Define a `mutex` together with the data it guards. Use `synchronized_value<T>` where possible

Reason

It should be obvious to a reader that the data is to be guarded and how. This decreases the chance of the wrong mutex being locked, or the mutex not being locked.

Using a synchronized_value<T> ensures that the data has a mutex, and the right mutex is locked when the data is accessed. See the WG21 proposal to add synchronized_value to a future TS or revision of the C++ standard.

Example

struct Record {
    std::mutex m;   // take this mutex before accessing other members
    // ...
};

class MyClass {
    struct DataRecord {
       // ...
    };
    synchronized_value<DataRecord> data; // Protect the data with a mutex
};

Enforcement

??? Possible?

CP.coro: Coroutines

This section focuses on uses of coroutines.

Coroutine rule summary:

• CP.51: Do not use capturing lambdas that are coroutines
• CP.52: Do not hold locks or other synchronization primitives across suspension points
• CP.53: Parameters to coroutines should not be passed by reference