Date: Fri, 11 Dec 1998 07:25:50 -0500 (EST) From: Daniel Eischen <eischen@vigrid.com> To: bde@zeta.org.au, cejkar@dcse.fee.vutbr.cz, freebsd-current@FreeBSD.ORG Subject: Re: mkfifo()/select() & O_RDONLY serious bug? Message-ID: <199812111225.HAA29472@pcnet1.pcnet.com>
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> >I have prepared small testing program (listed at the end) with mkfifo() > >and select() calls. Fifo is opened as O_RDONLY or O_RDWR with O_NONBLOCK. > >On FreeBSD 3.0-CURRENT, its behavior is different from other systems. > >I think it is serious bug: select() returns that there is ready file > >descriptor but descriptor is not ready in fact. I'm right? > > I think it's a feature :-). The descriptor is ready for reading. > read() will succeed and return 0 (EOF) because the mode is O_NONBLOCK and > there are no writers. This is as specified by POSIX.1. POSIX.1 doesn't > specify select(), and the FreeBSD implementation is simply that select() > returns success if read() would succeed immediately. I just caught this thread, so I may have missed something... This seems wrong. How do you wait for data availability from a file [descriptor] in non-blocking mode? You continuously spin in a select/read loop? If the file is opened in non-blocking mode, then a select (with timeout) is not needed to avoid blocking indefinitely because read() can do that. So if someone uses select with a non-blocking file descriptor, then you've got to assume that they want to know when data is ready and waiting; they don't want select to tell them that there isn't any data. Dan Eischen eischen@vigrid.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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