std: use futex-based locks and thread parker on Hermit

Cargo.lock

@@ -1656,12 +1656,13 @@ dependencies = [
 
 [[package]]
 name = "hermit-abi"
-version = "0.2.0"
+version = "0.2.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1ab7905ea95c6d9af62940f9d7dd9596d54c334ae2c15300c482051292d5637f"
+checksum = "ee512640fe35acbfb4bb779db6f0d80704c2cacfa2e39b601ef3e3f47d1ae4c7"
 dependencies = [
  "compiler_builtins",
  "libc",
+ "rustc-std-workspace-alloc",
  "rustc-std-workspace-core",
 ]
 
@@ -4608,7 +4609,7 @@ dependencies = [
  "dlmalloc",
  "fortanix-sgx-abi",
  "hashbrown",
- "hermit-abi 0.2.0",
+ "hermit-abi 0.2.6",
  "libc",
  "miniz_oxide 0.4.0",
  "object 0.26.2",

library/std/Cargo.toml

@@ -42,7 +42,7 @@ dlmalloc = { version = "0.2.3", features = ['rustc-dep-of-std'] }
 fortanix-sgx-abi = { version = "0.5.0", features = ['rustc-dep-of-std'] }
 
 [target.'cfg(target_os = "hermit")'.dependencies]
-hermit-abi = { version = "0.2.0", features = ['rustc-dep-of-std'] }
+hermit-abi = { version = "0.2.6", features = ['rustc-dep-of-std'] }
 
 [target.wasm32-wasi.dependencies]
 wasi = { version = "0.11.0", features = ['rustc-dep-of-std'], default-features = false }

library/std/src/sys/hermit/condvar.rs

@@ -1,90 +0,0 @@
-use crate::ffi::c_void;
-use crate::ptr;
-use crate::sync::atomic::{AtomicUsize, Ordering::SeqCst};
-use crate::sys::hermit::abi;
-use crate::sys::locks::Mutex;
-use crate::sys_common::lazy_box::{LazyBox, LazyInit};
-use crate::time::Duration;
-
-// The implementation is inspired by Andrew D. Birrell's paper
-// "Implementing Condition Variables with Semaphores"
-
-pub struct Condvar {
-    counter: AtomicUsize,
-    sem1: *const c_void,
-    sem2: *const c_void,
-}
-
-pub(crate) type MovableCondvar = LazyBox<Condvar>;
-
-impl LazyInit for Condvar {
-    fn init() -> Box<Self> {
-        Box::new(Self::new())
-    }
-}
-
-unsafe impl Send for Condvar {}
-unsafe impl Sync for Condvar {}
-
-impl Condvar {
-    pub fn new() -> Self {
-        let mut condvar =
-            Self { counter: AtomicUsize::new(0), sem1: ptr::null(), sem2: ptr::null() };
-        unsafe {
-            let _ = abi::sem_init(&mut condvar.sem1, 0);
-            let _ = abi::sem_init(&mut condvar.sem2, 0);
-        }
-        condvar
-    }
-
-    pub unsafe fn notify_one(&self) {
-        if self.counter.load(SeqCst) > 0 {
-            self.counter.fetch_sub(1, SeqCst);
-            abi::sem_post(self.sem1);
-            abi::sem_timedwait(self.sem2, 0);
-        }
-    }
-
-    pub unsafe fn notify_all(&self) {
-        let counter = self.counter.swap(0, SeqCst);
-        for _ in 0..counter {
-            abi::sem_post(self.sem1);
-        }
-        for _ in 0..counter {
-            abi::sem_timedwait(self.sem2, 0);
-        }
-    }
-
-    pub unsafe fn wait(&self, mutex: &Mutex) {
-        self.counter.fetch_add(1, SeqCst);
-        mutex.unlock();
-        abi::sem_timedwait(self.sem1, 0);
-        abi::sem_post(self.sem2);
-        mutex.lock();
-    }
-
-    pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
-        self.counter.fetch_add(1, SeqCst);
-        mutex.unlock();
-        let millis = dur.as_millis().min(u32::MAX as u128) as u32;
-
-        let res = if millis > 0 {
-            abi::sem_timedwait(self.sem1, millis)
-        } else {
-            abi::sem_trywait(self.sem1)
-        };
-
-        abi::sem_post(self.sem2);
-        mutex.lock();
-        res == 0
-    }
-}
-
-impl Drop for Condvar {
-    fn drop(&mut self) {
-        unsafe {
-            let _ = abi::sem_destroy(self.sem1);
-            let _ = abi::sem_destroy(self.sem2);
-        }
-    }
-}

