Auto merge of #96042 - m-ou-se:one-reentrant-mutex, r=Amanieu

Use a single ReentrantMutex implementation on all platforms.

This replaces all platform specific ReentrantMutex implementations by the one I added in #95727 for Linux, since that one does not depend on any platform specific details.

r? `@Amanieu`

Author: bors

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

@@ -1,6 +1,5 @@
 use crate::cell::UnsafeCell;
 use crate::collections::VecDeque;
-use crate::ffi::c_void;
 use crate::hint;
 use crate::ops::{Deref, DerefMut, Drop};
 use crate::ptr;
@@ -220,38 +219,3 @@ impl Mutex {
     #[inline]
     pub unsafe fn destroy(&self) {}
 }
-
-pub struct ReentrantMutex {
-    inner: *const c_void,
-}
-
-impl ReentrantMutex {
-    pub const unsafe fn uninitialized() -> ReentrantMutex {
-        ReentrantMutex { inner: ptr::null() }
-    }
-
-    #[inline]
-    pub unsafe fn init(&self) {
-        let _ = abi::recmutex_init(&self.inner as *const *const c_void as *mut _);
-    }
-
-    #[inline]
-    pub unsafe fn lock(&self) {
-        let _ = abi::recmutex_lock(self.inner);
-    }
-
-    #[inline]
-    pub unsafe fn try_lock(&self) -> bool {
-        true
-    }
-
-    #[inline]
-    pub unsafe fn unlock(&self) {
-        let _ = abi::recmutex_unlock(self.inner);
-    }
-
-    #[inline]
-    pub unsafe fn destroy(&self) {
-        let _ = abi::recmutex_destroy(self.inner);
-    }
-}

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

@@ -5,7 +5,6 @@ use super::{
     error::{expect_success, expect_success_aborting, fail, ItronError},
     spin::SpinIdOnceCell,
 };
-use crate::cell::UnsafeCell;
 
 pub struct Mutex {
     /// The ID of the underlying mutex object
@@ -89,95 +88,3 @@ impl Drop for MutexGuard<'_> {
         unsafe { self.0.unlock() };
     }
 }
-
-// All empty stubs because this platform does not yet support threads, so lock
-// acquisition always succeeds.
-pub struct ReentrantMutex {
-    /// The ID of the underlying mutex object
-    mtx: abi::ID,
-    /// The lock count.
-    count: UnsafeCell<usize>,
-}
-
-unsafe impl Send for ReentrantMutex {}
-unsafe impl Sync for ReentrantMutex {}
-
-impl ReentrantMutex {
-    pub const unsafe fn uninitialized() -> ReentrantMutex {
-        ReentrantMutex { mtx: 0, count: UnsafeCell::new(0) }
-    }
-
-    pub unsafe fn init(&mut self) {
-        self.mtx = expect_success(
-            unsafe {
-                abi::acre_mtx(&abi::T_CMTX {
-                    // Priority inheritance mutex
-                    mtxatr: abi::TA_INHERIT,
-                    // Unused
-                    ceilpri: 0,
-                })
-            },
-            &"acre_mtx",
-        );
-    }
-
-    pub unsafe fn lock(&self) {
-        match unsafe { abi::loc_mtx(self.mtx) } {
-            abi::E_OBJ => {
-                // Recursive lock
-                unsafe {
-                    let count = &mut *self.count.get();
-                    if let Some(new_count) = count.checked_add(1) {
-                        *count = new_count;
-                    } else {
-                        // counter overflow
-                        rtabort!("lock count overflow");
-                    }
-                }
-            }
-            er => {
-                expect_success(er, &"loc_mtx");
-            }
-        }
-    }
-
-    pub unsafe fn unlock(&self) {
-        unsafe {
-            let count = &mut *self.count.get();
-            if *count > 0 {
-                *count -= 1;
-                return;
-            }
-        }
-
-        expect_success_aborting(unsafe { abi::unl_mtx(self.mtx) }, &"unl_mtx");
-    }
-
-    pub unsafe fn try_lock(&self) -> bool {
-        let er = unsafe { abi::ploc_mtx(self.mtx) };
-        if er == abi::E_OBJ {
-            // Recursive lock
-            unsafe {
-                let count = &mut *self.count.get();
-                if let Some(new_count) = count.checked_add(1) {
-                    *count = new_count;
-                } else {
-                    // counter overflow
-                    rtabort!("lock count overflow");
-                }
-            }
-            true
-        } else if er == abi::E_TMOUT {
-            // Locked by another thread
-            false
-        } else {
-            expect_success(er, &"ploc_mtx");
-            // Top-level lock by the current thread
-            true
-        }
-    }
-
-    pub unsafe fn destroy(&self) {
-        expect_success_aborting(unsafe { abi::del_mtx(self.mtx) }, &"del_mtx");
-    }
-}

