Add caching to AM.getCurrentUserId().

The current foreground user doesn't change outside of a user
switch, which is a rare event on most user devices. Add a
IpcDataCache to AM.getCurrentUserId() in order to avoid
unncessary binder spam.

Flag: backstage_power/android.app.cache_get_current_user_id
Bug: 361853873
Test: atest UserControllerTest
Test: atest UserManagerTest
Test: atest ActivityManagerTest
Test: manually check logs for cache hits/misses
Change-Id: I94540ad4c76bcc62944ad8e19f0e9d6c2154b010

5 files changed, 67 insertions, 5 deletions

diff --git a/core/java/android/app/ActivityManager.java b/core/java/android/app/ActivityManager.java
index 68063c4a1a50..b83be6b86d04 100644
--- a/core/java/android/app/ActivityManager.java
+++ b/core/java/android/app/ActivityManager.java
@@ -66,6 +66,7 @@ import android.os.Bundle;
 import android.os.Debug;
 import android.os.Handler;
 import android.os.IBinder;
+import android.os.IpcDataCache;
 import android.os.LocaleList;
 import android.os.Parcel;
 import android.os.Parcelable;
@@ -238,6 +239,44 @@ public class ActivityManager {
             new RateLimitingCache<>(10, 2);
 
     /**
+     * Query handler for mGetCurrentUserIdCache - returns a cached value of the current foreground
+     * user id if the backstage_power/android.app.cache_get_current_user_id flag is enabled.
+     */
+    private static final IpcDataCache.QueryHandler<Void, Integer> mGetCurrentUserIdQuery =
+            new IpcDataCache.QueryHandler<>() {
+                @Override
+                public Integer apply(Void query) {
+                    try {
+                        return getService().getCurrentUserId();
+                    } catch (RemoteException e) {
+                        throw e.rethrowFromSystemServer();
+                    }
+                }
+
+                @Override
+                public boolean shouldBypassCache(Void query) {
+                    // If the flag to enable the new caching behavior is off, bypass the cache.
+                    return !Flags.cacheGetCurrentUserId();
+                }
+            };
+
+    /** A cache which maintains the current foreground user id. */
+    private static final IpcDataCache<Void, Integer> mGetCurrentUserIdCache =
+            new IpcDataCache<>(1, IpcDataCache.MODULE_SYSTEM,
+                    /* api= */ "getCurrentUserId", /* cacheName= */ "CurrentUserIdCache",
+                    mGetCurrentUserIdQuery);
+
+    /**
+     * The current foreground user has changed - invalidate the cache. Currently only called from
+     * UserController when a user switch occurs.
+     * @hide
+     */
+    public static void invalidateGetCurrentUserIdCache() {
+        IpcDataCache.invalidateCache(
+                IpcDataCache.MODULE_SYSTEM, /* api= */ "getCurrentUserId");
+    }
+
+    /**
      * Map of callbacks that have registered for {@link UidFrozenStateChanged} events.
      * Will be called when a Uid has become frozen or unfrozen.
      */
@@ -5244,11 +5283,7 @@ public class ActivityManager {
     })
     @android.ravenwood.annotation.RavenwoodReplace
     public static int getCurrentUser() {
-        try {
-            return getService().getCurrentUserId();
-        } catch (RemoteException e) {
-            throw e.rethrowFromSystemServer();
-        }
+        return mGetCurrentUserIdCache.query(null);
     }
 
     /** @hide */
diff --git a/core/java/android/app/activity_manager.aconfig b/core/java/android/app/activity_manager.aconfig
index 32e6e80cc3e9..4c97dbbb4d01 100644
--- a/core/java/android/app/activity_manager.aconfig
+++ b/core/java/android/app/activity_manager.aconfig
@@ -104,3 +104,13 @@ flag {
      }
 }
 
