Merge "Break out battery history reading into a separate class" into sc-dev

5 files changed, 424 insertions, 191 deletions

diff --git a/core/java/com/android/internal/os/BatteryStatsHistory.java b/core/java/com/android/internal/os/BatteryStatsHistory.java
index bdb65f33ad1a..879e0a8cfe10 100644
--- a/core/java/com/android/internal/os/BatteryStatsHistory.java
+++ b/core/java/com/android/internal/os/BatteryStatsHistory.java
@@ -16,6 +16,8 @@
 
 package com.android.internal.os;
 
+import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.os.BatteryStats;
 import android.os.Parcel;
 import android.os.StatFs;
@@ -61,6 +63,7 @@ public class BatteryStatsHistory {
     public static final String FILE_SUFFIX = ".bin";
     private static final int MIN_FREE_SPACE = 100 * 1024 * 1024;
 
+    @Nullable
     private final BatteryStatsImpl mStats;
     private final Parcel mHistoryBuffer;
     private final File mHistoryDir;
@@ -107,7 +110,8 @@ public class BatteryStatsHistory {
      * @param systemDir typically /data/system
      * @param historyBuffer The in-memory history buffer.
      */
-    public BatteryStatsHistory(BatteryStatsImpl stats, File systemDir, Parcel historyBuffer) {
+    public BatteryStatsHistory(@NonNull BatteryStatsImpl stats, File systemDir,
+            Parcel historyBuffer) {
         mStats = stats;
         mHistoryBuffer = historyBuffer;
         mHistoryDir = new File(systemDir, HISTORY_DIR);
@@ -149,11 +153,10 @@ public class BatteryStatsHistory {
     /**
      * Used when BatteryStatsImpl object is created from deserialization of a parcel,
      * such as Settings app or checkin file.
-     * @param stats BatteryStatsImpl object.
-     * @param historyBuffer the history buffer inside BatteryStatsImpl
+     * @param historyBuffer the history buffer
      */
-    public BatteryStatsHistory(BatteryStatsImpl stats, Parcel historyBuffer) {
-        mStats = stats;
+    public BatteryStatsHistory(Parcel historyBuffer) {
+        mStats = null;
         mHistoryDir = null;
         mHistoryBuffer = historyBuffer;
     }
@@ -184,10 +187,16 @@ public class BatteryStatsHistory {
      * create next history file.
      */
     public void startNextFile() {
+        if (mStats == null) {
+            Slog.wtf(TAG, "mStats should not be null when writing history");
+            return;
+        }
+
         if (mFileNumbers.isEmpty()) {
             Slog.wtf(TAG, "mFileNumbers should never be empty");
             return;
         }
+
         // The last number in mFileNumbers is the highest number. The next file number is highest
         // number plus one.
         final int next = mFileNumbers.get(mFileNumbers.size() - 1) + 1;
@@ -357,7 +366,7 @@ public class BatteryStatsHistory {
     private boolean skipHead(Parcel p) {
         p.setDataPosition(0);
         final int version = p.readInt();
-        if (version != mStats.VERSION) {
+        if (version != BatteryStatsImpl.VERSION) {
             return false;
         }
         // skip historyBaseTime field.
diff --git a/core/java/com/android/internal/os/BatteryStatsHistoryIterator.java b/core/java/com/android/internal/os/BatteryStatsHistoryIterator.java
new file mode 100644
index 000000000000..d99af8178feb
--- /dev/null
+++ b/core/java/com/android/internal/os/BatteryStatsHistoryIterator.java
@@ -0,0 +1,264 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.internal.os;
+
+import android.annotation.NonNull;
+import android.os.BatteryManager;
+import android.os.BatteryStats;
+import android.os.Parcel;
+import android.util.Slog;
+
+import java.util.List;
+
+/**
+ * An iterator for {@link BatteryStats.HistoryItem}'s.
+ */
+public class BatteryStatsHistoryIterator {
+    private static final boolean DEBUG = false;
+    private static final String TAG = "BatteryStatsHistoryItr";
+    private final BatteryStatsHistory mBatteryStatsHistory;
+    private final BatteryStats.HistoryStepDetails mReadHistoryStepDetails =
+            new BatteryStats.HistoryStepDetails();
+    private final String[] mReadHistoryStrings;
+    private final int[] mReadHistoryUids;
+
+    BatteryStatsHistoryIterator(@NonNull BatteryStatsHistory history,
+            @NonNull List<BatteryStats.HistoryTag> historyTagPool) {
+        mBatteryStatsHistory = history;
+
+        mBatteryStatsHistory.startIteratingHistory();
+
+        mReadHistoryStrings = new String[historyTagPool.size()];
+        mReadHistoryUids = new int[historyTagPool.size()];
+        for (int i = historyTagPool.size() - 1; i >= 0; i--) {
+            BatteryStats.HistoryTag tag = historyTagPool.get(i);
+            final int idx = tag.poolIdx;
+            mReadHistoryStrings[idx] = tag.string;
+            mReadHistoryUids[idx] = tag.uid;