library/std/src/sys/hermit/futex.rs

@@ -0,0 +1,39 @@
+use super::abi;
+use crate::ptr::null;
+use crate::sync::atomic::AtomicU32;
+use crate::time::Duration;
+
+pub fn futex_wait(futex: &AtomicU32, expected: u32, timeout: Option<Duration>) -> bool {
+    // Calculate the timeout as a relative timespec.
+    //
+    // Overflows are rounded up to an infinite timeout (None).
+    let timespec = timeout.and_then(|dur| {
+        Some(abi::timespec {
+            tv_sec: dur.as_secs().try_into().ok()?,
+            tv_nsec: dur.subsec_nanos().into(),
+        })
+    });
+
+    let r = unsafe {
+        abi::futex_wait(
+            futex.as_mut_ptr(),
+            expected,
+            timespec.as_ref().map_or(null(), |t| t as *const abi::timespec),
+            abi::FUTEX_RELATIVE_TIMEOUT,
+        )
+    };
+
+    r != -abi::errno::ETIMEDOUT
+}
+
+#[inline]
+pub fn futex_wake(futex: &AtomicU32) -> bool {
+    unsafe { abi::futex_wake(futex.as_mut_ptr(), 1) > 0 }
+}
+
+#[inline]
+pub fn futex_wake_all(futex: &AtomicU32) {
+    unsafe {
+        abi::futex_wake(futex.as_mut_ptr(), i32::MAX);
+    }
+}

library/std/src/sys/hermit/mod.rs

@@ -25,6 +25,7 @@ pub mod cmath;
 pub mod env;
 pub mod fd;
 pub mod fs;
+pub mod futex;
 #[path = "../unsupported/io.rs"]
 pub mod io;
 pub mod memchr;
@@ -45,14 +46,14 @@ pub mod thread_local_dtor;
 pub mod thread_local_key;
 pub mod time;
 
-mod condvar;
-mod mutex;
-mod rwlock;
-
+#[path = "../unix/locks"]
 pub mod locks {
-    pub use super::condvar::*;
-    pub use super::mutex::*;
-    pub use super::rwlock::*;
+    mod futex_condvar;
+    mod futex_mutex;
+    mod futex_rwlock;
+    pub(crate) use futex_condvar::MovableCondvar;
+    pub(crate) use futex_mutex::{MovableMutex, Mutex};
+    pub(crate) use futex_rwlock::{MovableRwLock, RwLock};
 }
 
 use crate::io::ErrorKind;

