Does the default value of the DataflowBlockOptions.EnsureOrdered property is true?

[moyanming]

Hi,
Does the default value of the DataflowBlockOptions.EnsureOrdered property is true?

[svick]

Yes, the default is true, you can see it in the XML documentation in the source code:

Gets or sets whether ordered processing should be enforced on a block's handling of messages.

By default, dataflow blocks enforce ordering on the processing of messages. This means that a
block like TransformBlock<TInput, TOutput> will ensure that messages are output in the same
order they were input, even if parallelism is employed by the block and the processing of a message N finishes
after the processing of a subsequent message N+1 (the block will reorder the results to maintain the input
ordering prior to making those results available to a consumer). Some blocks may allow this to be relaxed,
however. Setting EnsureOrdered to false tells a block that it may relax this ordering if
it's able to do so. This can be beneficial if the immediacy of a processed result being made available
is more important than the input-to-output ordering being maintained.

I have also created a Pull Request that copies this information to the docs: #2374.