For the kikuchiyo.pl script, the fix is initializing subdircount to maxforks - 1. That ensures safety, as each worker sets $i using the same range (starting at 0).

my $subdircount = $maxforks - 1;

[download]

Update: Added results for threads and MCE::Child.

Running with 512 workers:

########################################################
# threads, mod: init data after spawning threads
# https://www.perlmonks.org/?node_id=11149880
########################################################

$ rm -fr temp data.dat

$ time ../threads.pl ; ls -lh data.dat
Parsing 61441 files
maxthreads: 512
regex: 13.389084

real  0m13.443s
user  3m25.771s
sys   0m3.514s

-rw-r--r-- 1 mario mario 471M Jan 28 13:25 data.dat

########################################################
# kikuchiyo.pl, mod: my $subdircount = $maxforks - 1;
# https://www.perlmonks.org/?node_id=11149910
########################################################

$ rm -fr temp data.dat

$ time ../kikuchiyo.pl ; ls -lh data.dat
Parsing 61441 files
maxforks: 512
regex: 7.810577

real  0m9.393s
user  2m11.069s
sys   0m4.456s

-rw-r--r-- 1 mario mario 471M Jan 28 12:46 data.dat

########################################################
# MCE::Child, mod: init data after spawning processes
# https://www.perlmonks.org/?node_id=11149917
########################################################

$ rm -fr temp data.dat

$ time ../mcechild.pl ; ls -lh data.dat
Parsing 61441 files
maxforks: 512
regex: 7.858324

real  0m7.890s
user  2m11.238s
sys   0m4.026s

-rw-r--r-- 1 mario mario 471M Jan 28 13:31 data.dat

########################################################
# mceiter1.pl, MCE chunking
# https://www.perlmonks.org/?node_id=11149971
########################################################

$ rm -fr temp data.dat

$ time ../mceiter1.pl ; ls -lh data.dat
Parsing 61441 files
maxforks: 512
chunksize: 128
regex: 7.827401

real  0m7.885s
user  2m12.198s
sys   0m2.232s

-rw-r--r-- 1 mario mario 471M Jan 28 12:50 data.dat

########################################################
# mceiter2.pl, MCE chunking + workers appending data.dat
# https://www.perlmonks.org/?node_id=11149978
########################################################

$ rm -fr temp data.dat

$ time ../mceiter2.pl ; ls -lh data.dat
Parsing 61441 files
maxforks: 512
chunksize: 50
regex: 4.294076

real  0m4.328s
user  2m2.587s
sys   0m1.759s

-rw-r--r-- 1 mario mario 471M Jan 28 12:51 data.dat

[download]

For cpu-bound task, there's no reason to run many-many workers; beyond physical limitation.

$ time ../threads.pl 
Parsing 61441 files
maxthreads: 32
regex: 10.622881

real  0m10.649s
user  3m35.313s
sys   0m2.173s

$ time ../kikuchiyo.pl
Parsing 61441 files
maxforks: 32
regex: 7.71529

real  0m8.276s
user  2m7.270s
sys   0m2.150s

$ time ../mcechild.pl
Parsing 61441 files
maxforks: 32
regex: 7.859328

real  0m7.889s
user  2m4.981s
sys   0m2.286s

$ time ../mceiter1.pl
Parsing 61441 files
maxforks: 32
chunksize: 128
regex: 7.545659

real  0m7.581s
user  2m7.077s
sys   0m1.775s

$ time ../mceiter2.pl 
Parsing 61441 files
maxforks: 32
chunksize: 50
regex: 4.066287

real  0m4.100s
user  2m3.994s
sys   0m0.880s

[download]

In reply to Re^7: Script exponentially slower as number of files to process increases by marioroy
in thread Script exponentially slower as number of files to process increases by xnous

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