On Tue, Nov 16, 2010 at 04:51:04PM +0100, Ivan Voras wrote: > On 11/16/10 16:19, Joerg Sonnenberger wrote: > >On Tue, Nov 16, 2010 at 03:37:59PM +0100, Ivan Voras wrote: > >>Are there any standard-defined guarantees for TCP network sockets > >>used by multiple threads to do IO on them? > > > >System calls are atomic relative to each other. They may be partially > >executed from the perspective of a remote system, e.g. due to > >segmentation, but one system call will finish before the next call of > >the same category is started. > > It seems to me that with a multithreaded kernel and multithreaded > userland that cannot really be guaranteed in general (and really > should not be guaranteed for performance reasons), but maybe it's > true for e.g. sockets if they are protected by a mutex or two within > the kernel?
Of course it can be guaranteed. There are a few tricky bits like writing to a file with O_APPEND, but for sockets it is essentially all about taking a mutex before changes the socket buffer. > >>Specifically, will multiple write() or send() calls on the same > >>socket execute serially (i.e. not interfere with each other) and > >>blocking (until completion) even for large buffer sizes? What about > >>read() / recv()? > > > >All write operations are serialised against each other, just like all > >read operations are serialised against. > > To what degree is such serialization standardized (by POSIX?)? It is written somewhere, I forget where and can't find it right now :) Joerg _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[email protected]"