+        }
+    }
+
+    /**
+     * Retrieves the next HistoryItem from battery history, if available. Returns false if there
+     * are no more items.
+     */
+    public boolean next(BatteryStats.HistoryItem out) {
+        Parcel p = mBatteryStatsHistory.getNextParcel(out);
+        if (p == null) {
+            mBatteryStatsHistory.finishIteratingHistory();
+            return false;
+        }
+
+        final long lastRealtimeMs = out.time;
+        final long lastWalltimeMs = out.currentTime;
+        readHistoryDelta(p, out);
+        if (out.cmd != BatteryStats.HistoryItem.CMD_CURRENT_TIME
+                && out.cmd != BatteryStats.HistoryItem.CMD_RESET && lastWalltimeMs != 0) {
+            out.currentTime = lastWalltimeMs + (out.time - lastRealtimeMs);
+        }
+        return true;
+    }
+
+    void readHistoryDelta(Parcel src, BatteryStats.HistoryItem cur) {
+        int firstToken = src.readInt();
+        int deltaTimeToken = firstToken & BatteryStatsImpl.DELTA_TIME_MASK;
+        cur.cmd = BatteryStats.HistoryItem.CMD_UPDATE;
+        cur.numReadInts = 1;
+        if (DEBUG) {
+            Slog.i(TAG, "READ DELTA: firstToken=0x" + Integer.toHexString(firstToken)
+                    + " deltaTimeToken=" + deltaTimeToken);
+        }
+
+        if (deltaTimeToken < BatteryStatsImpl.DELTA_TIME_ABS) {
+            cur.time += deltaTimeToken;
+        } else if (deltaTimeToken == BatteryStatsImpl.DELTA_TIME_ABS) {
+            cur.readFromParcel(src);
+            if (DEBUG) Slog.i(TAG, "READ DELTA: ABS time=" + cur.time);
+            return;
+        } else if (deltaTimeToken == BatteryStatsImpl.DELTA_TIME_INT) {
+            int delta = src.readInt();
+            cur.time += delta;
+            cur.numReadInts += 1;
+            if (DEBUG) Slog.i(TAG, "READ DELTA: time delta=" + delta + " new time=" + cur.time);
+        } else {
+            long delta = src.readLong();
+            if (DEBUG) Slog.i(TAG, "READ DELTA: time delta=" + delta + " new time=" + cur.time);
+            cur.time += delta;
+            cur.numReadInts += 2;
+        }
+
+        final int batteryLevelInt;
+        if ((firstToken & BatteryStatsImpl.DELTA_BATTERY_LEVEL_FLAG) != 0) {
+            batteryLevelInt = src.readInt();
+            readBatteryLevelInt(batteryLevelInt, cur);
+            cur.numReadInts += 1;
+            if (DEBUG) {
+                Slog.i(TAG, "READ DELTA: batteryToken=0x"
+                        + Integer.toHexString(batteryLevelInt)
+                        + " batteryLevel=" + cur.batteryLevel
+                        + " batteryTemp=" + cur.batteryTemperature
+                        + " batteryVolt=" + (int) cur.batteryVoltage);
+            }
+        } else {
+            batteryLevelInt = 0;
+        }
+
+        if ((firstToken & BatteryStatsImpl.DELTA_STATE_FLAG) != 0) {
+            int stateInt = src.readInt();
+            cur.states = (firstToken & BatteryStatsImpl.DELTA_STATE_MASK) | (stateInt
+                    & (~BatteryStatsImpl.STATE_BATTERY_MASK));
+            cur.batteryStatus = (byte) ((stateInt >> BatteryStatsImpl.STATE_BATTERY_STATUS_SHIFT)
+                    & BatteryStatsImpl.STATE_BATTERY_STATUS_MASK);
+            cur.batteryHealth = (byte) ((stateInt >> BatteryStatsImpl.STATE_BATTERY_HEALTH_SHIFT)
+                    & BatteryStatsImpl.STATE_BATTERY_HEALTH_MASK);
+            cur.batteryPlugType = (byte) ((stateInt >> BatteryStatsImpl.STATE_BATTERY_PLUG_SHIFT)
+                    & BatteryStatsImpl.STATE_BATTERY_PLUG_MASK);
+            switch (cur.batteryPlugType) {
+                case 1:
+                    cur.batteryPlugType = BatteryManager.BATTERY_PLUGGED_AC;
+                    break;
+                case 2:
+                    cur.batteryPlugType = BatteryManager.BATTERY_PLUGGED_USB;
+                    break;
+                case 3:
+                    cur.batteryPlugType = BatteryManager.BATTERY_PLUGGED_WIRELESS;
+                    break;
+            }
+            cur.numReadInts += 1;
+            if (DEBUG) {
+                Slog.i(TAG, "READ DELTA: stateToken=0x"
+                        + Integer.toHexString(stateInt)
+                        + " batteryStatus=" + cur.batteryStatus
+                        + " batteryHealth=" + cur.batteryHealth
+                        + " batteryPlugType=" + cur.batteryPlugType
+                        + " states=0x" + Integer.toHexString(cur.states));
+            }
+        } else {
+            cur.states = (firstToken & BatteryStatsImpl.DELTA_STATE_MASK) | (cur.states
+                    & (~BatteryStatsImpl.STATE_BATTERY_MASK));
+        }
+
+        if ((firstToken & BatteryStatsImpl.DELTA_STATE2_FLAG) != 0) {
