Stream Out

In crossflow all services are able to have output streams, which allow services to produce output messages while still running. These are different from the final output in two ways:

• A service can have multiple output streams with different names and message types, whereas its final output has one fixed message type.
• Each output stream can produce any number of output messages per activation of the service, including 0—outputting no message at all—whereas the final output always produces exactly one output message per service activation, unless the service gets cancelled.

When you spawn a workflow it will be encapsulated as a service. The stream out operation is how your workflow can provide output streams as a service. This operation will take any messages passed to it and forward them out of the workflow session.

For example suppose you have a workflow that takes in a basket of apples and chops them one at a time:

You can design the workflow so that each time an apple is chopped, the slices are sent out through an output stream, and then the workflow continues on to chop the next apple. The workflow ends when there are no apples left, and the final output of the workflow is just a trigger message.