RE: [bug #33134] spurious error when stdout is already closed

[Martin Dorey]

> maybe there's a better way of checking for closure than ftell

http://software.jessies.org/svn/salma-hayek/trunk/native/all/ruby-launcher/ruby-launcher.cpp
 suggests:

    // This might look obscure but the man page suggests that it's a 
POSIX-compliant way
    // of testing whether a file descriptor is open.
    int rc = fcntl(targetFd, F_GETFL);
    if (rc != -1) {
        return;
    }
    if (errno != EBADF) {

Unlike make, that code only needs to worry about POSIX.  I quote it mainly, 
then, to suggest that doing this portably might prove surprisingly hard.  It 
would be portable and, if David's plausible explanation is right, more 
intention-revealing, but more complicated and less efficient, to keep track of 
whether stdout has ever been written to, and only close it then.

-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of David Boyce
Sent: Wednesday, April 20, 2011 21:32
To: Philip Guenther
Cc: bug-make
Subject: Re: [bug #33134] spurious error when stdout is already closed

On Thu, Apr 21, 2011 at 12:00 AM, Philip Guenther <address@hidden> wrote:
> Why is that a mistake?
>
> It appears you're saying that make should complain about failures to
> write to stdout for reasons like EIO, ENOSPC,  and EOVERFLOW, but
> *not* for EBADF.

I think you're still not getting my point here. I do not believe this
has anything to do with *writes* at all, failed or otherwise. Make is
attempting to close something that's already closed and complaining
when it doesn't work. POSIX is quite clear that fclose on a closed
stream results in an error condition.

> (Actually, your patch doesn't just ignore EBADF errors: it ignores
> EPIPE errors, as the ftell() will fail on the pipe.  Why is that a
> good idea?)

You're right on this. An earlier version of my change, when it was
implemented within close_stdout(), looked something like

    if (ftell(stdout) == -1 && errno == EBADF) ...

but I lost the EBADF test when I redid it. That was a mistake, and
maybe there's a better way of checking for closure than ftell anyway,
but the basic point of not closing something unless it was open
remains.

David B

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