fix(#2553) : AsyncSequence.asObservable() runs on background thread

CHANGELOG.md

@@ -11,6 +11,7 @@ All notable changes to this project will be documented in this file.
 * Provides `Infallible` versions of `combineLatest` without `resultSelector` requirement.
 * Provides `Infallible` versions of `CombineLatest+Collection` helpers.
 * Explicitly declare `APPLICATION_EXTENSION_API_ONLY` for CocoaPods 
+* Ensure `AsyncSequence.asObservable()` runs on background thread using `Task.detached`. 
 
 ## 6.5.0
 

RxSwift/Observable+Concurrency.swift

@@ -60,7 +60,7 @@ public extension AsyncSequence {
     /// - returns: An `Observable` of the async sequence's type
     func asObservable() -> Observable<Element> {
         Observable.create { observer in
-            let task = Task {
+            let task = Task.detached {
                 do {
                     for try await value in self {
                         observer.onNext(value)

Tests/RxSwiftTests/Observable+ConcurrencyTests.swift

@@ -90,5 +90,111 @@ extension ObservableConcurrencyTests {
         task.cancel()
     }
 
+    func testAsyncSequenceToObservableRunsOnBackgroundThread() async throws {
+
+        let asyncSequence = AsyncStream<Int> { continuation in
+            for i in 1...5 {
+                continuation.yield(i)
+            }
+            continuation.finish()
+        }
+
+        let expectation = XCTestExpectation(description: "Observable completes")
+
+        DispatchQueue.main.async {
+            let observable = asyncSequence.asObservable()
+
+            var threadIsNotMain = false
+            var values = [Int]()
+
+            _ = observable.subscribe(
+                onNext: { value in
+                    values.append(value)
+                    threadIsNotMain = !Thread.isMainThread
+                },
+                onCompleted: {
+                    XCTAssertEqual(values, [1, 2, 3, 4, 5])
+                    XCTAssertTrue(threadIsNotMain, "AsyncSequence.asObservable should not run on main thread")
+                    expectation.fulfill()
+                }
+            )
+        }
+
+        await fulfillment(of: [expectation], timeout: 5.0)
+    }
+
+    func testAsyncSequenceToObservableWithSleep() async throws {
+        let asyncSequence = AsyncStream<Int> { continuation in
+            Task {
+                for i in 1...3 {
+                    try? await Task.sleep(nanoseconds: 100_000_000)
+                    continuation.yield(i)
+                }
+                continuation.finish()
+            }
+        }
+
+        let expectation = XCTestExpectation(description: "Observable with sleep completes")
+
+        DispatchQueue.main.async {
+            let startTime = Date()
+            var values = [Int]()
+            var executionThreads = Set<String>()
+
+            _ = asyncSequence.asObservable().subscribe(
+                onNext: { value in
+                    values.append(value)
+                    let threadName = Thread.current.description
+                    executionThreads.insert(threadName)
+                },
+                onCompleted: {
+                    let duration = Date().timeIntervalSince(startTime)
+                    XCTAssertGreaterThanOrEqual(duration, 0.3)
+                    XCTAssertEqual(values, [1, 2, 3])
+                    XCTAssertFalse(executionThreads.contains(where: { $0.contains("main") }))
+
+                    expectation.fulfill()
+                }
+            )
+        }
+
+        await fulfillment(of: [expectation], timeout: 5.0)
+    }
+
+    func testAsyncSequenceToObservableWithError() async throws {
+        struct TestError: Error {}
+
+        let asyncSequence = AsyncThrowingStream<Int, Error> { continuation in
+            for i in 1...3 {
+                continuation.yield(i)
+            }
+            continuation.finish(throwing: TestError())
+        }
+
+        let expectation = XCTestExpectation(description: "Observable with error completes")
+
+        var values = [Int]()
+        var receivedError: Error?
+        var threadIsNotMain = false
+
+        DispatchQueue.main.async {
+            _ = asyncSequence.asObservable().subscribe(
+                onNext: { value in
+                    values.append(value)
+                    threadIsNotMain = !Thread.isMainThread
+                },
+                onError: { error in
+                    receivedError = error
+                    XCTAssertEqual(values, [1, 2, 3])
+                    XCTAssertTrue(threadIsNotMain, "Error handler should not run on main thread")
+                    expectation.fulfill()
+                }
+            )
+        }
+
+        await fulfillment(of: [expectation], timeout: 5.0)
+        XCTAssertTrue(receivedError is TestError)
+    }
+
 }
 #endif