hg serve keeps crashing with "bad file descriptor" in book.pyo

[Matt Mackall]

On Mon, 2012-11-19 at 23:02 +0100, Jaap Sperling wrote:
> After running quite happily for a couple of months, our Mercurial
> "server" has suddenly become really unstable. About 2 or 3 times a day
> it suddenly started crashing.

It probably coincided with someone configuring a new hook. Your server's
WSGI implementation appears to be hostile to our hook IO redirection
code. Interesting... what are you using?

> C:\Users\Mercurial>hg --version
> Mercurial Distributed SCM (version 2.3.2)

That was released Oct 1 (not yet months).

>   File "mercurial\hook.pyo", line 154, in hook
> OSError: [Errno 9] Bad file descriptor

This code prevents hooks from writing to stdout, etc. as that's prone to
causing protocol issues. WSGI servers often have dummy file objects
here, but yours seems to have bogus file descriptors instead that bypass
our checks:

            stdoutno = sys.__stdout__.fileno()
            stderrno = sys.__stderr__.fileno()
            # temporarily redirect stdout to stderr, if possible                                                                                                                                  
            if stdoutno >= 0 and stderrno >= 0:
                sys.__stdout__.flush()
->              oldstdout = os.dup(stdoutno)

..and this only gets run for hooks. In this case, seems to be a listkeys
hook.

-- 
Mathematics is the supreme nostalgia of our time.