diff options
Diffstat (limited to 'library/std/src/sys_common')
| -rw-r--r-- | library/std/src/sys_common/backtrace.rs | 9 | ||||
| -rw-r--r-- | library/std/src/sys_common/condvar.rs | 1 | ||||
| -rw-r--r-- | library/std/src/sys_common/condvar/check.rs | 1 | ||||
| -rw-r--r-- | library/std/src/sys_common/mod.rs | 10 | ||||
| -rw-r--r-- | library/std/src/sys_common/mutex.rs | 45 | ||||
| -rw-r--r-- | library/std/src/sys_common/net.rs | 20 | ||||
| -rw-r--r-- | library/std/src/sys_common/once/futex.rs | 134 | ||||
| -rw-r--r-- | library/std/src/sys_common/once/generic.rs | 282 | ||||
| -rw-r--r-- | library/std/src/sys_common/once/mod.rs | 43 | ||||
| -rw-r--r-- | library/std/src/sys_common/rwlock.rs | 1 | ||||
| -rw-r--r-- | library/std/src/sys_common/thread_local_key.rs | 24 |
11 files changed, 488 insertions, 82 deletions
diff --git a/library/std/src/sys_common/backtrace.rs b/library/std/src/sys_common/backtrace.rs index 31164afdc7b..8807077cb49 100644 --- a/library/std/src/sys_common/backtrace.rs +++ b/library/std/src/sys_common/backtrace.rs @@ -7,15 +7,14 @@ use crate::fmt; use crate::io; use crate::io::prelude::*; use crate::path::{self, Path, PathBuf}; -use crate::sys_common::mutex::StaticMutex; +use crate::sync::{Mutex, PoisonError}; /// Max number of frames to print. const MAX_NB_FRAMES: usize = 100; -// SAFETY: Don't attempt to lock this reentrantly. -pub unsafe fn lock() -> impl Drop { - static LOCK: StaticMutex = StaticMutex::new(); - LOCK.lock() +pub fn lock() -> impl Drop { + static LOCK: Mutex<()> = Mutex::new(()); + LOCK.lock().unwrap_or_else(PoisonError::into_inner) } /// Prints the current backtrace. diff --git a/library/std/src/sys_common/condvar.rs b/library/std/src/sys_common/condvar.rs index f3ac1061b89..8bc5b24115d 100644 --- a/library/std/src/sys_common/condvar.rs +++ b/library/std/src/sys_common/condvar.rs @@ -15,6 +15,7 @@ pub struct Condvar { impl Condvar { /// Creates a new condition variable for use. #[inline] + #[rustc_const_stable(feature = "const_locks", since = "1.63.0")] pub const fn new() -> Self { Self { inner: imp::MovableCondvar::new(), check: CondvarCheck::new() } } diff --git a/library/std/src/sys_common/condvar/check.rs b/library/std/src/sys_common/condvar/check.rs index ce8f3670487..4ac9e62bf86 100644 --- a/library/std/src/sys_common/condvar/check.rs +++ b/library/std/src/sys_common/condvar/check.rs @@ -50,6 +50,7 @@ pub struct NoCheck; #[allow(dead_code)] impl NoCheck { + #[rustc_const_stable(feature = "const_locks", since = "1.63.0")] pub const fn new() -> Self { Self } diff --git a/library/std/src/sys_common/mod.rs b/library/std/src/sys_common/mod.rs index 80f56bf7522..8c19f9332dc 100644 --- a/library/std/src/sys_common/mod.rs +++ b/library/std/src/sys_common/mod.rs @@ -27,17 +27,25 @@ pub mod io; pub mod lazy_box; pub mod memchr; pub mod mutex; +pub mod once; pub mod process; pub mod remutex; pub mod rwlock; pub mod thread; pub mod thread_info; pub mod thread_local_dtor; -pub mod thread_local_key; pub mod thread_parker; pub mod wtf8; cfg_if::cfg_if! { + if #[cfg(target_os = "windows")] { + pub use crate::sys::thread_local_key; + } else { + pub mod thread_local_key; + } +} + +cfg_if::cfg_if! { if #[cfg(any(target_os = "l4re", target_os = "hermit", feature = "restricted-std", diff --git a/library/std/src/sys_common/mutex.rs b/library/std/src/sys_common/mutex.rs index 48479f5bdb3..98046f20f89 100644 --- a/library/std/src/sys_common/mutex.rs +++ b/library/std/src/sys_common/mutex.rs @@ -1,49 +1,5 @@ use crate::sys::locks as imp; -/// An OS-based mutual exclusion lock, meant for use in static variables. -/// -/// This mutex has a const constructor ([`StaticMutex::new`]), does