[WS AI] Definition of weak exception safety

[qor-lb]

See AI9 discussed in https://github.com/orgs/eclipse-score/discussions/375

Owner: @elfenpiff

Extend the definition of weak exception safety in the discussion https://github.com/orgs/eclipse-score/discussions/301

[elfenpiff]

@qor-lb Is it possible to assign me all the issues I own? This would me help much more to track them.

[elfenpiff]

The Problem

A 100% MC/DC coverage must be achieved for all parts of the code. When implementing constructs that perform bounce checks, and on failure abort the execution and transition to a safe state, this must also be tested.

The standard approach is to override the fatal error handler and replace it with an exception. However, this approach can only be used if all underlying constructs are at least weak exception-safe and the test code does not contain any undefined behavior.

Weak Exception Safety

An operation providing a weak guarantee ensures that, in the event of errors or exceptions, related objects remain in a consistent but unspecified state. What constitutes "consistency" can vary, but at a minimum, each object can be safely destroyed or reassigned.

Strong Exception Safety

An operation providing a strong guarantee ensures that, in the event of errors or exceptions, all related objects remain in the same state they were in at the beginning.

Implementation: Copy-And-Swap Idiom

To reassign a complex object with a strong exception safety guarantee, the copy-and-swap idiom is often used in C++:

1. A temporary copy is created, with exceptions potentially occurring at multiple stages.
2. If a later stage of this construction fails, the no-throw destructors of earlier stages are invoked to reclaim resources allocated to the partially constructed object.
3. Only after all possible exceptions have been handled, a no-throw swap operation updates the contents of *this.
4. The no-throw destructor of the temporary object then destroys the old contents.

If the swap operation is never reached due to an exception, the contents of *this remain unchanged.

[qor-lb]

@qor-lb Is it possible to assign me all the issues I own? This would me help much more to track them.

@elfenpiff yes that is possible, however you have to be a contributor in order to get issues assigned. I added you in Eclipse to the S-CORE project as contributor. As soon as you accept the invite I can assign them to you.