2.x: fix buffer(time, maxSize) duplicating buffers on time-size race (#5427)

Author: akarnokd

src/main/java/io/reactivex/internal/operators/flowable/FlowableBufferTimed.java

@@ -460,12 +460,12 @@ public void onNext(T t) {
                 if (b.size() < maxSize) {
                     return;
                 }
-            }
 
-            if (restartTimerOnMaxSize) {
                 buffer = null;
                 producerIndex++;
+            }
 
+            if (restartTimerOnMaxSize) {
                 timer.dispose();
             }
 
@@ -480,17 +480,12 @@ public void onNext(T t) {
                 return;
             }
 
+            synchronized (this) {
+                buffer = b;
+                consumerIndex++;
+            }
             if (restartTimerOnMaxSize) {
-                synchronized (this) {
-                    buffer = b;
-                    consumerIndex++;
-                }
-
                 timer = w.schedulePeriodically(this, timespan, timespan, unit);
-            } else {
-                synchronized (this) {
-                    buffer = b;
-                }
             }
         }
 

src/main/java/io/reactivex/internal/operators/observable/ObservableBufferTimed.java

@@ -458,12 +458,11 @@ public void onNext(T t) {
                 if (b.size() < maxSize) {
                     return;
                 }
-            }
-
-            if (restartTimerOnMaxSize) {
                 buffer = null;
                 producerIndex++;
+            }
 
+            if (restartTimerOnMaxSize) {
                 timer.dispose();
             }
 
@@ -478,17 +477,12 @@ public void onNext(T t) {
                 return;
             }
 
+            synchronized (this) {
+                buffer = b;
+                consumerIndex++;
+            }
             if (restartTimerOnMaxSize) {
-                synchronized (this) {
-                    buffer = b;
-                    consumerIndex++;
-                }
-
                 timer = w.schedulePeriodically(this, timespan, timespan, unit);
-            } else {
-                synchronized (this) {
-                    buffer = b;
-                }
             }
         }
 

src/test/java/io/reactivex/internal/operators/flowable/FlowableBufferTest.java

@@ -1973,4 +1973,45 @@ public void skipBackpressure() {
         .test()
         .assertResult(Arrays.asList(1, 2), Arrays.asList(4, 5), Arrays.asList(7, 8), Arrays.asList(10));
     }
+
+    @Test
+    public void withTimeAndSizeCapacityRace() {
+        for (int i = 0; i < 1000; i++) {
+            final TestScheduler scheduler = new TestScheduler();
+
+            final PublishProcessor<Object> ps = PublishProcessor.create();
+
+            TestSubscriber<List<Object>> ts = ps.buffer(1, TimeUnit.SECONDS, scheduler, 5).test();
+
+            ps.onNext(1);
+            ps.onNext(2);
+            ps.onNext(3);
+            ps.onNext(4);
+
+            Runnable r1 = new Runnable() {
+                @Override
+                public void run() {
+                    ps.onNext(5);
+                }
+            };
+
+            Runnable r2 = new Runnable() {
+                @Override
+                public void run() {
+                    scheduler.advanceTimeBy(1, TimeUnit.SECONDS);
+                }
+            };
+
+            TestHelper.race(r1, r2);
+
+            ps.onComplete();
+
+            int items = 0;
+            for (List<Object> o : ts.values()) {
+                items += o.size();
+            }
+
+            assertEquals("Round: " + i, 5, items);
+        }
+    }
 }

src/test/java/io/reactivex/internal/operators/observable/ObservableBufferTest.java

@@ -1398,4 +1398,45 @@ public void bufferTimedExactBoundedError() {
         to
         .assertFailure(TestException.class);
     }
+
+    @Test
+    public void withTimeAndSizeCapacityRace() {
+        for (int i = 0; i < 1000; i++) {
+            final TestScheduler scheduler = new TestScheduler();
+
+            final PublishSubject<Object> ps = PublishSubject.create();
+
+            TestObserver<List<Object>> ts = ps.buffer(1, TimeUnit.SECONDS, scheduler, 5).test();
+
+            ps.onNext(1);
+            ps.onNext(2);
+            ps.onNext(3);
+            ps.onNext(4);
+
+            Runnable r1 = new Runnable() {
+                @Override
+                public void run() {
+                    ps.onNext(5);
+                }
+            };
+
+            Runnable r2 = new Runnable() {
+                @Override
+                public void run() {
+                    scheduler.advanceTimeBy(1, TimeUnit.SECONDS);
+                }
+            };
+
+            TestHelper.race(r1, r2);
+
+            ps.onComplete();
+
+            int items = 0;
+            for (List<Object> o : ts.values()) {
+                items += o.size();
+            }
+
+            assertEquals("Round: " + i, 5, items);
+        }
+    }
 }