not -/// implement `Drop` to cleanup resources, and causes UB when used reentrantly. -/// -/// This mutex does not implement poisoning. -/// -/// This is a wrapper around `imp::Mutex` that does *not* call `init()` and -/// `destroy()`. -pub struct StaticMutex(imp::Mutex); - -unsafe impl Sync for StaticMutex {} - -impl StaticMutex { - /// Creates a new mutex for use. - #[inline] - pub const fn new() -> Self { - Self(imp::Mutex::new()) - } - - /// Calls raw_lock() and then returns an RAII guard to guarantee the mutex - /// will be unlocked. - /// - /// It is undefined behaviour to call this function while locked by the - /// same thread. - #[inline] - pub unsafe fn lock(&'static self) -> StaticMutexGuard { - self.0.lock(); - StaticMutexGuard(&self.0) - } -} - -#[must_use] -pub struct StaticMutexGuard(&'static imp::Mutex); - -impl Drop for StaticMutexGuard { - #[inline] - fn drop(&mut self) { - unsafe { - self.0.unlock(); - } - } -} - /// An OS-based mutual exclusion lock. /// /// This mutex cleans up its resources in its `Drop` implementation, may safely @@ -61,6 +17,7 @@ unsafe impl Sync for MovableMutex {} impl MovableMutex { /// Creates a new mutex. #[inline] + #[rustc_const_stable(feature = "const_locks", since = "1.63.0")] pub const fn new() -> Self { Self(imp::MovableMutex::new()) } diff --git a/library/std/src/sys_common/net.rs b/library/std/src/sys_common/net.rs index 3ad802afa8f..fad4a63331b 100644 --- a/library/std/src/sys_common/net.rs +++ b/library/std/src/sys_common/net.rs @@ -2,12 +2,13 @@ mod tests; use crate::cmp; -use crate::ffi::CString; +use crate::convert::{TryFrom, TryInto}; use crate::fmt; use crate::io::{self, ErrorKind, IoSlice, IoSliceMut}; use crate::mem; use crate::net::{Ipv4Addr, Ipv6Addr, Shutdown, SocketAddr}; use crate::ptr; +use crate::sys::common::small_c_string::run_with_cstr; use crate::sys::net::netc as c; use crate::sys::net::{cvt, cvt_gai, cvt_r, init, wrlen_t, Socket}; use crate::sys_common::{AsInner, FromInner, IntoInner}; @@ -197,14 +198,15 @@ impl<'a> TryFrom<(&'a str, u16)> for LookupHost { fn try_from((host, port): (&'a str, u16)) -> io::Result<LookupHost> { init(); - let c_host = CString::new(host)?; - let mut hints: c::addrinfo = unsafe { mem::zeroed() }; - hints.ai_socktype = c::SOCK_STREAM; - let mut res = ptr::null_mut(); - unsafe { - cvt_gai(c::getaddrinfo(c_host.as_ptr(), ptr::null(), &hints, &mut res)) - .map(|_| LookupHost { original: res, cur: res, port }) - } + run_with_cstr(host.as_bytes(), |c_host| { + let mut hints: c::addrinfo = unsafe { mem::zeroed() }; + hints.ai_socktype = c::SOCK_STREAM; + let mut res = ptr::null_mut(); + unsafe { + cvt_gai(c::getaddrinfo(c_host.as_ptr(), ptr::null(), &hints, &mut res)) + .map(|_| LookupHost { original: res, cur: res, port }) + } + }) } } diff --git a/library/std/src/sys_common/once/futex.rs b/library/std/src/sys_common/once/futex.rs new file mode 100644 index 00000000000..5c7e6c01371 --- /dev/null +++ b/library/std/src/sys_common/once/futex.rs @@ -0,0 +1,134 @@ +use crate::cell::Cell; +use crate::sync as public; +use crate::sync::atomic::{ + AtomicU32, + Ordering::{Acquire, Relaxed, Release}, +}; +use crate::sys::futex::{futex_wait, futex_wake_all}; + +// On some platforms, the OS is very nice and handles the waiter queue for us. +// This means we only need one atomic value with 5 states: + +/// No initialization has run yet, and no thread is currently using the Once. +const INCOMPLETE: u32 = 0; +/// Some thread has previously attempted to initialize the Once, but it panicked, +/// so the Once is now poisoned. There are no other threads currently accessing +/// this Once. +const POISONED: u32 = 1; +/// Some