3.x: Fix takeLast(time) last events time window calculation. (#6648)

Author: akarnokd

src/main/java/io/reactivex/rxjava3/internal/operators/observable/ObservableTakeLastTimed.java

@@ -139,6 +139,7 @@ void drain() {
             final Observer<? super T> a = downstream;
             final SpscLinkedArrayQueue<Object> q = queue;
             final boolean delayError = this.delayError;
+            final long timestampLimit = scheduler.now(unit) - time;
 
             for (;;) {
                 if (cancelled) {
@@ -171,7 +172,7 @@ void drain() {
                 @SuppressWarnings("unchecked")
                 T o = (T)q.poll();
 
-                if ((Long)ts < scheduler.now(unit) - time) {
+                if ((Long)ts < timestampLimit) {
                     continue;
                 }
 

src/test/java/io/reactivex/rxjava3/internal/operators/flowable/FlowableTakeLastTimedTest.java

@@ -28,7 +28,7 @@
 import io.reactivex.rxjava3.processors.PublishProcessor;
 import io.reactivex.rxjava3.schedulers.*;
 import io.reactivex.rxjava3.subscribers.TestSubscriber;
-import io.reactivex.rxjava3.testsupport.TestHelper;
+import io.reactivex.rxjava3.testsupport.*;
 
 public class FlowableTakeLastTimedTest extends RxJavaTest {
 
@@ -338,4 +338,27 @@ public Publisher<Object> apply(Flowable<Object> f) throws Exception {
     public void badRequest() {
         TestHelper.assertBadRequestReported(PublishProcessor.create().takeLast(1, TimeUnit.SECONDS));
     }
+
+    @Test
+    public void lastWindowIsFixedInTime() {
+        TimesteppingScheduler scheduler = new TimesteppingScheduler();
+        scheduler.stepEnabled = false;
+
+        PublishProcessor<Integer> pp = PublishProcessor.create();
+
+        TestSubscriber<Integer> ts = pp
+        .takeLast(2, TimeUnit.SECONDS, scheduler)
+        .test();
+
+        pp.onNext(1);
+        pp.onNext(2);
+        pp.onNext(3);
+        pp.onNext(4);
+
+        scheduler.stepEnabled = true;
+
+        pp.onComplete();
+
+        ts.assertResult(1, 2, 3, 4);
+    }
 }

src/test/java/io/reactivex/rxjava3/internal/operators/observable/ObservableTakeLastTimedTest.java

@@ -26,7 +26,7 @@
 import io.reactivex.rxjava3.observers.TestObserver;
 import io.reactivex.rxjava3.schedulers.*;
 import io.reactivex.rxjava3.subjects.PublishSubject;
-import io.reactivex.rxjava3.testsupport.TestHelper;
+import io.reactivex.rxjava3.testsupport.*;
 
 public class ObservableTakeLastTimedTest extends RxJavaTest {
 
@@ -277,4 +277,27 @@ public void run() {
             TestHelper.race(r1, r2);
         }
     }
+
+    @Test
+    public void lastWindowIsFixedInTime() {
+        TimesteppingScheduler scheduler = new TimesteppingScheduler();
+        scheduler.stepEnabled = false;
+
+        PublishSubject<Integer> ps = PublishSubject.create();
+
+        TestObserver<Integer> to = ps
+        .takeLast(2, TimeUnit.SECONDS, scheduler)
+        .test();
+
+        ps.onNext(1);
+        ps.onNext(2);
+        ps.onNext(3);
+        ps.onNext(4);
+
+        scheduler.stepEnabled = true;
+
+        ps.onComplete();
+
+        to.assertResult(1, 2, 3, 4);
+    }
 }

src/test/java/io/reactivex/rxjava3/testsupport/TimesteppingScheduler.java

@@ -22,7 +22,7 @@
  * Basic scheduler that produces an ever increasing {@link #now(TimeUnit)} value.
  * Use this scheduler only as a time source!
  */
-public class TimesteppingScheduler extends Scheduler {
+public final class TimesteppingScheduler extends Scheduler {
 
     final class TimesteppingWorker extends Worker {
         @Override
@@ -42,11 +42,13 @@ public Disposable schedule(Runnable run, long delay, TimeUnit unit) {
 
         @Override
         public long now(TimeUnit unit) {
-            return time++;
+            return TimesteppingScheduler.this.now(unit);
         }
     }
 
-    long time;
+    public long time;
+
+    public boolean stepEnabled = true;
 
     @Override
     public Worker createWorker() {
@@ -55,6 +57,9 @@ public Worker createWorker() {
 
     @Override
     public long now(TimeUnit unit) {
-        return time++;
+        if (stepEnabled) {
+            return time++;
+        }
+        return time;
     }
 }