Re: [fuse-devel] RE: Thread safe ?

[Quentin A. <qa...@ya...>]

--- David Schwartz <davidavidsmaster.com> wrote:

> 
> > Hi,
> >
> > Are all calls to the user space file system
> > serialized?
> >
> > In other words, is it safe to have a global
> variable
> > that is touched by multiple functions?
> >
> > If not, I understand I will need to use locking.
> >
> > Thanks,
> >
> > Q
> 
> 	Even if all the calls were serialized, you could
> still need locking.
> Locking doesn't just provide serialization and
> mutual exclusion, it ensures
> memory visibility. If you're using POSIPOSIXeads and
> want to have one thread
> read a memory allocation, even if you are sure it is
> after another thread
> has modified it, you still must ensure memory
> visibility by one of the
> specific methods POSIPOSIXvides. Otherwise the other
> thread could read a
> stale value (or, theoretically, any value) even if
> you are sure it runs
> after the modifying thread.
> 

Thank you very much for your help.  I really
apriappreciate  Do you have any good pointers to good
sites which go over more of these types of cases?

Thanks again.



> 	To clarify, if you have:
> 
> int i=0;
> int j=0;
> 
> 	And one thread does:
> 
> i=5;
> j=2;
> 
> 	And another thread does:
> 
> if(j==2)
> {
>  if(i==0) bomb();
> }
> 
> 	There is no guarantee that 'bomb' will not be
> called. Serialization is not
> sufficient.
> 
> 	DS
DS
> 
> 
> 
>
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