No disagreement here, but I would point out that accumulating stuff in
memory like that is a bad idea. Once the display program starts to swap
(which it will at some point) its performance will deteriorate
drastically: maybe that's what he's seeing. In any case, before it
chokes itself it will have impacted everything else running on the computer.

The approach I suggested is ugly in many ways, but would have caused
minimal disruption to the OP's programs. Of course, what should have
been done was to use a background logging program to capture the data in
a log file. The display program would be rewritten to search, filter and
display the log.

Of course, if he IS using a *NIX its simple: use the system logger to
write his log file and less or tail to view it. The only actual
programming needed is to retrofit a syslogger interface to the source
program(s).