This commit performs a second pass over the `std::thread_local` module. Most of
the functionality remains explicitly unstable, but the specific actions taken
were:
* `thread_local` is now stable
* `thread_local!` is now stable
* `thread_local::Key` is now stable
* `thread_local::Key::with` is now stable
* `thread_local::Key::destroyed` is deprecated in favor of a more general
`state` function
* `thread_local::Key::state` was added to query the three states that a key can
be in: uninitialized, valid, or destroyed. This function, and the
corresponding `State` enum, are both marked unstable as we may wish to expand
it later on.
* `thread_local::scoped` is entirely unstable. There hasn't been a whole lot of
usage of this module in the standard distribution, so it remains unstable at
this time.
Note that while the structure `Key` is marked stable, it is currently forced to
expose all of its implementation details due to the use of
construction-via-macro. The use of construction-via-macro is currently required
in order to place the `#[thread_local]` attribute on static in a
platform-specific manner. These stability attributes were assigned assuming that
it will be acceptable to tweak the implementation of `Key` in the future.
This flag is somewhat tied to the `unwind` module rather than the `thread_info`
module, so this commit moves it into that module as well as allowing the same OS
thread to call `unwind::try` multiple times. Previously once a thread panicked
its panic flag was never reset, even after exiting the panic handler.
This commit is part of a series that introduces a `std::thread` API to
replace `std::task`.
In the new API, `spawn` returns a `JoinGuard`, which by default will
join the spawned thread when dropped. It can also be used to join
explicitly at any time, returning the thread's result. Alternatively,
the spawned thread can be explicitly detached (so no join takes place).
As part of this change, Rust processes now terminate when the main
thread exits, even if other detached threads are still running, moving
Rust closer to standard threading models. This new behavior may break code
that was relying on the previously implicit join-all.
In addition to the above, the new thread API also offers some built-in
support for building blocking abstractions in user space; see the module
doc for details.
Closes#18000
[breaking-change]
