Add a rate limiter to the getRunningAppProcesses() call

Allow at most 400 calls per second to system_server and
return a cached value at other times. This is distributed
as 4 calls every 10 ms.

Bug: 360374604
Test: Take a trace to verify AIDL call doesn't exceed
      4 every 10ms.
Flag: android.app.rate_limit_get_running_app_processes

Change-Id: I0781949fe3fcef170e8a3c09f6de4aeba4c2989d

2 files changed, 27 insertions, 0 deletions

diff --git a/core/java/android/app/ActivityManager.java b/core/java/android/app/ActivityManager.java
index be70de20c2e2..e57630bfd5ed 100644
--- a/core/java/android/app/ActivityManager.java
+++ b/core/java/android/app/ActivityManager.java
@@ -94,6 +94,7 @@ import com.android.internal.os.TransferPipe;
 import com.android.internal.util.FastPrintWriter;
 import com.android.internal.util.MemInfoReader;
 import com.android.internal.util.Preconditions;
+import com.android.internal.util.RateLimitingCache;
 import com.android.modules.utils.TypedXmlPullParser;
 import com.android.modules.utils.TypedXmlSerializer;
 import com.android.server.LocalServices;
@@ -228,6 +229,10 @@ public class ActivityManager {
 
     final ArrayMap<OnUidImportanceListener, MyUidObserver> mImportanceListeners = new ArrayMap<>();
 
+    /** Rate-Limiting Cache that allows no more than 400 calls to the service per second. */
+    private static final RateLimitingCache<List<RunningAppProcessInfo>> mRunningProcessesCache =
+            new RateLimitingCache<>(10, 4);
+
     /**
      * Map of callbacks that have registered for {@link UidFrozenStateChanged} events.
      * Will be called when a Uid has become frozen or unfrozen.
@@ -4213,6 +4218,16 @@ public class ActivityManager {
      * specified.
      */
     public List<RunningAppProcessInfo> getRunningAppProcesses() {
+        if (!Flags.rateLimitGetRunningAppProcesses()) {
+            return getRunningAppProcessesInternal();
+        } else {
+            return mRunningProcessesCache.get(() -> {
+                return getRunningAppProcessesInternal();
+            });
+        }
+    }
+
+    private List<RunningAppProcessInfo> getRunningAppProcessesInternal() {
         try {
             return getService().getRunningAppProcesses();
         } catch (RemoteException e) {
diff --git a/core/java/android/app/activity_manager.aconfig b/core/java/android/app/activity_manager.aconfig
index fa646a76768c..d9594d3e4c31 100644
--- a/core/java/android/app/activity_manager.aconfig
+++ b/core/java/android/app/activity_manager.aconfig
@@ -81,3 +81,15 @@ flag {
          purpose: PURPOSE_BUGFIX
      }
 }
+
+flag {
+     namespace: "backstage_power"
+     name: "rate_limit_get_running_app_processes"
+     description: "Rate limit calls to getRunningAppProcesses using a cache"
+     is_fixed_read_only: true
+     bug: "360374604"
+     metadata {
+         purpose: PURPOSE_BUGFIX
+     }
+}
+