复杂依赖任务（DAG）

如果有四个任务，a/b/c/d 我们希望首先执行 任务 a，然后执行 b/c，b/c 同时完成后，最后执行 d，如下图所示：

为了实现这个目标，需要引入 depends 字段。以任务 d为例，完成任务 d 需要首先完成任务 b/c，则depends 字段为：

    depends:
      - target: b
        type: whole
      - target: c
        type: whole

完整代码如下：

version: genecontainer_0_1
inputs:
  memory:
    default: 1g
    type: string
  cpu:
    default: 1c
    type: string
  tool:
    default: bwa:0.7.12
    type: string
  shell:
    default: sh
    type: string

workflow:
  a:
    tool: bwa:0.7.12
    type: GCS.Job
    resources:
      memory: 1g
      cpu: 1c
    commands:
      - echo "A"
  b:
    tool: bwa:0.7.12
    type: GCS.Job
    resources:
      memory: 1g
      cpu: 1c
    commands:
      - echo "B"
    depends:
      - target: a
        type: whole
  c:
    tool: bwa:0.7.12
    type: GCS.Job
    resources:
      memory: 1g
      cpu: 1c
    commands:
      - echo "C"
    depends:
      - target: a
        type: whole
  d:
    tool: bwa:0.7.12
    type: GCS.Job
    resources:
      memory: 1g
      cpu: 1c
    commands:
      - echo "D"
    depends:
      - target: b
        type: whole
      - target: c
        type: whole
volumes:
  sample-data:
    mount_path: /obs
    mount_from:
      pvc: ${GCS_DATA_PVC}
  temp-data:
    mount_path: /sfs
    mount_from:
      pvc: ${GCS_SFS_PVC}
  ref-data:
    mount_path: /ref
    mount_from:
      pvc: ${GCS_REF_PVC}