Another way to keep track number of foreground services in the device.

Add staic field sNumForegroundServices to keep track of number of
foreground services and apps in the device. This field is used
to report statsd atom LmkKillOccurred which can not hold
AMS lock.

Bug: 243768727
Test: statsd_testdrive 51
Change-Id: Id4e53ecf8902c8373e79537a2732586c8cb553d5

services/core/java/com/android/server/am/ActiveServices.java

@@ -192,6 +192,7 @@ import java.util.Comparator;
 import java.util.List;
 import java.util.Objects;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Predicate;
 
 public final class ActiveServices {
@@ -222,6 +223,11 @@ public final class ActiveServices {
                     | ServiceInfo.FOREGROUND_SERVICE_TYPE_CONNECTED_DEVICE
                     | ServiceInfo.FOREGROUND_SERVICE_TYPE_MEDIA_PROJECTION;
 
+    // Keep track of number of foreground services and number of apps that have foreground
+    // services in the device. This field is made to be directly accessed without holding AMS lock.
+    static final AtomicReference<Pair<Integer, Integer>> sNumForegroundServices =
+            new AtomicReference(new Pair<>(0, 0));
+
     // Foreground service is stopped for unknown reason.
     static final int FGS_STOP_REASON_UNKNOWN = 0;
     // Foreground service is stopped by app calling Service.stopForeground().
@@ -456,6 +462,7 @@ public final class ActiveServices {
         final ArrayList<ServiceRecord> mStartingBackground = new ArrayList<>();
 
         final ArrayMap<String, ActiveForegroundApp> mActiveForegroundApps = new ArrayMap<>();
+
         boolean mActiveForegroundAppsChanged;
 
         static final int MSG_BG_START_TIMEOUT = 1;
@@ -2027,6 +2034,7 @@ public final class ActiveServices {
                         logFGSStateChangeLocked(r,
                                 FrameworkStatsLog.FOREGROUND_SERVICE_STATE_CHANGED__STATE__ENTER,
                                 0, FGS_STOP_REASON_UNKNOWN);
+                        updateNumForegroundServicesLocked();
                     }
                     // Even if the service is already a FGS, we need to update the notification,
                     // so we need to call it again.
@@ -2118,6 +2126,7 @@ public final class ActiveServices {
                     mAm.updateLruProcessLocked(r.app, false, null);
                     updateServiceForegroundLocked(r.app.mServices, true);
                 }
+                updateNumForegroundServicesLocked();
             }
         }
     }
@@ -4836,6 +4845,7 @@ public final class ActiveServices {
         }
 
         smap.ensureNotStartingBackgroundLocked(r);
+        updateNumForegroundServicesLocked();
     }
 
     private void dropFgsNotificationStateLocked(ServiceRecord r) {
@@ -7040,6 +7050,10 @@ public final class ActiveServices {
                 fgsStopReasonToString(fgsStopReason));
     }
 
+    private void updateNumForegroundServicesLocked() {
+        sNumForegroundServices.set(mAm.mProcessList.getNumForegroundServices());
+    }
+
     boolean canAllowWhileInUsePermissionInFgsLocked(int callingPid, int callingUid,
             String callingPackage) {
         return shouldAllowFgsWhileInUsePermissionLocked(callingPackage, callingPid, callingUid,

services/core/java/com/android/server/am/ProcessList.java

@@ -814,12 +814,14 @@ public final class ProcessList {
                                                 < LmkdStatsReporter.KILL_OCCURRED_MSG_SIZE) {
                                             return false;
                                         }
-                                        Pair<Integer, Integer> temp = getNumForegroundServices();
+                                        // Note: directly access
-                                        final int totalForegroundServices = temp.first;
+                                        // ActiveServices.sNumForegroundServices, do not try to
-                                        final int procsWithForegroundServices = temp.second;
+                                        // hold AMS lock here, otherwise it is a potential deadlock.
+                                        Pair<Integer, Integer> foregroundServices =
+                                                ActiveServices.sNumForegroundServices.get();
                                         LmkdStatsReporter.logKillOccurred(inputData,
-                                                totalForegroundServices,
+                                                foregroundServices.first,
-                                                procsWithForegroundServices);
+                                                foregroundServices.second);
                                         return true;
                                     case LMK_STATE_CHANGED:
                                         if (receivedLen