Mutex should be ~Copyable

Author: swhitty

.github/workflows/build.yml

@@ -71,7 +71,7 @@ jobs:
 
   linux_swift_6_1:
     runs-on: ubuntu-latest
-    container: swift:6.1
+    container: swift:6.1.2
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -123,7 +123,7 @@ jobs:
 
   linux_swift_6_1_musl:
     runs-on: ubuntu-latest
-    container: swift:6.1
+    container: swift:6.1.2
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -146,7 +146,7 @@ jobs:
       - name: Install Swift
         uses: SwiftyLab/setup-swift@latest
         with:
-          swift-version: "6.1.0"
+          swift-version: "6.1.2"
       - name: Version
         run: swift --version
       - name: Build

Sources/AllocatedLock.swift

@@ -30,6 +30,7 @@
 //
 
 // Backports the Swift interface around OSAllocatedUnfairLock available in recent Darwin platforms
+@available(*, deprecated, message: "Unused by Mutex and will be removed in future versions.")
 public struct AllocatedLock<State>: @unchecked Sendable {
 
     @usableFromInline

Sources/Mutex.swift

@@ -29,82 +29,208 @@
 //  SOFTWARE.
 //
 
+#if compiler(>=6) && !canImport(WinSDK)
+
 // Backports the Swift 6 type Mutex<Value> to all Darwin platforms
 
-// @available(macOS, deprecated: 15.0, message: "use Mutex from Synchronization module included with Swift 6")
-// @available(iOS, deprecated: 18.0, message: "use Mutex from Synchronization module included with Swift 6")
-// @available(tvOS, deprecated: 18.0, message: "use Mutex from Synchronization module included with Swift 6")
-// @available(watchOS, deprecated: 11.0, message: "use Mutex from Synchronization module included with Swift 6")
-// @available(visionOS, deprecated: 2.0, message: "use Mutex from Synchronization module included with Swift 6")
-public struct Mutex<Value>: Sendable {
-    let lock: AllocatedLock<Value> // Compatible with OSAllocatedUnfairLock iOS 16+
-}
+@available(macOS, introduced: 13.0, deprecated: 15.0, message: "use Mutex from Synchronization module")
+@available(iOS, introduced: 16.0, deprecated: 18.0, message: "use Mutex from Synchronization module")
+@available(tvOS, introduced: 18.0, deprecated: 15.0, message: "use Mutex from Synchronization module")
+@available(watchOS, introduced: 11.0, deprecated: 15.0, message: "use Mutex from Synchronization module")
+@available(visionOS, introduced: 2.0, deprecated: 15.0, message: "use Mutex from Synchronization module")
+public struct Mutex<Value: ~Copyable>: @unchecked Sendable, ~Copyable {
+    let storage: Storage<Value>
 
-#if compiler(>=6)
-public extension Mutex {
-    init(_ initialValue: consuming sending Value) {
-        self.lock = AllocatedLock(uncheckedState: initialValue)
+    public init(_ initialValue: consuming sending Value) {
+        self.storage = Storage(initialValue)
     }
 
-    borrowing func withLock<Result, E: Error>(
+    public borrowing func withLock<Result, E: Error>(
         _ body: (inout sending Value) throws(E) -> sending Result
     ) throws(E) -> sending Result {
-        do {
-            return try lock.withLockUnchecked { value in
-                nonisolated(unsafe) var copy = value
-                defer { value = copy }
-                return try Transferring(body(&copy))
-            }.value
-        } catch let error as E {
-            throw error
-        } catch {
-            preconditionFailure("cannot occur")
-        }
-    }
-
-    borrowing func withLockIfAvailable<Result, E>(
+        storage.lock()
+        defer { storage.unlock() }
+        return try body(&storage.value)
+    }
+
+    public borrowing func withLockIfAvailable<Result, E: Error>(
         _ body: (inout sending Value) throws(E) -> sending Result
-    ) throws(E) -> sending Result? where E: Error {
-        do {
-            return try lock.withLockIfAvailableUnchecked { value in
-                nonisolated(unsafe) var copy = value
-                defer { value = copy }
-                return try Transferring(body(&copy))
-            }?.value
-        } catch let error as E {
-            throw error
-        } catch {
-            preconditionFailure("cannot occur")
-        }
+    ) throws(E) -> sending Result? {
+        guard storage.tryLock() else { return nil }
+        defer { storage.unlock() }
+        return try body(&storage.value)
     }
 }
-private struct Transferring<T> {
-    nonisolated(unsafe) var value: T
 
-    init(_ value: T) {
-        self.value = value
+#elseif compiler(>=6) && canImport(WinSDK)
+
+// Windows doesn't support ~Copyable yet
+
+public struct Mutex<Value>: @unchecked Sendable {
+    let storage: Storage<Value>
+
+    public init(_ initialValue: consuming sending Value) {
+        self.storage = Storage(initialValue)
+    }
+
+    public borrowing func withLock<Result, E: Error>(
+        _ body: (inout sending Value) throws(E) -> sending Result
+    ) throws(E) -> sending Result {
+        storage.lock()
+        defer { storage.unlock() }
+        return try body(&storage.value)
+    }
+
+    public borrowing func withLockIfAvailable<Result, E: Error>(
+        _ body: (inout sending Value) throws(E) -> sending Result
+    ) throws(E) -> sending Result? {
+        guard storage.tryLock() else { return nil }
+        defer { storage.unlock() }
+        return try body(&storage.value)
     }
 }
+
 #else
-public extension Mutex {
-    init(_ initialValue: consuming Value) {
-        self.lock = AllocatedLock(uncheckedState: initialValue)
+
+// Use Swift 5 compatible version
+
+public struct Mutex<Value>: @unchecked Sendable {
+    let storage: Storage<Value>
+
+    public init(_ initialValue: Value) {
+        self.storage = Storage(initialValue)
     }
 