thread is currently attempting to run initialization. It may succeed, +/// so all future threads need to wait for it to finish. +const RUNNING: u32 = 2; +/// Some thread is currently attempting to run initialization and there are threads +/// waiting for it to finish. +const QUEUED: u32 = 3; +/// Initialization has completed and all future calls should finish immediately. +const COMPLETE: u32 = 4; + +// Threads wait by setting the state to QUEUED and calling `futex_wait` on the state +// variable. When the running thread finishes, it will wake all waiting threads using +// `futex_wake_all`. + +pub struct OnceState { + poisoned: bool, + set_state_to: Cell<u32>, +} + +impl OnceState { + #[inline] + pub fn is_poisoned(&self) -> bool { + self.poisoned + } + + #[inline] + pub fn poison(&self) { + self.set_state_to.set(POISONED); + } +} + +struct CompletionGuard<'a> { + state: &'a AtomicU32, + set_state_on_drop_to: u32, +} + +impl<'a> Drop for CompletionGuard<'a> { + fn drop(&mut self) { + // Use release ordering to propagate changes to all threads checking + // up on the Once. `futex_wake_all` does its own synchronization, hence + // we do not need `AcqRel`. + if self.state.swap(self.set_state_on_drop_to, Release) == QUEUED { + futex_wake_all(&self.state); + } + } +} + +pub struct Once { + state: AtomicU32, +} + +impl Once { + #[inline] + pub const fn new() -> Once { + Once { state: AtomicU32::new(INCOMPLETE) } + } + + #[inline] + pub fn is_completed(&self) -> bool { + // Use acquire ordering to make all initialization changes visible to the + // current thread. + self.state.load(Acquire) == COMPLETE + } + + // This uses FnMut to match the API of the generic implementation. As this + // implementation is quite light-weight, it is generic over the closure and + // so avoids the cost of dynamic dispatch. + #[cold] + #[track_caller] + pub fn call(&self, ignore_poisoning: bool, f: &mut impl FnMut(&public::OnceState)) { + let mut state = self.state.load(Acquire); + loop { + match state { + POISONED if !ignore_poisoning => { + // Panic to propagate the poison. + panic!("Once instance has previously been poisoned"); + } + INCOMPLETE | POISONED => { + // Try to register the current thread as the one running. + if let Err(new) = + self.state.compare_exchange_weak(state, RUNNING, Acquire, Acquire) + { + state = new; + continue; + } + // `waiter_queue` will manage other waiting threads, and + // wake them up on drop. + let mut waiter_queue = + CompletionGuard { state: &self.state, set_state_on_drop_to: POISONED }; + // Run the function, letting it know if we're poisoned or not. + let f_state = public::OnceState { + inner: OnceState { + poisoned: state == POISONED, + set_state_to: Cell::new(COMPLETE), + }, + }; + f(&f_state); + waiter_queue.set_state_on_drop_to = f_state.inner.set_state_to.get(); + return; + } + RUNNING | QUEUED => { + // Set the state to QUEUED if it is not already. + if state == RUNNING + && let Err(new) = self.state.compare_exchange_weak(RUNNING, QUEUED, Relaxed, Acquire) + { + state = new; + continue; + } + + futex_wait(&self.state, QUEUED, None); + state = self.state.load(Acquire); + } + COMPLETE => return, + _ => unreachable!