tasks:
  a1:
    commands:
      - echo Begin a1
      - sleep 0.5
      - echo End a1
  a2:
    commands:
      - echo Begin a2
      - sleep 1
      - echo End a2
  b:
    commands:
      - echo Begin b
      - sleep 0.5
      - echo End b
    depends_on: [ a1, a2 ]
  c:
    commands:
      - echo Begin c
      - sleep 1
      - echo End c
    depends_on: [ a1 ]
  d:
    commands:
      - echo Begin d
      - sleep 0.5
      - echo End d
    depends_on: [ a1 ]
  e:
    commands:
      - echo Begin e
      - sleep 0.5
      - echo End e
    depends_on: [ b, c, d ]
  f:
    commands:
      - echo Begin f
      - sleep 1
      - echo End f
    depends_on: [ c ]
concurrency: 2