Rollup merge of #148765 - joboet:split-up-thread, r=ChrisDenton

std: split up the `thread` module

Almost all functionality in `std::thread` is currently implemented in `thread/mod.rs`, resulting in a *huge* file with more than 2000 lines and multiple, interoperating `unsafe` sections. This PR splits the file up into multiple different private modules, each implementing mostly independent parts of the functionality. The only remaining `unsafe` interplay is that of the `lifecycle` and `scope` modules, the `spawn_scoped` implementation relies on the live thread count being updated correctly by the `lifecycle` module.

This PR contains no functional changes and only moves code around for the most part, with a few notable exceptions:
* `with_current_name` is moved to the already existing `current` module and now uses the `name` method instead of calculating the name from private fields. The old code was just a reimplementation of that method anyway.
* The private `JoinInner` type used to implement both join handles now has some more methods (`is_finished`, `thread` and the `AsInner`/`IntoInner` implementations) to avoid having to expose private fields and their invariants.
* The private `spawn_unchecked_` (note the underscore) method of `Builder` is now a freestanding function in `lifecycle`.

The rest of the changes are just visibility annotations.

I realise this PR ended up quite large – let me know if there is anyway I can aid the review process.

Edit: I've simplified the diff by adding an intermediate commit that creates all the new files by duplicating `mod.rs`. The actual changes in the second commit thus appear to delete the non-relevant parts from the respective file.

Author: matthiaskrgr

tests/fail-dep/concurrency/libc_pthread_mutex_deadlock.stderr

@@ -12,8 +12,8 @@ LL |         let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
    |
    = note: BACKTRACE:
    = note: inside `std::sys::thread::PLATFORM::Thread::join` at RUSTLIB/std/src/sys/thread/PLATFORM.rs:LL:CC
-   = note: inside `std::thread::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
-   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
+   = note: inside `std::thread::lifecycle::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/lifecycle.rs:LL:CC
+   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/join_handle.rs:LL:CC
 note: inside `main`
   --> tests/fail-dep/concurrency/libc_pthread_mutex_deadlock.rs:LL:CC
    |

tests/fail-dep/concurrency/libc_pthread_rwlock_write_read_deadlock.stderr

@@ -12,8 +12,8 @@ LL |         let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
    |
    = note: BACKTRACE:
    = note: inside `std::sys::thread::PLATFORM::Thread::join` at RUSTLIB/std/src/sys/thread/PLATFORM.rs:LL:CC
-   = note: inside `std::thread::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
-   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
+   = note: inside `std::thread::lifecycle::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/lifecycle.rs:LL:CC
+   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/join_handle.rs:LL:CC
 note: inside `main`
   --> tests/fail-dep/concurrency/libc_pthread_rwlock_write_read_deadlock.rs:LL:CC
    |

tests/fail-dep/concurrency/libc_pthread_rwlock_write_write_deadlock.stderr

@@ -12,8 +12,8 @@ LL |         let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
    |
    = note: BACKTRACE:
    = note: inside `std::sys::thread::PLATFORM::Thread::join` at RUSTLIB/std/src/sys/thread/PLATFORM.rs:LL:CC
-   = note: inside `std::thread::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
-   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
+   = note: inside `std::thread::lifecycle::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/lifecycle.rs:LL:CC
+   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/join_handle.rs:LL:CC
 note: inside `main`
   --> tests/fail-dep/concurrency/libc_pthread_rwlock_write_write_deadlock.rs:LL:CC
    |

tests/fail-dep/concurrency/windows_join_detached.stderr

@@ -8,8 +8,8 @@ LL |         let rc = unsafe { c::WaitForSingleObject(self.handle.as_raw_handle(
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
    = note: BACKTRACE:
    = note: inside `std::sys::thread::PLATFORM::Thread::join` at RUSTLIB/std/src/sys/thread/PLATFORM.rs:LL:CC
-   = note: inside `std::thread::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
-   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
+   = note: inside `std::thread::lifecycle::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/lifecycle.rs:LL:CC
+   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/join_handle.rs:LL:CC
 note: inside `main`
   --> tests/fail-dep/concurrency/windows_join_detached.rs:LL:CC
    |

