Experimental Physics and
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Most of your reasoning regarding caRepeater is explained in the CA Spec/manual, but I figured I was missing a build-switch that would include caClient-stuff with the app. Later, -ps ----- Original Message ----- From: "Jeff Hill" <[email protected]> To: "'Paul Sichta'" <[email protected]>; <[email protected]> Sent: Thursday, February 03, 2005 12:58 PM Subject: RE: STATIC softIOC In past versions of EPICS, if the caRepeater executable could not be found, the repeater daemon process was created on POSIX by making a copy of the current process using the fork system call, but this has been a source of confusion and subtle problems (to put it mildly). With newer versions of EPICS this fall back behavior has been eliminated. It is certainly possible for the repeater daemon to be implemented as an independent thread inside of the IOC process. This is in fact what is done on RTEMS and vxWorks. However, on process based OS this causes issues if an external CA client becomes dependent on this IOC resident CA repeater and, at some later time, the IOC containing the repeater is stopped. Given a weak cause and effect pattern of behavior and the likelihood that configuration decisions made in the past will not be remembered when adding additional clients to the same host in the future then I am inclined to conclude that an IOC resident CA repeaters would be an error prone and confusing option on process based OS. I am open to suggestions, but my current perspective is that, on process based OS, the CA repeater must be an independent process started from an independent executable. The CA repeater's purpose is to receive CA server beacons and fan them out to all of the CA clients running in the same host. Most modern IP kernels now allow multiple listeners on the same UDP port, so that is no longer the reason for the CA Repeater. Unfortunately, there is still a defect in most IP kernels where UDP broadcasts reach multiple listeners on the same UDP port, but UDP unicasts (single host addressed datagrams) do not. Therefore, the CA repeater must still exist, and there can only be one of them on each host. Use of IP multicasts instead of IP broadcasts for CA beacons is something that could be considered for future versions. This might allow the CA repeater to be phased out. Jeff -----Original Message----- From: Paul Sichta [mailto:[email protected]] Sent: Thursday, February 03, 2005 9:49 AM To: [email protected] Subject: STATIC softIOC
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ANJ, 02 Sep 2010 |
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