Fix bindApplication starting activities late

With the attachApplication split introduced in
I659f2083f460701d858ebb7a8af9fa748ff4bfe9 apps send
a finishAttachApplication back to the system after
their initialization (Application#onCreate). The system
then dispatches Broadcast, Service and Activity starts
to the app. The delayed dispatch of Activity has 2 side
effects:

1. Apps could post messages on their main thread that will
run before activity start message which could slow down their
ttff.
2. The setFocusedApplication call is delayed and the system
doesn't know the focused application until after app init.

To mitigate this, we dispatch Activity start early before
app init.

Test: atest ActivityManagerTest
Bug: 319519089
Bug: 333663697
Bug: 382378705
Bug: 366147979
Bug: 358102320
Flag: com.android.server.am.expedite_activity_launch_on_cold_start

Change-Id: I762d6e943530133f8031a16f40eda97b4f476cd0

2 files changed, 30 insertions, 11 deletions

diff --git a/services/core/java/com/android/server/am/ActivityManagerService.java b/services/core/java/com/android/server/am/ActivityManagerService.java
index cd929c1883d0..a184e905d0fa 100644
--- a/services/core/java/com/android/server/am/ActivityManagerService.java
+++ b/services/core/java/com/android/server/am/ActivityManagerService.java
@@ -4799,9 +4799,6 @@ public class ActivityManagerService extends IActivityManager.Stub
             updateLruProcessLocked(app, false, null);
             checkTime(startTime, "attachApplicationLocked: after updateLruProcessLocked");
 
-            updateOomAdjLocked(app, OOM_ADJ_REASON_PROCESS_BEGIN);
-            checkTime(startTime, "attachApplicationLocked: after updateOomAdjLocked");
-
             final long now = SystemClock.uptimeMillis();
             synchronized (mAppProfiler.mProfilerLock) {
                 app.mProfile.setLastRequestedGc(now);
@@ -4815,6 +4812,15 @@ public class ActivityManagerService extends IActivityManager.Stub
             }
             mProcessesOnHold.remove(app);
 
+            // See if the top visible activity is waiting to run in this process...
+            if (com.android.server.am.Flags.expediteActivityLaunchOnColdStart()) {
+                if (normalMode) {
+                    mAtmInternal.attachApplication(app.getWindowProcessController());
+                }
+            }
+            updateOomAdjLocked(app, OOM_ADJ_REASON_PROCESS_BEGIN);
+            checkTime(startTime, "attachApplicationLocked: after updateOomAdjLocked");
+
             if (!mConstants.mEnableWaitForFinishAttachApplication) {
                 finishAttachApplicationInner(startSeq, callingUid, pid);
             }
@@ -4880,18 +4886,21 @@ public class ActivityManagerService extends IActivityManager.Stub
             // Mark the finish attach application phase as completed
             mProcessStateController.setPendingFinishAttach(app, false);
 
-            final boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
             final String processName = app.processName;
             boolean badApp = false;
             boolean didSomething = false;
 
-            // See if the top visible activity is waiting to run in this process...
-            if (normalMode) {
-                try {
-                    didSomething = mAtmInternal.attachApplication(app.getWindowProcessController());
-                } catch (Exception e) {
-                    Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
-                    badApp = true;
+            if (!com.android.server.am.Flags.expediteActivityLaunchOnColdStart()) {
+                final boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
+
+                if (normalMode) {
+                    try {
+                        didSomething |= mAtmInternal.attachApplication(
+                                app.getWindowProcessController());
+                    } catch (Exception e) {
+                        Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
+                        badApp = true;
+                    }
                 }
             }
 
diff --git a/services/core/java/com/android/server/am/flags.aconfig b/services/core/java/com/android/server/am/flags.aconfig
index 89e4a8d82676..cfcede8ee40d 100644
--- a/services/core/java/com/android/server/am/flags.aconfig
+++ b/services/core/java/com/android/server/am/flags.aconfig
@@ -288,3 +288,13 @@ flag {
         purpose: PURPOSE_BUGFIX
     }
 }
+
+flag {
+    name: "expedite_activity_launch_on_cold_start"
+    namespace: "system_performance"
+    description: "Notify ActivityTaskManager of cold starts early to fix app launch behavior."
+    bug: "319519089"
+    metadata {
+        purpose: PURPOSE_BUGFIX
+    }
+}