From b3a88dec85e27304d581b5daffff949b9b6f89b2 Mon Sep 17 00:00:00 2001 From: Lucas Baumann Date: Sun, 28 Sep 2025 11:50:34 +0200 Subject: [PATCH] v0.1: fix guard forget + organisation stuff --- CHANGELOG.md | 4 +++ LICENSES/Apache-2.0.txt | 73 +++++++++++++++++++++++++++++++++++++++++ LICENSES/MIT.txt | 18 ++++++++++ README.md | 5 +++ src/lib.rs | 68 ++++++++++++++++++++++++++++---------- src/shared.rs | 15 ++++----- tests/tests.rs | 4 +-- 7 files changed, 159 insertions(+), 28 deletions(-) create mode 100644 CHANGELOG.md create mode 100644 LICENSES/Apache-2.0.txt create mode 100644 LICENSES/MIT.txt diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 index 0000000..60647d8 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,4 @@ +# Changelog + +## [0.1.0] - Date +- Initial Release diff --git a/LICENSES/Apache-2.0.txt b/LICENSES/Apache-2.0.txt new file mode 100644 index 0000000..137069b --- /dev/null +++ b/LICENSES/Apache-2.0.txt @@ -0,0 +1,73 @@ +Apache License +Version 2.0, January 2004 +http://www.apache.org/licenses/ + +TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + +1. 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IN NO +EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER +IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE +USE OR OTHER DEALINGS IN THE SOFTWARE. diff --git a/README.md b/README.md index 6f2b315..f1b59c3 100644 --- a/README.md +++ b/README.md @@ -7,3 +7,8 @@ It is useful for communicating data from a realtime thread (for example the audi If the writer thread is the non realtime thread and reading should be nonblocking take a look at my other library [simple-left-right](https://crates.io/crates/simple-left-right). The implementation is similar, but the roles are reversed. +Hosted on [tangled](https://tangled.org/did:plc:54jgbo4psy24qu2bk4njtpc4/rt-write-lock/), [codeberg](https://codeberg.org/increasing/rt-write-lock) +and [github](https://github.com/luca3s/rt-write-lock). Open a PR or issue on any platform you like. + +## std::mem::forget +The library tries to detect if a Read/Write guard is forgotten and panics. Without this detection this could lead to UB. diff --git a/src/lib.rs b/src/lib.rs index 3617d53..84236ff 100644 --- a/src/lib.rs +++ b/src/lib.rs @@ -1,3 +1,13 @@ +// std::mem::forget creates issues because you can run a lock function without running the unlock function +// i deal with this by tracking for Reader and Writer if they are locked currently. If a new locked is aquired +// while it's still locked it panics. If Reader or Writer are dropped while locked it also panics. +// +// This could be circumvented by leaking Reader or Writer, but this doesn't lead to issues as then it's impossible +// to aquire a new Reader or Writer, because then the count also wasn't decremented. +// +// This panics more often than UB would occur without this detection, but this exact specs is a implementation detail +// and users just shouldn't forget the Guards. + #![no_std] extern crate alloc; @@ -14,14 +24,30 @@ use shared::{Ptr, Shared}; pub struct Reader { shared: NonNull>, + locked: bool, _owned: PhantomData, } impl Reader { - pub fn try_read(&mut self) -> Option> { + pub fn try_read(&mut self) -> Option> { + if self.locked { + self.locked = false; // don't also panic in the destructor + panic!("ReadGuard was forgotten"); + } let shared = self.get_shared(); let value = shared.try_read(); - value.map(|value| ReadLock { shared, value }) + // SAFETY: try_read returned Some to allowed to get a shared ref + let value = value.map(|v| unsafe { &*v.get() }); + if let Some(value) = value { + // only set locked if locking actually was successful + self.locked = true; + Some(ReadGuard { + reader: self, + value, + }) + } else { + None + } } fn get_shared(&self) -> &Shared { @@ -50,6 +76,7 @@ impl Reader { Self { shared: Shared::new(value), _owned: PhantomData, + locked: false, } } } @@ -59,6 +86,7 @@ impl Default for Reader { Self { shared: Shared::new_default(), _owned: PhantomData, + locked: false, } } } @@ -69,15 +97,16 @@ impl Drop for Reader { unsafe { Shared::drop(self.shared); } + assert!