tests/fail-dep/concurrency/windows_join_main.stderr

@@ -14,8 +14,8 @@ LL |         let rc = unsafe { c::WaitForSingleObject(self.handle.as_raw_handle(
    |
    = note: BACKTRACE:
    = note: inside `std::sys::thread::PLATFORM::Thread::join` at RUSTLIB/std/src/sys/thread/PLATFORM.rs:LL:CC
-   = note: inside `std::thread::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
-   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
+   = note: inside `std::thread::lifecycle::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/lifecycle.rs:LL:CC
+   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/join_handle.rs:LL:CC
 note: inside `main`
   --> tests/fail-dep/concurrency/windows_join_main.rs:LL:CC
    |

tests/fail-dep/concurrency/windows_join_self.stderr

@@ -12,8 +12,8 @@ LL |         let rc = unsafe { c::WaitForSingleObject(self.handle.as_raw_handle(
    |
    = note: BACKTRACE:
    = note: inside `std::sys::thread::PLATFORM::Thread::join` at RUSTLIB/std/src/sys/thread/PLATFORM.rs:LL:CC
-   = note: inside `std::thread::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
-   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
+   = note: inside `std::thread::lifecycle::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/lifecycle.rs:LL:CC
+   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/join_handle.rs:LL:CC
 note: inside `main`
   --> tests/fail-dep/concurrency/windows_join_self.rs:LL:CC
    |

tests/fail-dep/libc/eventfd_block_read_twice.stderr

@@ -6,8 +6,8 @@ LL |         let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
    |
    = note: BACKTRACE:
    = note: inside `std::sys::thread::PLATFORM::Thread::join` at RUSTLIB/std/src/sys/thread/PLATFORM.rs:LL:CC
-   = note: inside `std::thread::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
-   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
+   = note: inside `std::thread::lifecycle::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/lifecycle.rs:LL:CC
+   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/join_handle.rs:LL:CC
 note: inside `main`
   --> tests/fail-dep/libc/eventfd_block_read_twice.rs:LL:CC
    |

tests/fail-dep/libc/eventfd_block_write_twice.stderr

@@ -6,8 +6,8 @@ LL |         let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
    |
    = note: BACKTRACE:
    = note: inside `std::sys::thread::PLATFORM::Thread::join` at RUSTLIB/std/src/sys/thread/PLATFORM.rs:LL:CC
-   = note: inside `std::thread::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
-   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
+   = note: inside `std::thread::lifecycle::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/lifecycle.rs:LL:CC
+   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/join_handle.rs:LL:CC
 note: inside `main`
   --> tests/fail-dep/libc/eventfd_block_write_twice.rs:LL:CC
    |

tests/fail-dep/libc/libc_epoll_block_two_thread.stderr

@@ -6,8 +6,8 @@ LL |         let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
    |
    = note: BACKTRACE:
    = note: inside `std::sys::thread::PLATFORM::Thread::join` at RUSTLIB/std/src/sys/thread/PLATFORM.rs:LL:CC
-   = note: inside `std::thread::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
-   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
+   = note: inside `std::thread::lifecycle::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/lifecycle.rs:LL:CC
+   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/join_handle.rs:LL:CC
 note: inside `main`
   --> tests/fail-dep/libc/libc_epoll_block_two_thread.rs:LL:CC
    |

tests/fail-dep/libc/socketpair-close-while-blocked.stderr

@@ -6,8 +6,8 @@ LL |         let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
    |
    = note: BACKTRACE:
    = note: inside `std::sys::thread::PLATFORM::Thread::join` at RUSTLIB/std/src/sys/thread/PLATFORM.rs:LL:CC
-   = note: inside `std::thread::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
-   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/mod.rs:LL:CC
+   = note: inside `std::thread::lifecycle::JoinInner::<'_, ()>::join` at RUSTLIB/std/src/thread/lifecycle.rs:LL:CC
+   = note: inside `std::thread::JoinHandle::<()>::join` at RUSTLIB/std/src/thread/join_handle.rs:LL:CC
 note: inside `main`
   --> tests/fail-dep/libc/socketpair-close-while-blocked.rs:LL:CC
    |