5

Advanced Applications

This chapter describes several options needed only in advanced applications, including how to use the CINInit, CINDispose, CINAbort,

CINLoad, CINUnload, CINSave, and CINProperties routines. This chapter also describes how global data works within CIN source code, and how Windows users can call a DLL from a CIN.

CIN Routines

A CIN consists of several routines, as described by the .c file LabVIEW creates when you right-click the node on the block diagram and select Create .c File. Previous chapters have described only the CINRun routine. Other routines include CINLoad, CINInit, CINAbort, CINSave,

CINDispose, CINUnload, and CINProperties.

For most CINs, you need to write only the CINRun routine. The other routines are supplied mainly for special initialization needs, such as when your CIN is going to maintain information across calls and you want to preallocate or initialize global state information.

If you want to preallocate/initialize global state information, you need to understand more of how LabVIEW manages data and CINs, as described in the following sections.

Data Spaces and Code Resources

When you create a CIN, you compile your source into an object code file and load the code into the node. At that point, LabVIEW loads a copy of the code resource into memory and attaches it to the node. When you save the VI, this code resource is saved along with the VI as an attached component; the original object code file is no longer needed.

When LabVIEW loads a VI, it allocates a data space, a block of data storage memory, for that VI. LabVIEW uses this data space to store information such as the values in shift registers. If the VI is reentrant, LabVIEW allocates a data space for each usage of the VI. Refer to LabVIEW Help for more information about reentrancy and other execution properties.

Chapter 5 Advanced Applications

Within your CIN code resource, you might have declared global data. Global data includes variables declared outside of the scope of all routines and variables declared as static variables within routines. LabVIEW allocates space for this global data. As with the code itself, only one instance of these globals is in memory. Regardless of how many nodes reference the code resource and regardless of whether the surrounding VI is reentrant, only one copy of these global variables is ever in memory and their values are consistent.

When you create a CIN, LabVIEW allocates a CIN data space, a 4-byte storage location in the VI data space(s), strictly for the use of the CIN. Each CIN can have one or more CIN data spaces reserved for the node, depending on how many times the node appears in a VI or collection of VIs. You can use this CIN data space to store global data on a per data space basis, as described in the Code Globals and CIN Data Space Globals section later in this chapter. The following illustration shows a simple example of data storage spaces for one CIN.

VI

A CIN references the code resource by name, using the name you specified when you created the code resource. When you load a VI containing a CIN, LabVIEW looks in memory to see if a code resource with the desired name is already loaded. If so, LabVIEW links the CIN to the code resource for execution purposes.

This linking behaves the same way as links between VIs and subVIs. When you try to reference a subVI and another VI with the same name already exists in memory, LabVIEW references the one already in memory instead of the one you selected. In the same way, if you try to load references to two different code resources having the same name, only one code resource is