Initialize timestamp in AlarmManagerService with actual timestamps

AlarmManagerService sends android.intent.action.TIME_SET broadcast
if real time clock and boot time clock proceed differently which means
the real time is changed (e.g. by timezone change).

Kernel notifies the time change by returning ECANCELED on timerfd.
AlarmManagerService filteres the notifications with less than 1 second
difference out because kernel can notifies small adjustment.

With initializing timestamps (mLastTimeChangeClockTime,
mLastTimeChangeRealtime) as 0, AlarmManagerService always sends
android.intent.action.TIME_SET for the first time change notification
from the kernel even if the time adjustment was small.

While stale TIME_SET broadcast does not break any logic technically
because applications usually just reset their timers, waking up
BroadcastReceiver of applications simultaneously has a performance
impact on devices on which the processes for the applications had not
been launched and the system end up launching application processes.
ARCVM on ChromeOS can easily reproduce the stale TIME_SET broadcast by
suspending and resuming the device for the first time.

Initializing the timestamps as 0 was introduced from BatteryStatsImpl
logic by this commit:
https://gerrit.aospa.co/plugins/gitiles/AOSPA/android_frameworks_base/+/c352722e8af0a5510144b5f32ea87561db553f42%5E%21/

Before that BatteryStatsImpl had just monitored time change
notifications for a stats purpose and a stale notification did not have
much cost. However sending a broadcast to applications costs more on
AlarmManagerService.

The cost of initializing the 2 timestamps on the AlarmManager startup is
small enough to avoid the stale broadcast.

Bug: 356564926
Test: manually check that no TIME_SET broadcast is sent on the first
susupend/resume on ARCVM
Test: atest FrameworksMockingServicesTests:com.android.server.alarm
Flag: EXEMPT bugfix

Change-Id: Ibad10ad6a7c2812dc085f80c1a94a3026f9fb96f

1 files changed, 7 insertions, 3 deletions

diff --git a/apex/jobscheduler/service/java/com/android/server/alarm/AlarmManagerService.java b/apex/jobscheduler/service/java/com/android/server/alarm/AlarmManagerService.java
index 18ee6f2c7992..ba66ff72bfdd 100644
--- a/apex/jobscheduler/service/java/com/android/server/alarm/AlarmManagerService.java
+++ b/apex/jobscheduler/service/java/com/android/server/alarm/AlarmManagerService.java
@@ -4441,6 +4441,11 @@ public class AlarmManagerService extends SystemService {
         public void run() {
             ArrayList<Alarm> triggerList = new ArrayList<Alarm>();
 
+            synchronized (mLock) {
+                mLastTimeChangeClockTime = mInjector.getCurrentTimeMillis();
+                mLastTimeChangeRealtime = mInjector.getElapsedRealtimeMillis();
+            }
+
             while (true) {
                 int result = mInjector.waitForAlarm();
                 final long nowRTC = mInjector.getCurrentTimeMillis();
@@ -4464,10 +4469,9 @@ public class AlarmManagerService extends SystemService {
                         expectedClockTime = lastTimeChangeClockTime
                                 + (nowELAPSED - mLastTimeChangeRealtime);
                     }
-                    if (lastTimeChangeClockTime == 0 || nowRTC < (expectedClockTime - 1000)
+                    if (nowRTC < (expectedClockTime - 1000)
                             || nowRTC > (expectedClockTime + 1000)) {
-                        // The change is by at least +/- 1000 ms (or this is the first change),
-                        // let's do it!
+                        // The change is by at least +/- 1000 ms, let's do it!
                         if (DEBUG_BATCH) {
                             Slog.v(TAG, "Time changed notification from kernel; rebatching");
                         }