Date: Sun, 15 Jan 2006 03:09:04 +0800 From: prime <guomingyan@gmail.com> To: Tiffany Snyder <tiffany.snyder@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: How priority propagation works on read/write lock? Message-ID: <1fa17f810601141109u3e3a0586ud3b3cc86ebc6e80@mail.gmail.com> In-Reply-To: <b63e753b0601141040v1430da8ag28878e2a31aef486@mail.gmail.com> References: <1fa17f810601122232l25551bc5n4e4a01ff6b7921e@mail.gmail.com> <ac7deb50601130146y4abd573dn2ac47622374c1551@mail.gmail.com> <1fa17f810601130220h521590banff7d775a8bd4eaa6@mail.gmail.com> <b63e753b0601141040v1430da8ag28878e2a31aef486@mail.gmail.com>
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On 1/15/06, Tiffany Snyder <tiffany.snyder@gmail.com> wrote: > > Does FreeBSD support rwlocks? > > On 1/13/06, prime <guomingyan@gmail.com> wrote: > > > On 1/13/06, Kamal R. Prasad <kamalp@acm.org> wrote: > > > > > > Priority need not be propagated to readers as they will not block > > other > > > readers. > > > Most likely, you only need to propagate to the writer to avoid > > priority > > > inversron. > > > > > > regards > > > -kamal > > > > > > > > > On 1/13/06, prime < guomingyan@gmail.com> wrote: > > > > > > > Hi hackers, > > > > I have a question about how priority propagation works on > > > > read/write lock.On locks that have only one owner at a determinate > > > > moment,we can simply propagate the priority to the owner of lock,bu= t > > > > read/write lock may have many owners at some time,so how can we kno= w > > > > who are the owners? > > > > I browse the OpenSolaris' read/write lock implementation,and find > > > > that, it simply treats the owner of the lock as NULL when readers > > own > > > > the read/write lock.In this way,we can not propagate our priority t= o > > > > all threads that block us. > > > > > > > > Thanks very much. > > > > -- > > > > Three passions, simple but overwhelmingly strong, have governed my > > life: > > > > > > > > the longing for love, the search for knowledge, and unbearable pity > > for > > > > the suffering of mankind. > > > > ---------Bertrand Russell > > > > _______________________________________________ > > > > freebsd-hackers@freebsd.org mailing list > > > > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > > > > To unsubscribe, send any mail to " > > freebsd-hackers-unsubscribe@freebsd.org > > > > " > > > > > > > > > > > > Thanks your reply. > > But readers may block writers, aren't they? > > For example, there are three threads,A,B and C, and a read/write lock > > rwlock1 ,and a mutex mtx1. > > 1.A lock mtx1, > > 2.B get the read lock of rwlock1 and then want > > to get mtx1,but mtx1 is locked by A,so B has to > > wait on mtx1. > > 3.C want to get the write lock of rwlock1 and it > > has to wait,because rwlock1 is read locked by B. > > Now if C's priority < A's priority(in numerical), then we get priority > > inversion. > > > > How can avoid this priority inversion? > > Thanks. > > > > -- > > Three passions, simple but overwhelmingly strong, have governed my life= : > > the longing for love, the search for knowledge, and unbearable pity for > > the suffering of mankind. > > ---------Bertrand Russell > > _______________________________________________ > > freebsd-hackers@freebsd.org mailing list > > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > > To unsubscribe, send any mail to " > > freebsd-hackers-unsubscribe@freebsd.org" > > > > FreeBSD supports sx now,see sx(9).sx has the same semanteme as rwlock. -- Three passions, simple but overwhelmingly strong, have governed my life: the longing for love, the search for knowledge, and unbearable pity for the suffering of mankind. ---------Bertrand Russell
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