Rollup merge of #106372 - joboet:solid_id_parking, r=m-ou-se

Use id-based thread parking on SOLID

By using the [`slp_tsk`/`wup_tsk`](https://cs.uwaterloo.ca/~brecht/courses/702/Possible-Readings/embedded/uITRON-4.0-specification.pdf) system functions instead of an event-flag structure, `Parker` becomes cheaper to construct and SOLID can share the implementation used by NetBSD and SGX.

ping ``@kawadakk``
r? ``@m-ou-se``
``@rustbot`` label +T-libs

2 files changed, 1 insertions, 105 deletions

diff --git a/library/std/src/sys_common/thread_parking/mod.rs b/library/std/src/sys_common/thread_parking/mod.rs
index 0ead6633c35..e8e028bb330 100644
--- a/library/std/src/sys_common/thread_parking/mod.rs
+++ b/library/std/src/sys_common/thread_parking/mod.rs
@@ -14,12 +14,10 @@ cfg_if::cfg_if! {
     } 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 = "solid_asp3")] {
-        mod wait_flag;
-        pub use wait_flag::Parker;
     } else if #[cfg(any(windows, target_family = "unix"))] {
         pub use crate::sys::thread_parking::Parker;
     } else {
diff --git a/library/std/src/sys_common/thread_parking/wait_flag.rs b/library/std/src/sys_common/thread_parking/wait_flag.rs
deleted file mode 100644
index d0f8899a94e..00000000000
--- a/library/std/src/sys_common/thread_parking/wait_flag.rs
+++ /dev/null
@@ -1,102 +0,0 @@
-//! A wait-flag-based thread parker.
-//!
-//! Some operating systems provide low-level parking primitives like wait counts,
-//! event flags or semaphores which are not susceptible to race conditions (meaning
-//! the wakeup can occur before the wait operation). To implement the `std` thread
-//! parker on top of these primitives, we only have to ensure that parking is fast
-//! when the thread token is available, the atomic ordering guarantees are maintained
-//! and spurious wakeups are minimized.
-//!
-//! To achieve this, this parker uses an atomic variable with three states: `EMPTY`,
-//! `PARKED` and `NOTIFIED`:
-//! * `EMPTY` means the token has not been made available, but the thread is not
-//!    currently waiting on it.
-//! * `PARKED` means the token is not available and the thread is parked.
-//! * `NOTIFIED` means the token is available.
-//!
-//! `park` and `park_timeout` change the state from `EMPTY` to `PARKED` and from
-//! `NOTIFIED` to `EMPTY`. If the state was `NOTIFIED`, the thread was unparked and
-//! execution can continue without calling into the OS. If the state was `EMPTY`,
-//! the token is not available and the thread waits on the primitive (here called
-//! "wait flag").
-//!
-//! `unpark` changes the state to `NOTIFIED`. If the state was `PARKED`, the thread
-//! is or will be sleeping on the wait flag, so we raise it.
-
-use crate::pin::Pin;
-use crate::sync::atomic::AtomicI8;
-use crate::sync::atomic::Ordering::{Acquire, Relaxed, Release};
-use crate::sys::wait_flag::WaitFlag;
-use crate::time::Duration;
-
-const EMPTY: i8 = 0;
-const PARKED: i8 = -1;
-const NOTIFIED: i8 = 1;
-
-pub struct Parker {
-    state: AtomicI8,
-    wait_flag: WaitFlag,
-}
-
-impl Parker {
-    /// Construct a parker for the current thread. The UNIX parker
-    /// implementation requires this to happen in-place.
-    pub unsafe fn new_in_place(parker: *mut Parker) {
-        parker.write(Parker { state: AtomicI8::new(EMPTY), wait_flag: WaitFlag::new() })
-    }
-
-    // This implementation doesn't require `unsafe` and `Pin`, but other implementations do.
-    pub unsafe fn park(self: Pin<&Self>) {
-        match self.state.fetch_sub(1, Acquire) {
-            // NOTIFIED => EMPTY
-            NOTIFIED => return,
-            // EMPTY => PARKED
-            EMPTY => (),
-            _ => panic!("inconsistent park state"),
-        }
-
-        // Avoid waking up from spurious wakeups (these are quite likely, see below).
-        loop {
-            self.wait_flag.wait();
-
-            match self.state.compare_exchange(NOTIFIED, EMPTY, Acquire, Relaxed) {
-                Ok(_) => return,
-                Err(PARKED) => (),
-                Err(_) => panic!("inconsistent park state"),
-            }
-        }
-    }
-
-    // This implementation doesn't require `unsafe` and `Pin`, but other implementations do.
-    pub unsafe fn park_timeout(self: Pin<&Self>, dur: Duration) {
-        match self.state.fetch_sub(1, Acquire) {
-            NOTIFIED => return,
-            EMPTY => (),
-            _ => panic!("inconsistent park state"),
-        }
-
-        self.wait_flag.wait_timeout(dur);
-
-        // Either a wakeup or a timeout occurred. Wakeups may be spurious, as there can be
-        // a race condition when `unpark` is performed between receiving the timeout and
-        // resetting the state, resulting in the eventflag being set unnecessarily. `park`
-        // is protected against this by looping until the token is actually given, but
-        // here we cannot easily tell.
-
-        // Use `swap` to provide acquire ordering.
-        match self.state.swap(EMPTY, Acquire) {
-            NOTIFIED => (),
-            PARKED => (),
-            _ => panic!("inconsistent park state"),
-        }
-    }
-
-    // This implementation doesn't require `Pin`, but other implementations do.
-    pub fn unpark(self: Pin<&Self>) {
-        let state = self.state.swap(NOTIFIED, Release);
-
-        if state == PARKED {
-            self.wait_flag.raise();
-        }
-    }
-}