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README.md

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Cron scheduler

This project is an in-process cron scheduler designed to facilitate the periodic execution of jobs. The scheduler allows clients to define jobs with specific characteristics, enabling flexible and customized scheduling.

Table of Contents

Project File Structure

/main.rb: the main application file that has the interaction code that the client dealing with. let's see what is inside it:

Dependencies

  • require "./validate.rb": Imports custom validation methods for validating user inputs.
  • require "./scheduler.rb": Imports the scheduler class for scheduling jobs and managing them.
  • require "rufus-scheduler": Imports the Rufus-Scheduler gem for scheduling jobs.

Adding a Job (add_job function)

  • The add_job function allows users to add a new job by specifying the expected interval, scheduling frequency, a unique job identifier, and a job implementation.
  • It takes a job_list as a parameter, representing the list of job_identifiers to validate and ensure the uniqueness of job identifiers.
  • Users are prompted to enter the expected interval, schedule frequency, and job identifier, ensuring the inputs are valid.
  • The CronScheduler object is created, and a job is scheduled using the provided parameters.

User Interaction Loop

  • A loop enables continuous user interaction, presenting the user with options and allowing them to choose an action.
  • Options:
    • Option 1: Adding a job using the add_job function.
    • Option 2: Listing the jobs and displaying their execution logs.
    • Any other key: Closes the application and ends the loop.

/validate.rb: It contains custom validation methods for validating user inputs. let's see what is inside it:

validate_interval(interval)

  • This function validates the format of the expected interval entered by the user.
  • It checks if the interval is in the format of a positive integer followed by a valid unit (s, m, h, d for seconds, minutes, hours, and days, respectively).
  • If the format is valid, it returns true. Otherwise, it prints an error message and returns false.

validate_frequency(frequency)

  • Similar to validate_interval, this function validates the format of the scheduling frequency entered by the user.
  • It checks if the frequency is in the format of a positive integer followed by a valid unit (s, m, h, d for seconds, minutes, hours, and days, respectively).
  • If the format is valid, it returns true. If not, it prints an error message and returns false.

validate_uniqueness(job_id_list, job_identifier)

  • This function ensures that the provided job identifier is unique.
  • It checks if the job identifier already exists in the list of job IDs (job_id_list).
  • If the identifier is unique, it returns true. If not, it prints an error message and returns false.

/scheduler.rb: It contains The CronScheduler class encapsulates the scheduling functionality for the application. It utilizes the Rufus-Scheduler gem to manage job scheduling and execution. let's see what is inside it:

initialize

  • Initializes a new object of CronScheduler.
  • Sets up the Rufus scheduler and initializes an empty jobs hash to store job details.

start

  • Initiates the scheduler by creating a new thread that joins the scheduler, it's actually a wrapper because schedule.join blocks the current thread till the scheduled jobs are finished and we don't want that we actually need it to work concurrently so I creating a new thread and joining it.

schedule_job(identifier, frequency, expected, job)

  • Schedules a new job with the provided identifier, scheduling frequency, expected interval, and job implementation.

  • Adds the job details to the jobs hash and schedules the job using Rufus-Scheduler.

  • schedule_job_with_rufus(identifier, frequency)

    • Schedules the job using Rufus-Scheduler based on the given frequency.
    • Records job execution details like start time, end time, and execution time.

log_job_execution

  • Logs the last execution details of all scheduled jobs, including start time, end time, expected execution time, and actual execution time.

Example usage snippets

  • Insert the first job:

    Example Image

  • Insert the second job:

    Example Image

  • Instrument each job's details run after executing them

    Example Image

  • Instrument each job's details run after executing them for the second time

    Example Image

  • validation of expected interval and Scheduling frequency

    Example Image

  • validating the uniqueness of job identifiers

    Example Image

Installation

Build the Docker image using the docker build command.

docker build -t your_image_name .

Create a Docker container from the image you just built.

docker run -p  3000:3000 --name your_container_name -it your_image_name bash

write the command bundle install to ensure that all gems are installed.

bundle install

Run main.rb and enjoy ^-^.

ruby main.rb

Possible future improvements

  • We can add delete a job schedule option
  • we can make our script accept more Scheduling frequency format