From 5ecea7cdd07b0d24178da2406519a98d80a8e2f8 Mon Sep 17 00:00:00 2001
From: Jimmy Shiu <jimmyshiu@google.com>
Date: Wed, 19 Apr 2023 13:49:53 +0800
Subject: [PATCH] Fixed flaky
 HintManagerServiceTest#testReportActualWorkDuration

The flake is related to the running sequence. If Object#notify() is called before Object#wait(), the latter will block forever.

Using CountDownLatch to solve the problem.
CountDownLatch#await() will wait until its count reaches 0.
CountDownLatch with an initial count of 1, so the code after CountDownLatch#await() will only run after CountDownLatch#countDown() has been called.

Bug: 277881247
Test: atest HintManagerServiceTest
Test: verify by adding sleep between countdown() and await()
Change-Id: I1a2b0fbec5f48f504107e3c031bf6e9f3ff571f5
---
 .../power/hint/HintManagerServiceTest.java    | 53 +++++++++----------
 1 file changed, 26 insertions(+), 27 deletions(-)

diff --git a/services/tests/servicestests/src/com/android/server/power/hint/HintManagerServiceTest.java b/services/tests/servicestests/src/com/android/server/power/hint/HintManagerServiceTest.java
index 136507d429fc6..726a4e285d682 100644
--- a/services/tests/servicestests/src/com/android/server/power/hint/HintManagerServiceTest.java
+++ b/services/tests/servicestests/src/com/android/server/power/hint/HintManagerServiceTest.java
@@ -57,6 +57,8 @@ import org.junit.Test;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
+import java.util.concurrent.CountDownLatch;
+
 /**
  * Tests for {@link com.android.server.power.hint.HintManagerService}.
  *
@@ -149,29 +151,28 @@ public class HintManagerServiceTest {
         // Set session to background and calling updateHintAllowed() would invoke pause();
         service.mUidObserver.onUidStateChanged(
                 a.mUid, ActivityManager.PROCESS_STATE_TRANSIENT_BACKGROUND, 0, 0);
-        final Object sync = new Object();
+
+        // Using CountDownLatch to ensure above onUidStateChanged() job was digested.
+        final CountDownLatch latch = new CountDownLatch(1);
         FgThread.getHandler().post(() -> {
-            synchronized (sync) {
-                sync.notify();
-            }
+            latch.countDown();
         });
-        synchronized (sync) {
-            sync.wait();
-        }
+        latch.await();
+
         assumeFalse(a.updateHintAllowed());
         verify(mNativeWrapperMock, times(1)).halPauseHintSession(anyLong());
 
         // Set session to foreground and calling updateHintAllowed() would invoke resume();
         service.mUidObserver.onUidStateChanged(
                 a.mUid, ActivityManager.PROCESS_STATE_IMPORTANT_FOREGROUND, 0, 0);
+
+        // Using CountDownLatch to ensure above onUidStateChanged() job was digested.
+        final CountDownLatch latch2 = new CountDownLatch(1);
         FgThread.getHandler().post(() -> {
-            synchronized (sync) {
-                sync.notify();
-            }
+            latch2.countDown();
         });
-        synchronized (sync) {
-            sync.wait();
-        }
+        latch2.await();
+
         assumeTrue(a.updateHintAllowed());
         verify(mNativeWrapperMock, times(1)).halResumeHintSession(anyLong());
     }
@@ -237,15 +238,14 @@ public class HintManagerServiceTest {
         // Set session to background, then the duration would not be updated.
         service.mUidObserver.onUidStateChanged(
                 a.mUid, ActivityManager.PROCESS_STATE_TRANSIENT_BACKGROUND, 0, 0);
-        final Object sync = new Object();
+
+        // Using CountDownLatch to ensure above onUidStateChanged() job was digested.
+        final CountDownLatch latch = new CountDownLatch(1);
         FgThread.getHandler().post(() -> {
-            synchronized (sync) {
-                sync.notify();
-            }
+            latch.countDown();
         });
-        synchronized (sync) {
-            sync.wait();
-        }
+        latch.await();
+
         assumeFalse(a.updateHintAllowed());
         a.reportActualWorkDuration(DURATIONS_THREE, TIMESTAMPS_THREE);
         verify(mNativeWrapperMock, never()).halReportActualWorkDuration(anyLong(), any(), any());
@@ -287,15 +287,14 @@ public class HintManagerServiceTest {
 
         service.mUidObserver.onUidStateChanged(
                 a.mUid, ActivityManager.PROCESS_STATE_IMPORTANT_BACKGROUND, 0, 0);
-        final Object sync = new Object();
+
+        // Using CountDownLatch to ensure above onUidStateChanged() job was digested.
+        final CountDownLatch latch = new CountDownLatch(1);
         FgThread.getHandler().post(() -> {
-            synchronized (sync) {
-                sync.notify();
-            }
+            latch.countDown();
         });
-        synchronized (sync) {
-            sync.wait();
-        }
+        latch.await();
+
         assertFalse(a.updateHintAllowed());
     }