LabVIEW code generation error 61056

LabVIEW code generation error 61056

During the code generation process, the following error message "Error 61056: Sub VI is non-reentrant, is in a Single-cycle TimedLoop, and has more than one caller" appears.I'm not calling the non-reentrant subVI multiple times in the loop, why am I getting this error?

Answer: This problem does not depend solely on whether a subVI is called multiple times in a single-cycle Timed Loop.A subVI becomes a "shared resource" if it is called from multiple places in a program.A shared resource is anything that is used by multiple places.From an implementation perspective, sharing resources requires additional circuit logic—arbitration.The execution time of the arbitration circuit is usually more than one clock cycle, so it cannot appear in a single-cycle timed loop (SCTL).To solve this problem, you need to enable the VI's reentrant property in VIProperties>>Execution>>Reentrant Execution.This will generate multiple instances of the VI - placing a copy of the VI at each call, and the VI with the reentrant property is called multiple times, but is not a shared resource.It's important to remember that you cannot use functional global variables in a VI that is thus reentrant because new storage space is generated for them at each call site

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When should reentrant VIs, template VIs, and dynamic calling VIs be used?What is the difference between these three types?

Solution

Reentrant VI

Reentrant VIs are used when you want to run multiple instances of the same VI at the same time.When a VI is not reentrant, the VI has only one data space.Therefore, only one caller can run the VI at a time, so the caller may have to "wait for its turn" before using the VI.This is the default option for VIs, but VIs can be made reentrant.There are two types of reentrancy: shared and preallocated.

Shared reentrant VI

If the Shared Clone Reentrant Execution option is selected, the VI has a pool of data space (same as the clone pool).Initially only two clones are created at the beginning of the calling VI.The caller will use one of the data spaces, but it does not know which data space is used, and it may be a different instance in subsequent calls.When there is not enough data space (clone) in the pool for a certain number of callers to call simultaneously, new data space (clone) is created and added to the pool.Here the word "shared" in "shared clones between instances" means that the data space can be used by multiple callers over time.If there are 20 calls to the SubVI, but at most two of those calls happen at the same time, there will only be two data spaces in the pool, and they will be "shared" among the 20 calls.Memory usage is optimized because only the necessary number of clones are created based on current needs.This option is recommended for fastest execution rate and best memory optimization.

Pre-allocated reentrant VIs

If the preallocated clone reentrant execution option is selected, each caller has its own private data space (and clone).If there are 20 calls to the VI, 20 clones will be created and added to the pool when the calling VI starts.If the calling pattern is similar to the one above, it is possible that only two are busy at the same time.Use this type of reentrant VI if you want to use the same clone for each invocation of a given instance of the SubVI (for example, if the SubVI needs to persist data from one invocation to the next).Shared clones won't work in this case because it's never known which instance of the SubVI last used the clone that was going to be used, and the stored information will "crosstalk" unpredictably between the SubVIs."Preallocated" means that for each call, the data space and clone for that call are created.Preallocation occurs before the VI runs.If you are opening multiple front panels of the same VI, the reentrant SubVI option will not work.

If the VI to be opened multiple times is a top-level VI, you can copy the top-level VI on disk to a temporary directory with a unique name and open the new file instance, it is not necessary to copy any SubVIs.Simply copy the top-level VI, and you can open and run the copy with VI Server.

Template VI

You can make a multi-instance panel into a template VI and open the file from the template each time.VI templates are VIs with a .vit extension.You can create a new VI from a template under File»New»Start From Template.This creates a new instance of the VI with its own memory space.They are created with different storage locations and are only used as a starting point for making another VI.Then, you need to configure whether the newly created VI is reentrant.

Dynamic VI

You can use VI Server to open VIs and VI templates.VI Server is used to dynamically load and run VIs.When using a SubVI, the code and data space of the SubVI is loaded when the top-level VI is loaded.When dynamically loading a VI, its code is not loaded until the VI Server calls the SubVI, instead of using it as a SubVI and loading the code when the main program is called.This saves memory at startup.

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