Yes, you are right. In other tasks the lock is not strictly necessary but we
have one method in the base class that covers all tasks.
> On 11 Mar 2016, at 05:04, Ma GuoWei <maguo...@outlook.com> wrote:
>
> 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.
>>
