Auto merge of #124703 - matthiaskrgr:rollup-2lljptd, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #123356 (Reduce code size of `thread::set_current`)
 - #124159 (Move thread parking to `sys::sync`)
 - #124293 (Let miri and const eval execute intrinsics' fallback bodies)
 - #124677 (Set non-leaf frame pointers on Fuchsia targets)
 - #124692 (We do not coerce `&mut &mut T -> *mut mut T`)
 - #124698 (Rewrite `rustdoc-determinism` test in Rust)
 - #124700 (Remove an unnecessary cast)
 - #124701 (Docs: suggest `uN::checked_sub` instead of check-then-unchecked)

r? `@ghost`
`@rustbot` modify labels: rollup

21 files changed, 247 insertions, 54 deletions

diff --git a/library/std/src/sys/pal/sgx/thread.rs b/library/std/src/sys/pal/sgx/thread.rs
index e2df57b1a1f..7d271e6d2b6 100644
--- a/library/std/src/sys/pal/sgx/thread.rs
+++ b/library/std/src/sys/pal/sgx/thread.rs
@@ -67,7 +67,7 @@ mod task_queue {
 pub mod wait_notify {
     use crate::pin::Pin;
     use crate::sync::Arc;
-    use crate::sys_common::thread_parking::Parker;
+    use crate::sys::sync::Parker;
 
     pub struct Notifier(Arc<Parker>);
 
diff --git a/library/std/src/sys/pal/teeos/mod.rs b/library/std/src/sys/pal/teeos/mod.rs
index c392a0ea264..6dd465a12ed 100644
--- a/library/std/src/sys/pal/teeos/mod.rs
+++ b/library/std/src/sys/pal/teeos/mod.rs
@@ -30,8 +30,6 @@ pub mod thread;
 pub mod thread_local_dtor;
 #[path = "../unix/thread_local_key.rs"]
 pub mod thread_local_key;
-#[path = "../unsupported/thread_parking.rs"]
-pub mod thread_parking;
 #[allow(non_upper_case_globals)]
 #[path = "../unix/time.rs"]
 pub mod time;
diff --git a/library/std/src/sys/pal/uefi/mod.rs b/library/std/src/sys/pal/uefi/mod.rs
index 562b00c2c01..48b74df1384 100644
--- a/library/std/src/sys/pal/uefi/mod.rs
+++ b/library/std/src/sys/pal/uefi/mod.rs
@@ -30,8 +30,6 @@ pub mod stdio;
 pub mod thread;
 #[path = "../unsupported/thread_local_key.rs"]
 pub mod thread_local_key;
-#[path = "../unsupported/thread_parking.rs"]
-pub mod thread_parking;
 pub mod time;
 
 mod helpers;
diff --git a/library/std/src/sys/pal/unix/thread_parking/netbsd.rs b/library/std/src/sys/pal/unix/thread_parking.rs
index 5eeb37f8763..66ffc006057 100644
--- a/library/std/src/sys/pal/unix/thread_parking/netbsd.rs
+++ b/library/std/src/sys/pal/unix/thread_parking.rs
@@ -1,3 +1,7 @@
+// Only used on NetBSD. If other platforms start using id-based parking, use
+// separate modules for each platform.
+#![cfg(target_os = "netbsd")]
+
 use crate::ffi::{c_int, c_void};
 use crate::ptr;
 use crate::time::Duration;
diff --git a/library/std/src/sys/pal/unix/thread_parking/mod.rs b/library/std/src/sys/pal/unix/thread_parking/mod.rs
deleted file mode 100644
index c7fa39f07b6..00000000000
--- a/library/std/src/sys/pal/unix/thread_parking/mod.rs
+++ /dev/null
@@ -1,24 +0,0 @@
-//! Thread parking on systems without futex support.
-
-#![cfg(not(any(
-    target_os = "linux",
-    target_os = "android",
-    all(target_os = "emscripten", target_feature = "atomics"),
-    target_os = "freebsd",
-    target_os = "openbsd",
-    target_os = "dragonfly",
-    target_os = "fuchsia",
-)))]
-
-cfg_if::cfg_if! {
-    if #[cfg(all(target_vendor = "apple", not(miri)))] {
-        mod darwin;
-        pub use darwin::Parker;
-    } else if #[cfg(target_os = "netbsd")] {
-        mod netbsd;
-        pub use netbsd::{current, park, park_timeout, unpark, ThreadId};
-    } else {
-        mod pthread;
-        pub use pthread::Parker;
-    }
-}
diff --git a/library/std/src/sys/pal/unsupported/mod.rs b/library/std/src/sys/pal/unsupported/mod.rs
index be344fb7cae..01f5cfd4297 100644
--- a/library/std/src/sys/pal/unsupported/mod.rs
+++ b/library/std/src/sys/pal/unsupported/mod.rs
@@ -14,7 +14,6 @@ pub mod thread;
 #[cfg(target_thread_local)]
 pub mod thread_local_dtor;
 pub mod thread_local_key;
-pub mod thread_parking;
 pub mod time;
 
