Public Requests w/Reply

Worker APIs

Overview

The images below are taken from the Workers Fundamentals example project.

Public Request with Reply Purpose

A Public Request with Reply is a message that can be sent to a Worker from an external source, such as from a Worker's Caller (within a Workers application), from another LabVIEW application or framework, or from TestStand. The VI that sends the message will wait until a Reply message is received back from the Worker that the Request message was sent to.

Public Request with Reply usage example

The image below demonstrates the use of a Public Request with Reply VI sending a message from a MHL case of Worker A to a MHL case of Worker C, and receiving data back from Worker C. In order for the a Public Request with Reply VI to know which instance of Worker C to send a message to, the Worker's Data Wire must be wired to the top-left input terminal of the Public Request with Reply VI.

Public Request with Reply VI

A Public Request with Reply VI is required to be wired in-line with a Caller's Main Data Wire, as shown in the block diagram image above. The Public Request with Reply VI will send a message to the Worker who's data wire is connected to its top-left input terminal. The message will be received by the Worker's MHL case that has the same name as the Request VI. The Public Request with Reply VI will then wait until it receives a Reply message back from the Worker that it sent the Request message to, or until a timeout duration has been exceeded.

Data in

Data that will be sent along with the message. By default, this is a typedef that has the same filename as the Public Request VI.

Message Priority

The priority of the message (default is Normal) can be set to either Low, Normal or High.

Show in Debugger?

When this flag is TRUE, then meta-data about this message will be sent to the Workers Debug Server.

timeout (ms)

The time in milliseconds that the VI will wait until it receives a Reply message back from the Worker it sent the Request message to. A value of -1 means that this VI will wait indefinitely.

Reply Data out

Data that was sent back from the Worker that the Request message was sent to.

Public Request with Reply Typedefs

Public Request with Reply typedefs are created with the same icon and filename as their matching Public Request with Reply VI. Their purpose is to provide a custom container (cluster) for the data that will be sent along with the message to the Public Request with Reply's MHL case.

Two typedefs are created for every Public Request with Reply. The first (green icon glyph) is for the Request message that is being sent from the external source to the Worker. The second (purple icon glyph) is for the Reply message that is being sent back to the Request with Reply VI.

Public Request with Reply MHL Cases

For every Public Request with Reply, a MHL case will be created to receive the message sent by the Public Request with Reply VI. Public Request with Reply MHL cases will automatically be added to the Worker's case structure section called --- PUBLIC API CASES ---. To convert the data sent with the message to its specific data type, a Variant to Data node is required at the beginning of every Public Request with Reply MHL case (this will automatically be added to the MHL case when the MHL case is created by the Public API Builder tool).

Public Request with Reply Folders

Public Request with Reply VIs created by the Public API Builder tool are added to a Worker's Public API >> Request w/Reply folder. Their scope is set to public because they are designed to be used from code that is external to the Worker that owns them.

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