("state is never set to invalid values"), + } + } + } +} diff --git a/library/std/src/sys_common/once/generic.rs b/library/std/src/sys_common/once/generic.rs new file mode 100644 index 00000000000..acf5f247164 --- /dev/null +++ b/library/std/src/sys_common/once/generic.rs @@ -0,0 +1,282 @@ +// Each `Once` has one word of atomic state, and this state is CAS'd on to +// determine what to do. There are four possible state of a `Once`: +// +// * Incomplete - no initialization has run yet, and no thread is currently +// using the Once. +// * Poisoned - some thread has previously attempted to initialize the Once, but +// it panicked, so the Once is now poisoned. There are no other +// threads currently accessing this Once. +// * Running - some thread is currently attempting to run initialization. It may +// succeed, so all future threads need to wait for it to finish. +// Note that this state is accompanied with a payload, described +// below. +// * Complete - initialization has completed and all future calls should finish +// immediately. +// +// With 4 states we need 2 bits to encode this, and we use the remaining bits +// in the word we have allocated as a queue of threads waiting for the thread +// responsible for entering the RUNNING state. This queue is just a linked list +// of Waiter nodes which is monotonically increasing in size. Each node is +// allocated on the stack, and whenever the running closure finishes it will +// consume the entire queue and notify all waiters they should try again. +// +// You'll find a few more details in the implementation, but that's the gist of +// it! +// +// Atomic orderings: +// When running `Once` we deal with multiple atomics: +// `Once.state_and_queue` and an unknown number of `Waiter.signaled`. +// * `state_and_queue` is used (1) as a state flag, (2) for synchronizing the +// result of the `Once`, and (3) for synchronizing `Waiter` nodes. +// - At the end of the `call` function we have to make sure the result +// of the `Once` is acquired. So every load which can be the only one to +// load COMPLETED must have at least acquire ordering, which means all +// three of them. +// - `WaiterQueue::drop` is the only place that may store COMPLETED, and +// must do so with release ordering to make the result available. +// - `wait` inserts `Waiter` nodes as a pointer in `state_and_queue`, and +// needs to make the nodes available with release ordering. The load in +// its `compare_exchange` can be relaxed because it only has to compare +// the atomic, not to read other data. +// - `WaiterQueue::drop` must see the `Waiter` nodes, so it must load +// `state_and_queue` with acquire ordering. +// - There is just one store where `state_and_queue` is used only as a +// state flag, without having to synchronize data: switching the state +// from INCOMPLETE to RUNNING in `call`. This store can be Relaxed, +// but the read has to be Acquire because of the requirements mentioned +// above. +// * `Waiter.signaled` is both used as a flag, and to protect a field with +// interior mutability in `Waiter`. `Waiter.thread` is changed in +// `WaiterQueue::drop` which then sets `signaled` with release ordering. +// After `wait` loads `signaled` with acquire ordering and sees it is true, +// it needs to see the changes to drop the `Waiter` struct correctly. +// * There is one place where the two atomics `Once.state_and_queue` and +// `Waiter.signaled` come together, and might be reordered by the compiler or +// processor. Because both use acquire ordering such a reordering is not +// allowed, so no need for `SeqCst`. + +use crate::cell::Cell; +use crate::fmt; +use crate::ptr; +use crate::sync as public; +use crate::sync::atomic::{AtomicBool, AtomicPtr, Ordering}; +use crate::thread::{self, Thread}; + +type Masked = (); + +pub struct Once { + state_and_queue: AtomicPtr<Masked>, +} + +pub struct OnceState { + poisoned: bool, + set_state_on_drop_to: Cell<*mut Masked>, +} + +// Four states that a Once can be in, encoded into the lower bits of +// `state_and_queue` in the Once structure. +const INCOMPLETE: usize = 0x0; +const POISONED: usize = 0x1; +const RUNNING: usize = 