fix: resolve MPMC queue contention

.github/workflows/build.yml

@@ -86,6 +86,11 @@ jobs:
       - name: Run cargo test
         run: cargo test --features="alloc,defmt,mpmc_large,portable-atomic-critical-section,serde,ufmt,bytes,zeroize"
 
+      - name: Run loom tests
+        run: cargo test -- loom
+        continue-on-error: true
+        env:
+          RUSTFLAGS: '--cfg loom'
   # Run cargo fmt --check
   style:
     name: style

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Implement `TryFrom` for `Deque` from array.
 - Switch from `serde` to `serde_core` for enabling faster compilations.
 - Implement `Zeroize` trait for all data structures with the `zeroize` feature to securely clear sensitive data from memory.
+- `mpmc::Queue`: document non-lock free behaviour, and add loom tests
 
 ## [v0.9.1] - 2025-08-19
 

Cargo.toml

@@ -53,11 +53,15 @@ zeroize = ["dep:zeroize"]
 # Enable larger MPMC sizes.
 mpmc_large = []
 
+# Enable crossbeam ArrayQueue MPMC implementation.
+mpmc_crossbeam = ["dep:crossbeam-utils"]
+
 # Implement some alloc Vec interoperability
 alloc = []
 
 nightly = []
 
+
 [dependencies]
 bytes = { version = "1", default-features = false, optional = true }
 portable-atomic = { version = "1.0", optional = true }
@@ -67,6 +71,7 @@ ufmt = { version = "0.2", optional = true }
 ufmt-write = { version = "0.1", optional = true }
 defmt = { version = "1.0.1", optional = true }
 zeroize = { version = "1.8", optional = true, default-features = false, features = ["derive"] }
+crossbeam-utils = { version = "0.8", optional = true }
 
 # for the pool module
 [target.'cfg(any(target_arch = "arm", target_pointer_width = "32", target_pointer_width = "64"))'.dependencies]
@@ -76,6 +81,9 @@ stable_deref_trait = { version = "1", default-features = false }
 critical-section = { version = "1.1", features = ["std"] }
 static_assertions = "1.1.0"
 
+[target.'cfg(loom)'.dependencies]
+loom = "0.7.2"
+
 [package.metadata.docs.rs]
 features = [
     "bytes",
@@ -89,3 +97,6 @@ features = [
 # for the pool module
 targets = ["i686-unknown-linux-gnu"]
 rustdoc-args = ["--cfg", "docsrs"]
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(loom)'] }