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

@@ -1,8 +1,4 @@
-use fortanix_sgx_abi::Tcs;
-
-use super::abi::thread;
-
-use super::waitqueue::{try_lock_or_false, NotifiedTcs, SpinMutex, WaitQueue, WaitVariable};
+use super::waitqueue::{try_lock_or_false, SpinMutex, WaitQueue, WaitVariable};
 
 pub struct Mutex {
     inner: SpinMutex<WaitVariable<bool>>,
@@ -60,84 +56,3 @@ impl Mutex {
     #[inline]
     pub unsafe fn destroy(&self) {}
 }
-
-struct ReentrantLock {
-    owner: Option<Tcs>,
-    count: usize,
-}
-
-pub struct ReentrantMutex {
-    inner: SpinMutex<WaitVariable<ReentrantLock>>,
-}
-
-impl ReentrantMutex {
-    pub const fn uninitialized() -> ReentrantMutex {
-        ReentrantMutex {
-            inner: SpinMutex::new(WaitVariable::new(ReentrantLock { owner: None, count: 0 })),
-        }
-    }
-
-    #[inline]
-    pub unsafe fn init(&self) {}
-
-    #[inline]
-    pub unsafe fn lock(&self) {
-        let mut guard = self.inner.lock();
-        match guard.lock_var().owner {
-            Some(tcs) if tcs != thread::current() => {
-                // Another thread has the lock, wait
-                WaitQueue::wait(guard, || {});
-                // Another thread has passed the lock to us
-            }
-            _ => {
-                // We are just now obtaining the lock
-                guard.lock_var_mut().owner = Some(thread::current());
-                guard.lock_var_mut().count += 1;
-            }
-        }
-    }
-
-    #[inline]
-    pub unsafe fn unlock(&self) {
-        let mut guard = self.inner.lock();
-        if guard.lock_var().count > 1 {
-            guard.lock_var_mut().count -= 1;
-        } else {
-            match WaitQueue::notify_one(guard) {
-                Err(mut guard) => {
-                    // No other waiters, unlock
-                    guard.lock_var_mut().count = 0;
-                    guard.lock_var_mut().owner = None;
-                }
-                Ok(mut guard) => {
-                    // There was a thread waiting, just pass the lock
-                    if let NotifiedTcs::Single(tcs) = guard.notified_tcs() {
-                        guard.lock_var_mut().owner = Some(tcs)
-                    } else {
-                        unreachable!() // called notify_one
-                    }
-                }
-            }
-        }
-    }
-
-    #[inline]
-    pub unsafe fn try_lock(&self) -> bool {
-        let mut guard = try_lock_or_false!(self.inner);
-        match guard.lock_var().owner {
-            Some(tcs) if tcs != thread::current() => {
-                // Another thread has the lock
-                false
-            }
-            _ => {
-                // We are just now obtaining the lock
-                guard.lock_var_mut().owner = Some(thread::current());
-                guard.lock_var_mut().count += 1;
-                true
-            }
-        }
-    }
-
-    #[inline]
-    pub unsafe fn destroy(&self) {}
-}

