Re: FPATH/autoload still strange in -dev-21

[Sven Wischnowsky <wischnow@informatik.hu-berlin.de>]

Bart Schaefer wrote:

> I just got -dev-21 + patches to 10477 compiled and installed, and I'm still
> having the strange problems with exported FPATH and (autoload -U) failing
> that I described in 10316.  I examined strace output and discovered that
> in the expression:
> 
> 	if (autoload -U 2> /dev/null); then
> 
> First zsh forks the subshell, and then the subshell forks again, apparently
> in order to redirect the output of the builtin; but then the subshell exits
> for some reason I can't follow, leaving the autoload running as an orphan.
> So zsh never sees the exit status of autoload.  (The process forked from
> the subshell is plugging away close()ing each of 256 file descriptors, 
> except for 0, 1, and 2, most of which are returning EBADF, while its parent
> subshell is exiting.)

Bart sent me the strace output and there he also repeated the line
above, but slightly different:

    if (autoload -U 2>& /dev/null); then

So, Bart, if that is the form you have in .zshenv, this explains the
processes. `2>& /dev/null' makes the shell look at the word after the
redirection. This isn't a number, so the whole thing is treated like
`&>' on file descriptor 2. This makes it treat it as a multio and the
funny chap with the many close()s is the zsh-tee process.

This is ugly. `&>' on file descriptor 2 makes no sense at all and if
even Bart is confused, I think we should do something about it. But
what? Make `2>& <non-number>' be silently treated like `2> <non-number>'?
Make it emit a warning, or even an error?

With the line above, my strace output is exactly the same as for
Bart. But I still can't reproduce the bug Bart gets when FPATH is
exported.

> Now, the odd thing is, the subshell calls _exit(0), so you'd think that zsh
> would take the "then" branch of the "if" -- but it doesn't, it takes the
> "else" branch.  So there must be two race conditions (?) here -- one in the
> subshell where it loses track of its child, and another where the topmost
> zsh mishandles the exit of that subshell.

I'm not sure any more if this is really a race condition. I suspect a
memory corruption of some kind, triggered by importing $FPATH from the 
environment (which would also explain why I can't reproduce, with
different allocation behaviours and all that).

And the initial setup of fpath also depends on the site-function dirs
that are automatically added and so on... Hm, I would try to debug the 
fpath initialisation in setupvals() and createparamtable().


Bye
 Sven


--
Sven Wischnowsky                         wischnow@informatik.hu-berlin.de