+            cur.states2 = src.readInt();
+            if (DEBUG) {
+                Slog.i(TAG, "READ DELTA: states2=0x"
+                        + Integer.toHexString(cur.states2));
+            }
+        }
+
+        if ((firstToken & BatteryStatsImpl.DELTA_WAKELOCK_FLAG) != 0) {
+            int indexes = src.readInt();
+            int wakeLockIndex = indexes & 0xffff;
+            int wakeReasonIndex = (indexes >> 16) & 0xffff;
+            if (wakeLockIndex != 0xffff) {
+                cur.wakelockTag = cur.localWakelockTag;
+                readHistoryTag(wakeLockIndex, cur.wakelockTag);
+                if (DEBUG) {
+                    Slog.i(TAG, "READ DELTA: wakelockTag=#" + cur.wakelockTag.poolIdx
+                            + " " + cur.wakelockTag.uid + ":" + cur.wakelockTag.string);
+                }
+            } else {
+                cur.wakelockTag = null;
+            }
+            if (wakeReasonIndex != 0xffff) {
+                cur.wakeReasonTag = cur.localWakeReasonTag;
+                readHistoryTag(wakeReasonIndex, cur.wakeReasonTag);
+                if (DEBUG) {
+                    Slog.i(TAG, "READ DELTA: wakeReasonTag=#" + cur.wakeReasonTag.poolIdx
+                            + " " + cur.wakeReasonTag.uid + ":" + cur.wakeReasonTag.string);
+                }
+            } else {
+                cur.wakeReasonTag = null;
+            }
+            cur.numReadInts += 1;
+        } else {
+            cur.wakelockTag = null;
+            cur.wakeReasonTag = null;
+        }
+
+        if ((firstToken & BatteryStatsImpl.DELTA_EVENT_FLAG) != 0) {
+            cur.eventTag = cur.localEventTag;
+            final int codeAndIndex = src.readInt();
+            cur.eventCode = (codeAndIndex & 0xffff);
+            final int index = ((codeAndIndex >> 16) & 0xffff);
+            readHistoryTag(index, cur.eventTag);
+            cur.numReadInts += 1;
+            if (DEBUG) {
+                Slog.i(TAG, "READ DELTA: event=" + cur.eventCode + " tag=#"
+                        + cur.eventTag.poolIdx + " " + cur.eventTag.uid + ":"
+                        + cur.eventTag.string);
+            }
+        } else {
+            cur.eventCode = BatteryStats.HistoryItem.EVENT_NONE;
+        }
+
+        if ((batteryLevelInt & BatteryStatsImpl.BATTERY_DELTA_LEVEL_FLAG) != 0) {
+            cur.stepDetails = mReadHistoryStepDetails;
+            cur.stepDetails.readFromParcel(src);
+        } else {
+            cur.stepDetails = null;
+        }
+
+        if ((firstToken & BatteryStatsImpl.DELTA_BATTERY_CHARGE_FLAG) != 0) {
+            cur.batteryChargeUah = src.readInt();
+        }
+        cur.modemRailChargeMah = src.readDouble();
+        cur.wifiRailChargeMah = src.readDouble();
+    }
+
+    int getHistoryStringPoolSize() {
+        return mReadHistoryStrings.length;
+    }
+
+    int getHistoryStringPoolBytes() {
+        int totalChars = 0;
+        for (int i = mReadHistoryStrings.length - 1; i >= 0; i--) {
+            if (mReadHistoryStrings[i] != null) {
+                totalChars += mReadHistoryStrings[i].length() + 1;
+            }
+        }
+
+        // Each entry is a fixed 12 bytes: 4 for index, 4 for uid, 4 for string size
+        // Each string character is 2 bytes.
+        return (mReadHistoryStrings.length * 12) + (totalChars * 2);
+    }
+
+    String getHistoryTagPoolString(int index) {
+        return mReadHistoryStrings[index];
+    }
+
+    int getHistoryTagPoolUid(int index) {
+        return mReadHistoryUids[index];
+    }
+
+    private void readHistoryTag(int index, BatteryStats.HistoryTag tag) {
+        if (index < mReadHistoryStrings.length) {
+            tag.string = mReadHistoryStrings[index];
+            tag.uid = mReadHistoryUids[index];
+        } else {
+            tag.string = null;
+            tag.uid = 0;
+        }
+        tag.poolIdx = index;
+    }
+
+    private static void readBatteryLevelInt(int batteryLevelInt, BatteryStats.HistoryItem out) {
+        out.batteryLevel = (byte) ((batteryLevelInt & 0xfe000000) >>> 25);
+        out.batteryTemperature = (short) ((batteryLevelInt & 0x01ff8000) >>> 15);
+        out.batteryVoltage = (char) ((batteryLevelInt & 0x00007ffe) >>> 1);
+    }
+}
diff --git a/core/java/com/android/internal/os/BatteryStatsImpl.java b/core/java/com/android/internal/os/BatteryStatsImpl.java
index e4c8ddbbd256..73527d4a80d8 100644
--- a/core/java/com/android/internal/os/BatteryStatsImpl.java
+++ b/core/java/com/android/internal/os/BatteryStatsImpl.java
@@ -737,14 +737,11 @@ public class BatteryStatsImpl extends BatteryStats {
     protected boolean mRecordingHistory = false;
     int mNumHistoryItems;
 
