machma - Easy parallel execution of commands with live feedback

Introduction

In order to fully utilize modern machines, jobs need to be run in parallel. For example, resizing images sequentially takes a lot of time, whereas working on multiple images in parallel makes much better use of a multi-core CPU and therefore is much faster. This tool makes it very easy to execute tasks in parallel and provides live feedback. In case of errors or lines printed by the program, the messages are tagged with the job name.

machma by default reads newline-separated values and replaces all command-line arguments set to {} with the file name. The number of jobs is set to the number of cores for the CPU of the host machma is running on.

Sample Usage

Resize all images found in the current directory and sub-directories to 1200x1200 pixel at most:

$ find . -iname '*.jpg' | machma --  mogrify -resize 1200x1200 -filter Lanczos {}

The command specified after the double dash (--) is executed with each parameter that is set to {} replaced with the file name. At the bottom, a few status lines are printed after a summary line. The lines below visualize the status of the instances of the program running in parallel. The line for an instance will either contain the name of the file (in this case) that is being processed followed by the newest message printed by the program.

Ping a large number of hosts, but only run two jobs in parallel:

$ cat /tmp/ips | machma -p 2 -- ping -c 2 -q {}

The program ping will exit with an error code when the host is not reachable, and machma prints an error message for all jobs which returned an error code.

A slightly more sophisticated (concerning shell magic) example is the following, which does the same but recduces the output printed by ping a lot:

$ cat /tmp/ips | machma -- sh -c 'ping -c 2 -q $0 > /dev/null && echo alive' {}

Using --timeout you can limit the time mogrify is allowed to run per picture. (Prevent jobs from 'locking up') The value for timeout is formatted in golang time.Duration format. When the timeout is reached the program gets canceled.

$ find . -iname '*.jpg' | machma --timeout 5s --  mogrify -resize 1200x1200 -filter Lanczos {}

Files With Spaces

Sometimes filenames have spaces, which may be problematic with shell commands. Most of the time, this should not be a problem at all, since machma runs programs directly (using the execve syscall on Linux for example) instead of using system(). For all other cases there's the --null (short: -0) option which instructs machma to read items separated by null bytes from stdin. This can be used with the option -print0 of the find command like this:

$ find . -iname '*.jpg' -print0 | machma --null --  mogrify -resize 1200x1200 -filter Lanczos {}

Installation

Installation is very easy, install a recent version of Go and run:

$ go run build.go

Afterwards you can view the online help:

$ ./machma --help
Usage of ./machma:
      --no-id              hide the job id in the log
      --no-name            hide the job name in the log
      --no-timestamp       hide the time stamp in the log
  -0, --null               use null bytes as input separator
  -p, --procs int          number of parallel programs (default 2)
      --replace string     replace this string in the command to run (default "{}")
      --timeout duration   set maximum runtime per queued job (0s == no limit)