Live C++ coding: adding and testing threadsafe::UnlockedBase смотреть онлайн

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My https://github.com/CarloWood/threadsafe C++ "library" (git submodule, and cmake OBJECT library) has existed for roughly 6 years now. All this time it existed of a Wrapper class (now renamed to Unlocked) that wrapped a user class T together with an arbitrary (read/write) mutex, where it is only possible to access the underlying object by first obtaining a lock on that mutex.

Recently I am extending this to include two more objects, UnlockedBase and ConstUnlockedBase, that can be used as drop-in replacement for an Unlocked type, but that do not wrap an object but rather wrap a pointer to (a base class of) an object wrapped inside an Unlocked as well as a pointer to the mutex of that Unlocked.

The Const- version can subsequently only be used to obtain read-access to the underlying object (a `crat` or const-read-access-type, which can not be converted to a `rat` or `wat` (write-access-type; a rat CAN be converted to a wat).

This has parallels with the standard iterator and const_iterator types, that are also "pointers".
Note that there is no ConstUnlocked: since an ⟨UnlockedT, policy⟩ is derived from (a protected) T, the proper way to talk about a read-only Unlocked is by making it const (aka, an `Unlocked⟨T, ...⟩ const&`).

There are (still) three policies: ReadWrite, which requires a read/write mutex, Primitive, which requires a normal mutex like std::mutex, and OneThread which doesn't use a mutex but checks under the hood that access is single threaded (aka using external synchronization).