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.. index::
single: embedded triggers (tutorial)
.. _tutorial-embedded-triggers:
Using embedded triggers
=======================
This section provides a exercise showing the use of embedded triggers.
These are trigger expressions embedded within the task scrips using the :code:`--wait` command.
Whilst the expression is **not** true, the job will hold i.e. continue to wait.
Whenever possible, giving preference to triggers on the :term:`suite definition` is considered
a better approach, as this allows extra validation upon creation, whereas embedded triggers are
checked at run time.
Update Task Script
------------------
Consider the :term:`task` :code:`t2.ecf` script as follows:
.. code-block:: shell
:caption: $HOME/course/test/f1/t2.ecf
%include <head.h>
ecflow_client --wait="t1 == complete" # wait for expression to become true
%include <tail.h>
Update Suite Definition
-----------------------
Consider the following :term:`suite definition`, with no :term:`trigger` on task **t2**.
.. tabs::
.. tab:: Text
.. code-block:: shell
# Definition of the suite test.
suite test
edit ECF_INCLUDE "{{HOME}}/course" # replace '{{HOME}}' appropriately
edit ECF_HOME "{{HOME}}/course"
family f1
edit SLEEP 20
task t1
task t2
endfamily
endsuite
.. tab:: Python
.. literalinclude:: src/embedded-triggers.py
:language: python
:caption: $HOME/course/test.py
**What to do**
#. Modify the task script and the suite definition as shown above.
#. Replace the :term:`suite`, using:
.. tabs::
.. tab:: Text
.. code-block:: shell
ecflow_client --suspend /test
ecflow_client --replace /test test.def
.. tab:: Python
.. code-block:: shell
python3 test.py
python3 client.py
#. Observe the tasks in :term:`ecflow_ui`.
#. Notice the wait icon on task t2.
#. Introduce an error in the wait expression and requeue the suite. Observe how the job now aborts:
.. code-block:: shell
:caption: Introduce error in wait expression
ecflow_client --wait="t == complete" # Error: no node with name `t`
#. Introduce an impossible expression in the wait expression and requeue the suite. What is the effect?
.. code-block:: shell
:caption: expression that will never be satisfied
ecflow_client --wait="1 == 0"
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