说说Android的广播(5) - 广播的历史

广播的历史

AMS中的历史信息

处理完广播之后，BroadcastQueue会记录一段历史用于调试：

• mBroadcastHistory记录最近的BroadcastRecord
• mBroadcastSummaryHistory记录最近的Intent
• mSummaryHistoryEnqueueTime记录最近的enqueueTime
• mSummaryHistoryDispatchTime记录最近的dispatchTime
• mSummaryHistoryFinishTime记录最近的finishTime

具体的定义如下：

/**
 * 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中的历史信息

BroadcastRecord中，除了前面我们讲的这几个时间：

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.

还有记录的ANR的次数：

int anrCount;           // has this broadcast record hit any ANRs?

可惜这两部分信息只是被打日志调试时用到。

BroadcastQueue中记录历史的过程

BroadcastQueue中提供了addBroadcastToHistoryLocked方法来记录历史信息。

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的实现是这样的。从循环计数的角度来讲，Android这段写得并不好。只在increment为+1或者-1的情况下还算工作正常吧。

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一共被调用两次，全部都在processNextBroadcast函数中。一处是在并发队列处理完之后，另一个是在有序队列返回值以后。下节我们分析processNextBroadcast的时候，会把这些都串起来。