=head1 YouTube video

GNU Parallel is a tool with lots of uses in shell. Every time you use
xargs or a for-loop GNU Parallel can probably do that faster, safer
and more readable.

If you have access to more computers through ssh, GNU Parallel makes
it easy to distribute jobs to these.

terminal2: ssh parallel@vh2.pi.dk
ssh parallel@vh2.pi.dk


PS1="\e[7mGNU Parallel:\[\033[01;34m\]\w\[\033[00m\]\e[27m$ "
gunzip logs/*gz
rm logs/*bz2
rm -rf zip/*[^p]

# GET GNU PARALLEL
wget ftp://ftp.gnu.org/gnu/parallel/parallel-20100601.tar.bz2
tar xvjf parallel-20100601.tar.bz2
cd parallel-20100601
./configure && make   ##
su
make install
exit
cd

# YOUR FIRST PARALLEL JOBS
cd logs
du
/usr/bin/time gzip *
/usr/bin/time gunzip *
ls | time parallel gzip
ls | time parallel gunzip

# RECOMPRESS gz TO bz2
ls | time parallel gzip
ls *.gz | time parallel 'zcat {} | bzip2 > {.}.bz2'
## vis top local
# RECOMPRESS gz TO bz2 USING local(:) AND REMOTE server1
ls *.gz | time parallel -S server1,: --trc {.}.bz2 \
'zcat {} | bzip2 > {.}.bz2'
## vis top local
## vis top remote

# MAKING SMALL SCRIPTS
cd ../zip
ls -l
ls *.zip | parallel 'mkdir {.} && cd {.} && unzip ../{}' ###
ls -l

# GROUP OUTPUT
traceroute debian.org
traceroute debian.org & traceroute freenetproject.org  ###
(echo debian.org; echo freenetproject.org) \
| parallel traceroute

# KEEP ORDER
(echo debian.org; echo freenetproject.org) \
| parallel -k traceroute

# RUN MANY JOBS. USE OUTPUT
# Find the number of hosts responding to ping
seq 1 255 | parallel -j255 ping -c 1 178.63.11.{} 2>&1 \
| grep '64 bytes' | wc -l
seq 1 255 | parallel -j0 ping -c 1 178.63.11.{} 2>&1 \
| grep '64 bytes' | wc -l

# MULTIPLE ARGUMENTS
# make dir: (1-20000).dir
cd ../dirs
rm -rf *; sync
seq 1 20000 | time parallel mkdir {}.dir
rm -rf *; sync
seq 1 20000 | time parallel -X mkdir {}.dir

# CALLING GNU PARALLEL FROM GNU PARALLEL
# make dir: top-(1-100)/sub-(1-300)
rm -rf *; sync
seq 1 100 | time parallel -I /// \
'mkdir top-///;cd top-///; seq 1 300 | parallel -X mkdir sub-{}'
find | wc -l

# Thanks for watching
# Find GNU Parallel at http://www.gnu.org/software/parallel/

# GIVE ME THE FIRST RESULT
(echo foss.org.my; echo debian.org; echo freenetproject.org) | parallel -H2 traceroute {}";false"

find . -type f | parallel -k -j150% -n 1000 -m grep -H -n STRING {}

(echo foss.org.my; echo debian.org; echo freenetproject.org) | parallel traceroute


=head1 IDEAS

Kan vi lave flere ssh'er, hvis vi venter lidt?
En ssh med 20% loss og 900 ms delay, så kan login nås på 15 sek.

Test if -0 works on filenames ending in '\n'

monitor to see which jobs are currently running
http://code.google.com/p/ppss/

If there are nomore jobs (STDIN is closed) then make sure to
distribute the arguments evenly if running -X.

=head1 options

One char options not used: F G J K P Q Y

Skilletegn i sshlogin:
#=item B<--sshlogin> I<[ncpu/]sshlogin[,[ncpu/]sshlogin[,...]]> (beta testing)
# Skilletegn:
# No: "#!&()?\<>|;*'~ shellspecial
# No: @.- part of user@i.p.n.r i.p.n.r host-name
# No: , separates different sshlogins
# No: space Will make it hard to do: 8/server1,server2
# Maybe: / 8//usr/bin/myssh,//usr/bin/ssh
# %/=:_^



=head2 mutex

mutex -b -n -l lockid -m max_locks [command]
mutex -u lockid

-b run command in background 
-l lockfile will lock using the lockid
-n nonblocking
-m maximal number of locks (default 1)
-u unlock

If command given works like: mutex -l lockfile -n number_of_locks ; command; mutex -u lockfile
If -b given works like: mutex -l lockfile -n number_of_locks ; (command; mutex -u lockfile)&

Kan vi finde på lockid som giver mening?

Parallelize so this can be done:
mdm.screen find dir -execdir mdm-run cmd {} \;
Maybe:
find dir -execdir par$ --communication-file /tmp/comfile cmd {} \;

find dir -execdir mutex -j4 -b cmd {} \;

=head2 Comfile

This will put a lock on /tmp/comfile. The number of locks is the number of running commands.
If the number is smaller than -j then it will start a process in the background ( cmd & ),
otherwise wait.

par$ --wait /tmp/comfile will wait until no more locks on the file



=head1 Unlikely

Accept signal INT instead of TERM to complete current running jobs but
do not start new jobs. Print out the number of jobs waiting to
complete on STDERR. Accept sig INT again to kill now. This seems to be
hard, as all foreground processes get the INT from the shell.