+    final HashMap<HistoryTag, Integer> mHistoryTagPool = new HashMap<>();
     final Parcel mHistoryBuffer = Parcel.obtain();
     final HistoryItem mHistoryLastWritten = new HistoryItem();
     final HistoryItem mHistoryLastLastWritten = new HistoryItem();
     final HistoryItem mHistoryAddTmp = new HistoryItem();
-    final HashMap<HistoryTag, Integer> mHistoryTagPool = new HashMap<>();
-    String[] mReadHistoryStrings;
-    int[] mReadHistoryUids;
-    int mReadHistoryChars;
     int mNextHistoryTagIdx = 0;
     int mNumHistoryTagChars = 0;
     int mHistoryBufferLastPos = -1;
@@ -785,6 +782,7 @@ public class BatteryStatsImpl extends BatteryStats {
     private final HashMap<Integer, PowerForUid> mUidToPower = ENABLE_FOREGROUND_STATS_COLLECTION
             ? new HashMap<>() : null;
 
+    @NonNull
     final BatteryStatsHistory mBatteryStatsHistory;
 
     final HistoryItem mHistoryCur = new HistoryItem();
@@ -827,9 +825,9 @@ public class BatteryStatsImpl extends BatteryStats {
     long mCurStepStatSoftIrqTimeMs;
     long mCurStepStatIdleTimeMs;
 
+    private BatteryStatsHistoryIterator mBatteryStatsHistoryIterator;
     private HistoryItem mHistoryIterator;
     private boolean mReadOverflow;
-    private boolean mIteratingHistory;
 
     int mStartCount;
 
@@ -1193,7 +1191,7 @@ public class BatteryStatsImpl extends BatteryStats {
         mStatsFile = null;
         mCheckinFile = null;
         mDailyFile = null;
-        mBatteryStatsHistory = null;
+        mBatteryStatsHistory = new BatteryStatsHistory(mHistoryBuffer);
         mHandler = null;
         mPlatformIdleStateCallback = null;
         mMeasuredEnergyRetriever = null;
@@ -3240,17 +3238,6 @@ public class BatteryStatsImpl extends BatteryStats {
         return idx;
     }
 
-    private void readHistoryTag(int index, HistoryTag tag) {
-        if (index < mReadHistoryStrings.length) {
-            tag.string = mReadHistoryStrings[index];
-            tag.uid = mReadHistoryUids[index];
-        } else {
-            tag.string = null;
-            tag.uid = 0;
-        }
-        tag.poolIdx = index;
-    }
-
     /*
         The history delta format uses flags to denote further data in subsequent ints in the parcel.
 