library/std/src/sys/unix/locks/futex.rs

@@ -1,6 +1,5 @@
-use crate::cell::UnsafeCell;
 use crate::sync::atomic::{
-    AtomicU32, AtomicUsize,
+    AtomicU32,
     Ordering::{Acquire, Relaxed, Release},
 };
 use crate::sys::futex::{futex_wait, futex_wake, futex_wake_all};
@@ -163,98 +162,3 @@ impl Condvar {
         r
     }
 }
-
-/// A reentrant mutex. Used by stdout().lock() and friends.
-///
-/// The 'owner' field tracks which thread has locked the mutex.
-///
-/// We use current_thread_unique_ptr() as the thread identifier,
-/// which is just the address of a thread local variable.
-///
-/// If `owner` is set to the identifier of the current thread,
-/// we assume the mutex is already locked and instead of locking it again,
-/// we increment `lock_count`.
-///
-/// When unlocking, we decrement `lock_count`, and only unlock the mutex when
-/// it reaches zero.
-///
-/// `lock_count` is protected by the mutex and only accessed by the thread that has
-/// locked the mutex, so needs no synchronization.
-///
-/// `owner` can be checked by other threads that want to see if they already
-/// hold the lock, so needs to be atomic. If it compares equal, we're on the
-/// same thread that holds the mutex and memory access can use relaxed ordering
-/// since we're not dealing with multiple threads. If it compares unequal,
-/// synchronization is left to the mutex, making relaxed memory ordering for
-/// the `owner` field fine in all cases.
-pub struct ReentrantMutex {
-    mutex: Mutex,
-    owner: AtomicUsize,
-    lock_count: UnsafeCell<u32>,
-}
-
-unsafe impl Send for ReentrantMutex {}
-unsafe impl Sync for ReentrantMutex {}
-
-impl ReentrantMutex {
-    #[inline]
-    pub const unsafe fn uninitialized() -> Self {
-        Self { mutex: Mutex::new(), owner: AtomicUsize::new(0), lock_count: UnsafeCell::new(0) }
-    }
-
-    #[inline]
-    pub unsafe fn init(&self) {}
-
-    #[inline]
-    pub unsafe fn destroy(&self) {}
-
-    pub unsafe fn try_lock(&self) -> bool {
-        let this_thread = current_thread_unique_ptr();
-        if self.owner.load(Relaxed) == this_thread {
-            self.increment_lock_count();
-            true
-        } else if self.mutex.try_lock() {
-            self.owner.store(this_thread, Relaxed);
-            debug_assert_eq!(*self.lock_count.get(), 0);
-            *self.lock_count.get() = 1;
-            true
-        } else {
-            false
-        }
-    }
-
-    pub unsafe fn lock(&self) {
-        let this_thread = current_thread_unique_ptr();
-        if self.owner.load(Relaxed) == this_thread {
-            self.increment_lock_count();
-        } else {
-            self.mutex.lock();
-            self.owner.store(this_thread, Relaxed);
-            debug_assert_eq!(*self.lock_count.get(), 0);
-            *self.lock_count.get() = 1;
-        }
-    }
-
-    unsafe fn increment_lock_count(&self) {
-        *self.lock_count.get() = (*self.lock_count.get())
-            .checked_add(1)
-            .expect("lock count overflow in reentrant mutex");
-    }
-
-    pub unsafe fn unlock(&self) {
-        *self.lock_count.get() -= 1;
-        if *self.lock_count.get() == 0 {
-            self.owner.store(0, Relaxed);
-            self.mutex.unlock();
-        }
-    }
-}
-
-/// Get an address that is unique per running thread.
-///
-/// This can be used as a non-null usize-sized ID.
-pub fn current_thread_unique_ptr() -> usize {
-    // Use a non-drop type to make sure it's still available during thread destruction.
-    thread_local! { static X: u8 = const { 0 } }
-    X.with(|x| <*const _>::addr(x))
-}

library/std/src/sys/unix/locks/mod.rs

@@ -5,15 +5,13 @@ cfg_if::cfg_if! {
     ))] {
         mod futex;
         mod futex_rwlock;
-        pub use futex::{Mutex, MovableMutex, Condvar, MovableCondvar, ReentrantMutex};
+        pub use futex::{Mutex, MovableMutex, Condvar, MovableCondvar};
         pub use futex_rwlock::{RwLock, MovableRwLock};
     } else {
         mod pthread_mutex;
-        mod pthread_remutex;
         mod pthread_rwlock;
         mod pthread_condvar;
         pub use pthread_mutex::{Mutex, MovableMutex};
-        pub use pthread_remutex::ReentrantMutex;
         pub use pthread_rwlock::{RwLock, MovableRwLock};
         pub use pthread_condvar::{Condvar, MovableCondvar};
     }