it is very helpful。 thanks a lot now i know the souce task needs the lock。
Other tasks like the StreamTask will handle broadcast and checkpoint then process element so lock is “no use” in those tasks。 am i right？ thanks your help very much！ 发自我的 iPhone > 在 2016年3月10日，下午7:45，Aljoscha Krettek <aljos...@apache.org> 写道： > > Hi, > that call needs to be in the lock scope because we need to ensure that no > element processing/element emission happens while we forward the checkpoint > barrier and perform the checkpoint. > > Let me illustrate with an example. Say we have a source. What can happen in > the source if the call is not in the checkpoint lock scope is the following > scenario: > > Source Forwards Checkpoint Barrier > Source Emits Element 13 > Source Emits Element 14 > Source Performs Checkpoint > > Now, the operations downstream from the source also performs a checkpoint. In > the state of this checkpoint we don’t have the changes caused by Element 13 > and Element 14 reflected. The source checkpoint, however, says that we > correctly forwarded Elements 13 and 14. Therefore the checkpoints of the > source and the downstream operations are not consistent. > > Basically the lock ensures that nothing can happen between “Forward > Checkpoint Barrier” and “Perform Checkpoint”. So the scenarios could be this, > for example: > > Source Emits Element 13 > Source Emits Element 14 > Source Forwards Checkpoint Barrier > Source Performs Checkpoint > > Now, both the checkpoint in the source and the checkpoints of downstream > operations correctly say that elements 13 and 14 are reflected in state > changes. > > I hope this helps but let me know if you need to know more. > > Cheers, > Aljoscha > > > >> On 10 Mar 2016, at 06:58, Ma GuoWei <maguo...@outlook.com> wrote: >> >> hi,all >> Why does the broadcastCheckpointBarrier need in the lock scope? >> >> thanks a lot. >
