Fix Reactor adapter async-context race in SentinelReactorSubscriber.currentContext (#1)

* Initial plan

* fix(reactor): avoid async context race in currentContext and add regression test

Agent-Logs-Url: https://github.com/wuwen5/Sentinel/sessions/1d7e9bbc-a643-4695-a906-b0575add87f0

Co-authored-by: wuwen5 <5037807+wuwen5@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wuwen5 <5037807+wuwen5@users.noreply.github.com>

Author: Copilot

sentinel-adapter/sentinel-reactor-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/reactor/SentinelReactorSubscriber.java

@@ -67,7 +67,7 @@ public Context currentContext() {
             return actual.currentContext();
         }
         return actual.currentContext()
-            .put(SentinelReactorConstants.SENTINEL_CONTEXT_KEY, currentEntry.getAsyncContext());
+            .put(SentinelReactorConstants.SENTINEL_CONTEXT_KEY, sentinelContext);
     }
 
     private void doWithContextOrCurrent(Supplier<Optional<com.alibaba.csp.sentinel.context.Context>> contextSupplier,

sentinel-adapter/sentinel-reactor-adapter/src/test/java/com/alibaba/csp/sentinel/adapter/reactor/SentinelReactorSubscriberTest.java

@@ -0,0 +1,86 @@
+package com.alibaba.csp.sentinel.adapter.reactor;
+
+import java.lang.reflect.Field;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+
+import com.alibaba.csp.sentinel.AsyncEntry;
+
+import org.junit.Test;
+import org.reactivestreams.Subscription;
+import reactor.core.CoreSubscriber;
+import reactor.util.context.Context;
+
+import static org.junit.Assert.*;
+
+public class SentinelReactorSubscriberTest {
+
+    @Test
+    public void testCurrentContextShouldUseCapturedAsyncContextWhenExitHappensDuringContextRead() throws Exception {
+        AtomicBoolean allowCancelInContextRead = new AtomicBoolean(false);
+        AtomicBoolean canceledInContextRead = new AtomicBoolean(false);
+        AtomicReference<SentinelReactorSubscriber<Integer>> subscriberRef = new AtomicReference<>();
+
+        CoreSubscriber<Integer> actual = new CoreSubscriber<Integer>() {
+            @Override
+            public Context currentContext() {
+                SentinelReactorSubscriber<Integer> subscriber = subscriberRef.get();
+                if (allowCancelInContextRead.get() && subscriber != null
+                    && canceledInContextRead.compareAndSet(false, true)) {
+                    subscriber.cancel();
+                }
+                return Context.empty();
+            }
+
+            @Override
+            public void onSubscribe(Subscription s) {
+            }
+
+            @Override
+            public void onNext(Integer integer) {
+            }
+
+            @Override
+            public void onError(Throwable t) {
+                fail("Unexpected error: " + t);
+            }
+
+            @Override
+            public void onComplete() {
+            }
+        };
+
+        SentinelReactorSubscriber<Integer> subscriber =
+            new SentinelReactorSubscriber<>(new EntryConfig("testCurrentContextRace"), actual, false);
+        subscriberRef.set(subscriber);
+        subscriber.onSubscribe(new NoopSubscription());
+
+        AsyncEntry currentEntry = getCurrentEntry(subscriber);
+        assertNotNull(currentEntry);
+        com.alibaba.csp.sentinel.context.Context asyncContextBeforeExit = currentEntry.getAsyncContext();
+        assertNotNull(asyncContextBeforeExit);
+
+        allowCancelInContextRead.set(true);
+        Context reactorContext = subscriber.currentContext();
+
+        assertTrue(canceledInContextRead.get());
+        assertSame(asyncContextBeforeExit, reactorContext.get(SentinelReactorConstants.SENTINEL_CONTEXT_KEY));
+        assertNull(currentEntry.getAsyncContext());
+    }
+
+    private static AsyncEntry getCurrentEntry(SentinelReactorSubscriber<?> subscriber) throws Exception {
+        Field field = SentinelReactorSubscriber.class.getDeclaredField("currentEntry");
+        field.setAccessible(true);
+        return (AsyncEntry)field.get(subscriber);
+    }
+
+    private static final class NoopSubscription implements Subscription {
+        @Override
+        public void request(long n) {
+        }
+
+        @Override
+        public void cancel() {
+        }
+    }
+}