adopt swift-atomics

Package.resolved

@@ -45,6 +45,15 @@
           "revision": "6094e6f23a02b52b5d211fd114a4750c4f3ecef3",
           "version": "0.2.1"
         }
+      },
+      {
+        "package": "swift-atomics",
+        "repositoryURL": "https://github.com/apple/swift-atomics.git",
+        "state": {
+          "branch": null,
+          "revision": "3e95ba32cd1b4c877f6163e8eea54afc4e63bf9f",
+          "version": "0.0.3"
+        }
       }
     ]
   },

Package.swift

@@ -7,6 +7,9 @@ let package = Package(
     products: [
         .library(name: "CombineX", targets: ["CombineX", "CXFoundation"]),
     ],
+    dependencies: [
+        // TODO: use swift-atomics which requires swift 5.1
+    ],
     targets: [
         .target(name: "CXUtility"),
         .target(name: "CombineX", dependencies: ["CXUtility"]),

Package@swift-5.2.swift

@@ -15,14 +15,22 @@ let package = Package(
         .library(name: "CombineX", targets: ["CombineX", "CXFoundation"]),
     ],
     dependencies: [
+        .package(url: "https://github.com/apple/swift-atomics.git", .upToNextMinor(from: "0.0.3")),
         .package(url: "https://github.com/Quick/Quick.git", from: "3.0.0"),
         .package(url: "https://github.com/Quick/Nimble.git", from: "9.0.0"),
         .package(url: "https://github.com/ddddxxx/Semver.git", .upToNextMinor(from: "0.2.1")),
     ],
     targets: [
         .target(name: "CXUtility"),
-        .target(name: "CombineX", dependencies: ["CXUtility"]),
-        .target(name: "CXFoundation", dependencies: ["CXUtility", "CombineX"]),
+        .target(
+            name: "CombineX",
+            dependencies: [
+                "CXUtility",
+                .product(name: "Atomics", package: "swift-atomics")],
+            swiftSettings: [.define("CX_LOCK_FREE_ATOMIC")]),
+        .target(
+            name: "CXFoundation",
+            dependencies: ["CXUtility", "CombineX"]),
 
         // We have circular dependency CombineXTests -> CXTest -> CXShim -> CombineX
         //

Sources/CXTestUtility/Common.swift

@@ -0,0 +1,8 @@
+@inline(never)
+public func blackHole<T>(_ x: T) {
+}
+
+@inline(never)
+public func identity<T>(_ x: T) -> T {
+    return x
+}

Sources/CombineX/CombineIdentifier.swift

@@ -1,15 +1,23 @@
+#if CX_LOCK_FREE_ATOMIC
+@_implementationOnly import Atomics
+private let counter = UnsafeAtomic<UInt64>.create(0)
+#else
 #if !COCOAPODS
 import CXUtility
 #endif
-
 private let counter = LockedAtomic<UInt64>(0)
+#endif
 
 public struct CombineIdentifier: Hashable, CustomStringConvertible {
 
     private let value: UInt64
 
     public init() {
+        #if CX_LOCK_FREE_ATOMIC
+        self.value = counter.loadThenWrappingIncrement(ordering: .relaxed)
+        #else
         self.value = counter.loadThenWrappingIncrement()
+        #endif
     }
 
     public init(_ obj: AnyObject) {

Tests/CombineXTests/CombineIdentifierSpec.swift

@@ -39,3 +39,23 @@ class CombineIdentifierSpec: QuickSpec {
         }
     }
 }
+
+import XCTest
+
+class CombineIdentifierTests: XCTestCase {
+
+    func testPerformance() {
+        measure {
+            let g = DispatchGroup()
+            for _ in 0..<1000 {
+                DispatchQueue.global().async(group: g) {
+                    for _ in 0..<1000 {
+                        blackHole(CombineIdentifier())
+                    }
+                }
+            }
+            g.wait()
+        }
+    }
+}
+