(!self.locked, "ReadGuard was forgotten") } } -pub struct ReadLock<'a, T> { - shared: &'a Shared, +pub struct ReadGuard<'a, T> { + reader: &'a mut Reader, value: &'a T, } -impl Deref for ReadLock<'_, T> { +impl Deref for ReadGuard<'_, T> { type Target = T; fn deref(&self) -> &Self::Target { @@ -85,9 +114,10 @@ impl Deref for ReadLock<'_, T> { } } -impl Drop for ReadLock<'_, T> { +impl Drop for ReadGuard<'_, T> { fn drop(&mut self) { - self.shared.remove_current_read(); + self.reader.locked = false; + self.reader.get_shared().remove_current_read(); } } @@ -103,20 +133,21 @@ impl Writer { unsafe { self.shared.as_ref() } } - pub fn write(&mut self) -> WriteLock<'_, T> { - assert!( - !self.locked, - "writelock destructor wasn't run. Create a new writer to " - ); + pub fn write(&mut self) -> WriteGuard<'_, T> { + if self.locked { + self.locked = false; // don't also panic in the destructor + panic!("WriteGuard was forgotten"); + } + // locking here is always successfull, so we set it unconditionally + self.locked = true; let shared = self.get_shared(); // SAFETY: won't be called again while the mut ref is still live, as the write method needs a mut ref let pre_res = unsafe { shared.write() }; // SAFETY: was just locked let value = unsafe { &mut *pre_res.0.get() }; let ptr = pre_res.1; - self.locked = true; - WriteLock { + WriteGuard { writer: self, value, next_read: ptr, @@ -130,6 +161,7 @@ impl Drop for Writer { unsafe { Shared::drop(self.shared); } + assert!(!self.locked, "WriteGuard was forgotten") } } @@ -141,7 +173,7 @@ unsafe impl Send for Writer {} /// /// I still offer DerefMut instead of just taking a new T, because this allows reusing allocations inside of T instead of /// dropping and reallocing. This is important for realtime usecases. -pub struct WriteLock<'a, T> { +pub struct WriteGuard<'a, T> { writer: &'a mut Writer, value: &'a mut T, // if some: set the next_read bit to the ptr value for unlocking @@ -151,7 +183,7 @@ pub struct WriteLock<'a, T> { // i don't really want this. I would prefer to only write, but i need a mut ref to be able to write rt-safe. // and for DerefMut i need Deref. -impl Deref for WriteLock<'_, T> { +impl Deref for WriteGuard<'_, T> { type Target = T; fn deref(&self) -> &Self::Target { @@ -159,13 +191,13 @@ impl Deref for WriteLock<'_, T> { } } -impl DerefMut for WriteLock<'_, T> { +impl DerefMut for WriteGuard<'_, T> { fn deref_mut(&mut self) -> &mut Self::Target { self.value } } -impl Drop for WriteLock<'_, T> { +impl Drop for WriteGuard<'_, T> { fn drop(&mut self) { self.writer.get_shared().unlock_write(self.next_read); self.writer.locked = false; diff --git a/src/shared.rs b/src/shared.rs index dd5aa8c..3b8f022 100644 --- a/src/shared.rs +++ b/src/shared.rs @@ -141,7 +141,8 @@ impl Shared { } impl Shared { - pub fn try_read(&self) -> Option<&T> { + // returns a unsafecell to allow some lifetime stuff + pub fn try_read(&self) -> Option<&UnsafeCell> { let result = self .state .fetch_update(Ordering::Acquire, Ordering::Relaxed, |value| { @@ -156,8 +157,8 @@ impl Shared { let ptr = State::new(v).get_next_read().unwrap(); // SAFETY: atomic was just locked and the read state was set. Some(match ptr { - Ptr::Value1 => unsafe { &*self.value_1.get() }, - Ptr::Value2 => unsafe { &*self.value_2.get() }, + Ptr::Value1 => &self.value_1, + Ptr::Value2 => &self.value_2, }) } // read isn't allowed @@ -176,11 +177,9 @@ impl Shared { .fetch_update(Ordering::Acquire, Ordering::Acquire, |v| { let state = State::new(v); let current_read = state.get_current_read(); - // this can be None if WriteLock was forgotten instead of dropped. The state of the library is completely - // broken at this point. - let next_read = state - .get_next_read() - .expect("Destructor of WriteLock didn't run"); + // this can't be None because if WriteLock was forgotten instead of dropped the outer API layer panics, + // before calling this function + let next_read = unsafe { state.get_next_read().unwrap_unchecked() }; match (current_read, next_read) { (Some(c), n) if c != n => Some(state.disallow_read().0), diff --git a/tests/tests.rs b/tests/tests.rs index 613a64c..282d6bb 100644 --- a/tests/tests.rs +++ b/tests/tests.rs @@ -46,14 +46,14 @@ mod usage_test { } #[test] - #[ignore = "need to find a complete design for preventing forgetting locks"] + #[should_panic] fn double_write() { let mut reader: Reader = Reader::default(); let mut writer = reader.get_writer().unwrap(); let write = writer.write(); core::mem::forget(write); - let write = writer.write(); + writer.write(); } #[test] -- 2.51.2