+flag {
+     namespace: "backstage_power"
+     name: "cache_get_current_user_id"
+     description: "Add caching for getCurrentUserId"
+     is_fixed_read_only: true
+     bug: "361853873"
+     metadata {
+         purpose: PURPOSE_BUGFIX
+     }
+}
diff --git a/services/core/java/com/android/server/am/UserController.java b/services/core/java/com/android/server/am/UserController.java
index bdba6bcf66c0..b186eaacab74 100644
--- a/services/core/java/com/android/server/am/UserController.java
+++ b/services/core/java/com/android/server/am/UserController.java
@@ -1978,6 +1978,7 @@ class UserController implements Handler.Callback {
                 boolean userSwitchUiEnabled;
                 synchronized (mLock) {
                     mCurrentUserId = userId;
+                    ActivityManager.invalidateGetCurrentUserIdCache();
                     userSwitchUiEnabled = mUserSwitchUiEnabled;
                 }
                 mInjector.updateUserConfiguration();
@@ -2239,6 +2240,7 @@ class UserController implements Handler.Callback {
                 return true;
             }
             mTargetUserId = targetUserId;
+            ActivityManager.invalidateGetCurrentUserIdCache();
             userSwitchUiEnabled = mUserSwitchUiEnabled;
         }
         if (userSwitchUiEnabled) {
@@ -2316,6 +2318,7 @@ class UserController implements Handler.Callback {
         synchronized (mLock) {
             nextUserId = ObjectUtils.getOrElse(mPendingTargetUserIds.poll(), UserHandle.USER_NULL);
             mTargetUserId = UserHandle.USER_NULL;
+            ActivityManager.invalidateGetCurrentUserIdCache();
         }
         if (nextUserId != UserHandle.USER_NULL) {
             switchUser(nextUserId);
@@ -3021,6 +3024,9 @@ class UserController implements Handler.Callback {
         mInjector.getUserManagerInternal().addUserLifecycleListener(mUserLifecycleListener);
         updateProfileRelatedCaches();
         mInjector.reportCurWakefulnessUsageEvent();
+
+        // IpcDataCache must be invalidated before it starts caching.
+        ActivityManager.invalidateGetCurrentUserIdCache();
     }
 
     // TODO(b/266158156): remove this method if initial system user boot logic is refactored?
@@ -3184,6 +3190,9 @@ class UserController implements Handler.Callback {
 
     @GuardedBy("mLock")
     private int getCurrentOrTargetUserIdLU() {
+        // Note: this result is currently cached by ActivityManager.getCurrentUser() - changes to
+        // the logic here may require updating how the cache is invalidated.
+        // See ActivityManager.invalidateGetCurrentUserIdCache() for more details.
         return mTargetUserId != UserHandle.USER_NULL ? mTargetUserId : mCurrentUserId;
     }
 
diff --git a/services/tests/servicestests/src/com/android/server/am/UserControllerTest.java b/services/tests/servicestests/src/com/android/server/am/UserControllerTest.java
index 1db46bf17655..f7733242d491 100644
--- a/services/tests/servicestests/src/com/android/server/am/UserControllerTest.java
+++ b/services/tests/servicestests/src/com/android/server/am/UserControllerTest.java
@@ -89,6 +89,7 @@ import android.os.Bundle;
 import android.os.Handler;
 import android.os.HandlerThread;
 import android.os.IRemoteCallback;
+import android.os.IpcDataCache;
 import android.os.Looper;
 import android.os.Message;
 import android.os.PowerManagerInternal;
@@ -197,6 +198,9 @@ public class UserControllerTest {
     @Before
     public void setUp() throws Exception {
         runWithDexmakerShareClassLoader(() -> {
+            // Disable binder caches in this process.
+            IpcDataCache.disableForTestMode();
+
             mInjector = spy(new TestInjector(getInstrumentation().getTargetContext()));
             doNothing().when(mInjector).clearAllLockedTasks(anyString());
             doNothing().when(mInjector).startHomeActivity(anyInt(), anyString());
diff --git a/services/tests/servicestests/src/com/android/server/pm/UserManagerTest.java b/services/tests/servicestests/src/com/android/server/pm/UserManagerTest.java
index 791215695f57..e652df5cdf1a 100644
--- a/services/tests/servicestests/src/com/android/server/pm/UserManagerTest.java
+++ b/services/tests/servicestests/src/com/android/server/pm/UserManagerTest.java
@@ -34,6 +34,7 @@ import android.content.pm.UserProperties;
 import android.content.res.Resources;
 import android.graphics.drawable.Drawable;
 import android.os.Bundle;
+import android.os.IpcDataCache;
 import android.os.PersistableBundle;
 import android.os.UserHandle;
 import android.os.UserManager;
@@ -100,6 +101,9 @@ public final class UserManagerTest {
 
     @Before
     public void setUp() throws Exception {
+        // Disable binder caches in this process.
+        IpcDataCache.disableForTestMode();
+
         mOriginalCurrentUserId = ActivityManager.getCurrentUser();
         mUserManager = UserManager.get(mContext);
         mActivityManager = mContext.getSystemService(ActivityManager.class);