Linux build (sideeffect-io#37)

Import Locking.swift from upstream AsyncAlgorithms to enable non-Darwin builds

Sources/Supporting/Locking.swift

@@ -0,0 +1,154 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Async Algorithms open source project
+//
+// Copyright (c) 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+#if canImport(Darwin)
+import Darwin
+#elseif canImport(Glibc)
+import Glibc
+#elseif canImport(WinSDK)
+import WinSDK
+#endif
+
+internal struct Lock {
+#if canImport(Darwin)
+  typealias Primitive = os_unfair_lock
+#elseif canImport(Glibc)
+  typealias Primitive = pthread_mutex_t
+#elseif canImport(WinSDK)
+  typealias Primitive = SRWLOCK
+#else
+  typealias Primitive = Int
+#endif
+
+  typealias PlatformLock = UnsafeMutablePointer<Primitive>
+  let platformLock: PlatformLock
+
+  private init(_ platformLock: PlatformLock) {
+    self.platformLock = platformLock
+  }
+
+  fileprivate static func initialize(_ platformLock: PlatformLock) {
+#if canImport(Darwin)
+    platformLock.initialize(to: os_unfair_lock())
+#elseif canImport(Glibc)
+    let result = pthread_mutex_init(platformLock, nil)
+    precondition(result == 0, "pthread_mutex_init failed")
+#elseif canImport(WinSDK)
+    InitializeSRWLock(platformLock)
+#endif
+  }
+
+  fileprivate static func deinitialize(_ platformLock: PlatformLock) {
+#if canImport(Glibc)
+    let result = pthread_mutex_destroy(platformLock)
+    precondition(result == 0, "pthread_mutex_destroy failed")
+#endif
+    platformLock.deinitialize(count: 1)
+  }
+
+  fileprivate static func lock(_ platformLock: PlatformLock) {
+#if canImport(Darwin)
+    os_unfair_lock_lock(platformLock)
+#elseif canImport(Glibc)
+    pthread_mutex_lock(platformLock)
+#elseif canImport(WinSDK)
+    AcquireSRWLockExclusive(platformLock)
+#endif
+  }
+
+  fileprivate static func unlock(_ platformLock: PlatformLock) {
+#if canImport(Darwin)
+    os_unfair_lock_unlock(platformLock)
+#elseif canImport(Glibc)
+    let result = pthread_mutex_unlock(platformLock)
+    precondition(result == 0, "pthread_mutex_unlock failed")
+#elseif canImport(WinSDK)
+    ReleaseSRWLockExclusive(platformLock)
+#endif
+  }
+
+  static func allocate() -> Lock {
+    let platformLock = PlatformLock.allocate(capacity: 1)
+    initialize(platformLock)
+    return Lock(platformLock)
+  }
+
+  func deinitialize() {
+    Lock.deinitialize(platformLock)
+  }
+
+  func lock() {
+    Lock.lock(platformLock)
+  }
+
+  func unlock() {
+    Lock.unlock(platformLock)
+  }
+
+    /// Acquire the lock for the duration of the given block.
+    ///
+    /// This convenience method should be preferred to `lock` and `unlock` in
+    /// most situations, as it ensures that the lock will be released regardless
+    /// of how `body` exits.
+    ///
+    /// - Parameter body: The block to execute while holding the lock.
+    /// - Returns: The value returned by the block.
+    func withLock<T>(_ body: () throws -> T) rethrows -> T {
+        self.lock()
+        defer {
+            self.unlock()
+        }
+        return try body()
+    }
+
+    // specialise Void return (for performance)
+    func withLockVoid(_ body: () throws -> Void) rethrows -> Void {
+        try self.withLock(body)
+    }
+}
+
+struct ManagedCriticalState<State> {
+  private final class LockedBuffer: ManagedBuffer<State, Lock.Primitive> {
+    deinit {
+      withUnsafeMutablePointerToElements { Lock.deinitialize($0) }
+    }
+  }
+
+  private let buffer: ManagedBuffer<State, Lock.Primitive>
+
+  init(_ initial: State) {
+    buffer = LockedBuffer.create(minimumCapacity: 1) { buffer in
+      buffer.withUnsafeMutablePointerToElements { Lock.initialize($0) }
+      return initial
+    }
+  }
+
+  @discardableResult  
+  func withCriticalRegion<R>(_ critical: (inout State) throws -> R) rethrows -> R {
+    try buffer.withUnsafeMutablePointers { header, lock in
+      Lock.lock(lock)
+      defer { Lock.unlock(lock) }
+      return try critical(&header.pointee)
+    }
+  }
+
+  func apply(criticalState newState: State) {
+    self.withCriticalRegion { actual in
+      actual = newState
+    }
+  }
+
+  var criticalState: State {
+    self.withCriticalRegion { $0 }
+  }
+}
+
+extension ManagedCriticalState: @unchecked Sendable where State: Sendable { }