- improved await() performance

Author: Alex Belozierov

Sources/SwiftCoroutine/Coroutine/SharedCoroutineDispatcher/SharedCoroutine.swift

@@ -22,6 +22,7 @@ internal final class SharedCoroutine {
     private var environment: UnsafeMutablePointer<CoroutineContext.SuspendData>!
     private var stackBuffer: StackBuffer!
     private var isCanceled = 0
+    private var awaitTag = 0
 
     internal init(dispatcher: SharedCoroutineDispatcher, queue: SharedCoroutineQueue, scheduler: CoroutineScheduler) {
         self.dispatcher = dispatcher
@@ -96,9 +97,13 @@ extension SharedCoroutine: CoroutineProtocol {
     internal func await<T>(_ callback: (@escaping (T) -> Void) -> Void) throws -> T {
         if isCanceled == 1 { throw CoroutineError.canceled }
         state = .suspending
-        var result: T!, resultState = 0
+        let tag = awaitTag
+        var result: T!
         callback { value in
-            if atomicExchange(&resultState, with: 1) == 1 { return }
+            while true {
+                guard self.awaitTag == tag else { return }
+                if atomicCAS(&self.awaitTag, expected: tag, desired: tag + 1) { break }
+            }
             result = value
             self.resumeIfSuspended()
         }

SwiftCoroutine.xcodeproj/xcshareddata/xcbaselines/F8CD25A920199D1000952299.xcbaseline/DEB0EA3A-457C-4029-95F2-69E53CE6D25D.plist

@@ -19,6 +19,26 @@
 		</dict>
 		<key>CoFutureAwaitTests</key>
 		<dict>
+			<key>testAbc()</key>
+			<dict>
+				<key>com.apple.XCTPerformanceMetric_WallClockTime</key>
+				<dict>
+					<key>baselineAverage</key>
+					<real>0.50477</real>
+					<key>baselineIntegrationDisplayName</key>
+					<string>Local Baseline</string>
+				</dict>
+			</dict>
+			<key>testAwaitMeasure()</key>
+			<dict>
+				<key>com.apple.XCTPerformanceMetric_WallClockTime</key>
+				<dict>
+					<key>baselineAverage</key>
+					<real>0.056</real>
+					<key>baselineIntegrationDisplayName</key>
+					<string>Local Baseline</string>
+				</dict>
+			</dict>
 			<key>testMultipleAwaits()</key>
 			<dict>
 				<key>com.apple.XCTPerformanceMetric_WallClockTime</key>
@@ -44,7 +64,7 @@
 				<key>com.apple.XCTPerformanceMetric_WallClockTime</key>
 				<dict>
 					<key>baselineAverage</key>
-					<real>0.121</real>
+					<real>0.0836</real>
 					<key>baselineIntegrationDisplayName</key>
 					<string>Local Baseline</string>
 				</dict>

Tests/SwiftCoroutineTests/CoFutureTests/CoFutureAwaitTests.swift

@@ -45,6 +45,16 @@ class CoFutureAwaitTests: XCTestCase {
         XCTAssertTrue(array.enumerated().allSatisfy { $0.element == $0.offset })
         array.deallocate()
     }
+    
+    func testAwaitMeasure() {
+        measure {
+            ImmediateScheduler().startCoroutine {
+                for index in 0..<100_000 {
+                    let _ = try Coroutine.await { $0(index) }
+                }
+            }
+        }
+    }
 
     func testNestetAwaits() {
         let queue = DispatchQueue.global(qos: .userInteractive)