implement a safe concurrent dictionary

Sources/Voxelotl/Common/ConcurrentDictionary.swift

@@ -0,0 +1,73 @@
+import Foundation
+
+public class ConcurrentDictionary<V: Hashable, T>: Collection {
+  private var inner: [V : T]
+  private var lock: NSLock = .init()
+
+  public var keys: Dictionary<V, T>.Keys {
+    self.locked {
+      inner.keys
+    }
+  }
+
+  public var values: Dictionary<V, T>.Values {
+      self.locked {
+        self.inner.values
+      }
+  }
+
+  public var startIndex: Dictionary<V, T>.Index {
+      self.locked {
+          self.inner.startIndex
+      }
+  }
+
+  public var endIndex: Dictionary<V, T>.Index {
+      self.locked {
+          self.inner.endIndex
+      }
+  }
+
+  public init(inner: [V:T]) {
+    self.inner = inner
+  }
+
+  public convenience init() {
+    self.init(inner: [:])
+  }
+
+  public func index(after i: Dictionary<V, T>.Index) -> Dictionary<V, T>.Index {
+    self.locked {
+      self.inner.index(after: i)
+    }
+  }
+
+  public subscript(key: V) -> T? {
+      set(newValue) {
+          self.locked {
+            self.inner[key] = newValue
+          }
+      }
+
+      get {
+        self.locked {
+          self.inner[key]
+        }
+      }
+  }
+
+  public subscript(index: Dictionary<V, T>.Index) -> Dictionary<V, T>.Element {
+      self.locked {
+        self.inner[index]
+      }
+  }
+
+  fileprivate func locked<X>(_ perform: () -> X) -> X {
+    self.lock.lock()
+    defer {
+      self.lock.unlock()
+    }
+    let value = perform()
+    return value
+  }
+}