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[Scheduler] Document hashed Cron expression #19441

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Jan 22, 2024
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[Scheduler] Document hashed Cron expression #19441

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82 changes: 67 additions & 15 deletions scheduler.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,7 @@ the task of creating a report::

class SendDailySalesReports
{
public function __construct(private string $id) {}
public function __construct(private int $id) {}

public function getId(): int
{
Expand All @@ -61,6 +61,9 @@ Next, create the handler that processes that kind of message::
// src/Scheduler/Handler/SendDailySalesReportsHandler.php
namespace App\Scheduler\Handler;

use App\Scheduler\Message\SendDailySalesReports;
use Symfony\Component\Messenger\Attribute\AsMessageHandler;

#[AsMessageHandler]
class SendDailySalesReportsHandler
{
Expand Down Expand Up @@ -105,9 +108,13 @@ The :class:`Symfony\\Component\\Scheduler\\Attribute\\AsSchedule` attribute,
which by default references the schedule named ``default``, allows you to register
on a particular schedule::

// src/Scheduler/MyScheduleProvider.php
// src/Scheduler/SaleTaskProvider.php
namespace App\Scheduler;

use Symfony\Component\Scheduler\Attribute\AsSchedule;
use Symfony\Component\Scheduler\Schedule;
use Symfony\Component\Scheduler\ScheduleProviderInterface;

#[AsSchedule]
class SaleTaskProvider implements ScheduleProviderInterface
{
Expand Down Expand Up @@ -168,22 +175,67 @@ Then, define the trigger date/time using the same syntax as the

RecurringMessage::cron('* * * * *', new Message());

.. tip::

Check out the `crontab.guru website`_ if you need help to construct/understand
cron expressions.

You can also use some special values that represent common cron expressions:

* ``#yearly``, ``#annually`` - Run once a year, midnight, Jan. 1 - ``0 0 1 1 *``
* ``#monthly`` - Run once a month, midnight, first of month - ``0 0 1 * *``
* ``#weekly`` - Run once a week, midnight on Sun - ``0 0 * * 0``
* ``#daily``, ``#midnight`` - Run once a day, midnight - ``0 0 * * *``
* ``#hourly`` - Run once an hour, first minute - ``0 * * * *``
* ``@yearly``, ``@annually`` - Run once a year, midnight, Jan. 1 - ``0 0 1 1 *``
* ``@monthly`` - Run once a month, midnight, first of month - ``0 0 1 * *``
* ``@weekly`` - Run once a week, midnight on Sun - ``0 0 * * 0``
* ``@daily``, ``@midnight`` - Run once a day, midnight - ``0 0 * * *``
* ``@hourly`` - Run once an hour, first minute - ``0 * * * *``

For example::

RecurringMessage::cron('#daily', new Message());
RecurringMessage::cron('@daily', new Message());

Hashed Cron Expression
~~~~~~~~~~~~~~~~~~~~~~
Comment on lines +195 to +196
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I want to make a sub section, which char should I use ?

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@javiereguiluz javiereguiluz Jan 22, 2024 •
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We use the ........... separator for those sections. I did this while merging your PR.


If you have many trigger scheduled at same time (for example, at midnight, ``0 0 * * *``)
this will create a very long running schedules list right at this time.
This may cause an issue if a task has a memory leak.
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I don't like this sentence. Maybe we should talk about real use case.
If I remember fabpot talk about email campaign

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what about writing bottle neck like lot of I/O, memory spike, etc etc?


You can add a ``#``(for hash) symbol in expression to generate random value. The value
is deterministic based on the message. This means that while the value is random, it is
predictable and consistent. A message with string representation ``my task``
and a defined frequency of ``# # * * *`` will have an idempotent frequency
of ``56 20 * * *`` (every day at 8:56pm).

A hash range ``#(x-y)`` can also be used. For example, ``# #(0-7) * * *`` means daily,
some time between midnight and 7am. Using the ``#`` without a range creates a range
of any valid value for the field. ``# # # # #`` is short for ``#(0-59) #(0-23) #(1-28)
#(1-12) #(0-6)``.

You can also use some special values that represent common hashed cron expressions:

====================== ========================================================================
Alias Converts to
====================== ========================================================================
``#hourly`` ``# * * * *`` (at some minute every hour)
``#daily`` ``# # * * *`` (at some time every day)
``#weekly`` ``# # * * #`` (at some time every week)
``#weekly@midnight`` ``# #(0-2) * * #`` (at ``#midnight`` one day every week)
``#monthly`` ``# # # * *`` (at some time on some day, once per month)
``#monthly@midnight`` ``# #(0-2) # * *`` (at ``#midnight`` on some day, once per month)
``#annually`` ``# # # # *`` (at some time on some day, once per year)
``#annually@midnight`` ``# #(0-2) # # *`` (at ``#midnight`` on some day, once per year)
``#yearly`` ``# # # # *`` alias for ``#annually``
``#yearly@midnight`` ``# #(0-2) # # *`` alias for ``#annually@midnight``
``#midnight`` ``# #(0-2) * * *`` (at some time between midnight and 2:59am, every day)
====================== ========================================================================

.. tip::
For example::

Check out the `crontab.guru website`_ if you need help to construct/understand
cron expressions.
RecurringMessage::cron('#midnight', new Message());

.. note::

The day of month range is ``1-28``, this is to account for February
which has a minimum of 28 days.

.. versionadded:: 6.4

Expand Down Expand Up @@ -260,7 +312,7 @@ Then, define your recurring message::

Finally, the recurring messages has to be attached to a schedule::

// src/Scheduler/MyScheduleProvider.php
// src/Scheduler/SaleTaskProvider.php
namespace App\Scheduler;

#[AsSchedule('uptoyou')]
Expand Down Expand Up @@ -344,7 +396,7 @@ via the ``stateful`` option (and the :doc:`Cache component </components/cache>`)
This way, when it wakes up again, it looks at all the dates and can catch up on
what it missed::

// src/Scheduler/MyScheduleProvider.php
// src/Scheduler/SaleTaskProvider.php
namespace App\Scheduler;

#[AsSchedule('uptoyou')]
Expand All @@ -366,7 +418,7 @@ To scale your schedules more effectively, you can use multiple workers. In such
cases, a good practice is to add a :doc:`lock </components/lock>` to prevent the
same task more than once::

// src/Scheduler/MyScheduleProvider.php
// src/Scheduler/SaleTaskProvider.php
namespace App\Scheduler;

#[AsSchedule('uptoyou')]
Expand Down Expand Up @@ -395,7 +447,7 @@ your message in a :class:`Symfony\\Component\\Messenger\\Message\\RedispatchMess
This allows you to specify a transport on which your message will be redispatched
before being further redispatched to its corresponding handler::

// src/Scheduler/MyScheduleProvider.php
// src/Scheduler/SaleTaskProvider.php
namespace App\Scheduler;

#[AsSchedule('uptoyou')]
Expand Down