$ tree
.
|-- 503170.pl
|-- A
|-- B
`-- C
$ perl -l 503170.pl
All done
$ tree
.
|-- 503170.pl
|-- A
|   `-- analysis_completed
|-- B
`-- C


##</code><code>##

my @dirs = qw[ ... ];
my @rFiles = map{ "$_/analysis_completed" } @dirs;

while (@rFiles and sleep 15) {
    -e $rFiles[$_] and splice @rFiles, $_, 1 for reverse 0..$#rFiles;
}
print "All done";