In the previous exercise we saw that the two tasks were running simultaneously.
We would like now to make sure that t2 only runs once t1 is complete.
For this we have to define a trigger
Triggers are used to declare dependencies
between two tasks.
For instance, the second task might need data created by the first task.
When ecFlow tries to start a task, it evaluates the trigger
If the condition is correct, the task is started, otherwise the task stays queued
Triggers can be between tasks, or between families, or a mixture.
Remember the two rules:
- A family is complete when all its tasks are complete
- A task will be started if its triggers and the triggers of all its parent families evaluate to true
can only have one trigger expression, but very complex expressions can be built (and keep in mind that the triggers of the parent nodes are also implicit triggers).
Sometimes triggers are also used to prevent too many jobs from running at the same time. In this case the use of a limit
may be a better solution (we will cover limits later on, in the Limits
Nodes can be addressed in trigger expressions using full names: /test/f1/t1
refers to the task t1
, and /test/f1
refers to the family f1
In some contexts, ecFlow will accept relative names, such as ../t1.
trigger /test/f1/t1 == complete
Triggers can be very complex, and ecFlow supports all kinds of conditions
(not, and, or, ...), in addition they can also reference Node attributes like
# Definition of the suite test.
edit ECF_INCLUDE "$HOME/course" # replace '$HOME' with the path to your home directory
edit ECF_HOME "$HOME/course"
edit SLEEP 20
trigger t1 eq complete
The trigger expression can be checked, this is especially important when dealing with very large suites and complex triggers.
from ecflow import Defs,Suite,Family,Task,Edit,Trigger
Task("t2",Trigger("t1 == complete")))
print("Creating suite definition")
home = os.path.join(os.getenv("HOME"), "course")
defs = Defs(
print("check trigger expressions")
check = defs.check()
assert len(check) == 0, check
print("Checking job creation: .ecf -> .job0")
print("Saving definition to file 'test.def'")
What to do
- Edit the suite definition file to add the trigger.
- Replace the suite
python: python test.py ; python client.py
text: ecflow_client --suspend=/test ; ecflow_client --replace=/test test.def
- Observe the tasks in ecflow_ui .
- See the triggers by selecting t1 or t2.
- See the trigger relation by clicking on the trigger tab.
- Search any reference to t1 by using the search menu.
Introduce an error in the trigger expression and ensure that this error is trapped. i.e. change trigger to.
Trigger("t == complete") # there is no node with name t, this should be reported as an error