, making it impossible to return a value from the thread,
> > to check after joining the thread.
> 
> virThreadCreate has an 'opaque' parameter which allows to pass arbitrary
> data to the trhead. You can use it to pass also data back, just apply
> thread safety rules.
> 
> > I'd need to know if the thread execution is successful or not then I join the thread,
> > so what is the reason for this choice?
> 
> Could you elaborate what you are trying to achieve?
> 
> > Should I use pthread directly instead?
> 
> Generally no, please use the internal helpers for code consistency.

Though we should really be phasing out much of virthread.h in favour
of just using GLib's portable thread APIs. So personally I'd be fine
with patches that use GThread in new code.

With regards,
Daniel
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