@@ -3627,137 +3614,6 @@ public class BatteryStatsImpl extends BatteryStats {
         mLastStepStatIdleTimeMs = mCurStepStatIdleTimeMs;
     }
 
-    public void readHistoryDelta(Parcel src, HistoryItem cur) {
-        int firstToken = src.readInt();
-        int deltaTimeToken = firstToken&DELTA_TIME_MASK;
-        cur.cmd = HistoryItem.CMD_UPDATE;
-        cur.numReadInts = 1;
-        if (DEBUG) Slog.i(TAG, "READ DELTA: firstToken=0x" + Integer.toHexString(firstToken)
-                + " deltaTimeToken=" + deltaTimeToken);
-
-        if (deltaTimeToken < DELTA_TIME_ABS) {
-            cur.time += deltaTimeToken;
-        } else if (deltaTimeToken == DELTA_TIME_ABS) {
-            cur.readFromParcel(src);
-            if (DEBUG) Slog.i(TAG, "READ DELTA: ABS time=" + cur.time);
-            return;
-        } else if (deltaTimeToken == DELTA_TIME_INT) {
-            int delta = src.readInt();
-            cur.time += delta;
-            cur.numReadInts += 1;
-            if (DEBUG) Slog.i(TAG, "READ DELTA: time delta=" + delta + " new time=" + cur.time);
-        } else {
-            long delta = src.readLong();
-            if (DEBUG) Slog.i(TAG, "READ DELTA: time delta=" + delta + " new time=" + cur.time);
-            cur.time += delta;
-            cur.numReadInts += 2;
-        }
-
-        final int batteryLevelInt;
-        if ((firstToken&DELTA_BATTERY_LEVEL_FLAG) != 0) {
-            batteryLevelInt = src.readInt();
-            readBatteryLevelInt(batteryLevelInt, cur);
-            cur.numReadInts += 1;
-            if (DEBUG) Slog.i(TAG, "READ DELTA: batteryToken=0x"
-                    + Integer.toHexString(batteryLevelInt)
-                    + " batteryLevel=" + cur.batteryLevel
-                    + " batteryTemp=" + cur.batteryTemperature
-                    + " batteryVolt=" + (int)cur.batteryVoltage);
-        } else {
-            batteryLevelInt = 0;
-        }
-
-        if ((firstToken&DELTA_STATE_FLAG) != 0) {
-            int stateInt = src.readInt();
-            cur.states = (firstToken&DELTA_STATE_MASK) | (stateInt&(~STATE_BATTERY_MASK));
-            cur.batteryStatus = (byte)((stateInt>>STATE_BATTERY_STATUS_SHIFT)
-                    & STATE_BATTERY_STATUS_MASK);
-            cur.batteryHealth = (byte)((stateInt>>STATE_BATTERY_HEALTH_SHIFT)
-                    & STATE_BATTERY_HEALTH_MASK);
-            cur.batteryPlugType = (byte)((stateInt>>STATE_BATTERY_PLUG_SHIFT)
-                    & STATE_BATTERY_PLUG_MASK);
-            switch (cur.batteryPlugType) {
-                case 1:
-                    cur.batteryPlugType = BatteryManager.BATTERY_PLUGGED_AC;
-                    break;
-                case 2:
-                    cur.batteryPlugType = BatteryManager.BATTERY_PLUGGED_USB;
-                    break;
-                case 3:
-                    cur.batteryPlugType = BatteryManager.BATTERY_PLUGGED_WIRELESS;
-                    break;
-            }
-            cur.numReadInts += 1;
-            if (DEBUG) Slog.i(TAG, "READ DELTA: stateToken=0x"
-                    + Integer.toHexString(stateInt)
-                    + " batteryStatus=" + cur.batteryStatus
-                    + " batteryHealth=" + cur.batteryHealth
-                    + " batteryPlugType=" + cur.batteryPlugType
-                    + " states=0x" + Integer.toHexString(cur.states));
-        } else {
-            cur.states = (firstToken&DELTA_STATE_MASK) | (cur.states&(~STATE_BATTERY_MASK));
-        }
-
-        if ((firstToken&DELTA_STATE2_FLAG) != 0) {
-            cur.states2 = src.readInt();
-            if (DEBUG) Slog.i(TAG, "READ DELTA: states2=0x"
-                    + Integer.toHexString(cur.states2));
-        }
-
-        if ((firstToken&DELTA_WAKELOCK_FLAG) != 0) {
-            int indexes = src.readInt();
-            int wakeLockIndex = indexes&0xffff;
-            int wakeReasonIndex = (indexes>>16)&0xffff;
-            if (wakeLockIndex != 0xffff) {
-                cur.wakelockTag = cur.localWakelockTag;
-                readHistoryTag(wakeLockIndex, cur.wakelockTag);
-                if (DEBUG) Slog.i(TAG, "READ DELTA: wakelockTag=#" + cur.wakelockTag.poolIdx
-                    + " " + cur.wakelockTag.uid + ":" + cur.wakelockTag.string);
-            } else {
-                cur.wakelockTag = null;
-            }
-            if (wakeReasonIndex != 0xffff) {
-                cur.wakeReasonTag = cur.localWakeReasonTag;
-                readHistoryTag(wakeReasonIndex, cur.wakeReasonTag);
-                if (DEBUG) Slog.i(TAG, "READ DELTA: wakeReasonTag=#" + cur.wakeReasonTag.poolIdx
-                    + " " + cur.wakeReasonTag.uid + ":" + cur.wakeReasonTag.string);
-            } else {
-                cur.wakeReasonTag = null;
-            }
-            cur.numReadInts += 1;
-        } else {
-            cur.wakelockTag = null;
-            cur.wakeReasonTag = null;
-        }
-
-        if ((firstToken&DELTA_EVENT_FLAG) != 0) {
-            cur.eventTag = cur.localEventTag;
-            final int codeAndIndex = src.readInt();
-            cur.eventCode = (codeAndIndex&0xffff);
-            final int index = ((codeAndIndex>>16)&0xffff);
-            readHistoryTag(index, cur.eventTag);
-            cur.numReadInts += 1;
-            if (DEBUG) Slog.i(TAG, "READ DELTA: event=" + cur.eventCode + " tag=#"
-                    + cur.eventTag.poolIdx + " " + cur.eventTag.uid + ":"
-                    + cur.eventTag.string);
-        } else {
-            cur.eventCode = HistoryItem.EVENT_NONE;
-        }
-
-        if ((batteryLevelInt&BATTERY_DELTA_LEVEL_FLAG) != 0) {
-            cur.stepDetails = mReadHistoryStepDetails;
-            cur.stepDetails.readFromParcel(src);
-        } else {
-            cur.stepDetails = null;
-        }
-
-        if ((firstToken&DELTA_BATTERY_CHARGE_FLAG) != 0) {
-            cur.batteryChargeUah = src.readInt();
-        }
-        cur.modemRailChargeMah = src.readDouble();
-        cur.wifiRailChargeMah = src.readDouble();
-    }
-
     @Override
     public void commitCurrentHistoryBatchLocked() {
         mHistoryLastWritten.cmd = HistoryItem.CMD_NULL;
@@ -3869,7 +3725,7 @@ public class BatteryStatsImpl extends BatteryStats {
     }
 
