說(shuō)說(shuō)Android的廣播(5) - 廣播的歷史
廣播的歷史
AMS中的歷史信息
處理完廣播之后，BroadcastQueue會(huì)記錄一段歷史用于調(diào)試：
- mBroadcastHistory記錄最近的BroadcastRecord
- mBroadcastSummaryHistory記錄最近的Intent
- mSummaryHistoryEnqueueTime記錄最近的enqueueTime
- mSummaryHistoryDispatchTime記錄最近的dispatchTime
- mSummaryHistoryFinishTime記錄最近的finishTime
具體的定義如下：
/**
* Historical data of past broadcasts, for debugging. This is a ring buffer
* whose last element is at mHistoryNext.
*/
final BroadcastRecord[] mBroadcastHistory = new BroadcastRecord[MAX_BROADCAST_HISTORY];
int mHistoryNext = 0;
/**
* Summary of historical data of past broadcasts, for debugging. This is a
* ring buffer whose last element is at mSummaryHistoryNext.
*/
final Intent[] mBroadcastSummaryHistory = new Intent[MAX_BROADCAST_SUMMARY_HISTORY];
int mSummaryHistoryNext = 0;
/**
* Various milestone timestamps of entries in the mBroadcastSummaryHistory ring
* buffer, also tracked via the mSummaryHistoryNext index. These are all in wall
* clock time, not elapsed.
*/
final long[] mSummaryHistoryEnqueueTime = new long[MAX_BROADCAST_SUMMARY_HISTORY];
final long[] mSummaryHistoryDispatchTime = new long[MAX_BROADCAST_SUMMARY_HISTORY];
final long[] mSummaryHistoryFinishTime = new long[MAX_BROADCAST_SUMMARY_HISTORY];
BroadcastRecord中的歷史信息
BroadcastRecord中，除了前面我們講的這幾個(gè)時(shí)間：
long enqueueClockTime; // the clock time the broadcast was enqueued
long dispatchTime; // when dispatch started on this set of receivers
long dispatchClockTime; // the clock time the dispatch started
long receiverTime; // when current receiver started for timeouts.
long finishTime; // when we finished the broadcast.
還有記錄的ANR的次數(shù)：
int anrCount; // has this broadcast record hit any ANRs?
可惜這兩部分信息只是被打日志調(diào)試時(shí)用到。
BroadcastQueue中記錄歷史的過(guò)程
BroadcastQueue中提供了addBroadcastToHistoryLocked方法來(lái)記錄歷史信息。
1221 private final void addBroadcastToHistoryLocked(BroadcastRecord r) {
1222 if (r.callingUid < 0) {
1223 // This was from a registerReceiver() call; ignore it.
1224 return;
1225 }
1226 r.finishTime = SystemClock.uptimeMillis();
1227
1228 mBroadcastHistory[mHistoryNext] = r;
1229 mHistoryNext = ringAdvance(mHistoryNext, 1, MAX_BROADCAST_HISTORY);
1230
1231 mBroadcastSummaryHistory[mSummaryHistoryNext] = r.intent;
1232 mSummaryHistoryEnqueueTime[mSummaryHistoryNext] = r.enqueueClockTime;
1233 mSummaryHistoryDispatchTime[mSummaryHistoryNext] = r.dispatchClockTime;
1234 mSummaryHistoryFinishTime[mSummaryHistoryNext] = System.currentTimeMillis();
1235 mSummaryHistoryNext = ringAdvance(mSummaryHistoryNext, 1, MAX_BROADCAST_SUMMARY_HISTORY);
1236 }
其中，ringAdvance的實(shí)現(xiàn)是這樣的。從循環(huán)計(jì)數(shù)的角度來(lái)講，Android這段寫得并不好。只在increment為+1或者-1的情況下還算工作正常吧。
1214 private final int ringAdvance(int x, final int increment, final int ringSize) {
1215 x += increment;
1216 if (x < 0) return (ringSize - 1);
1217 else if (x >= ringSize) return 0;
1218 else return x;
1219 }
addBroadcastToHistoryLocked一共被調(diào)用兩次，全部都在processNextBroadcast函數(shù)中。一處是在并發(fā)隊(duì)列處理完之后，另一個(gè)是在有序隊(duì)列返回值以后。下節(jié)我們分析processNextBroadcast的時(shí)候，會(huì)把這些都串起來(lái)。