-    borrowing func withLock<Result>(
+    public borrowing func withLock<Result>(
         _ body: (inout Value) throws -> Result
     ) rethrows -> Result {
-        try lock.withLockUnchecked {
-            return try body(&$0)
-        }
+        storage.lock()
+        defer { storage.unlock() }
+        return try body(&storage.value)
     }
 
-    borrowing func withLockIfAvailable<Result>(
+    public borrowing func withLockIfAvailable<Result>(
         _ body: (inout Value) throws -> Result
     ) rethrows -> Result? {
-        try lock.withLockIfAvailableUnchecked {
-            return try body(&$0)
-        }
+        guard storage.tryLock() else { return nil }
+        defer { storage.unlock() }
+        return try body(&storage.value)
     }
 }
+
+#endif
+
+#if canImport(Darwin)
+
+import struct os.os_unfair_lock_t
+import struct os.os_unfair_lock
+import func os.os_unfair_lock_lock
+import func os.os_unfair_lock_unlock
+import func os.os_unfair_lock_trylock
+
+final class Storage<Value: ~Copyable> {
+    private let _lock: os_unfair_lock_t
+
+    var value: Value
+
+    init(_ initialValue: consuming Value) {
+        self._lock = .allocate(capacity: 1)
+        self._lock.initialize(to: os_unfair_lock())
+        self.value = initialValue
+    }
+
+    func lock() {
+        os_unfair_lock_lock(_lock)
+    }
+
+    func unlock() {
+        os_unfair_lock_unlock(_lock)
+    }
+
+    func tryLock() -> Bool {
+        os_unfair_lock_trylock(_lock)
+    }
+
+    deinit {
+        self._lock.deinitialize(count: 1)
+        self._lock.deallocate()
+    }
+}
+
+
+#elseif canImport(Glibc) || canImport(Musl) || canImport(Bionic)
+
+#if canImport(Musl)
+import Musl
+#elseif canImport(Bionic)
+import Android
+#else
+import Glibc
+#endif
+
+final class Storage<Value: ~Copyable> {
+    private let _lock: UnsafeMutablePointer<pthread_mutex_t>
+
+    var value: Value
+
+    init(_ initialValue: consuming Value) {
+        var attr = pthread_mutexattr_t()
+        pthread_mutexattr_init(&attr)
+        self._lock = .allocate(capacity: 1)
+        let err = pthread_mutex_init(self._lock, &attr)
+        precondition(err == 0, "pthread_mutex_init error: \(err)")
+        self.value = initialValue
+    }
+
+    func lock() {
+        let err = pthread_mutex_lock(_lock)
+        precondition(err == 0, "pthread_mutex_lock error: \(err)")
+    }
+
+    func unlock() {
+        let err = pthread_mutex_unlock(_lock)
+        precondition(err == 0, "pthread_mutex_unlock error: \(err)")
+    }
+
+    func tryLock() -> Bool {
+        pthread_mutex_trylock(_lock) == 0
+    }
+
+    deinit {
+        let err = pthread_mutex_destroy(self._lock)
+        precondition(err == 0, "pthread_mutex_destroy error: \(err)")
+        self._lock.deallocate()
+    }
+}
+
+
+#elseif canImport(WinSDK)
+
+import ucrt
+import WinSDK
+
+final class Storage<Value> {
+    private let _lock: UnsafeMutablePointer<SRWLOCK>
+
+    var value: Value
+
+    init(_ initialValue: Value) {
+        self._lock = .allocate(capacity: 1)
+        InitializeSRWLock(self._lock)
+        self.value = initialValue
+    }
+
+    func lock() {
+        AcquireSRWLockExclusive(_lock)
+    }
+
+    func unlock() {
+        ReleaseSRWLockExclusive(_lock)
+    }
+
+    func tryLock() -> Bool {
+        TryAcquireSRWLockExclusive(_lock) != 0
+    }
+}
+
 #endif

Tests/MutexTests.swift

@@ -55,11 +55,11 @@ struct MutexTests {
     @Test
     func lockIfAvailable_ReturnsValue() {
         let mutex = Mutex("fish")
-        mutex.lock.unsafeLock()
+        mutex.unsafeLock()
         #expect(
             mutex.withLockIfAvailable { _ in "chips" } == nil
         )
-        mutex.lock.unsafeUnlock()
+        mutex.unsafeUnlock()
         #expect(
             mutex.withLockIfAvailable { _ in "chips" } == "chips"
         )
@@ -74,3 +74,8 @@ struct MutexTests {
     }
 }
 #endif
+
+extension Mutex {
+    func unsafeLock() { storage.lock() }
+    func unsafeUnlock() { storage.unlock() }
+}

Tests/MutexXCTests.swift

@@ -52,11 +52,11 @@ final class MutexTests: XCTestCase {
 
     func testLockIfAvailable_ReturnsValue() {
         let mutex = Mutex("fish")
-        mutex.lock.unsafeLock()
+        mutex.unsafeLock()
         XCTAssertNil(
             mutex.withLockIfAvailable { _ in "chips" }
         )
-        mutex.lock.unsafeUnlock()
+        mutex.unsafeUnlock()
         XCTAssertEqual(
             mutex.withLockIfAvailable { _ in "chips" },
             "chips"