Data commit

Task/Atomic-updates/Swift/atomic-updates.swift

@@ -0,0 +1,87 @@
+import Foundation
+
+final class AtomicBuckets: CustomStringConvertible {
+  var count: Int {
+    return buckets.count
+  }
+
+  var description: String {
+    return withBucketsLocked { "\(buckets)" }
+  }
+
+  var total: Int {
+    return withBucketsLocked { buckets.reduce(0, +) }
+  }
+
+  private let lock = DispatchSemaphore(value: 1)
+
+  private var buckets: [Int]
+
+  subscript(n: Int) -> Int {
+    return withBucketsLocked { buckets[n] }
+  }
+
+  init(with buckets: [Int]) {
+    self.buckets = buckets
+  }
+
+  func transfer(amount: Int, from: Int, to: Int) {
+    withBucketsLocked {
+      let transferAmount = buckets[from] >= amount ? amount : buckets[from]
+
+      buckets[from] -= transferAmount
+      buckets[to] += transferAmount
+    }
+  }
+
+  private func withBucketsLocked<T>(do: () -> T) -> T {
+    let ret: T
+
+    lock.wait()
+    ret = `do`()
+    lock.signal()
+
+    return ret
+  }
+}
+
+let bucks = AtomicBuckets(with: [21, 39, 40, 20])
+let order = DispatchSource.makeTimerSource()
+let chaos = DispatchSource.makeTimerSource()
+let printer = DispatchSource.makeTimerSource()
+
+printer.setEventHandler {
+  print("\(bucks) = \(bucks.total)")
+}
+
+printer.schedule(deadline: .now(), repeating: .seconds(1))
+printer.activate()
+
+order.setEventHandler {
+  let (b1, b2) = (Int.random(in: 0..<bucks.count), Int.random(in: 0..<bucks.count))
+  let (v1, v2) = (bucks[b1], bucks[b2])
+
+  guard v1 != v2 else {
+    return
+  }
+
+  if v1 > v2 {
+    bucks.transfer(amount: (v1 - v2) / 2, from: b1, to: b2)
+  } else {
+    bucks.transfer(amount: (v2 - v1) / 2, from: b2, to: b1)
+  }
+}
+
+order.schedule(deadline: .now(), repeating: .milliseconds(5))
+order.activate()
+
+chaos.setEventHandler {
+  let (b1, b2) = (Int.random(in: 0..<bucks.count), Int.random(in: 0..<bucks.count))
+
+  bucks.transfer(amount: Int.random(in: 0..<(bucks[b1] + 1)), from: b1, to: b2)
+}
+
+chaos.schedule(deadline: .now(), repeating: .milliseconds(5))
+chaos.activate()
+
+dispatchMain()