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A simple, non-polling cron-like facility written in Erlang [BSD license]
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crone

This is the reference distribution for crone, a simple cron-like facility written in Erlang. Unlike most crons, it does not periodically wake up and run whatever tasks are due to run; instead, it calculates the amount of time between now and when the next task is due to run, and sleeps exactly that long.

crone differs from cron in the following ways:

  • crone does not support multiple users. Of course, individual users may run their own copies of crone as desired.
  • No configuration files are used. crone is simply started with a list of task descriptions. These could easily be stored in a file to be read with file:consult/1 if desired.
  • crone launches, not system executables, but Erlang functions. Of course, system programs can be launched with the Erlang function os:cmd/1.
  • The synax of a task description is quite different from crontab. It is (in this author's opinion) easier to read and is much more in keeping with the Erlang tradition. It is not quite as expressive as cron but this can be compensated for by adding multiple tasks.
  • No output is logged or mailed to anyone. If you want output to be logged or mailed, you must explicitly specify that as part of the task.
  • crone does not poll the system on a minute-by-minute basis like cron does. Each task is assigned to a single (Erlang) process. The time until it is to run next is calculated, and the process sleeps for exactly that long.
  • Unlike cron's one-minute resolution, crone has a 2-second resolution (actually 1 second, but after running the task, the process waits an extra second to avoid accidentally running it more than once.)
  • Because it does not wake up every minute, and because it does not have a fixed configuration file, crone must be stopped and restarted if the user wishes to change the scheduled tasks.
  • crone does not handle Daylight Savings Time (or other cases when the system clock is altered) gracefully, and it is recommended that it be stopped and restarted on such occasions.

Usage

To build the crone module, run the script make.sh. Then import the crone module in some Erlang code and use it as you see fit.

Documentation for the crone module's API can be found in the source, crone.erl. Stand-alone HTML documentation can also be extracted from the source with edoc.

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