Implement Mutex behaviour for lock_api

Cargo.toml

@@ -13,6 +13,11 @@ repository = "https://github.com/bertptrs/tracing-mutex"
 
 [dependencies]
 lazy_static = "1"
+lock_api = { version = "0.4", optional = true }
 
 [dev-dependencies]
 rand = "0.8"
+
+[features]
+# Feature names do not match crate names pending namespaced features.
+lockapi = ["lock_api"]

src/lib.rs

@@ -60,10 +60,14 @@ use std::sync::Once;
 use std::sync::PoisonError;
 
 use lazy_static::lazy_static;
+#[cfg(feature = "lockapi")]
+pub use lock_api;
 
 use crate::graph::DiGraph;
 
 mod graph;
+#[cfg(feature = "lockapi")]
+pub mod lockapi;
 pub mod stdsync;
 
 /// Counter for Mutex IDs. Atomic avoids the need for locking.
@@ -120,6 +124,16 @@ impl MutexId {
     ///
     /// This method panics if the new dependency would introduce a cycle.
     pub fn get_borrowed(&self) -> BorrowedMutex {
+        self.mark_held();
+        BorrowedMutex(self)
+    }
+
+    /// Mark this lock as held for the purposes of dependency tracking.
+    ///
+    /// # Panics
+    ///
+    /// This method panics if the new dependency would introduce a cycle.
+    pub fn mark_held(&self) {
         let creates_cycle = HELD_LOCKS.with(|locks| {
             if let Some(&previous) = locks.borrow().last() {
                 let mut graph = get_dependency_graph();
@@ -136,7 +150,22 @@ impl MutexId {
         }
 
         HELD_LOCKS.with(|locks| locks.borrow_mut().push(self.value()));
-        BorrowedMutex(self)
+    }
+
+    pub unsafe fn mark_released(&self) {
+        HELD_LOCKS.with(|locks| {
+            let mut locks = locks.borrow_mut();
+
+            for (i, &lock) in locks.iter().enumerate().rev() {
+                if lock == self.value() {
+                    locks.remove(i);
+                    return;
+                }
+            }
+
+            // Drop impls shouldn't panic but if this happens something is seriously broken.
+            unreachable!("Tried to drop lock for mutex {:?} but it wasn't held", self)
+        });
     }
 }
 
@@ -187,6 +216,12 @@ impl fmt::Debug for LazyMutexId {
     }
 }
 
+impl Default for LazyMutexId {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// Safety: the UnsafeCell is guaranteed to only be accessed mutably from a `Once`.
 unsafe impl Sync for LazyMutexId {}
 
@@ -241,21 +276,8 @@ struct BorrowedMutex<'a>(&'a MutexId);
 /// that is an indication of a serious design flaw in this library.
 impl<'a> Drop for BorrowedMutex<'a> {
     fn drop(&mut self) {
-        let id = self.0;
-
-        HELD_LOCKS.with(|locks| {
-            let mut locks = locks.borrow_mut();
-
-            for (i, &lock) in locks.iter().enumerate().rev() {
-                if lock == id.value() {
-                    locks.remove(i);
-                    return;
-                }
-            }
-
-            // Drop impls shouldn't panic but if this happens something is seriously broken.
-            unreachable!("Tried to drop lock for mutex {:?} but it wasn't held", id)
-        });
+        // Safety: the only way to get a BorrowedMutex is by locking the mutex.
+        unsafe { self.0.mark_released() };
     }
 }
 

src/lockapi.rs

@@ -0,0 +1,118 @@
+//! Wrapper implementations for [`lock_api`].
+use lock_api::GuardNoSend;
+use lock_api::RawMutex;
+use lock_api::RawMutexFair;
+use lock_api::RawMutexTimed;
+
+use crate::LazyMutexId;
+
+/// Tracing wrapper for all [`lock_api`] traits.
+///
+/// This wrapper implements any of the locking traits available, given that the wrapped type
+/// implements them. As such, this wrapper can be used both for normal mutexes and rwlocks.
+#[derive(Debug, Default)]
+pub struct TracingWrapper<T> {
+    inner: T,
+    id: LazyMutexId,
+}
+
+impl<T> TracingWrapper<T> {
+    /// Mark this lock as held in the dependency graph.
+    fn mark_held(&self) {
+        self.id.mark_held();
+    }
+
+    /// Mark this lock as released in the dependency graph.
+    ///
+    /// # Safety
+    ///
+    /// This function should only be called when the lock has been previously acquired by this
+    /// thread.
+    unsafe fn mark_released(&self) {
+        self.id.mark_released();
+    }
+
+    /// Conditionally lock the mutex.
+    ///
+    /// First acquires the lock, then runs the provided function. If that function returns true,
+    /// then the lock is kept, otherwise the mutex is immediately marked as relased.
+    fn conditionally_lock(&self, f: impl FnOnce() -> bool) -> bool {
+        // Mark as locked while we try to do the thing
+        self.mark_held();
+
+        if f() {
+            true
+        } else {
+            // Safety: we just locked it above.
+            unsafe { self.mark_released() }
+            false
+        }
+    }
+}
+
+unsafe impl<T> RawMutex for TracingWrapper<T>
+where
+    T: RawMutex,
+{
+    const INIT: Self = Self {
+        inner: T::INIT,
+        id: LazyMutexId::new(),
+    };
+
+    /// Always equal to [`GuardNoSend`], as an implementation detail in the tracking system requires
+    /// this behaviour. May change in the future to reflect the actual guard type from the wrapped
+    /// primitive.
+    type GuardMarker = GuardNoSend;
+
+    fn lock(&self) {
+        self.mark_held();
+        self.inner.lock();
+    }
+
+    fn try_lock(&self) -> bool {
+        self.conditionally_lock(|| self.inner.try_lock())
+    }
+
+    unsafe fn unlock(&self) {
+        self.inner.unlock();
+        self.mark_released();
+    }
+
+    fn is_locked(&self) -> bool {
+        // Can't use the default implementation as the inner type might've overwritten it.
+        self.inner.is_locked()
+    }
+}
+
+unsafe impl<T> RawMutexFair for TracingWrapper<T>
+where
+    T: RawMutexFair,
+{
+    unsafe fn unlock_fair(&self) {
+        self.inner.unlock_fair();
+        self.mark_released();
+    }
+
+    unsafe fn bump(&self) {
+        // Bumping effectively doesn't change which locks are held, so we don't need to manage the
+        // lock state.
+        self.inner.bump();
+    }
+}
+
+unsafe impl<T> RawMutexTimed for TracingWrapper<T>
+where
+    T: RawMutexTimed,
+{
+    type Duration = T::Duration;
+
+    type Instant = T::Instant;
+
+    fn try_lock_for(&self, timeout: Self::Duration) -> bool {
+        self.conditionally_lock(|| self.inner.try_lock_for(timeout))
+    }
+
+    fn try_lock_until(&self, timeout: Self::Instant) -> bool {
+        self.conditionally_lock(|| self.inner.try_lock_until(timeout))
+    }
+}