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Dataflow Programming

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Summary: In this section, you will learn about dataflow programming.

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LabVIEW follows a dataflow model for running VIs. A block diagram node executes when all its inputs are available. When a node completes execution, it supplies data to its output terminals and passes the output data to the next node in the dataflow path.

Visual Basic, C++, JAVA, and most other text-based programming languages follow a control flow model of program execution. In control flow, the sequential order of program elements determines the execution order of a program.

Example 1

For a dataflow programming example, consider a block diagram that adds two numbers and then subtracts 50.00 50.00 from the result of the addition. In this case, the block diagram executes from left to right, not because the objects are placed in that order, but because the Subtract function cannot execute until the Add function finishes executing and passes the data to the Subtract function. Remember that a node executes only when data are available at all of its input terminals, and it supplies data to its output terminals only when it finishes execution.

Figure 1
Figure 1 (dataflow.png)

Example 2

In the following example, consider which code segment would execute first-the Add, Random Number, or Divide function. You cannot know because inputs to the Add and Divide functions are available at the same time, and the Random Number function has no inputs. In a situation where one code segment must execute before another, and no data dependency exists between the functions, use other programming methods, such as error clusters, to force the order of execution. Refer to the Error Handling section of Clusters for more information about error clusters.

Figure 2
Figure 2 (dataflowno.png)

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