Add CI/CD configuration and API documentation

iOS-SwiftUI-Code/GRDB.swift-6.29.3/GRDB/Utils/LockedBox.swift

@@ -0,0 +1,72 @@
+import Foundation
+
+/// A LockedBox protects a value with an NSLock.
+@propertyWrapper
+final class LockedBox<T> {
+    private var _wrappedValue: T
+    private var lock = NSLock()
+    
+    var wrappedValue: T {
+        get { read { $0 } }
+        set { update { $0 = newValue } }
+    }
+    
+    var projectedValue: LockedBox<T> { self }
+    
+    init(wrappedValue: T) {
+        _wrappedValue = wrappedValue
+    }
+    
+    /// Runs the provided closure while holding a lock on the value.
+    ///
+    /// For example:
+    ///
+    ///     // Prints "0"
+    ///     @LockedBox var count = 0
+    ///     $count.read { print($0) }
+    ///
+    /// - parameter block: A closure that accepts the value.
+    @inline(__always)
+    @usableFromInline
+    func read<U>(_ block: (T) throws -> U) rethrows -> U {
+        lock.lock()
+        defer { lock.unlock() }
+        return try block(_wrappedValue)
+    }
+    
+    /// Runs the provided closure while holding a lock on the value.
+    ///
+    /// For example:
+    ///
+    ///     // Prints "1"
+    ///     @LockedBox var count = 0
+    ///     $count.update { $0 += 1 }
+    ///     print(count)
+    ///
+    /// - parameter block: A closure that can modify the value.
+    func update<U>(_ block: (inout T) throws -> U) rethrows -> U {
+        lock.lock()
+        defer { lock.unlock() }
+        return try block(&_wrappedValue)
+    }
+}
+
+extension LockedBox where T: Numeric {
+    @discardableResult
+    func increment() -> T {
+        update { n in
+            n += 1
+            return n
+        }
+    }
+    
+    @discardableResult
+    func decrement() -> T {
+        update { n in
+            n -= 1
+            return n
+        }
+    }
+}
+
+extension LockedBox: @unchecked Sendable where T: Sendable { }