Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site opus.UUCP Path: utzoo!watmath!clyde!floyd!harpo!seismo!hao!cires!nbires!opus!mccallum From: mccallum@opus.UUCP Newsgroups: net.unix-wizards Subject: Re: UNIX IPC Datagram Reliability under 4.2BSD Message-ID: <176@opus.UUCP> Date: Wed, 1-Feb-84 10:36:01 EST Article-I.D.: opus.176 Posted: Wed Feb 1 10:36:01 1984 Date-Received: Tue, 7-Feb-84 12:59:07 EST References: <2392@fortune.UUCP> <4930@umcp-cs.UUCP> Organization: NBI, Boulder Lines: 20 AF_UNIX datagrams under 4.2 are definitely NOT reliable. They are effectively reliable if the reading process receives the datagrams in a reasonable time, but if the reader is slow and the sender keeps sending then datagrams are dropped. This can be demonstrated by setting up a receiving process that receives a message then sleeps a second and having a sending process that keeps sending. If part of the data is a sequence number, the receiver will see that some messages have been dropped. The sender does not see an error and never blocks on the send. Most applications that would use datagrams don't need strict reliability and should be using an application dependent protocol to guarantee reliablity. There are other problems with the 4.2 AF_UNIX datagrams. Has anyone tried to connect a datagram socket and then use it? Doug McCallum NBI, Inc. {allegra,ucbvax,hao}!nbires!mccallum