A more efficient slice comparison implementation for T: !BytewiseEq
(This is a follow up PR on #113654)
This PR changes the implementation for `[T]` slice comparison when `T: !BytewiseEq`. The previous implementation using zip was not optimized properly by the compiler, which didn't leverage the fact that both length were equal. Performance improvements are for example 20% when testing that `[Some(0_u64); 4096].as_slice() == [Some(0_u64); 4096].as_slice()`.
Making `User<T>` and `User<[T]>` `Send`
All `User` types in SGX point to owned memory in userspace. Special care is always needed when accessing this memory as it must be assumed that an attacker is always able to change its content. Therefore, we can also easily transfer this memory between thread boundaries.
cc: ``@mzohreva`` ``@vn971`` ``@belalH`` ``@jethrogb``
Fix broken build for ESP IDF due to #119026
`target_os = "espidf"` in `libc` lacks the `SOMAXCONN` constant, but that's probably irrelevant in this context, as `UnixListener` is not supported on ESP IDF - it being a single process "OS" only.
The PR just re-uses the `128` constant so that the code builds. Trying to use the listener on ESP IDF will fail with `ENOSYS`, which is fine.
*UPDATE* Might not fail with `ENOSYS` - need to test what error code would be returned, but that doesn`t change anything.
Use `assert_unsafe_precondition` for `char::from_u32_unchecked`
Use `assert_unsafe_precondition` in `char::from_u32_unchecked` so that it can be stabilized as `const`.
Rewrite `pin` module documentation to clarify usage and invariants
The documentation of `pin` today does not give a complete treatment of pinning from first principles, nor does it adequately help build intuition and understanding for how the different elements of the pinning story fit together.
This rewrite attempts to address these in a way that makes the concept more approachable while also making the documentation more normative.
This PR picks up where `@mcy` left off in #88500 (thanks to him for the original work and `@Manishearth` for mentioning it such that I originally found it). I've directly incorporated much of the feedback left on the original PR and have rewritten and changed some of the main conceits of the prose to better adhere to the feedback from the reviewers on that PR or just explain something in (hopefully) a better way.
The documentation today does not give a complete treatment of pinning
from first principles, which appropriately describes how to design types
that use it, nor does it provide formal statements of the guarantees
users need to be aware of.
This rewrite attempts to address these in a way that makes the concept
more approachable while also making the documentation more normative.
