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author | Valentin Popov <valentin@popov.link> | 2024-07-19 15:37:58 +0300 |
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committer | Valentin Popov <valentin@popov.link> | 2024-07-19 15:37:58 +0300 |
commit | a990de90fe41456a23e58bd087d2f107d321f3a1 (patch) | |
tree | 15afc392522a9e85dc3332235e311b7d39352ea9 /vendor/portable-atomic/src/imp/fallback/seq_lock.rs | |
parent | 3d48cd3f81164bbfc1a755dc1d4a9a02f98c8ddd (diff) | |
download | fparkan-a990de90fe41456a23e58bd087d2f107d321f3a1.tar.xz fparkan-a990de90fe41456a23e58bd087d2f107d321f3a1.zip |
Deleted vendor folder
Diffstat (limited to 'vendor/portable-atomic/src/imp/fallback/seq_lock.rs')
-rw-r--r-- | vendor/portable-atomic/src/imp/fallback/seq_lock.rs | 147 |
1 files changed, 0 insertions, 147 deletions
diff --git a/vendor/portable-atomic/src/imp/fallback/seq_lock.rs b/vendor/portable-atomic/src/imp/fallback/seq_lock.rs deleted file mode 100644 index fb6803f..0000000 --- a/vendor/portable-atomic/src/imp/fallback/seq_lock.rs +++ /dev/null @@ -1,147 +0,0 @@ -// SPDX-License-Identifier: Apache-2.0 OR MIT - -// Adapted from https://github.com/crossbeam-rs/crossbeam/blob/crossbeam-utils-0.8.7/crossbeam-utils/src/atomic/seq_lock.rs. - -use core::{ - mem::ManuallyDrop, - sync::atomic::{self, Ordering}, -}; - -use super::utils::Backoff; - -// See mod.rs for details. -#[cfg(any(target_pointer_width = "16", target_pointer_width = "32"))] -pub(super) use core::sync::atomic::AtomicU64 as AtomicStamp; -#[cfg(not(any(target_pointer_width = "16", target_pointer_width = "32")))] -pub(super) use core::sync::atomic::AtomicUsize as AtomicStamp; -#[cfg(not(any(target_pointer_width = "16", target_pointer_width = "32")))] -pub(super) type Stamp = usize; -#[cfg(any(target_pointer_width = "16", target_pointer_width = "32"))] -pub(super) type Stamp = u64; - -// See mod.rs for details. -pub(super) type AtomicChunk = AtomicStamp; -pub(super) type Chunk = Stamp; - -/// A simple stamped lock. -pub(super) struct SeqLock { - /// The current state of the lock. - /// - /// All bits except the least significant one hold the current stamp. When locked, the state - /// equals 1 and doesn't contain a valid stamp. - state: AtomicStamp, -} - -impl SeqLock { - #[inline] - pub(super) const fn new() -> Self { - Self { state: AtomicStamp::new(0) } - } - - /// If not locked, returns the current stamp. - /// - /// This method should be called before optimistic reads. - #[inline] - pub(super) fn optimistic_read(&self) -> Option<Stamp> { - let state = self.state.load(Ordering::Acquire); - if state == 1 { - None - } else { - Some(state) - } - } - - /// Returns `true` if the current stamp is equal to `stamp`. - /// - /// This method should be called after optimistic reads to check whether they are valid. The - /// argument `stamp` should correspond to the one returned by method `optimistic_read`. - #[inline] - pub(super) fn validate_read(&self, stamp: Stamp) -> bool { - atomic::fence(Ordering::Acquire); - self.state.load(Ordering::Relaxed) == stamp - } - - /// Grabs the lock for writing. - #[inline] - pub(super) fn write(&self) -> SeqLockWriteGuard<'_> { - let mut backoff = Backoff::new(); - loop { - let previous = self.state.swap(1, Ordering::Acquire); - - if previous != 1 { - atomic::fence(Ordering::Release); - - return SeqLockWriteGuard { lock: self, state: previous }; - } - - while self.state.load(Ordering::Relaxed) == 1 { - backoff.snooze(); - } - } - } -} - -/// An RAII guard that releases the lock and increments the stamp when dropped. -#[must_use] -pub(super) struct SeqLockWriteGuard<'a> { - /// The parent lock. - lock: &'a SeqLock, - - /// The stamp before locking. - state: Stamp, -} - -impl SeqLockWriteGuard<'_> { - /// Releases the lock without incrementing the stamp. - #[inline] - pub(super) fn abort(self) { - // We specifically don't want to call drop(), since that's - // what increments the stamp. - let this = ManuallyDrop::new(self); - - // Restore the stamp. - // - // Release ordering for synchronizing with `optimistic_read`. - this.lock.state.store(this.state, Ordering::Release); - } -} - -impl Drop for SeqLockWriteGuard<'_> { - #[inline] - fn drop(&mut self) { - // Release the lock and increment the stamp. - // - // Release ordering for synchronizing with `optimistic_read`. - self.lock.state.store(self.state.wrapping_add(2), Ordering::Release); - } -} - -#[cfg(test)] -mod tests { - use super::SeqLock; - - #[test] - fn smoke() { - let lock = SeqLock::new(); - let before = lock.optimistic_read().unwrap(); - assert!(lock.validate_read(before)); - { - let _guard = lock.write(); - } - assert!(!lock.validate_read(before)); - let after = lock.optimistic_read().unwrap(); - assert_ne!(before, after); - } - - #[test] - fn test_abort() { - let lock = SeqLock::new(); - let before = lock.optimistic_read().unwrap(); - { - let guard = lock.write(); - guard.abort(); - } - let after = lock.optimistic_read().unwrap(); - assert_eq!(before, after, "aborted write does not update the stamp"); - } -} |