     private void addHistoryBufferLocked(long elapsedRealtimeMs, byte cmd, HistoryItem cur) {
-        if (mIteratingHistory) {
+        if (mBatteryStatsHistoryIterator != null) {
             throw new IllegalStateException("Can't do this while iterating history!");
         }
         mHistoryBufferLastPos = mHistoryBuffer.dataPosition();
@@ -10680,7 +10536,7 @@ public class BatteryStatsImpl extends BatteryStats {
 
         if (systemDir == null) {
             mStatsFile = null;
-            mBatteryStatsHistory = new BatteryStatsHistory(this, mHistoryBuffer);
+            mBatteryStatsHistory = new BatteryStatsHistory(mHistoryBuffer);
         } else {
             mStatsFile = new AtomicFile(new File(systemDir, "batterystats.bin"));
             mBatteryStatsHistory = new BatteryStatsHistory(this, systemDir, mHistoryBuffer);
@@ -10802,7 +10658,7 @@ public class BatteryStatsImpl extends BatteryStats {
         mExternalSync = null;
         mConstants = new Constants(mHandler);
         clearHistoryLocked();
-        mBatteryStatsHistory = new BatteryStatsHistory(this, mHistoryBuffer);
+        mBatteryStatsHistory = new BatteryStatsHistory(mHistoryBuffer);
         readFromParcel(p);
         mPlatformIdleStateCallback = null;
         mMeasuredEnergyRetriever = null;
@@ -11180,67 +11036,55 @@ public class BatteryStatsImpl extends BatteryStats {
     @Override
     @UnsupportedAppUsage
     public boolean startIteratingHistoryLocked() {
-        mBatteryStatsHistory.startIteratingHistory();
         mReadOverflow = false;
-        mIteratingHistory = true;
-        mReadHistoryStrings = new String[mHistoryTagPool.size()];
-        mReadHistoryUids = new int[mHistoryTagPool.size()];
-        mReadHistoryChars = 0;
-        for (HashMap.Entry<HistoryTag, Integer> ent : mHistoryTagPool.entrySet()) {
-            final HistoryTag tag = ent.getKey();
-            final int idx = ent.getValue();
-            mReadHistoryStrings[idx] = tag.string;
-            mReadHistoryUids[idx] = tag.uid;
-            mReadHistoryChars += tag.string.length() + 1;
-        }
+        mBatteryStatsHistoryIterator = createBatteryStatsHistoryIterator();
         return true;
     }
 
