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Add noexcept specifiers where appropriate #91

Merged
merged 2 commits into from
Jul 17, 2024
Merged

Add noexcept specifiers where appropriate #91

merged 2 commits into from
Jul 17, 2024

Commits on Jul 15, 2024

  1. Add noexcept specifiers where appropriate 

    We can mark the following as `noexcept`:
- ~ScopedConnection
- ~Signal
- ConnectionHandle::disconnect
- several move constructors

There are some caveats though:
When disconnecting, we need to lock the mutex in the ConnectionEvaluator
and allocate in the GenerationalIndexArray, which can both throw
exceptions.
However, we currently do not have any out of memory guarantees in
KDBindings, so terminating in that case should be a sufficient way of
handling this case.
The same goes for when locking a mutex isn't possible. This likely
indicates some kind of OS issue from which we can't really recover, so
terminating is appropriate.

We could improve the situation by avoiding allocations in the GenerationalIndexArray
when erasing slots.
This would be possible by using an inline linked-list inside the array
to store free indices.
Which would save memory and would no longer require us to allocate
memory when erasing entries.
However, it's also not trivial to implement, so leave this as a TODO.

Error checking in ConnectionEvaluator
-------------------------------------
This patch also adds some basic exception handling to the
ConnectionEvaluator.
It is now somewhat protected from slots disconnecting themselves while they are
evaluated and slots throwing exceptions.
However, this error-handling is rather basic and will simply **not**
dequeue any slots while the evaluator is already evaluating and will
dequeue all slots if any slot throws an exception.
We could improve this situation by using a queue and popping elements 1-by-1
when evaluating without actually iterating over it.
That way we could erase from the queue while its being evaluated.
And when a slot throws, calling evaluate again could simply continue
with the next slot, instead of skipping all queued slots.

However, we should ideally implement this queue as a ring-buffer to
avoid excessive allocations by std::list or std::dequeu.
But this isn't part of the STL, so would require us to roll our own
ring-buffer implementation.

For now, this error handling isn't publicly documented and throwing
within a slot or dequeuing while evaluating remains *undefined*,
so that we can improve the situation in the future.
    @LeonMatthesKDAB
    LeonMatthesKDAB committed Jul 15, 2024
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  2. Document that throwing within a slot is UB 

    We currently don't really deal with this correctly.
Until we do so, at least mention that it's UB.
    @LeonMatthesKDAB
    LeonMatthesKDAB committed Jul 15, 2024
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