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School/Analyse/Periode 2/Week 1.md
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@ -111,10 +111,29 @@ These bugs are hard to detect and fix.
# Correctness
Sequetial programs wil always give the same result. Debugging makes sense.
Concurrent programs do not behave like this. Some instances may give correct output and some not.
Concurrent programs do not behave like this. Some instances may give correct output and some not. (Without protections)
This implies that we cannot debug a concurrent program in the
normal way, because each time we run the program, we will likely
have a different order of interleaving.
Correctness of (non-terminating) concurrent programs is defined in
terms of properties of computations, rather than a functional result.
Types:
- Safety properties: the property must always be true.
Example: Always, mouse cursor is displayed.
- Liveness properties: The property must become true at some point.
Example: Click with a mouse, eventually the mouse cursor changes.
# Fairness
Arbitrary interleaving assumes no order of speed executing statements for diffrent processes/tasks.
- However, it does not make sense to assume that statements from any
specific process are never selected in the interleaving.
A scenario of executing statements is (weakly) fair if a statement that
is continually enabled, eventually is selected to execute.