[qmtest] [PATCH] Mark fd's close-on-exec in qm.executable.

[Mark Mitchell]

> +    def _MakeCloseOnExec(self, fd):
> +        """Modifies 'fd' to not be inherited across 'exec'.

"""Prevent 'fd' from being inherited across 'exec'."""

> +
> +        UNIX only."""

Needs documentation for 'fd'.

> +        inheritable by child processes.  On UNIX the fds will always be
> +        >= 3 and in close-on-exec mode."""

I'd just say "and not inherited across 'exec'."

> +            pipe = os.pipe()
> +            for fd in pipe:
> +                # Push the fd up above 2, to make sure it won't conflict
> +                # with stdin/stdout/stderr.
> +                closable = []
> +                while fd <= 2:
> +                    closable.append(fd)
> +                    fd = os.dup(fd)
> +                for old in closable:
> +                    os.close(old)
> +                # And make it close-on-exec.
> +                self._MakeCloseOnExec(fd)
> +            return pipe

This logic has an inefficiency and a corner-case bug.

The former is that you might as well accumulate closable across both
iterations.  In other words, move it outside the loop.  That could save
some open/close calls.

The latter is that if there are no new available fds when you call dup,
we will (a) crash, and (b) leak the fds in closable.

-- 
Mark Mitchell
CodeSourcery, LLC
mark at codesourcery.com