use Fcntl; #contains codes to use for flock
...
open(STORE,">$storable_file") || die "Could not open $storable_file: $!\n";
flock STORE,LOCK_EX;
store_fd \%hash,\*STORE;
... # code code code
flock STORE,LOCK_UN;
close(STORE); # closing file also unlocks it, but I prefer explicit unlocking