 mod common;
diff --git a/library/std/src/sys/pal/wasi/mod.rs b/library/std/src/sys/pal/wasi/mod.rs
index a78547261ad..c1266619b36 100644
--- a/library/std/src/sys/pal/wasi/mod.rs
+++ b/library/std/src/sys/pal/wasi/mod.rs
@@ -39,13 +39,6 @@ pub mod thread_local_dtor;
 pub mod thread_local_key;
 pub mod time;
 
-cfg_if::cfg_if! {
-    if #[cfg(not(target_feature = "atomics"))] {
-        #[path = "../unsupported/thread_parking.rs"]
-        pub mod thread_parking;
-    }
-}
-
 #[path = "../unsupported/common.rs"]
 #[deny(unsafe_op_in_unsafe_fn)]
 #[allow(unused)]
diff --git a/library/std/src/sys/pal/wasip2/mod.rs b/library/std/src/sys/pal/wasip2/mod.rs
index 94aa458d2f9..6787ffb4bed 100644
--- a/library/std/src/sys/pal/wasip2/mod.rs
+++ b/library/std/src/sys/pal/wasip2/mod.rs
@@ -41,15 +41,6 @@ pub mod thread_local_key;
 #[path = "../wasi/time.rs"]
 pub mod time;
 
-cfg_if::cfg_if! {
-    if #[cfg(target_feature = "atomics")] {
-        compile_error!("The wasm32-wasip2 target does not support atomics");
-    } else {
-        #[path = "../unsupported/thread_parking.rs"]
-        pub mod thread_parking;
-    }
-}
-
 #[path = "../unsupported/common.rs"]
 #[deny(unsafe_op_in_unsafe_fn)]
 #[allow(unused)]
diff --git a/library/std/src/sys/pal/wasm/mod.rs b/library/std/src/sys/pal/wasm/mod.rs
index 5cbc3e45341..75dd10826cc 100644
--- a/library/std/src/sys/pal/wasm/mod.rs
+++ b/library/std/src/sys/pal/wasm/mod.rs
@@ -50,8 +50,6 @@ cfg_if::cfg_if! {
     } else {
         #[path = "../unsupported/thread.rs"]
         pub mod thread;
-        #[path = "../unsupported/thread_parking.rs"]
-        pub mod thread_parking;
     }
 }
 
diff --git a/library/std/src/sys/pal/windows/mod.rs b/library/std/src/sys/pal/windows/mod.rs
index ff41f6e77be..402a205977b 100644
--- a/library/std/src/sys/pal/windows/mod.rs
+++ b/library/std/src/sys/pal/windows/mod.rs
@@ -33,7 +33,6 @@ pub mod stdio;
 pub mod thread;
 pub mod thread_local_dtor;
 pub mod thread_local_key;
-pub mod thread_parking;
 pub mod time;
 cfg_if::cfg_if! {
     if #[cfg(not(target_vendor = "uwp"))] {
diff --git a/library/std/src/sys/pal/xous/mod.rs b/library/std/src/sys/pal/xous/mod.rs
index 7914a255aea..68189bcc2e3 100644
--- a/library/std/src/sys/pal/xous/mod.rs
+++ b/library/std/src/sys/pal/xous/mod.rs
@@ -18,7 +18,6 @@ pub mod process;
 pub mod stdio;
 pub mod thread;
 pub mod thread_local_key;
-pub mod thread_parking;
 pub mod time;
 
 #[path = "../unsupported/common.rs"]
diff --git a/library/std/src/sys/pal/zkvm/mod.rs b/library/std/src/sys/pal/zkvm/mod.rs
index 4f79f8c4961..0b22eabca6d 100644
--- a/library/std/src/sys/pal/zkvm/mod.rs
+++ b/library/std/src/sys/pal/zkvm/mod.rs
@@ -32,9 +32,6 @@ pub mod time;
 #[path = "../unsupported/thread.rs"]
 pub mod thread;
 
