Paralllel

A: Have you ever tried GNU parallel? Did it work for you?
B: Ehm, yes.
A: That's great, how many hours did you spend? Can you add more threads during runtime? Did it show you how long it takes to finish?
B: ... You are weird.

Paralllel is a minimalistic and easy to use parallel job executor. It supports adding more threads and reducing threads during runtime. It even calculates an ETA. It's written in Rust (Yey!) and not in Perl (Buhh!)!

Usage

Usage: paralllel [OPTIONS] <COMMAND>

Arguments:
    <COMMAND>  Execute this command (in parallel), replaces {N} with the Nth value (index starts at 0)

Options:
    -i, --input-file <INPUT_FILE>        Name of the input file (if omitted, stdin is used)
    -t, --threads <THREADS>              Number of threads initially created [default: 1]
    -d, --delimiter <DELIMITER>          Delimiter for input values [default: "\t"]
    -s, --show-output-instead-of-status  Does not show the progress, prints stdout and stderr of the subprocesses
    -h, --help                           Print help information
    -V, --version                        Print version information

Minimal example

Launch three parameterized sleeps in parallel (with two threads):

$ printf '1\n2\n3' | paralllel -t 2 'sleep {0}'

It's that simple!

A more advanced example

For the following example we use this as the input file (corresponds to four jobs):

$ cat test-input.txt
1|/
2|/tmp
2|.
3|/

Per default, each value is separated by tabs but here we use -d to set a custom delimiter. To start with three threads and no status bar (stdout and stderr as output) run the following:

$ paralllel -i test-input.txt -d '|' -t 3 -s 'sleep {0} && ls {1}'

Again, It's that simple!

BTW, Ctrl+C'ing paralllel does not SIGINT the subprocesses, paralllel waits for the current jobs to finish and then exits. In other words: Ctrl+C means no new jobs.

To save the output of each job while still printing it, just use tee:

$ paralllel -i test-input.txt -d '|' -t 2 -s 'sleep {0} && ls {1} | tee /tmp/{0}_$(date +%s).txt'

Increase and decrease threads

Use SIGUSR1 to increase and SIGUSR2 to decrease the number of threads by one:

$ printf '2\n2\n2\n2\n2\n2\n2\n2\n2\n2\n' | paralllel 'sleep {0}'
$
$ # In another terminal:
$ kill -SIGUSR1 $(pgrep -f paralllel)  # to increase threads or
$ kill -SIGUSR2 $(pgrep -f paralllel)  # to to decrease threads

Currently running threads are not affected when decreasing the number of threads.

Clone, build and install

We use rustup. Clone, build and install:

git clone https://github.com/jbaumg93/paralllel
cd paralllel
cargo b --release
cp target/release/paralllel [SOME_$PATH_YOU_LIKE]

Known bugs

• Status bar can be incorrect near the end due to the final join().