Date: Fri, 5 Nov 2010 15:06:12 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-arch@freebsd.org Cc: Matthew Fleming <mdf356@gmail.com>, Weongyo Jeong <weongyo.jeong@gmail.com>, freebsd-current@freebsd.org, freebsd-usb@freebsd.org Subject: Re: [RFC] Outline of USB process integration in the kernel taskqueue system Message-ID: <201011051506.12643.jhb@freebsd.org> In-Reply-To: <201011052000.37188.hselasky@c2i.net> References: <201011012054.59551.hselasky@c2i.net> <AANLkTimOTwtRQ_cF8WBYE6X7q0hfP37Gv7TKOXLY5k2U@mail.gmail.com> <201011052000.37188.hselasky@c2i.net>
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On Friday, November 05, 2010 3:00:37 pm Hans Petter Selasky wrote: > On Friday 05 November 2010 19:48:05 Matthew Fleming wrote: > > On Fri, Nov 5, 2010 at 11:45 AM, Hans Petter Selasky <hselasky@c2i.net> > wrote: > > > On Friday 05 November 2010 19:39:45 Matthew Fleming wrote: > > >> True, but no taskqueue(9) code can handle that. Only the caller can > > >> prevent a task from becoming enqueued again. The same issue exists > > >> with taskqueue_drain(). > > > > > > I find that strange, because that means if I queue a task again while it > > > is running, then I doesn't get run? Are you really sure? > > > > If a task is currently running when enqueued, the task struct will be > > re-enqueued to the taskqueue. When that task comes up as the head of > > the queue, it will be run again. > > Right, and the taskqueue_cancel has to cancel in that state to, but it doesn't > because it only checks pending if !running() :-) ?? You can't close that race in taskqueue_cancel(). You have to manage that race yourself in your task handler. For the callout(9) API we are only able to close that race if you use callout_init_mtx() so that the code managing the callout wheel can make use of your lock to resolve the races. If you use callout_init() you have to explicitly manage these races in your callout handler. -- John Baldwin
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