-#[path = "../unsupported/thread_parking.rs"]
-pub mod thread_parking;
-
 mod abi;
 
 use crate::io as std_io;
diff --git a/library/std/src/sys/sync/mod.rs b/library/std/src/sys/sync/mod.rs
index 623e6bccd51..52fac5902a2 100644
--- a/library/std/src/sys/sync/mod.rs
+++ b/library/std/src/sys/sync/mod.rs
@@ -2,8 +2,10 @@ mod condvar;
 mod mutex;
 mod once;
 mod rwlock;
+mod thread_parking;
 
 pub use condvar::Condvar;
 pub use mutex::Mutex;
 pub use once::{Once, OnceState};
 pub use rwlock::RwLock;
+pub use thread_parking::Parker;
diff --git a/library/std/src/sys/pal/unix/thread_parking/darwin.rs b/library/std/src/sys/sync/thread_parking/darwin.rs
index 8231f3cba2d..973c08f0317 100644
--- a/library/std/src/sys/pal/unix/thread_parking/darwin.rs
+++ b/library/std/src/sys/sync/thread_parking/darwin.rs
@@ -10,6 +10,8 @@
 //! provided by libdispatch, as the underlying Mach semaphore is only dubiously
 //! public.
 
+#![allow(non_camel_case_types)]
+
 use crate::pin::Pin;
 use crate::sync::atomic::{
     AtomicI8,
diff --git a/library/std/src/sys/sync/thread_parking/futex.rs b/library/std/src/sys/sync/thread_parking/futex.rs
new file mode 100644
index 00000000000..588e7b27826
--- /dev/null
+++ b/library/std/src/sys/sync/thread_parking/futex.rs
@@ -0,0 +1,97 @@
+use crate::pin::Pin;
+use crate::sync::atomic::AtomicU32;
+use crate::sync::atomic::Ordering::{Acquire, Release};
+use crate::sys::futex::{futex_wait, futex_wake};
+use crate::time::Duration;
+
+const PARKED: u32 = u32::MAX;
+const EMPTY: u32 = 0;
+const NOTIFIED: u32 = 1;
+
+pub struct Parker {
+    state: AtomicU32,
+}
+
+// Notes about memory ordering:
+//
+// Memory ordering is only relevant for the relative ordering of operations
+// between different variables. Even Ordering::Relaxed guarantees a
+// monotonic/consistent order when looking at just a single atomic variable.
+//
+// So, since this parker is just a single atomic variable, we only need to look
+// at the ordering guarantees we need to provide to the 'outside world'.
+//
+// The only memory ordering guarantee that parking and unparking provide, is
+// that things which happened before unpark() are visible on the thread
+// returning from park() afterwards. Otherwise, it was effectively unparked
+// before unpark() was called while still consuming the 'token'.
+//
+// In other words, unpark() needs to synchronize with the part of park() that
+// consumes the token and returns.
+//
+// This is done with a release-acquire synchronization, by using
+// Ordering::Release when writing NOTIFIED (the 'token') in unpark(), and using
+// Ordering::Acquire when checking for this state in park().
+impl Parker {
+    /// Construct the futex parker. The UNIX parker implementation
+    /// requires this to happen in-place.
+    pub unsafe fn new_in_place(parker: *mut Parker) {
+        parker.write(Self { state: AtomicU32::new(EMPTY) });
+    }
+
+    // Assumes this is only called by the thread that owns the Parker,
+    // which means that `self.state != PARKED`.
+    pub unsafe fn park(self: Pin<&Self>) {
+        // Change NOTIFIED=>EMPTY or EMPTY=>PARKED, and directly return in the
+        // first case.
+        if self.state.fetch_sub(1, Acquire) == NOTIFIED {
+            return;
+        }
+        loop {
+            // Wait for something to happen, assuming it's still set to PARKED.
+            futex_wait(&self.state, PARKED, None);
+            // Change NOTIFIED=>EMPTY and return in that case.
+            if self.state.compare_exchange(NOTIFIED, EMPTY, Acquire, Acquire).is_ok() {
+                return;
+            } else {
+                // Spurious wake up. We loop to try again.
+            }
+        }
+    }
+
+    // Assumes this is only called by the thread that owns the Parker,
+    // which means that `self.state != PARKED`. This implementation doesn't
+    // require `Pin`, but other implementations do.
+    pub unsafe fn park_timeout(self: Pin<&Self>, timeout: Duration) {
+        // Change NOTIFIED=>EMPTY or EMPTY=>PARKED, and directly return in the
+        // first case.
+        if self.state.fetch_sub(1, Acquire) == NOTIFIED {
+            return;
+        }
