实现素材下发并发限流控制

solve()

Download scheduler (max_concurrent=5):
  Submit DL-00000: started
  Submit DL-00001: started
  Submit DL-00002: started
  Submit DL-00003: started
  Submit DL-00004: started
  Submit DL-00005: queued
  Submit DL-00006: queued
  Submit DL-00007: queued
  Submit DL-00008: queued
  Submit DL-00009: queued
Status: {'active': 5, 'queued': 5, 'completed': 0}
After complete DL-00001: {'active': 5, 'queued': 4, 'completed': 1}