3.x: better leak detection via GC/sleep loop (#6628)

* 3.x: better leak detection via GC/sleep loop

* Remove the unnecessary sleeps

Author: akarnokd

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

@@ -676,11 +676,7 @@ public Object call() throws Exception {
 
         source.subscribe();
 
-        Thread.sleep(100);
-        System.gc();
-        Thread.sleep(100);
-
-        long after = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage().getUsed();
+        long after = TestHelper.awaitGC(GC_SLEEP_TIME, 20, start + 20 * 1000 * 1000);
 
         source = null;
         assertTrue(String.format("%,3d -> %,3d%n", start, after), start + 20 * 1000 * 1000 > after);
@@ -712,11 +708,7 @@ public Object call() throws Exception {
         d1 = null;
         d2 = null;
 
-        Thread.sleep(100);
-        System.gc();
-        Thread.sleep(100);
-
-        long after = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage().getUsed();
+        long after = TestHelper.awaitGC(GC_SLEEP_TIME, 20, start + 20 * 1000 * 1000);
 
         source = null;
         assertTrue(String.format("%,3d -> %,3d%n", start, after), start + 20 * 1000 * 1000 > after);
@@ -752,10 +744,7 @@ public Object call() throws Exception {
 
         source.subscribe(Functions.emptyConsumer(), Functions.emptyConsumer());
 
-        System.gc();
-        Thread.sleep(GC_SLEEP_TIME);
-
-        long after = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage().getUsed();
+        long after = TestHelper.awaitGC(GC_SLEEP_TIME, 20, start + 20 * 1000 * 1000);
 
         source = null;
 
@@ -787,10 +776,7 @@ public Object call() throws Exception {
         d1 = null;
         d2 = null;
 
-        System.gc();
-        Thread.sleep(GC_SLEEP_TIME);
-
-        long after = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage().getUsed();
+        long after = TestHelper.awaitGC(GC_SLEEP_TIME, 20, start + 20 * 1000 * 1000);
 
         source = null;
         assertTrue(String.format("%,3d -> %,3d%n", start, after), start + 20 * 1000 * 1000 > after);

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

@@ -652,10 +652,7 @@ public Object call() throws Exception {
 
         source.subscribe();
 
-        System.gc();
-        Thread.sleep(100);
-
-        long after = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage().getUsed();
+        long after = TestHelper.awaitGC(GC_SLEEP_TIME, 20, start + 20 * 1000 * 1000);
 
         source = null;
         assertTrue(String.format("%,3d -> %,3d%n", start, after), start + 20 * 1000 * 1000 > after);
@@ -686,10 +683,7 @@ public Object call() throws Exception {
         d1 = null;
         d2 = null;
 
-        System.gc();
-        Thread.sleep(100);
-
-        long after = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage().getUsed();
+        long after = TestHelper.awaitGC(GC_SLEEP_TIME, 20, start + 20 * 1000 * 1000);
 
         source = null;
         assertTrue(String.format("%,3d -> %,3d%n", start, after), start + 20 * 1000 * 1000 > after);
@@ -725,19 +719,7 @@ public Object call() throws Exception {
 
         source.subscribe(Functions.emptyConsumer(), Functions.emptyConsumer());
 
-        long after = 0L;
-
-        for (int i = 0; i < 10; i++) {
-            System.gc();
-
-            after = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage().getUsed();
-
-            if (start + 20 * 1000 * 1000 > after) {
-                break;
-            }
-
-            Thread.sleep(GC_SLEEP_TIME);
-        }
+        long after = TestHelper.awaitGC(GC_SLEEP_TIME, 20, start + 20 * 1000 * 1000);
 
         source = null;
         assertTrue(String.format("%,3d -> %,3d%n", start, after), start + 20 * 1000 * 1000 > after);
@@ -768,10 +750,7 @@ public Object call() throws Exception {
         d1 = null;
         d2 = null;
 
-        System.gc();
-        Thread.sleep(GC_SLEEP_TIME);
-
-        long after = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage().getUsed();
+        long after = TestHelper.awaitGC(GC_SLEEP_TIME, 20, start + 20 * 1000 * 1000);
 
         source = null;
         assertTrue(String.format("%,3d -> %,3d%n", start, after), start + 20 * 1000 * 1000 > after);

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

@@ -18,6 +18,7 @@
 import static org.mockito.Mockito.mock;
 
 import java.io.File;
+import java.lang.management.*;
 import java.lang.reflect.*;
 import java.net.URL;
 import java.util.*;
@@ -3391,4 +3392,31 @@ public Integer apply(Integer v) throws Throwable {
             RxJavaPlugins.reset();
         }
     }
+
+    /**
+     * Repeatedly calls System.gc() and sleeps until the current memory usage
+     * is less than the given expected usage or the given number of wait loop/time
+     * has passed.
+     * @param oneSleep how many milliseconds to sleep after a GC.
+     * @param maxLoop the maximum number of GC/sleep calls.
+     * @param expectedMemoryUsage the memory usage in bytes at max
+     * @return the actual memory usage after the loop
+     * @throws InterruptedException if the sleep is interrupted
+     */
+    public static long awaitGC(long oneSleep, int maxLoop, long expectedMemoryUsage) throws InterruptedException {
+        MemoryMXBean bean = ManagementFactory.getMemoryMXBean();
+
+        System.gc();
+
+        int i = maxLoop;
+        while (i-- != 0) {
+            long usage = bean.getHeapMemoryUsage().getUsed();
+            if (usage <= expectedMemoryUsage) {
+                return usage;
+            }
+            System.gc();
+            Thread.sleep(oneSleep);
+        }
+        return bean.getHeapMemoryUsage().getUsed();
+    }
 }