# Probe effect

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{{other uses|Observer effect}}
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'''Probe effect''' is an unintended alteration in system behavior caused by measuring that system. In code profiling and performance measurements, the delays introduced by insertion or removal of code instrumentation may result in a non-functioning application, or unpredictable behavior.

==Examples==
In electronics, by attaching a [multimeter](/source/multimeter), [oscilloscope](/source/oscilloscope), or other testing device via a [test probe](/source/test_probe), small amounts of [capacitance](/source/capacitance), [resistance](/source/Electrical_resistance), or [inductance](/source/inductance) may be introduced. Though good scopes have very slight effects, in sensitive circuitry these can lead to unexpected failures, or conversely, unexpected fixes to failures.

In [debugging](/source/debugging) of [parallel](/source/Parallel_computing) [computer](/source/computer) programs, sometimes failures (such as [deadlock](/source/Deadlock_(computer_science))s) are not present when the debugger's code (which was meant to help to find a reason for deadlocks by visualising points of interest in the program code) is attached to the program. This is because additional code changed the timing of the execution of parallel processes, and because of that deadlocks were avoided.<ref>[https://books.google.com/books?id=vOE0s6Zfk6gC&dq=Probe+effect&pg=PA287 Event manipulation for Nondeterministic Shared-Memory Programs] / High-Performance Computing and Networking. 9th International Conference, HPCN Europe 2001, Amsterdam, the Netherlands, June 25–27, 2001,</ref> This type of bug is known colloquially as a [Heisenbug](/source/Heisenbug), by analogy with the [observer effect](/source/Observer_effect_(physics)) in quantum mechanics.

== See also ==
* [Observer effect (physics)](/source/Observer_effect_(physics))
* [Observer's paradox](/source/Observer's_paradox)

== Sources==
{{Reflist}}

{{DEFAULTSORT:Probe Effect}}
Category:Software testing
Category:Debugging

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Adapted from the Wikipedia article [Probe effect](https://en.wikipedia.org/wiki/Probe_effect) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Probe_effect?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.