Only rewrite file when there has been a change to a list of users

Due to I/O operations being performed on BG thread, every call, especially during user boot, adds to the overall performance impact. This change adds extra checks to ensure writing only happens when the change occured.

Bug: 331980379
Bug: 335667295
Test: perfetto trace && manual
Change-Id: I86c04ef7307b10e6336b80699c1091f107d8d1bc

apex/jobscheduler/service/java/com/android/server/alarm/UserWakeupStore.java

@@ -136,10 +136,9 @@ public class UserWakeupStore {
      * Remove wakeup scheduled for the user with given userId if present.
      */
     public void removeUserWakeup(int userId) {
-        synchronized (mUserWakeupLock) {
-            mUserStarts.delete(userId);
+        if (deleteWakeupFromUserStarts(userId)) {
+            updateUserListFile();
         }
-        updateUserListFile();
     }
 
     /**
@@ -186,7 +185,7 @@ public class UserWakeupStore {
      * Return scheduled start time for user or -1 if user does not have alarm set.
      */
     @VisibleForTesting
-    long getWakeupTimeForUserForTest(int userId) {
+    long getWakeupTimeForUser(int userId) {
         synchronized (mUserWakeupLock) {
             return mUserStarts.get(userId, -1);
         }
@@ -197,8 +196,11 @@ public class UserWakeupStore {
      */
     public void onUserStarting(int userId) {
         synchronized (mUserWakeupLock) {
-            mStartingUsers.put(userId, getWakeupTimeForUserForTest(userId));
-            mUserStarts.delete(userId);
+            final long wakeup = getWakeupTimeForUser(userId);
+            if (wakeup >= 0) {
+                mStartingUsers.put(userId, wakeup);
+                mUserStarts.delete(userId);
+            }
         }
     }
 
@@ -206,21 +208,48 @@ public class UserWakeupStore {
      * Remove userId from starting user list once start is complete.
      */
     public void onUserStarted(int userId) {
-        synchronized (mUserWakeupLock) {
-            mStartingUsers.delete(userId);
+        if (deleteWakeupFromStartingUsers(userId)) {
+            updateUserListFile();
         }
-        updateUserListFile();
     }
 
     /**
      * Remove userId from the store when the user is removed.
      */
     public void onUserRemoved(int userId) {
+        if (deleteWakeupFromUserStarts(userId) || deleteWakeupFromStartingUsers(userId)) {
+            updateUserListFile();
+        }
+    }
+
+    /**
+     * Remove wakeup for a given userId from mUserStarts.
+     * @return true if an entry is found and the list of wakeups changes.
+     */
+    private boolean deleteWakeupFromUserStarts(int userId) {
+        int index;
         synchronized (mUserWakeupLock) {
-            mUserStarts.delete(userId);
-            mStartingUsers.delete(userId);
+            index = mUserStarts.indexOfKey(userId);
+            if (index >= 0) {
+                mUserStarts.removeAt(index);
+            }
         }
-        updateUserListFile();
+        return index >= 0;
+    }
+
+    /**
+     * Remove wakeup for a given userId from mStartingUsers.
+     * @return true if an entry is found and the list of wakeups changes.
+     */
+    private boolean deleteWakeupFromStartingUsers(int userId) {
+        int index;
+        synchronized (mUserWakeupLock) {
+            index = mStartingUsers.indexOfKey(userId);
+            if (index >= 0) {
+                mStartingUsers.removeAt(index);
+            }
+        }
+        return index >= 0;
     }
 
     /**

services/tests/mockingservicestests/src/com/android/server/alarm/UserWakeupStoreTest.java

