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cadence-workflowtemporal-workflow
Krishna Chaithanya Ganta
Krishna Chaithanya Ganta

Reputation: 89

Resume Cadence Workflow based on signal without blocking the thread

We want to build a workflow which contains below steps in that order

  1. Execute some synchronous activities.
  2. Trigger an external operation via kafka event.
  3. Listen to the kafka events for the result of the operation.
  4. Execute some other activities based on the result.

Kafka may contain events not related to workflow, so we need a separate workflow to filter the events for that particular workflow.

Using cadence I'm planning to split it into two workflows

Is it possible to wait for a signal in workflow1 without actually blocking the thread, so that the thread can process another workflow in the meantime.

Upvotes: 2

Views: 1157

Answers (2)

Gordon Sun
Gordon Sun

Reputation: 298

I have some experience writing Kafka/Kinesis consumers (not working with Cadence but plan to do so soon). My feeling is that you only need 1 consumer thread blocked and waiting for new events from the Kafka stream. And this consumer can live anywhere as long as it can talk to your Cadence system to send a signal to a workflow. For each Kafka message (after filter out non related), if it can be designed to contain all the information for the consumer to decide which workflow to signal, it will be very simple. If you have no control over what is in the message (sounds like you have an existing stream), it is a little trick. Your consumer may need to look up which workflow to call based on some other identifier in the message

Upvotes: 0

Maxim Fateev
Maxim Fateev

Reputation: 6890

I think there is some misunderstanding on how Temporal/Cadence works. There is no requirement to not block a thread for other workflows to be able to make progress. Worker instance will have no problem dealing with such situation.

So I would recommend to block the thread in the workflow one to wait for the signal as it is the simplest way to solve your business requirements.

As a side note I don't understand why you need a second workflow. There is no need to have a workflow to filter Kafka events. You can do it directly in a Kafka consumer that signals the first workflow.

Upvotes: 1

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