0x2; +const COMPLETE: usize = 0x3; + +// Mask to learn about the state. All other bits are the queue of waiters if +// this is in the RUNNING state. +const STATE_MASK: usize = 0x3; + +// Representation of a node in the linked list of waiters, used while in the +// RUNNING state. +// Note: `Waiter` can't hold a mutable pointer to the next thread, because then +// `wait` would both hand out a mutable reference to its `Waiter` node, and keep +// a shared reference to check `signaled`. Instead we hold shared references and +// use interior mutability. +#[repr(align(4))] // Ensure the two lower bits are free to use as state bits. +struct Waiter { + thread: Cell<Option<Thread>>, + signaled: AtomicBool, + next: *const Waiter, +} + +// Head of a linked list of waiters. +// Every node is a struct on the stack of a waiting thread. +// Will wake up the waiters when it gets dropped, i.e. also on panic. +struct WaiterQueue<'a> { + state_and_queue: &'a AtomicPtr<Masked>, + set_state_on_drop_to: *mut Masked, +} + +impl Once { + #[inline] + pub const fn new() -> Once { + Once { state_and_queue: AtomicPtr::new(ptr::invalid_mut(INCOMPLETE)) } + } + + #[inline] + pub fn is_completed(&self) -> bool { + // An `Acquire` load is enough because that makes all the initialization + // operations visible to us, and, this being a fast path, weaker + // ordering helps with performance. This `Acquire` synchronizes with + // `Release` operations on the slow path. + self.state_and_queue.load(Ordering::Acquire).addr() == COMPLETE + } + + // This is a non-generic function to reduce the monomorphization cost of + // using `call_once` (this isn't exactly a trivial or small implementation). + // + // Additionally, this is tagged with `#[cold]` as it should indeed be cold + // and it helps let LLVM know that calls to this function should be off the + // fast path. Essentially, this should help generate more straight line code + // in LLVM. + // + // Finally, this takes an `FnMut` instead of a `FnOnce` because there's + // currently no way to take an `FnOnce` and call it via virtual dispatch + // without some allocation overhead. + #[cold] + #[track_caller] + pub fn call(&self, ignore_poisoning: bool, init: &mut dyn FnMut(&public::OnceState)) { + let mut state_and_queue = self.state_and_queue.load(Ordering::Acquire); + loop { + match state_and_queue.addr() { + COMPLETE => break, + POISONED if !ignore_poisoning => { + // Panic to propagate the poison. + panic!("Once instance has previously been poisoned"); + } + POISONED | INCOMPLETE => { + // Try to register this thread as the one RUNNING. + let exchange_result = self.state_and_queue.compare_exchange( + state_and_queue, + ptr::invalid_mut(RUNNING), + Ordering::Acquire, + Ordering::Acquire, + ); + if let Err(old) = exchange_result { + state_and_queue = old; + continue; + } + // `waiter_queue` will manage other waiting threads, and + // wake them up on drop. + let mut waiter_queue = WaiterQueue { + state_and_queue: &self.state_and_queue, + set_state_on_drop_to: ptr::invalid_mut(POISONED), + }; + // Run the initialization function, letting it know if we're + // poisoned or not. + let init_state = public::OnceState { + inner: OnceState { + poisoned: state_and_queue.addr() == POISONED, + set_state_on_drop_to: Cell::new(ptr::invalid_mut(COMPLETE)), + }, + }; + init(&init_state); + waiter_queue.set_state_on_drop_to = init_state.inner.set_state_on_drop_to.get(); + break; + } + _ => { + // All other values must be RUNNING with possibly a + // pointer to the waiter queue in the more significant bits. + assert!