use NSCache for client-side object cache

Author: lhoward

Sources/SwiftOCA/OCA/OcaObjectCache.swift

@@ -0,0 +1,103 @@
+//
+// Copyright (c) 2026 PADL Software Pty Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the License);
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an 'AS IS' BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+@preconcurrency
+import Foundation
+
+final class OcaObjectCache: NSObject, @unchecked Sendable, NSCacheDelegate {
+  private let _cache = NSCache<NSNumber, OcaRoot>()
+  private let _objectNumbers = Mutex(Set<OcaONo>())
+
+  override init() {
+    super.init()
+    _cache.delegate = self
+  }
+
+  convenience init(countLimit: Int) {
+    self.init()
+    if countLimit > 0 {
+      _cache.countLimit = countLimit
+    }
+  }
+
+  subscript(key: OcaONo) -> OcaRoot? {
+    get {
+      _cache.object(forKey: NSNumber(value: key))
+    }
+    set {
+      if let newValue {
+        _cache.setObject(newValue, forKey: NSNumber(value: key))
+        _ = _objectNumbers.withLock { $0.insert(key) }
+      } else {
+        _cache.removeObject(forKey: NSNumber(value: key))
+        _ = _objectNumbers.withLock { $0.remove(key) }
+      }
+    }
+  }
+
+  var count: Int {
+    _objectNumbers.withLock { $0.count }
+  }
+
+  var keys: Set<OcaONo> {
+    _objectNumbers.withLock { $0 }
+  }
+
+  var values: [OcaRoot] {
+    let keysCopy = _objectNumbers.withLock { $0 }
+    return keysCopy.compactMap { _cache.object(forKey: NSNumber(value: $0)) }
+  }
+
+  func removeAll() {
+    _cache.removeAllObjects()
+    _objectNumbers.withLock { $0.removeAll() }
+  }
+
+  func removeValue(forKey key: OcaONo) {
+    _cache.removeObject(forKey: NSNumber(value: key))
+    _ = _objectNumbers.withLock { $0.remove(key) }
+  }
+
+  fileprivate func removeKeyTracking(for key: OcaONo) {
+    _ = _objectNumbers.withLock { $0.remove(key) }
+  }
+
+  func cache(
+    _ cache: NSCache<AnyObject, AnyObject>,
+    willEvictObject obj: Any
+  ) {
+    if let object = obj as? OcaRoot {
+      removeKeyTracking(for: object.objectNumber)
+    }
+  }
+}
+
+// MARK: - Sequence Conformance
+
+extension OcaObjectCache: Sequence {
+  func makeIterator() -> AnyIterator<(key: OcaONo, value: OcaRoot)> {
+    let keysCopy = _objectNumbers.withLock { $0 }
+    var iterator = keysCopy.makeIterator()
+    return AnyIterator {
+      guard let key = iterator.next(),
+            let value = self[key]
+      else {
+        return nil
+      }
+      return (key, value)
+    }
+  }
+}

Sources/SwiftOCA/OCP.1/Ocp1Connection.swift

@@ -257,7 +257,7 @@ open class Ocp1Connection: CustomStringConvertible {
   public let connectionState: AnyAsyncSequence<Ocp1ConnectionState>
 
   /// Object interning
-  var objects = [OcaONo: OcaRoot]()
+  var objects = OcaObjectCache()
 
   /// Root block, immutable
   public let rootBlock = OcaBlock(objectNumber: OcaRootBlockONo)
@@ -425,7 +425,7 @@ open class Ocp1Connection: CustomStringConvertible {
   open func connectDevice() async throws {}
 
   public func clearObjectCache() async {
-    objects = [:]
+    objects.removeAll()
   }
 
   open func disconnectDevice() async throws {}