Advanced Guide#

This is an advanced level tutorial.

App Configuration#

There are several configurations options for the application.

The configurations can be set by:

app = RedEngine(config={
    'task_execution': 'process',
    'task_pre_exist': 'raise',
    'force_status_from_logs': True,

    'silence_task_prerun': False,
    'silence_cond_check': False,

    'max_process_count': 5,
    'restarting': 'replace'

These are the default options.

  • task_execution: How tasks are run by default. Options:

    • process: on separate process

    • thread: on separate thread

    • main: no parallelization

  • task_pre_exist: What happens if a task with given name already exists. Options:

    • raise: An error is thrown

    • rename: the task is renamed (numbers added after the name)

    • ignore: The task is simply not inserted to the session

  • force_status_from_logs: Use logs always to determine the task statuses. If:

    • True: Logs are always read when checking the statuses. Robust but less performant.

    • False: If cached status found, it is used instead.

  • silence_task_prerun: Whether to silence errors occurred before running a task. If:

    • True: The scheduler does not crash on errors occurred on the startup of a task

    • False: The scheduler crashes. Useful for debug but not for production

  • silence_cond_check: Whether to silence errors occurred when checking conditions’ values. If:

    • True: The scheduler does not crash on errors occurred on checking conditions

    • False: The scheduler crashes. Useful for debug but not for production

  • max_process_count: Maximum number of processes allowed to be started

    • By default the number of CPUs

  • restarting: How the scheduler is restarted (if restart is called)

    • replace: Restart by replacing the current process

    • relaunch: Restart by starting a new process

    • fresh: Restart by starting a new process (on new window on Windows)

    • recall: Restart by calling the start method again. Useful for testing the restart

Task Types#

So far, we have only used FuncTask with passing a callable. There are other task types as well to cover most common use cases:

  • FuncTask: Executes a Python function

  • CommandTask: Executes a shell command

  • CodeTask: Executes raw code as string. Potentially dangerous.

Here are the ways to initialize tasks:

def do_things():

def run_things():

app.task('daily', func=run_things)

app.task('daily', func_name="main", path="path/to/")

app.task('daily', command='echo "Hello world"')

app.task('daily', code='print("Hello world")')

Modifying the System on Runtime#

The scheduler system can be modified in runtime. You could during the runtime:

  • shut down the scheduler

  • restart the scheduler

  • force a task to be run

  • disable a task

  • create, update or delete tasks

To do there, you can create a task that runs either as a separate thread or on the main loop. Tasks parallelized as separate processes cannot alter the scheduling environment due to limitations with sharing memory.

To alter the session:

from redengine.args import Session

@app.task('every 20 hours', execution="thread")
def do_shutdown(session=Session()):

@app.task('every 20 hours', execution="thread")
def do_restart(session=Session()):

@app.task('every 10 minutes', execution="thread")
def do_modify_tasks(session=Session()):

    task = session['do_restart']
    task.force_run = True

    for task in session.tasks:
        task.disable = True