Move forward the alarm timestamp when config is added to statsd.

Test: statsd test
BUG: b/77344187

Change-Id: Ieacffaa29422829b8956f2b3fcb2c647c8c3eed9
diff --git a/cmds/statsd/src/anomaly/AlarmTracker.cpp b/cmds/statsd/src/anomaly/AlarmTracker.cpp
index 249cb59..70e6e84 100644
--- a/cmds/statsd/src/anomaly/AlarmTracker.cpp
+++ b/cmds/statsd/src/anomaly/AlarmTracker.cpp
@@ -30,7 +30,8 @@
 namespace os {
 namespace statsd {
 
-AlarmTracker::AlarmTracker(uint64_t startMillis,
+AlarmTracker::AlarmTracker(const uint64_t startMillis,
+                           const uint64_t currentMillis,
                            const Alarm& alarm, const ConfigKey& configKey,
                            const sp<AlarmMonitor>& alarmMonitor)
     : mAlarmConfig(alarm),
@@ -38,7 +39,11 @@
       mAlarmMonitor(alarmMonitor) {
     VLOG("AlarmTracker() called");
     mAlarmSec = (startMillis + mAlarmConfig.offset_millis()) / MS_PER_SEC;
+    // startMillis is the time statsd is created. We need to find the 1st alarm timestamp after
+    // the config is added to statsd.
+    mAlarmSec = findNextAlarmSec(currentMillis / MS_PER_SEC);  // round up
     mInternalAlarm = new InternalAlarm{static_cast<uint32_t>(mAlarmSec)};
+    VLOG("AlarmTracker sets the periodic alarm at: %lld", (long long)mAlarmSec);
     if (mAlarmMonitor != nullptr) {
         mAlarmMonitor->add(mInternalAlarm);
     }
@@ -55,9 +60,13 @@
     mSubscriptions.push_back(subscription);
 }
 
-uint64_t AlarmTracker::findNextAlarmSec(uint64_t currentTimeSec) {
-    int periodsForward = (currentTimeSec - mAlarmSec) * MS_PER_SEC / mAlarmConfig.period_millis();
-    return mAlarmSec + (periodsForward + 1) * mAlarmConfig.period_millis() / MS_PER_SEC;
+int64_t AlarmTracker::findNextAlarmSec(int64_t currentTimeSec) {
+    if (currentTimeSec <= mAlarmSec) {
+        return mAlarmSec;
+    }
+    int64_t periodsForward =
+        ((currentTimeSec - mAlarmSec) * MS_PER_SEC - 1) / mAlarmConfig.period_millis() + 1;
+    return mAlarmSec + periodsForward * mAlarmConfig.period_millis() / MS_PER_SEC;
 }
 
 void AlarmTracker::informAlarmsFired(
@@ -68,12 +77,14 @@
         return;
     }
     if (!mSubscriptions.empty()) {
+        VLOG("AlarmTracker triggers the subscribers.");
         triggerSubscribers(mAlarmConfig.id(), DEFAULT_METRIC_DIMENSION_KEY, mConfigKey,
                            mSubscriptions);
     }
     firedAlarms.erase(mInternalAlarm);
     mAlarmSec = findNextAlarmSec((timestampNs-1) / NS_PER_SEC + 1); // round up
     mInternalAlarm = new InternalAlarm{static_cast<uint32_t>(mAlarmSec)};
+    VLOG("AlarmTracker sets the periodic alarm at: %lld", (long long)mAlarmSec);
     if (mAlarmMonitor != nullptr) {
         mAlarmMonitor->add(mInternalAlarm);
     }