From bf641100e745cc676c56d6e77ea5ae0c94c28859 Mon Sep 17 00:00:00 2001
From: Arthur Liu <arthurliu1994@gmail.com>
Date: Wed, 22 Jul 2026 10:42:38 -0700
Subject: [PATCH] Fix concurrent share subscriptions

---
 RxSwift/Observables/ShareReplayScope.swift |  2 +-
 Sources/AllTestz/main.swift                |  1 +
 Tests/RxSwiftTests/Anomalies.swift         | 54 ++++++++++++++++++++++
 3 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/RxSwift/Observables/ShareReplayScope.swift b/RxSwift/Observables/ShareReplayScope.swift
index dab3e82f2..e5732404e 100644
--- a/RxSwift/Observables/ShareReplayScope.swift
+++ b/RxSwift/Observables/ShareReplayScope.swift
@@ -408,8 +408,8 @@ private final class ShareWhileConnected<Element>:
         let connection = synchronized_subscribe(observer)
         let count = connection.observers.count
 
-        lock.unlock()
         let disposable = connection.synchronized_subscribe(observer)
+        lock.unlock()
 
         if count == 0 {
             connection.connect()
diff --git a/Sources/AllTestz/main.swift b/Sources/AllTestz/main.swift
index 511927e7e..5cf128a41 100644
--- a/Sources/AllTestz/main.swift
+++ b/Sources/AllTestz/main.swift
@@ -24,6 +24,7 @@ final class AnomaliesTest_ : AnomaliesTest, RxTestCase {
     ("test1323", AnomaliesTest.test1323),
     ("test1344", AnomaliesTest.test1344),
     ("testSeparationBetweenOnAndSubscriptionLocks", AnomaliesTest.testSeparationBetweenOnAndSubscriptionLocks),
+    ("test2718ShareWithoutReplayConnectsOnceForConcurrentFirstSubscriptions", AnomaliesTest.test2718ShareWithoutReplayConnectsOnceForConcurrentFirstSubscriptions),
     ("test2653ShareReplayOneInitialEmissionDeadlock", AnomaliesTest.test2653ShareReplayOneInitialEmissionDeadlock),
     ("test2653ShareReplayMoreInitialEmissionDeadlock", AnomaliesTest.test2653ShareReplayMoreInitialEmissionDeadlock),
     ("test2653ShareReplayOneForeverInitialEmissionDeadlock", AnomaliesTest.test2653ShareReplayOneForeverInitialEmissionDeadlock),
diff --git a/Tests/RxSwiftTests/Anomalies.swift b/Tests/RxSwiftTests/Anomalies.swift
index aa0a56bc4..b66da73ad 100644
--- a/Tests/RxSwiftTests/Anomalies.swift
+++ b/Tests/RxSwiftTests/Anomalies.swift
@@ -176,6 +176,60 @@ extension AnomaliesTest {
         }
     }
 
+    func test2718ShareWithoutReplayConnectsOnceForConcurrentFirstSubscriptions() {
+        let subscriberCount = 32
+
+        for _ in 0 ..< 100 {
+            let subscriptionsLock = NSLock()
+            var sourceSubscriptionCount = 0
+            var subscriptions = [Disposable]()
+
+            let shared = Observable<Never>.never()
+                .do(onSubscribe: {
+                    subscriptionsLock.lock()
+                    sourceSubscriptionCount += 1
+                    subscriptionsLock.unlock()
+                })
+                .share(replay: 0, scope: .whileConnected)
+
+            let ready = DispatchGroup()
+            let finished = DispatchGroup()
+            let start = DispatchSemaphore(value: 0)
+
+            for _ in 0 ..< subscriberCount {
+                ready.enter()
+                finished.enter()
+
+                DispatchQueue.global(qos: .userInitiated).async {
+                    ready.leave()
+                    start.wait()
+
+                    let subscription = shared.subscribe()
+
+                    subscriptionsLock.lock()
+                    subscriptions.append(subscription)
+                    subscriptionsLock.unlock()
+
+                    finished.leave()
+                }
+            }
+
+            XCTAssertEqual(ready.wait(timeout: .now() + 5), .success)
+            for _ in 0 ..< subscriberCount {
+                start.signal()
+            }
+            XCTAssertEqual(finished.wait(timeout: .now() + 5), .success)
+
+            subscriptionsLock.lock()
+            let subscriptionCount = sourceSubscriptionCount
+            let subscriptionsToDispose = subscriptions
+            subscriptionsLock.unlock()
+
+            XCTAssertEqual(subscriptionCount, 1)
+            subscriptionsToDispose.forEach { $0.dispose() }
+        }
+    }
+
     func test2653ShareReplayOneInitialEmissionDeadlock() {
         let immediatelyEmittingSource = Observable<Void>.create { observer in
             observer.on(.next(()))