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RE: libstdc++/9533: Regression: Can't read from tty with ifstream
- From: Pétur Runólfsson <peturr02 at ru dot is>
- To: <paolo at gcc dot gnu dot org>,<gcc-bugs at gcc dot gnu dot org>,<nobody at gcc dot gnu dot org>,<gcc-gnats at gcc dot gnu dot org>
- Cc: <libstdc++ at gcc dot gnu dot org>
- Date: Mon, 3 Mar 2003 13:09:06 -0000
- Subject: RE: libstdc++/9533: Regression: Can't read from tty with ifstream
> Patching: indeed, reverting this hunk of 6746 commit:
> + // Set input to nonblocking for fifos.
> + if (__mode & ios_base::in)
> + fcntl(this->fd(), F_SETFL, O_NONBLOCK);
> Fixes the problem without regressing on 6746.
Interesting. I would have thought that removing this would
cause the call to underflow() in basic_filebuf::open() to
block, causing the test case to wait for input *before*
printing out the prompt (this seems to be the reason that
non-blocking input is specified).
So far, this is what I think is going on:
* non-blocking input is specified so underflow() doesn't
block (which is wrong, underflow() should block).
* underflow() must not block because it is called from
open() which must not block.
* open() calls underflow() so that in_avail() will return
non-zero after open() (libstdc++/6746).
However, I don't see how calling underflow() from open()
fixes libstdc++/6746. Unless I am missing something,
readsome will return up to BUFSIZ characters, and then
return 0 until the end of time.