(state_and_queue.addr() & STATE_MASK == RUNNING); + wait(&self.state_and_queue, state_and_queue); + state_and_queue = self.state_and_queue.load(Ordering::Acquire); + } + } + } + } +} + +fn wait(state_and_queue: &AtomicPtr<Masked>, mut current_state: *mut Masked) { + // Note: the following code was carefully written to avoid creating a + // mutable reference to `node` that gets aliased. + loop { + // Don't queue this thread if the status is no longer running, + // otherwise we will not be woken up. + if current_state.addr() & STATE_MASK != RUNNING { + return; + } + + // Create the node for our current thread. + let node = Waiter { + thread: Cell::new(Some(thread::current())), + signaled: AtomicBool::new(false), + next: current_state.with_addr(current_state.addr() & !STATE_MASK) as *const Waiter, + }; + let me = &node as *const Waiter as *const Masked as *mut Masked; + + // Try to slide in the node at the head of the linked list, making sure + // that another thread didn't just replace the head of the linked list. + let exchange_result = state_and_queue.compare_exchange( + current_state, + me.with_addr(me.addr() | RUNNING), + Ordering::Release, + Ordering::Relaxed, + ); + if let Err(old) = exchange_result { + current_state = old; + continue; + } + + // We have enqueued ourselves, now lets wait. + // It is important not to return before being signaled, otherwise we + // would drop our `Waiter` node and leave a hole in the linked list + // (and a dangling reference). Guard against spurious wakeups by + // reparking ourselves until we are signaled. + while !node.signaled.load(Ordering::Acquire) { + // If the managing thread happens to signal and unpark us before we + // can park ourselves, the result could be this thread never gets + // unparked. Luckily `park` comes with the guarantee that if it got + // an `unpark` just before on an unparked thread it does not park. + thread::park(); + } + break; + } +} + +#[stable(feature = "std_debug", since = "1.16.0")] +impl fmt::Debug for Once { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("Once").finish_non_exhaustive() + } +} + +impl Drop for WaiterQueue<'_> { + fn drop(&mut self) { + // Swap out our state with however we finished. + let state_and_queue = + self.state_and_queue.swap(self.set_state_on_drop_to, Ordering::AcqRel); + + // We should only ever see an old state which was RUNNING. + assert_eq!(state_and_queue.addr() & STATE_MASK, RUNNING); + + // Walk the entire linked list of waiters and wake them up (in lifo + // order, last to register is first to wake up). + unsafe { + // Right after setting `node.signaled = true` the other thread may + // free `node` if there happens to be has a spurious wakeup. + // So we have to take out the `thread` field and copy the pointer to + // `next` first. + let mut queue = + state_and_queue.with_addr(state_and_queue.addr() & !STATE_MASK) as *const Waiter; + while !queue.is_null() { + let next = (*queue).next; + let thread = (*queue).thread.take().unwrap(); + (*queue).signaled.store(true, Ordering::Release); + // ^- FIXME (maybe): This is another case of issue #55005 + // `store()` has a potentially dangling ref to `signaled`. + queue = next; + thread.unpark(); + } + } + } +} + +impl OnceState { + #[inline] + pub fn is_poisoned(&self) -> bool { + self.poisoned + } + + #[inline] + pub fn poison(&self) { + self.set_state_on_drop_to.set(ptr::invalid_mut(POISONED)); + } +} diff --git a/library/std/src/sys_common/once/mod.rs b/library/std/src/sys_common/once/mod.rs new file mode 100644 index 00000000000..8742e68cc7a --- /dev/null +++ b/library/std/src/sys_common/once/mod.rs @@ -0,0 +1,43 @@ +// A "once" is a relatively simple primitive, and it's also typically provided +// by the OS as well (see `pthread_once` or `InitOnceExecuteOnce`). The OS +// primitives, however, tend to have surprising restrictions, such as the Unix +// one doesn't allow an argument to be passed to the function. +// +// As a result, we end up implementing it ourselves in the standard library. +// This also gives us the opportunity to optimize the implementation a bit which +// should help the fast path on call sites. +// +// So to recap, the guarantees of a Once are that it will call the +// initialization closure at most once, and it will never return until the one +// that's running has finished running. This means that we need some form of +// blocking here while the custom callback is running at the very least. +// Additionally, we add on the restriction of **poisoning**. Whenever an +// initialization closure panics, the Once enters a "poisoned" state which means +// that all future calls will immediately panic as well. +// +// So to implement this, one might first reach for a `Mutex`, but those cannot +// be put into a `static`. It also gets a lot harder with poisoning to figure +// out when the mutex needs to be deallocated because it's not after the closure +// finishes, but after the first successful closure finishes. +// +// All in all, this is instead implemented with atomics and lock-free +// operations! Whee! + +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::{Once, OnceState}; + } else { + mod generic; + pub use generic::{Once, OnceState}; + } +} diff --git a/library/std/src/sys_common/rwlock.rs b/library/std/src/sys_common/rwlock.rs index 36d721fcbcb..042981dac60 100644 --- a/library/std/src/sys_common/rwlock.rs +++ b/library/std/src/sys_common/rwlock.rs @@ -15,6 +15,7 @@ pub struct MovableRwLock(imp::MovableRwLock); impl MovableRwLock { /// Creates a new reader-writer lock for use. #[inline] + #[rustc_const_stable(feature = "const_locks", since = "1.63.0")] pub const fn new() -> Self { Self(imp::MovableRwLock::new()) } diff --git a/library/std/src/sys_common/thread_local_key.rs b/library/std/src/sys_common/thread_local_key.rs index 032bf604d73..747579f1781 100644 --- a/library/std/src/sys_common/thread_local_key.rs +++ b/library/std/src/sys_common/thread_local_key.rs @@ -53,7 +53,6 @@ mod tests; use crate::sync::atomic::{self, AtomicUsize, Ordering}; use crate::sys::thread_local_key as imp; -use crate::sys_common::mutex::StaticMutex; /// A type for TLS keys that are statically allocated. /// @@ -151,25 +150,6 @@ impl StaticKey { } unsafe fn lazy_init(&self) -> usize { - // Currently the Windows implementation of TLS is pretty hairy, and - // it greatly simplifies creation if we just synchronize everything. - // - // Additionally a 0-index of a tls key hasn't been seen on windows, so - // we just simplify the whole branch. - if imp::requires_synchronized_create() { - // We never call `INIT_LOCK.init()`, so it is UB to attempt to - // acquire this mutex reentrantly! - static INIT_LOCK: StaticMutex = StaticMutex::new(); - let _guard = INIT_LOCK.lock(); - let mut key = self.key.load(Ordering::SeqCst); - if key == 0 { - key = imp::create(self.dtor) as usize; - self.key.store(key, Ordering::SeqCst); - } - rtassert!(key != 0); - return key; - } - // POSIX allows the key created here to be 0, but the compare_exchange // below relies on using 0 as a sentinel value to check who won the // race to set the shared TLS key. As far as I know, there is no @@ -232,8 +212,6 @@ impl Key { impl Drop for Key { fn drop(&mut self) { - // Right now Windows doesn't support TLS key destruction, but this also - // isn't used anywhere other than tests, so just leak the TLS key. - // unsafe { imp::destroy(self.key) } + unsafe { imp::destroy(self.key) } } } |