Add mc-sgx-sync::sys::locks::RwLock

sync/src/sys/locks.rs

@@ -4,6 +4,7 @@
 
 mod condvar;
 mod mutex;
+mod rwlock;
 
 pub(crate) use condvar::Condvar;
 pub(crate) use mutex::Mutex;

sync/src/sys/locks/rwlock.rs

@@ -0,0 +1,116 @@
+// Copyright (c) 2023 The MobileCoin Foundation
+
+//! Rust RwLock implementation used in SGX environments
+
+#![allow(dead_code)]
+
+use mc_sgx_tstdc::RwLock as SgxRwLock;
+
+/// SGX rwlock backend to use with the common Rust std lib
+/// [`RwLock`](https://doc.rust-lang.org/std/sync/struct.RwLock.html) interface.
+///
+///
+/// Read locks are implemented using a reference count. This means that clients
+/// are responsible for managing which threads hold the read locks and ensuring
+/// threads only unlock if they are currently holding a reader lock. Write locks
+/// do track which thread owns them.
+pub(crate) struct RwLock {
+    inner: SgxRwLock,
+}
+
+unsafe impl Send for RwLock {}
+unsafe impl Sync for RwLock {}
+
+impl RwLock {
+    /// Create a new [`RwLock`]
+    pub const fn new() -> RwLock {
+        RwLock {
+            inner: SgxRwLock::new(),
+        }
+    }
+
+    /// Acquire a read lock on the [`RwLock`]
+    ///
+    /// NB: This acquires **a** reader lock on the [`RwLock`] instance, it does
+    ///     not keep track of which threads have reader locks.
+    ///
+    /// # Panics
+    /// Panics if the [`RwLock`] got into an invalid state. Invalid states
+    /// include:
+    /// - Corrupted underlying data
+    /// - Trying to obtain a read lock when thread has write lock
+    pub fn read(&self) {
+        self.inner
+            .read()
+            .expect("RwLock got into an invalid state.")
+    }
+
+    /// Try to acquire a read lock on the [`RwLock`]
+    ///
+    /// NB: This acquires **a** reader lock on the [`RwLock`] instance, it does
+    ///     not keep track of which threads have reader locks.
+    ///
+    /// # Returns
+    /// `true` if a read lock was acquired, `false` otherwise.
+    pub fn try_read(&self) -> bool {
+        self.inner
+            .try_read()
+            .expect("RwLock got into an invalid state.")
+    }
+
+    /// Acquire a write lock on the [`RwLock`]
+    ///
+    /// # Panics
+    /// Panics if the [`RwLock`] got into an invalid state. Invalid states
+    /// include:
+    /// - Corrupted underlying data
+    /// - Trying to obtain a write lock when the thread already has the write
+    ///   lock
+    pub fn write(&self) {
+        self.inner
+            .read()
+            .expect("RwLock got into an invalid state.")
+    }
+
+    /// Try to acquire a read lock on the [`RwLock`]
+    ///
+    /// # Returns
+    /// `true` if a read lock was acquired, `false` otherwise.
+    pub fn try_write(&self) -> bool {
+        self.inner
+            .try_write()
+            .expect("RwLock got into an invalid state.")
+    }
+
+    /// Release a read lock on the [`RwLock`]
+    ///
+    /// NB: This release **a** reader lock on the [`RwLock`] instance, it does
+    ///     not validate that the current thread created the reader lock.
+    ///
+    /// # Panics
+    /// Panics if the [`RwLock`] got into an invalid state. Invalid states
+    /// include:
+    /// - Corrupted underlying data
+    /// - Trying to unlock when there are no read locks currently held
+    pub fn read_unlock(&self) {
+        self.inner
+            .read_unlock()
+            .expect("RwLock got into an invalid state.")
+    }
+
+    /// Release the write lock on the [`RwLock`]
+    ///
+    /// # Panics
+    /// Panics if the [`RwLock`] got into an invalid state. Invalid states
+    /// include:
+    /// - Corrupted underlying data
+    /// - Trying to unlock when the current thread doesn't hold the write lock
+    pub fn write_unlock(&self) {
+        // Note on the `expect()` statement, though unlock can fail due to out
+        // of memory it's unlikely to happen as unlocking only allocates a
+        // `void *` per waiting reader thread.
+        self.inner
+            .write_unlock()
+            .expect("RwLock got into an invalid state.")
+    }
+}