@@ -116,7 +116,7 @@ public class UserWakeupStoreTest {
         mUserWakeupStore.addUserWakeup(USER_ID_1, TEST_TIMESTAMP - 7_000);
         mUserWakeupStore.addUserWakeup(USER_ID_1, finalAlarmTime);
         assertEquals(1, mUserWakeupStore.getUserIdsToWakeup(TEST_TIMESTAMP).length);
-        final long alarmTime = mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_1)
+        final long alarmTime = mUserWakeupStore.getWakeupTimeForUser(USER_ID_1)
                 + BUFFER_TIME_MS;
         assertTrue(finalAlarmTime + USER_START_TIME_DEVIATION_LIMIT_MS >= alarmTime);
         assertTrue(finalAlarmTime - USER_START_TIME_DEVIATION_LIMIT_MS <= alarmTime);
@@ -129,8 +129,8 @@ public class UserWakeupStoreTest {
         mUserWakeupStore.addUserWakeup(USER_ID_3, TEST_TIMESTAMP - 13_000);
         assertEquals(3, mUserWakeupStore.getUserIdsToWakeup(TEST_TIMESTAMP).length);
         mUserWakeupStore.removeUserWakeup(USER_ID_3);
-        assertEquals(-1, mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_3));
-        assertTrue(mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_2) > 0);
+        assertEquals(-1, mUserWakeupStore.getWakeupTimeForUser(USER_ID_3));
+        assertTrue(mUserWakeupStore.getWakeupTimeForUser(USER_ID_2) > 0);
     }
 
     @Test
@@ -139,10 +139,10 @@ public class UserWakeupStoreTest {
         mUserWakeupStore.addUserWakeup(USER_ID_2, TEST_TIMESTAMP - 3_000);
         mUserWakeupStore.addUserWakeup(USER_ID_3, TEST_TIMESTAMP - 13_000);
         assertEquals(mUserWakeupStore.getNextWakeupTime(),
-                mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_1));
+                mUserWakeupStore.getWakeupTimeForUser(USER_ID_1));
         mUserWakeupStore.removeUserWakeup(USER_ID_1);
         assertEquals(mUserWakeupStore.getNextWakeupTime(),
-                mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_3));
+                mUserWakeupStore.getWakeupTimeForUser(USER_ID_3));
     }
 
     @Test
@@ -154,16 +154,16 @@ public class UserWakeupStoreTest {
         mUserWakeupStore.init();
         final long realtime = SystemClock.elapsedRealtime();
         assertEquals(0, mUserWakeupStore.getUserIdsToWakeup(TEST_TIMESTAMP).length);
-        assertTrue(mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_2) > realtime);
-        assertTrue(mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_1)
-                < mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_3));
-        assertTrue(mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_3)
-                < mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_2));
-        assertTrue(mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_1) - realtime
+        assertTrue(mUserWakeupStore.getWakeupTimeForUser(USER_ID_2) > realtime);
+        assertTrue(mUserWakeupStore.getWakeupTimeForUser(USER_ID_1)
+                < mUserWakeupStore.getWakeupTimeForUser(USER_ID_3));
+        assertTrue(mUserWakeupStore.getWakeupTimeForUser(USER_ID_3)
+                < mUserWakeupStore.getWakeupTimeForUser(USER_ID_2));
+        assertTrue(mUserWakeupStore.getWakeupTimeForUser(USER_ID_1) - realtime
                 < BUFFER_TIME_MS + USER_START_TIME_DEVIATION_LIMIT_MS);
-        assertTrue(mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_3) - realtime
+        assertTrue(mUserWakeupStore.getWakeupTimeForUser(USER_ID_3) - realtime
                 < 2 * BUFFER_TIME_MS + USER_START_TIME_DEVIATION_LIMIT_MS);
-        assertTrue(mUserWakeupStore.getWakeupTimeForUserForTest(USER_ID_2) - realtime
+        assertTrue(mUserWakeupStore.getWakeupTimeForUser(USER_ID_2) - realtime
                 < 3 * BUFFER_TIME_MS + USER_START_TIME_DEVIATION_LIMIT_MS);
     }
     //TODO: b/330264023 - Add tests for I/O in usersWithAlarmClocks.xml.