+        // Wait for something to happen, assuming it's still set to PARKED.
+        futex_wait(&self.state, PARKED, Some(timeout));
+        // This is not just a store, because we need to establish a
+        // release-acquire ordering with unpark().
+        if self.state.swap(EMPTY, Acquire) == NOTIFIED {
+            // Woke up because of unpark().
+        } else {
+            // Timeout or spurious wake up.
+            // We return either way, because we can't easily tell if it was the
+            // timeout or not.
+        }
+    }
+
+    // This implementation doesn't require `Pin`, but other implementations do.
+    #[inline]
+    pub fn unpark(self: Pin<&Self>) {
+        // Change PARKED=>NOTIFIED, EMPTY=>NOTIFIED, or NOTIFIED=>NOTIFIED, and
+        // wake the thread in the first case.
+        //
+        // Note that even NOTIFIED=>NOTIFIED results in a write. This is on
+        // purpose, to make sure every unpark() has a release-acquire ordering
+        // with park().
+        if self.state.swap(NOTIFIED, Release) == PARKED {
+            futex_wake(&self.state);
+        }
+    }
+}
diff --git a/library/std/src/sys/sync/thread_parking/id.rs b/library/std/src/sys/sync/thread_parking/id.rs
new file mode 100644
index 00000000000..04667439660
--- /dev/null
+++ b/library/std/src/sys/sync/thread_parking/id.rs
@@ -0,0 +1,103 @@
+//! Thread parking using thread ids.
+//!
+//! Some platforms (notably NetBSD) have thread parking primitives whose semantics
+//! match those offered by `thread::park`, with the difference that the thread to
+//! be unparked is referenced by a platform-specific thread id. Since the thread
+//! parker is constructed before that id is known, an atomic state variable is used
+//! to manage the park state and propagate the thread id. This also avoids platform
+//! calls in the case where `unpark` is called before `park`.
+
+use crate::cell::UnsafeCell;
+use crate::pin::Pin;
+use crate::sync::atomic::{
+    fence, AtomicI8,
+    Ordering::{Acquire, Relaxed, Release},
+};
+use crate::sys::thread_parking::{current, park, park_timeout, unpark, ThreadId};
+use crate::time::Duration;
+
+pub struct Parker {
+    state: AtomicI8,
+    tid: UnsafeCell<Option<ThreadId>>,
+}
+
+const PARKED: i8 = -1;
+const EMPTY: i8 = 0;
+const NOTIFIED: i8 = 1;
+
+impl Parker {
+    pub fn new() -> Parker {
+        Parker { state: AtomicI8::new(EMPTY), tid: UnsafeCell::new(None) }
+    }
+
+    /// Create a new thread parker. UNIX requires this to happen in-place.
+    pub unsafe fn new_in_place(parker: *mut Parker) {
+        parker.write(Parker::new())
+    }
+
+    /// # Safety
+    /// * must always be called from the same thread
+    /// * must be called before the state is set to PARKED
+    unsafe fn init_tid(&self) {
+        // The field is only ever written to from this thread, so we don't need
+        // synchronization to read it here.
+        if self.tid.get().read().is_none() {
+            // Because this point is only reached once, before the state is set
+            // to PARKED for the first time, the non-atomic write here can not
+            // conflict with reads by other threads.
+            self.tid.get().write(Some(current()));
+            // Ensure that the write can be observed by all threads reading the
+            // state. Synchronizes with the acquire barrier in `unpark`.
+            fence(Release);
+        }
+    }
+
+    pub unsafe fn park(self: Pin<&Self>) {
+        self.init_tid();
+
+        // Changes NOTIFIED to EMPTY and EMPTY to PARKED.
+        let state = self.state.fetch_sub(1, Acquire);
+        if state == EMPTY {
+            // Loop to guard against spurious wakeups.
+            // The state must be reset with acquire ordering to ensure that all
+            // calls to `unpark` synchronize with this thread.
+            while self.state.compare_exchange(NOTIFIED, EMPTY, Acquire, Relaxed).is_err() {
+                park(self.state.as_ptr().addr());
+            }
+        }
+    }
+
+    pub unsafe fn park_timeout(self: Pin<&Self>, dur: Duration) {
+        self.init_tid();
+
+        let state = self.state.fetch_sub(1, Acquire).wrapping_sub(1);
