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Subject: RE: Channel Access PV Gateway Server Problems (more investigation)
From: "Jeff Hill" <[email protected]>
To: "'Ralph Lange'" <[email protected]>, "'Ernest L. Williams Jr.'" <[email protected]>
Cc: <[email protected]>, "'Carl Lionberger'" <[email protected]>, "'David H. Thompson'" <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, <[email protected]>, "'Greg Lawson'" <[email protected]>, <[email protected]>, <[email protected]>, "'Core-Talk Archive'" <[email protected]>
Date: Mon, 27 Jan 2003 09:32:46 -0700
There are known problems with the R3.14 gateway and the "gateway.killer"
script. The problem appears to be with proper delivery and dispatch of
the kill signal in a multi-threaded POSIX process. There will probably
need to be new code that calls ca_task_exit(), but not of course from
within the signal handler.

> If a second Gateway starts and detects the port is taken, it
> prints an error message and exits. There is no code in CA 
> that would allow it to take a higher port.

It is possible for two processes to listen to the same UDP port, but
there are serious limitations with unicasts. With most IP kernels only
one of the servers will see unicasts addressed to the shared port.
Broadcasts and multicasts work fine. 

Needless to say, it is not possible for two processes to share the same
TCP port. 

If there are two CA servers using the same port on the same host, then
the first one to start up gets the specified TCP and UDP ports. The
second CA server listens to the specified UDP port, but it must
compromise with an ephemeral TCP port assignment. If the 2nd server
receives a UDP search message matching one of its PVs then it replies
with its ephemeral TCP port, and the client connects to that port.

There are some notes on this topic in the latest R3.14 CA reference
manual.

Jeff


Replies:
RE: Channel Access PV Gateway Server Problems (more investigation) Kenneth Evans, Jr.
References:
Re: Channel Access PV Gateway Server Problems (more investigation) Ralph Lange

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