Date: Tue, 22 Apr 1997 16:54:37 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: fenyo@email.enst.fr Cc: freebsd-hackers@FreeBSD.org, jb@cimlogic.com.au Subject: Re: fd locking problem with libc_r ? Message-ID: <199704222354.QAA27858@phaeton.artisoft.com> In-Reply-To: <199704222308.BAA20563@nikopol.enst.fr> from "Alex Fenyo" at Apr 23, 97 01:08:06 am
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> Suppose you have 2 threads and a file descriptor, for instance a socket. [ ... ] > I wonder why is there such a read-write lock when just a write > lock would be sufficient (and would solve the problem) ??? > Perhaps it's because a write lock wouldn't be sufficient ??? > (I can't find a reason for that ?) It's because only one blocking operation can be outstanding on an FD at a time in a user space threading implementation. Look at it as if it were an operation queueing interface, and there was a single queue for servicing both reads and writes (VMS and many UNIX multidrop board drivers have exactly thjis restriction on their non-threaded I/O!). Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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