From a995fa637740fea7804a7452542ef3db184cf405 Mon Sep 17 00:00:00 2001
From: Xander Deng <dengxiang2010@gmail.com>
Date: Wed, 30 Jun 2021 16:33:27 +0800
Subject: [PATCH] adopt swift-atomics

---
 Package.resolved                              |  9 +++++++++
 Package.swift                                 |  3 +++
 Package@swift-5.2.swift                       | 12 +++++++++--
 Sources/CXTestUtility/Common.swift            |  8 ++++++++
 Sources/CombineX/CombineIdentifier.swift      | 10 +++++++++-
 .../CombineXTests/CombineIdentifierSpec.swift | 20 +++++++++++++++++++
 6 files changed, 59 insertions(+), 3 deletions(-)
 create mode 100644 Sources/CXTestUtility/Common.swift

diff --git a/Package.resolved b/Package.resolved
index 8d1e7e2e..8bead854 100644
--- a/Package.resolved
+++ b/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"
+        }
       }
     ]
   },
diff --git a/Package.swift b/Package.swift
index 9272ef40..d7846a93 100644
--- a/Package.swift
+++ b/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"]),
diff --git a/Package@swift-5.2.swift b/Package@swift-5.2.swift
index 39a49557..0ce15b94 100644
--- a/Package@swift-5.2.swift
+++ b/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
         //
diff --git a/Sources/CXTestUtility/Common.swift b/Sources/CXTestUtility/Common.swift
new file mode 100644
index 00000000..0e5db7ac
--- /dev/null
+++ b/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
+}
diff --git a/Sources/CombineX/CombineIdentifier.swift b/Sources/CombineX/CombineIdentifier.swift
index dfe36966..a10ea9b0 100644
--- a/Sources/CombineX/CombineIdentifier.swift
+++ b/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) {
diff --git a/Tests/CombineXTests/CombineIdentifierSpec.swift b/Tests/CombineXTests/CombineIdentifierSpec.swift
index c2e065bb..d1b8a8ea 100644
--- a/Tests/CombineXTests/CombineIdentifierSpec.swift
+++ b/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()
+        }
+    }
+}
+