library/std/src/sys/hermit/mutex.rs

@@ -1,212 +0,0 @@
-use crate::cell::UnsafeCell;
-use crate::collections::VecDeque;
-use crate::hint;
-use crate::ops::{Deref, DerefMut, Drop};
-use crate::sync::atomic::{AtomicUsize, Ordering};
-use crate::sys::hermit::abi;
-
-/// This type provides a lock based on busy waiting to realize mutual exclusion
-///
-/// # Description
-///
-/// This structure behaves a lot like a common mutex. There are some differences:
-///
-/// - By using busy waiting, it can be used outside the runtime.
-/// - It is a so called ticket lock and is completely fair.
-#[cfg_attr(target_arch = "x86_64", repr(align(128)))]
-#[cfg_attr(not(target_arch = "x86_64"), repr(align(64)))]
-struct Spinlock<T: ?Sized> {
-    queue: AtomicUsize,
-    dequeue: AtomicUsize,
-    data: UnsafeCell<T>,
-}
-
-unsafe impl<T: ?Sized + Send> Sync for Spinlock<T> {}
-unsafe impl<T: ?Sized + Send> Send for Spinlock<T> {}
-
-/// A guard to which the protected data can be accessed
-///
-/// When the guard falls out of scope it will release the lock.
-struct SpinlockGuard<'a, T: ?Sized + 'a> {
-    dequeue: &'a AtomicUsize,
-    data: &'a mut T,
-}
-
-impl<T> Spinlock<T> {
-    pub const fn new(user_data: T) -> Spinlock<T> {
-        Spinlock {
-            queue: AtomicUsize::new(0),
-            dequeue: AtomicUsize::new(1),
-            data: UnsafeCell::new(user_data),
-        }
-    }
-
-    #[inline]
-    fn obtain_lock(&self) {
-        let ticket = self.queue.fetch_add(1, Ordering::SeqCst) + 1;
-        let mut counter: u16 = 0;
-        while self.dequeue.load(Ordering::SeqCst) != ticket {
-            counter += 1;
-            if counter < 100 {
-                hint::spin_loop();
-            } else {
-                counter = 0;
-                unsafe {
-                    abi::yield_now();
-                }
-            }
-        }
-    }
-
-    #[inline]
-    pub unsafe fn lock(&self) -> SpinlockGuard<'_, T> {
-        self.obtain_lock();
-        SpinlockGuard { dequeue: &self.dequeue, data: &mut *self.data.get() }
-    }
-}
-
-impl<T: ?Sized + Default> Default for Spinlock<T> {
-    fn default() -> Spinlock<T> {
-        Spinlock::new(Default::default())
-    }
-}
-
-impl<'a, T: ?Sized> Deref for SpinlockGuard<'a, T> {
-    type Target = T;
-    fn deref(&self) -> &T {
-        &*self.data
-    }
-}
-
-impl<'a, T: ?Sized> DerefMut for SpinlockGuard<'a, T> {
-    fn deref_mut(&mut self) -> &mut T {
-        &mut *self.data
-    }
-}
-
-impl<'a, T: ?Sized> Drop for SpinlockGuard<'a, T> {
-    /// The dropping of the SpinlockGuard will release the lock it was created from.
-    fn drop(&mut self) {
-        self.dequeue.fetch_add(1, Ordering::SeqCst);
-    }
-}
-
-/// Realize a priority queue for tasks
-struct PriorityQueue {
-    queues: [Option<VecDeque<abi::Tid>>; abi::NO_PRIORITIES],
-    prio_bitmap: u64,
-}
-
-impl PriorityQueue {
-    pub const fn new() -> PriorityQueue {
-        PriorityQueue {
-            queues: [
-                None, None, None, None, None, None, None, None, None, None, None, None, None, None,
-                None, None, None, None, None, None, None, None, None, None, None, None, None, None,
-                None, None, None,
-            ],
-            prio_bitmap: 0,
-        }
-    }
-
-    /// Add a task id by its priority to the queue
-    pub fn push(&mut self, prio: abi::Priority, id: abi::Tid) {
-        let i: usize = prio.into().into();
-        self.prio_bitmap |= (1 << i) as u64;
-        if let Some(queue) = &mut self.queues[i] {
-            queue.push_back(id);
-        } else {
-            let mut queue = VecDeque::new();
-            queue.push_back(id);
-            self.queues[i] = Some(queue);
-        }
-    }
-
-    fn pop_from_queue(&mut self, queue_index: usize) -> Option<abi::Tid> {
-        if let Some(queue) = &mut self.queues[queue_index] {
-            let id = queue.pop_front();
-
-            if queue.is_empty() {
-                self.prio_bitmap &= !(1 << queue_index as u64);
-            }
-
-            id
-        } else {
-            None
-        }
-    }
-
-    /// Pop the task handle with the highest priority from the queue
-    pub fn pop(&mut self) -> Option<abi::Tid> {
-        for i in 0..abi::NO_PRIORITIES {
-            if self.prio_bitmap & (1 << i) != 0 {
-                return self.pop_from_queue(i);
-            }
-        }
-
-        None
-    }
-}
-
-struct MutexInner {
-    locked: bool,
-    blocked_task: PriorityQueue,
-}
-
-impl MutexInner {
-    pub const fn new() -> MutexInner {
-        MutexInner { locked: false, blocked_task: PriorityQueue::new() }
-    }
-}
-
-pub struct Mutex {
-    inner: Spinlock<MutexInner>,
-}
-
-pub type MovableMutex = Mutex;
-
-unsafe impl Send for Mutex {}
-unsafe impl Sync for Mutex {}
-
-impl Mutex {
-    pub const fn new() -> Mutex {
-        Mutex { inner: Spinlock::new(MutexInner::new()) }
-    }
-
-    #[inline]
-    pub unsafe fn lock(&self) {
-        loop {
-            let mut guard = self.inner.lock();
-            if guard.locked == false {
-                guard.locked = true;
-                return;
-            } else {
-                let prio = abi::get_priority();
-                let id = abi::getpid();
-
-                guard.blocked_task.push(prio, id);
-                abi::block_current_task();
-                drop(guard);
-                abi::yield_now();
-            }
-        }
-    }
-
-    #[inline]
-    pub unsafe fn unlock(&self) {
-        let mut guard = self.inner.lock();
-        guard.locked = false;
-        if let Some(tid) = guard.blocked_task.pop() {
-            abi::wakeup_task(tid);
-        }
-    }
-
-    #[inline]
-    pub unsafe fn try_lock(&self) -> bool {
-        let mut guard = self.inner.lock();
-        if guard.locked == false {
-            guard.locked = true;
-        }
-        guard.locked
-    }
-}

