A common question for beginning labview programming is: but is LabVIEW execution order determined? can it flow left to right? prime to bottom? the answer is that it follows a dataflow execution model. throughout this episode, we tend to tend to look at what that is.
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In the video, we tend to tend to say that there ar some ways that of determinant execution order. we'll scrutinize victimization the error cluster next time around, that's sometimes the simplest means that. simply connecting the error cluster of VIs in associate degree extremely chain will force them to execute at intervals the proper order.
Experience Level: Basic
“I initial saw a LabVIEW diagram whereas in operation in associate degree extremely biomass combustion research lab at school. I tested the diagram and asked my senior analysis partner: but do i apprehend what executes first? can it go left to right? prime to bottom? He explained it as a mix of science, magic, and love and told Pine Tree State to induce back to work building the reactor chamber. Let’s clarify, clarify, and understand dataflow and execution order.
Data in fifty five flows through nodes. Nodes ar objects on the diagram that have inputs and/or outputs and perform operations once a VI runs. therefore on total execution order, LabVIEW follows a combine of dataflow rules:
1. associate object executes once all info at its input terminals is on the market, and
2. associate object outputs info from its output terminals once it's finished execution
For instance, this diagram includes a combine of nodes: this add operate and this multiply operate. but am i ready to make sure that of these will execute first? Intuitively you may say that it’s the add operate as a results of it comes “first”, or it’s over to the left. but the vital reason is that it meets the need for execution to keep with rule one that we tend to tend to easily looked at: it's all the info out there at every input terminals as a results of every of these controls can forthwith supply knowledge to the terminals. watching the multiply operate, we tend to tend to check the lower input can forthwith receive its info from this constant, but the upper input is waiting on info from the output of the add operate. which we tend to apprehend that the Add operate won’t output its info until it's finished penalty, to keep with rule a combine of. therefore we have associate inherent execution order: the add operate ought to execute before the multiply operate. And if we tend to tend to observe in highlight execution, we tend to tend to check that’s precisely what happens.
Now let’s scrutinize this diagram. we have the chain of VIs we tend to tend to easily examined, then another am keen on it. once I hit the run button, that of these functions will execute first? clearly of the Add and Multiply functions, we tend to all understand that the Add will execute initial. And of the figure and Divide operate, the figure will execute initial. but that of the Add or figure functions will execute first? this will be to a small degree plenty of inauspicious as there does not exist a dataflow dependency between these a combine of functions, in different words they don’t share inputs and outputs. throughout this case, LabVIEW will simply pick whichever it is a heap of economical for it to run initial. this may be either, reckoning on an expansion of things.
Now we tend to tend to don’t would like to grant the impression that fifty five is erratic or unpredictable, as a results of if we tend to truly wanted to dictate that one amongst these functions would go initial we'll try this really merely. However, throughout this case, by programming the diagram throughout this fashion, we tend to tend to’ve primarily told fifty five that we tend to don’t care that of these will go initial, then fifty five merely chooses one. There ar some ways that of dictating execution order, and we’ll take a look at that next time.