Relax memory orderings

For the BSEC we need to use Acquire and Release to ensure the
manipulations of the unsafe bsec library are not order outside of the
the area holding the BSEC_IN_USE lock. However, no AcqRel is required
because we need to establish no memory access get ordered after the
write of the lock.

For the FakeClock there is no critical section, purely incrementing the
counter in an atomic way is sufficient. Thus, relaxed ordering is fine
here.

CHANGELOG.md

@@ -4,6 +4,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.3.1] - 2021-11-09
+
+### Fixed
+
+* Memory orderings for aquireing and releasing BSEC have been slightly relaxed.
+* Memory orderings for the `FakeClock` (only used in tests) have been relaxed.
+
+
 ## [0.3.0] - 2021-05-15
 
 ### Added
@@ -40,8 +48,9 @@ Try to get documentation to build on docs.rs.
 Initial release.
 
 
-[Unreleased]: https://github.com/jgosmann/bsec/compare/v0.3.0...HEAD
-[0.3.0]: https://github.com/jgosmann/bsec/compare/v0.3.0...v0.3.0
+[Unreleased]: https://github.com/jgosmann/bsec/compare/v0.3.1...HEAD
+[0.3.0]: https://github.com/jgosmann/bsec/compare/v0.3.0...v0.3.1
+[0.3.0]: https://github.com/jgosmann/bsec/compare/v0.2.0...v0.3.0
 [0.2.0]: https://github.com/jgosmann/bsec/compare/v0.1.2...v0.2.0
 [0.1.2]: https://github.com/jgosmann/bsec/compare/v0.1.1...v0.1.2
 [0.1.1]: https://github.com/jgosmann/bsec/compare/v0.1.0...v0.1.1

Cargo.toml

@@ -1,20 +1,20 @@
 [package]
-name = "bsec"
-version = "0.3.0"
 authors = ["Jan Gosmann <[email protected]>"]
+categories = ["embedded"]
+description = "Rust API to the Bosch BSEC library."
 edition = "2018"
+keywords = ["bindings", "bsec"]
 license = "MIT OR Apache-2.0"
-description = "Rust API to the Bosch BSEC library."
-repository = "https://github.com/jgosmann/bsec"
+name = "bsec"
 readme = "README.md"
-keywords = ["bindings", "bsec"]
-categories = ["embedded"]
+repository = "https://github.com/jgosmann/bsec"
+version = "0.3.1"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-bme680 = { version = "0.5.1", optional = true }
-embedded-hal = { version = "0.2.5", optional = true }
+bme680 = {version = "0.5.1", optional = true}
+embedded-hal = {version = "0.2.5", optional = true}
 libalgobsec-sys = "0.1.0"
 nb = "1.0.0"
 

src/clock.rs

@@ -80,7 +80,10 @@ pub mod tests {
 /// This module is only available if the **test-support** feature is enabled.
 #[cfg(any(test, feature = "test-support"))]
 pub mod test_support {
-    use std::{sync::atomic::{AtomicI64, Ordering}, time::Duration};
+    use std::{
+        sync::atomic::{AtomicI64, Ordering},
+        time::Duration,
+    };
 
     use super::*;
 
@@ -114,14 +117,15 @@ pub mod test_support {
     impl Clock for FakeClock {
         /// Returns the current timestamp and advances it by one.
         fn timestamp_ns(&self) -> i64 {
-            self.timestamp_ns.fetch_add(1, Ordering::AcqRel)
+            self.timestamp_ns.fetch_add(1, Ordering::Relaxed)
         }
     }
 
     impl FakeClock {
         /// Advance the clock's internal time by `duration`.
         pub fn advance_by(&self, duration: Duration) {
-            self.timestamp_ns.fetch_add(duration.as_nanos() as i64, Ordering::AcqRel);
+            self.timestamp_ns
+                .fetch_add(duration.as_nanos() as i64, Ordering::Relaxed);
         }
     }
 }

src/lib.rs

@@ -229,7 +229,7 @@ impl<S: BmeSensor, C: Clock, B: Borrow<C>> Bsec<S, C, B> {
     /// * `clock`: [`Clock`] implementation to obtain timestamps.
     pub fn init(bme: S, clock: B) -> Result<Self, Error<S::Error>> {
         if BSEC_IN_USE
-            .compare_exchange(false, true, Ordering::AcqRel, Ordering::Relaxed)
+            .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
             .is_ok()
         {
             unsafe {
@@ -479,7 +479,7 @@ impl<S: BmeSensor, C: Clock, B: Borrow<C>> Bsec<S, C, B> {
 
 impl<S: BmeSensor, C: Clock, B: Borrow<C>> Drop for Bsec<S, C, B> {
     fn drop(&mut self) {
-        BSEC_IN_USE.store(false, Ordering::SeqCst);
+        BSEC_IN_USE.store(false, Ordering::Release);
     }
 }