library/std/src/sys/hermit/rwlock.rs

@@ -1,143 +0,0 @@
-use crate::cell::UnsafeCell;
-use crate::sys::locks::{MovableCondvar, Mutex};
-
-pub struct RwLock {
-    lock: Mutex,
-    cond: MovableCondvar,
-    state: UnsafeCell<State>,
-}
-
-pub type MovableRwLock = RwLock;
-
-enum State {
-    Unlocked,
-    Reading(usize),
-    Writing,
-}
-
-unsafe impl Send for RwLock {}
-unsafe impl Sync for RwLock {}
-
-// This rwlock implementation is a relatively simple implementation which has a
-// condition variable for readers/writers as well as a mutex protecting the
-// internal state of the lock. A current downside of the implementation is that
-// unlocking the lock will notify *all* waiters rather than just readers or just
-// writers. This can cause lots of "thundering stampede" problems. While
-// hopefully correct this implementation is very likely to want to be changed in
-// the future.
-
-impl RwLock {
-    pub const fn new() -> RwLock {
-        RwLock {
-            lock: Mutex::new(),
-            cond: MovableCondvar::new(),
-            state: UnsafeCell::new(State::Unlocked),
-        }
-    }
-
-    #[inline]
-    pub unsafe fn read(&self) {
-        self.lock.lock();
-        while !(*self.state.get()).inc_readers() {
-            self.cond.wait(&self.lock);
-        }
-        self.lock.unlock();
-    }
-
-    #[inline]
-    pub unsafe fn try_read(&self) -> bool {
-        self.lock.lock();
-        let ok = (*self.state.get()).inc_readers();
-        self.lock.unlock();
-        return ok;
-    }
-
-    #[inline]
-    pub unsafe fn write(&self) {
-        self.lock.lock();
-        while !(*self.state.get()).inc_writers() {
-            self.cond.wait(&self.lock);
-        }
-        self.lock.unlock();
-    }
-
-    #[inline]
-    pub unsafe fn try_write(&self) -> bool {
-        self.lock.lock();
-        let ok = (*self.state.get()).inc_writers();
-        self.lock.unlock();
-        return ok;
-    }
-
-    #[inline]
-    pub unsafe fn read_unlock(&self) {
-        self.lock.lock();
-        let notify = (*self.state.get()).dec_readers();
-        self.lock.unlock();
-        if notify {
-            // FIXME: should only wake up one of these some of the time
-            self.cond.notify_all();
-        }
-    }
-
-    #[inline]
-    pub unsafe fn write_unlock(&self) {
-        self.lock.lock();
-        (*self.state.get()).dec_writers();
-        self.lock.unlock();
-        // FIXME: should only wake up one of these some of the time
-        self.cond.notify_all();
-    }
-}
-
-impl State {
-    fn inc_readers(&mut self) -> bool {
-        match *self {
-            State::Unlocked => {
-                *self = State::Reading(1);
-                true
-            }
-            State::Reading(ref mut cnt) => {
-                *cnt += 1;
-                true
-            }
-            State::Writing => false,
-        }
-    }
-
-    fn inc_writers(&mut self) -> bool {
-        match *self {
-            State::Unlocked => {
-                *self = State::Writing;
-                true
-            }
-            State::Reading(_) | State::Writing => false,
-        }
-    }
-
-    fn dec_readers(&mut self) -> bool {
-        let zero = match *self {
-            State::Reading(ref mut cnt) => {
-                *cnt -= 1;
-                *cnt == 0
-            }
-            State::Unlocked | State::Writing => invalid(),
-        };
-        if zero {
-            *self = State::Unlocked;
-        }
-        zero
-    }
-
-    fn dec_writers(&mut self) {
-        match *self {
-            State::Writing => {}
-            State::Unlocked | State::Reading(_) => invalid(),
-        }
-        *self = State::Unlocked;
-    }
-}
-
-fn invalid() -> ! {
-    panic!("inconsistent rwlock");
-}

library/std/src/sys_common/thread_parker/mod.rs

@@ -7,6 +7,7 @@ cfg_if::cfg_if! {
         target_os = "openbsd",
         target_os = "dragonfly",
         target_os = "fuchsia",
+        target_os = "hermit",
     ))] {
         mod futex;
         pub use futex::Parker;