TYPO3 v15 dev-main snapshot ()

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+..  include:: /Includes.rst.txt
+..  _introduction:
+
+============
+Introduction
+============
+
+The Scheduler is a system extension that provides a simple interface to automate
+the running of tasks in TYPO3. It provides an easier alternative to having to set
+up command-line scripts in cron jobs.
+
+..  _task-management:
+
+Task management
+===============
+
+A task is created by extending the Scheduler base class and then registering it so
+that it appears in the Scheduler backend module.
+
+..  _screenshots:
+
+Screenshots
+===========
+
+Below is the Scheduler backend module, showing a task that has been registered.
+The module shows details about the tasks, i.e. status, type and whether it failed during the
+last execution, and individual tasks can be rerun manually by clicking on the
+'play' button.
+
+..  figure:: ../Images/BackendModuleMainView.png
+    :alt: Scheduler main screen
+
+    Main screen of the Scheduler BE module
+
+..  _tasks-execution:
+
+Task execution
+==============
+
+The Scheduler includes a command-line script that needs to be registered once
+in the server's crontab to set it up. It is run by the TYPO3 command-line
+dispatcher. Every time the Scheduler is launched by the cron daemon it looks for
+tasks that are due (or overdue) and executes them.
+
+When a task is executed it is marked as being
+executed in the Scheduler database record (in the
+`serialized_executions` field). When the task has finished running, the
+execution status is removed from the database record. This makes it
+clear whether a task is currently running and also
+prevents multiple executions. If a task requires
+more time to run than the frequency it is set up for, a
+new run will start (which is not always desirable). It is possible
+to prevent such parallel (or multiple) executions.
+
+..  _follow-up:
+
+Follow-up
+=========
+
+Log messages are written out to the TYPO3 system :guilabel:`Administration > Log`
+when a task starts and ends and when parallel execution has been blocked. This
+provides a trace of events of the tasks.
+
+A task that fails may also raise an exception reporting the reasons for failure.
+The exception message will be logged in the Scheduler database table and
+displayed in the backend module.
+
+Tasks have no command-line output as they are designed to run in the background.
+
+Symfony Console commands can also be run as tasks (see
+`https://docs.typo3.org/permalink/t3coreapi:symfony-console-commands`__).
+These tasks can specify all commandline arguments that are available to Symfony
+Console commands.
+
+..  _glossary:
+
+Glossary
+========
+
+Task
+    Specifically, a piece of code that does a precise task and can be registered
+    with the Scheduler in order to execute that piece of code at a precise time,
+    either once or recurrently.
+
+Task class
+    A type of task, for example, the "IP Anonymization" task is one
+    particular task class. Its function is to anonymize IP addresses to enforce
+    the privacy of persisted data. The "Optimize MySQL database tables"
+    task executes "OPTIMIZE TABLE" statements on selected database tables.
+
+Registered task
+    An instance of a task class that has been
+    registered with the Scheduler. A given task class may be registered
+    several times, for example if it needs to be executed with different
+    parameters.
+
+..  _credits:
+
+Credits
+=======
+
+The Scheduler is a derivation of the Gabriel extension originally developed by
+Christian Jul Jensen and further developed by Markus Friedrich.