principles:fail_fast
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Table of Contents
Fail Fast (FF)
Variants and Alternative Names
Context
Principle Statement
A design is better when fails fast, i.e. as soon as an unrepairable erroneous condition is encountered.
Description
Check for erroneous conditions like wrong parameter values, unmet preconditions, violated invariants, etc. In case of methods this means that it checks for errors and reports them for example by means of throwing an exception.
Rationale
Then a failure remains undetected, it propagates through the system ultimately causing other modules to fail. This results in in a more complicated fault removal. Furthermore undesired side effects like corrupted files may occur. A crashed program clearly communicates that there is a problem and is often a better situation than a misbehaving program.
Strategies
- Check input parameters for validity – especially non-nullness.
- Throw an Exception.
- Use assertions.
Origin
Evidence
Relations to Other Principles
Generalizations
Specializations
Contrary Principles
Complementary Principles
- Postel's Law: While FF is (amongst others) about checking for erroneous parameters, Postel's Law is about not being too strict with parameters. It says that the design should allow for uncommon or strangely arranged (yet meaningful) input data. This does not contradict FF as Postel's Law does not demand to process meaningless or erroneous data.
- Principle of Least Surprise (PLS): FF is about what a module should do in the case of error. PLS on the other hand is about how the module should behave normally. Furthermore it normally is not a surprise that a module fails when there is an error but a module that doesn't fail when it should, behaves strangely.
- Murphy's Law (ML): Even better than failing fast is to make errors logically impossible. ML is about this.
Principle Collections
Example
Description Status
Further Reading
- Eric S. Raymond: The Art of Unix Programming: Rule of Repair
- Andrew Hund and David Thomas The Pragmatic Programmer
- Joshua Bloch: How to Design a Good API & Why it Matters
1)
Eric S. Raymond: The Art of Unix Programming: Rule of Repair
2)
Andrew Hund and David Thomas The Pragmatic Programmer, p. 120
principles/fail_fast.1360083799.txt.gz · Last modified: 2013-05-19 22:20 (external edit)