So there is no temp file concept. I have to create unique names to use
+ in the same file.
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Process ID + timestamp + a counter.

my $counter = 0;
sub unique_stamp {
    return join '_', $$, time, $counter++;
}
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The PID makes it unique between processes. The time makes it unique in case of PID rollover. The counter makes it unique when the same process issues two stamps inside the granularity of the timer. It also makes the granularity of the time not so important.