Date: Tue, 20 Oct 1998 10:30:01 -0700 (PDT) From: Bruce Evans <bde@zeta.org.au> To: freebsd-bugs@FreeBSD.ORG Subject: Re: kern/8324: failure to deliver SIGIO when fildes marked for async i/o Message-ID: <199810201730.KAA29972@freefall.freebsd.org>
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The following reply was made to PR kern/8324; it has been noted by GNATS. From: Bruce Evans <bde@zeta.org.au> To: archie@whistle.com Cc: Subject: Re: kern/8324: failure to deliver SIGIO when fildes marked for async i/o Date: Thu, 15 Oct 1998 17:52:43 +1000 >>Description: > > Run the program below. It will periodically hang until > you press return (which causes a readability condition). > It should (as far as I can tell) generate continuous > output without pausing at all. The program seems to only make sense for ttys (fcntl returns a value which is always ignored...) and seems to only hang for ptys. It hangs because wakeups for output-wouldn't block are only sent to processes in the kernel - for output there are only select-style wakeups, not SIGIO wakeups. The select-style wakeups are poorly implemented too - processes gets woken up whenever the space in the output buffer increases, and then usually go back to sleep until the space reaches a watermark. While debugging this, I was reminded of other problems: the O_NONBLOCK and O_ASYNC flags are sticky, and syscons is not reentrant - a breakpoint in ttwakeup() soon caused a panic. Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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