CLAD Debugging & Troubleshooting Techniques 3

Question 1

In LabVIEW, what is the effect of placing a breakpoint on a wire versus on a node?

Accepted Answer

Wire breakpoints pause before the downstream node executes; node breakpoints pause before the node begins

Answer

A breakpoint on a wire pauses execution after the upstream node finishes and before the data is consumed by the downstream node, while a node breakpoint pauses just before that node executes.

Question 2

Which built-in LabVIEW VI is commonly used to display the call chain when an error occurs, helping identify which subVI generated the error?

Accepted Answer

General Error Handler

Answer

The General Error Handler provides more detail than the Simple Error Handler, including the full call chain source string that shows which VI in the hierarchy generated the error.

Question 3

You suspect a race condition in a parallel loop structure. Which LabVIEW mechanism is the correct fix to ensure safe shared variable access?

Accepted Answer

Use a functional global variable or shift register pattern to serialize access

Answer

Functional global variables (action engine pattern) serialize access to shared data by using an uninitialized shift register inside a subVI that can only be called by one caller at a time.

Question 4

When LabVIEW reports 'Warning: VI is reentrant; data may not be preserved between calls,' what does this mean for debugging?

Accepted Answer

Each reentrant clone has its own uninitialized memory, so probes may show different values per clone

Answer

Each reentrant clone maintains its own data space, so probes on different simultaneous calls may display different values, making debugging more complex.

Question 5

What is the primary purpose of the 'Find All Instances' feature when debugging a global variable usage issue?

Accepted Answer

It locates every node in the project that reads or writes the global variable

Answer

Find All Instances shows every location in the project where a specific global variable is read or written, helping you track down unexpected writers causing data corruption.

CLAD Practice Test

CLAD Practice Test

CLAD Debugging & Troubleshooting Techniques 3