Why it's dangerous to fork off a new process in Glasgow Haskell

[George Russell]

Dean Herington wrote:
> 
> George Russell wrote:
> 
> > > > Posix.runProcess really should use it I think.
> > >
> > > No, it's better to be able to choose the way to handle this.
> > > Maybe add a flag to Posix.runProcess. But the whole
> > > GHC.Conc.forkProcess isn't finished, yet, anyway.
> > I don't really see the point of allowing the user to choose the old way.
> > Posix.runProcess is supposed to fork off a new process outside of this
> > runtime system.  I don't see any way this can be helped by allowing other
> > threads to continue in the child until the actual time of exec, unless for
> > some reason the evaluation of the arguments to exec somehow relies on other
> > threads.  But this would surely at least require argument evaluation to
> > unsafely conceal IO, and in any case could be better fixed by forcing the
> > arguments to be fully evaluated before the fork.
> 
> Let's not forget that the new (child) process may never do exec().  I have an interpreter that
> forks to replicate itself, relying on the runtime system to carry over.
Er, are you confusing Posix.forkProcess (which I was talking about) with Posix.runProcess (which
is what I am talking about now)?