+    /**
+     * Creates an iterator for battery stats history.
+     */
+    @VisibleForTesting
+    public BatteryStatsHistoryIterator createBatteryStatsHistoryIterator() {
+        ArrayList<HistoryTag> tags = new ArrayList<>(mHistoryTagPool.size());
+        for (Map.Entry<HistoryTag, Integer> entry: mHistoryTagPool.entrySet()) {
+            final HistoryTag tag = entry.getKey();
+            tag.poolIdx = entry.getValue();
+            tags.add(tag);
+        }
+
+        return new BatteryStatsHistoryIterator(mBatteryStatsHistory, tags);
+    }
+
     @Override
     public int getHistoryStringPoolSize() {
-        return mReadHistoryStrings.length;
+        return mBatteryStatsHistoryIterator.getHistoryStringPoolSize();
     }
 
     @Override
     public int getHistoryStringPoolBytes() {
-        // Each entry is a fixed 12 bytes: 4 for index, 4 for uid, 4 for string size
-        // Each string character is 2 bytes.
-        return (mReadHistoryStrings.length * 12) + (mReadHistoryChars * 2);
+        return mBatteryStatsHistoryIterator.getHistoryStringPoolBytes();
     }
 
     @Override
     public String getHistoryTagPoolString(int index) {
-        return mReadHistoryStrings[index];
+        return mBatteryStatsHistoryIterator.getHistoryTagPoolString(index);
     }
 
     @Override
     public int getHistoryTagPoolUid(int index) {
-        return mReadHistoryUids[index];
+        return mBatteryStatsHistoryIterator.getHistoryTagPoolUid(index);
     }
 
     @Override
     @UnsupportedAppUsage
     public boolean getNextHistoryLocked(HistoryItem out) {
-        Parcel p = mBatteryStatsHistory.getNextParcel(out);
-        if (p == null) {
-            return false;
-        }
-        final long lastRealtimeMs = out.time;
-        final long lastWalltimeMs = out.currentTime;
-        readHistoryDelta(p, out);
-        if (out.cmd != HistoryItem.CMD_CURRENT_TIME
-                && out.cmd != HistoryItem.CMD_RESET && lastWalltimeMs != 0) {
-            out.currentTime = lastWalltimeMs + (out.time - lastRealtimeMs);
-        }
-        return true;
+        return mBatteryStatsHistoryIterator.next(out);
     }
 
     @Override
     public void finishIteratingHistoryLocked() {
-        mBatteryStatsHistory.finishIteratingHistory();
-        mIteratingHistory = false;
-        mReadHistoryStrings = null;
-        mReadHistoryUids = null;
+        mBatteryStatsHistoryIterator = null;
     }
 