+        if state == PARKED {
+            park_timeout(dur, self.state.as_ptr().addr());
+            // Swap to ensure that we observe all state changes with acquire
+            // ordering.
+            self.state.swap(EMPTY, Acquire);
+        }
+    }
+
+    pub fn unpark(self: Pin<&Self>) {
+        let state = self.state.swap(NOTIFIED, Release);
+        if state == PARKED {
+            // Synchronize with the release fence in `init_tid` to observe the
+            // write to `tid`.
+            fence(Acquire);
+            // # Safety
+            // The thread id is initialized before the state is set to `PARKED`
+            // for the first time and is not written to from that point on
+            // (negating the need for an atomic read).
+            let tid = unsafe { self.tid.get().read().unwrap_unchecked() };
+            // It is possible that the waiting thread woke up because of a timeout
+            // and terminated before this call is made. This call then returns an
+            // error or wakes up an unrelated thread. The platform API and
+            // environment does allow this, however.
+            unpark(tid, self.state.as_ptr().addr());
+        }
+    }
+}
+
+unsafe impl Send for Parker {}
+unsafe impl Sync for Parker {}
diff --git a/library/std/src/sys/sync/thread_parking/mod.rs b/library/std/src/sys/sync/thread_parking/mod.rs
new file mode 100644
index 00000000000..ed1a6437faa
--- /dev/null
+++ b/library/std/src/sys/sync/thread_parking/mod.rs
@@ -0,0 +1,37 @@
+cfg_if::cfg_if! {
+    if #[cfg(any(
+        target_os = "linux",
+        target_os = "android",
+        all(target_arch = "wasm32", target_feature = "atomics"),
+        target_os = "freebsd",
+        target_os = "openbsd",
+        target_os = "dragonfly",
+        target_os = "fuchsia",
+        target_os = "hermit",
+    ))] {
+        mod futex;
+        pub use futex::Parker;
+    } else if #[cfg(any(
+        target_os = "netbsd",
+        all(target_vendor = "fortanix", target_env = "sgx"),
+        target_os = "solid_asp3",
+    ))] {
+        mod id;
+        pub use id::Parker;
+    } else if #[cfg(target_os = "windows")] {
+        mod windows;
+        pub use windows::Parker;
+    } else if #[cfg(all(target_vendor = "apple", not(miri)))] {
+        mod darwin;
+        pub use darwin::Parker;
+    } else if #[cfg(target_os = "xous")] {
+        mod xous;
+        pub use xous::Parker;
+    } else if #[cfg(target_family = "unix")] {
+        mod pthread;
+        pub use pthread::Parker;
+    } else {
+        mod unsupported;
+        pub use unsupported::Parker;
+    }
+}
diff --git a/library/std/src/sys/pal/unix/thread_parking/pthread.rs b/library/std/src/sys/sync/thread_parking/pthread.rs
index 8e295453d76..fdac1096dbf 100644
--- a/library/std/src/sys/pal/unix/thread_parking/pthread.rs
+++ b/library/std/src/sys/sync/thread_parking/pthread.rs
@@ -134,7 +134,7 @@ impl Parker {
     // This implementation doesn't require `unsafe`, but other implementations
     // may assume this is only called by the thread that owns the Parker.
     //
-    // For memory ordering, see std/src/sys_common/thread_parking/futex.rs
+    // For memory ordering, see futex.rs
     pub unsafe fn park(self: Pin<&Self>) {
         // If we were previously notified then we consume this notification and
         // return quickly.
diff --git a/library/std/src/sys/pal/unsupported/thread_parking.rs b/library/std/src/sys/sync/thread_parking/unsupported.rs
index 197078bb186..197078bb186 100644
--- a/library/std/src/sys/pal/unsupported/thread_parking.rs
+++ b/library/std/src/sys/sync/thread_parking/unsupported.rs
diff --git a/library/std/src/sys/pal/windows/thread_parking.rs b/library/std/src/sys/sync/thread_parking/windows.rs
index 4b8102d505a..4b8102d505a 100644
--- a/library/std/src/sys/pal/windows/thread_parking.rs
+++ b/library/std/src/sys/sync/thread_parking/windows.rs
diff --git a/library/std/src/sys/pal/xous/thread_parking.rs b/library/std/src/sys/sync/thread_parking/xous.rs
index 0bd0462d77d..0bd0462d77d 100644
--- a/library/std/src/sys/pal/xous/thread_parking.rs
+++ b/library/std/src/sys/sync/thread_parking/xous.rs