[c++-pthreads] Re: FW: RE: Re: I'm Lost

[Meredith, Alisdair]

Sorry to be dense, or if I am covering old ground - just confirming I understand correctly:
Also sorry for HTML format - it is all I can get remotely from our Exchange server :¬(
 
i/  cancellation will propogate as an (uncatchable?) exception, implying stack unwinding.
ii/ if cancellation passes through an exception specification, we call unexpected and abort which pretty much achieves the same thing
iii/ if cancellation interupts a dtor during regular stack unwinding, we call terminate which pretty much has the same effect, so everyone is still happy.
 
I am still not sure about:
iv/ if an exception is thrown but not caught in main, it is implementation defined whether stack unwinding occurs, so it will really be implementation defined whether the stack is unwound for thread cancellation in this scheme.
 
I am also not clear whether unexpected / terminate will kill just the thread, or the whole process.  I am currently expecting the latter as the status quo, although not with a strong opinion to fight for <g>
 
AlisdairM

________________________________

From: Mark Mitchell [mailto:mark at codesourcery.com]
Sent: Wed 08/03/2006 23:15
To: Jason Merrill
Cc: Wil Evers; David Abrahams; c++-pthreads at codesourcery.com
Subject: Re: [c++-pthreads] Re: FW: RE: Re: I'm Lost



Jason Merrill wrote:

> If you can interrupt cancellation, re-cancellation is implemented
> trivially simply by just having the cancellation exception destructor
> call 'pthread_cancel (pthread_self ())'.  The sticking point is being
> able to abort the cancellation in the first place, which is what Uli has
> been opposed to.

It sounds like we really are close to a solution then; I think everyone
here would be happy with the re-cancellation thing, and the destructor
trick means that there's really no way the thread can permanently
discard the cancellation request, short of things like longjmp -- and,
of course, if the thread is really determined not to go away it can just
hang around anyhow.  So, it seems like this ought to satisfy everyone
from the user-level perspective.

> I don't think he's opposed to catching it, just to doing anything that
> would involve backing out of the cancellation once it's started.

Would the above satisfy him?

--
Mark Mitchell
CodeSourcery
mark at codesourcery.com
(650) 331-3385 x713


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