Fail-fast

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Fail-fast is a property of a system or module with respect to its response to failures. A fail-fast system is designed to immediately report at its interface any failure or condition that is likely to lead to failure. Fail-fast systems are usually designed to stop normal operation rather than attempt to continue a possibly flawed process. Such designs often check the system's state at several points in an operation, so any failures can be detected early. A fail-fast module passes the responsibility for handling errors, but not detecting them, to the next-higher system design level.

Fail-fast systems or modules are desirable in several circumstances:

  • When building a fault-tolerant system by means of redundant components, the individual components should be fail-fast to give the system enough information to successfully tolerate a failure.
  • Fail-fast components are often used in situations where failure in one component might not be visible until it leads to failure in another component.
  • Finding the cause of a failure is easier in a fail-fast system, because the system reports the failure with as much information as possible as close to the time of failure as possible. In a fault-tolerant system, the failure might go undetected, whereas in a system that is neither fault-tolerant nor fail-fast the failure might be temporarily hidden until it causes some seemingly unrelated problem later.
  • A fail-fast system that is designed to halt as well as report the error on failure is less likely to erroneously perform an irreversible or costly operation.

Examples[edit]

From the field of software engineering, a Fail Fast Iterator is an iterator that attempts to raise an error if the sequence of elements processed by the iterator is changed during iteration.

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