     @Override
diff --git a/core/tests/coretests/src/com/android/internal/os/BatteryStatsHistoryIteratorTest.java b/core/tests/coretests/src/com/android/internal/os/BatteryStatsHistoryIteratorTest.java
new file mode 100644
index 000000000000..263daf0cd625
--- /dev/null
+++ b/core/tests/coretests/src/com/android/internal/os/BatteryStatsHistoryIteratorTest.java
@@ -0,0 +1,115 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.internal.os;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.os.BatteryManager;
+import android.os.BatteryStats;
+import android.os.Process;
+
+import androidx.test.filters.SmallTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+@RunWith(AndroidJUnit4.class)
+@SmallTest
+public class BatteryStatsHistoryIteratorTest {
+    private static final int APP_UID = Process.FIRST_APPLICATION_UID + 42;
+
+    @Rule
+    public final BatteryUsageStatsRule mStatsRule = new BatteryUsageStatsRule();
+
+    @Test
+    public void testIterator() {
+        MockBatteryStatsImpl batteryStats = mStatsRule.getBatteryStats();
+        batteryStats.setRecordAllHistoryLocked(true);
+        batteryStats.forceRecordAllHistory();
+
+        mStatsRule.setTime(1000, 1000);
+        batteryStats.setNoAutoReset(true);
+
+        batteryStats.setBatteryStateLocked(BatteryManager.BATTERY_STATUS_DISCHARGING, 100,
+                /* plugType */ 0, 90, 72, 3700, 3_600_000, 4_000_000, 0, 1_000_000,
+                1_000_000, 1_000_000);
+        batteryStats.setBatteryStateLocked(BatteryManager.BATTERY_STATUS_DISCHARGING, 100,
+                /* plugType */ 0, 80, 72, 3700, 2_400_000, 4_000_000, 0, 2_000_000,
+                2_000_000, 2_000_000);
+
+        batteryStats.noteAlarmStartLocked("foo", null, APP_UID, 3_000_000, 2_000_000);
+        batteryStats.noteAlarmFinishLocked("foo", null, APP_UID, 3_001_000, 2_001_000);
+
+        final BatteryStatsHistoryIterator iterator =
+                batteryStats.createBatteryStatsHistoryIterator();
+
+        BatteryStats.HistoryItem item = new BatteryStats.HistoryItem();
+
+        assertThat(iterator.next(item)).isTrue();
+        assertHistoryItem(item,
+                BatteryStats.HistoryItem.CMD_RESET, BatteryStats.HistoryItem.EVENT_NONE,
+                null, 0, 3_600_000, 90, 1_000_000);
+
+        assertThat(iterator.next(item)).isTrue();
+        assertHistoryItem(item,
+                BatteryStats.HistoryItem.CMD_UPDATE, BatteryStats.HistoryItem.EVENT_NONE,
+                null, 0, 3_600_000, 90, 1_000_000);
+
+        assertThat(iterator.next(item)).isTrue();
+        assertHistoryItem(item,
+                BatteryStats.HistoryItem.CMD_UPDATE, BatteryStats.HistoryItem.EVENT_NONE,
+                null, 0, 2_400_000, 80, 2_000_000);
+
+        assertThat(iterator.next(item)).isTrue();
+        assertHistoryItem(item,
+                BatteryStats.HistoryItem.CMD_UPDATE, BatteryStats.HistoryItem.EVENT_NONE,
+                null, 0, 2_400_000, 80, 2_000_000);
+
+        assertThat(iterator.next(item)).isTrue();
+        assertHistoryItem(item,
+                BatteryStats.HistoryItem.CMD_UPDATE,
+                BatteryStats.HistoryItem.EVENT_ALARM | BatteryStats.HistoryItem.EVENT_FLAG_START,
+                "foo", APP_UID, 2_400_000, 80, 3_000_000);
+
+        assertThat(iterator.next(item)).isTrue();
+        assertHistoryItem(item,
+                BatteryStats.HistoryItem.CMD_UPDATE,
+                BatteryStats.HistoryItem.EVENT_ALARM | BatteryStats.HistoryItem.EVENT_FLAG_FINISH,
+                "foo", APP_UID, 2_400_000, 80, 3_001_000);
+
+        assertThat(iterator.next(item)).isFalse();
+    }
+
+    private void assertHistoryItem(BatteryStats.HistoryItem item, int command, int eventCode,
+            String tag, int uid, int batteryChargeUah, int batteryLevel,
+            long elapsedTimeMs) {
+        assertThat(item.cmd).isEqualTo(command);
+        assertThat(item.eventCode).isEqualTo(eventCode);
+        if (tag == null) {
+            assertThat(item.eventTag).isNull();
+        } else {
+            assertThat(item.eventTag.string).isEqualTo(tag);
+            assertThat(item.eventTag.uid).isEqualTo(uid);
+        }
+        assertThat(item.batteryChargeUah).isEqualTo(batteryChargeUah);
+        assertThat(item.batteryLevel).isEqualTo(batteryLevel);
+
+        assertThat(item.time).isEqualTo(elapsedTimeMs);
+    }
+}
diff --git a/core/tests/coretests/src/com/android/internal/os/BatteryStatsTests.java b/core/tests/coretests/src/com/android/internal/os/BatteryStatsTests.java
index d276bc34d05a..74c37ada2054 100644
--- a/core/tests/coretests/src/com/android/internal/os/BatteryStatsTests.java
+++ b/core/tests/coretests/src/com/android/internal/os/BatteryStatsTests.java
@@ -30,6 +30,7 @@ import org.junit.runners.Suite;
         BatteryStatsDualTimerTest.class,
         BatteryStatsDurationTimerTest.class,
         BatteryStatsHelperTest.class,
+        BatteryStatsHistoryIteratorTest.class,
         BatteryStatsHistoryTest.class,
         BatteryStatsImplTest.class,
         BatteryStatsNoteTest.class,