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Triggers define a dependency on a task or family . There can be only one trigger dependency per node, but that can be a complex boolean expression of the status of several nodes. Triggers can not be added to the suite node. A node with a trigger can only be activated when its trigger has expired. A trigger holds the node as long as the trigger’s expression evaluation returns false.

Trigger evaluation occurs whenever the child command communicates with the server. i.e. whenever there is a state change in the suite definition and at least once every 60 seconds. The keywords in trigger expressions are: unknown , suspended , complete , queued , submitted , active , aborted and clear and set for event status. Triggers can also reference Node attributes like event , meter , variable , repeat and generated variables and limits. Triggers can also reference the late flag on a node. Trigger evaluation for node attributes uses integer arithmetic. See Glossary

from ecflow import Defs,Suite,Task,Trigger,Complete
defs = Defs( 
        Suite("s1",
           Task("t1"),
           Task("t2",
             Trigger("t1 == active and t3 == aborted"),
             Complete("t3 == complete")),
           Task("t3")))

The following examples show alternative styles that produce the same definition:

defs = Defs()
s1 = defs.add_suite("s1") 
t1 = s1.add_task("t1")
t2 = s1.add_task("t2")
t2.add_trigger( "t1 == active and t3 == aborted" )
t2.add_complete( "t3 == complete" )
t3 = s1.add_task("t3")

...

defs = Defs().add(
         Suite("s1").add(
           Task("t1"),
           Task("t2").add(
              Trigger("t1 == active and t3 == aborted"),
              Complete("t3 == complete")),
           Task("t3")))

defs = Defs(

Suite("s1"))
defs.s1 += [ Task("t{}".format(i)) for i in range(1,4) ]
defs.s1.t2 += [ Trigger("t1 == active and t3 == aborted"),
                        Complete("t3 == complete") ]

Adding triggers like '<nodepath> == complete' is extremely common. Hence there are a few short cuts;

...

There are many times where we want to add a chain of tasktasks, i,.e. where task tasks must be run sequentially one after the other. The following examples show different styles of chaining tasks which are identical:

from ecflow import *
defs = Defs(
        Suite("s1",
            Task("t1"),
            Task("t2",Trigger( "t1 == complete" )),
            Task("t3",Trigger( "t2 == complete" )),
            Task("t4",Trigger( "t3 == complete" )))) 

from ecflow import *
defs = Defs() + Suite("s1")
defs.s1 += [ Task("t1"),Task("t2"),
             Task("t3"),Task("t4") ]
defs.s1.t2 += Trigger( ["t1 == complete"] ) 
defs.s1.t3 += Trigger( ["t2 == complete"] )
defs.s1.t4 += Trigger( ["t3 == complete"] )

from ecflow import *
defs = Defs() + Suite("s1")
defs.s1 >> Task("t1") >> Task("t2") >> Task("t3") >> Task("t4")
# >> relies on the leading node to be a Family or Suite

Reverse Chaining

It is also possible to << to reverse chain task.

The following suites are identical:

defs = Defs() + Suite("s1")
defs.s1 += [ Task("t1"),Task("t2"),Task("t3"),Task("t4") ]
defs.s1.t2t1 += Trigger( ["t1"]"t2 == complete" ) 
defs.s1.t3t2 += Trigger( ["t2"]"t3 == complete" )
defs.s1.t4t3 += Trigger( ["t3"]"t4 == complete" )

from ecflow import *
defs = Defs() + (Suite("s1") + 
defs.s1 <<      Task("t1") >><< Task("t2") >><< Task("t3") >><< Task("t4"))
# << relies on the leading node to be a Suite or Family