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 --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 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 task t2.ecf script as follows:

Listing 27 $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 suite definition, with no trigger on task t2.

# 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

Listing 28 $HOME/course/test.py

import os
from ecflow import Defs, Suite, Family, Task, Edit, Trigger


def create_family_f1():
    return Family("f1", Edit(SLEEP=20), Task("t1"), Task("t2"))


print("Creating suite definition")
home = os.path.join(os.getenv("HOME"), "course")
defs = Defs(Suite("test", Edit(ECF_INCLUDE=home, ECF_HOME=home), create_family_f1()))
print(defs)

print("check trigger expressions")
check = defs.check()
assert len(check) == 0, check

print("Checking job creation: .ecf -> .job0")
print(defs.check_job_creation())

print("Saving definition to file 'test.def'")
defs.save_as_defs("test.def")

What to do

Modify the task script and the suite definition as shown above.

Replace the suite, using:

ecflow_client --suspend /test
ecflow_client --replace /test test.def

python3 test.py
python3 client.py

Observe the tasks in 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:
Listing 29 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?
Listing 30 expression that will never be satisfied
```
ecflow_client --wait="1 == 0"
```