Define dependencies between workflows in Argo Workflows

I'm assuming A and B run in parallel.

If you could incorporate workflows A and B into a single workflow AB with parallel steps A and B, then you could use a mutex to delay the execution of C until after AB finishes.

apiVersion: argoproj.io/v1alpha1
kind: CronWorkflow
metadata:
  name: AB
spec:
  schedule: "* * * * *"
  workflowSpec:
    entrypoint: AB
    synchronization:
      mutex:
        name: AB-C-mutex
    templates:
      - name: AB
        steps:
          - - name: A
              templateRef:
                name: A
                template: A
            - name: B
              templateRef:
                name: B
                template: B
---
apiVersion: argoproj.io/v1alpha1
kind: CronWorkflow
metadata:
  name: C
spec:
  schedule: "* * * * *"
  workflowSpec:
    entrypoint: C
    synchronization:
      mutex:
        name: AB-C-mutex   
 templates:
# The rest of the workflow.

You would need to make sure C starts long enough after AB for AB to claim the mutex.

You could avoid combining A and B into one workflow if Argo supported using more than one mutex/semaphore per workflow. Currently, there are no plans to support that.

Another option would be to combine all three workflows into a single workflow (with A and B running in parallel before C).