MetricsReader.java revision f33926abed907faf31093544303ea51723738214 
1/*
2 * Copyright (C) 2017 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16package android.metrics;
17
18import android.annotation.SystemApi;
19import android.util.EventLog;
20import android.util.EventLog.Event;
21import android.util.Log;
22
23import com.android.internal.logging.MetricsLogger;
24
25import java.io.IOException;
26import java.util.ArrayList;
27import java.util.LinkedList;
28import java.util.Queue;
29
30/**
31 * Read platform logs.
32 * @hide
33 */
34@SystemApi
35public class MetricsReader {
36    private Queue<LogMaker> mEventQueue = new LinkedList<>();
37    private long mLastEventMs;
38    private long mCheckpointMs;
39    private int[] LOGTAGS = { MetricsLogger.LOGTAG };
40
41    /**
42     * Read the available logs into a new session.
43     *
44     * The session will contain events starting from the oldest available
45     * log on the system up to the most recent at the time of this call.
46     *
47     * A call to {@link #checkpoint()} will cause the session to contain
48     * only events that occured after that call.
49     *
50     * This call will not return until the system buffer overflows the
51     * specified timestamp. If the specified timestamp is 0, then the
52     * call will return immediately since any logs 1970 have already been
53     * overwritten (n.b. if the underlying system has the capability to
54     * store many decades of system logs, this call may fail in
55     * interesting ways.)
56     *
57     * @param horizonMs block until this timestamp is overwritten, 0 for non-blocking read.
58     */
59    public void read(long horizonMs) {
60        ArrayList<Event> nativeEvents = new ArrayList<>();
61        try {
62            EventLog.readEventsOnWrapping(LOGTAGS, horizonMs, nativeEvents);
63        } catch (IOException e) {
64            e.printStackTrace();
65        }
66        mEventQueue.clear();
67        for (EventLog.Event event : nativeEvents) {
68            final long eventTimestampMs = event.getTimeNanos() / 1000000;
69            if (eventTimestampMs > mCheckpointMs) {
70                Object data = event.getData();
71                Object[] objects;
72                if (data instanceof Object[]) {
73                    objects = (Object[]) data;
74                } else {
75                    // wrap scalar objects
76                    objects = new Object[1];
77                    objects[0] = data;
78                }
79                mEventQueue.add(new LogMaker(objects)
80                        .setTimestamp(eventTimestampMs));
81                mLastEventMs = eventTimestampMs;
82            }
83        }
84    }
85
86    /** Cause this session to only contain events that occur after this call. */
87    public void checkpoint() {
88        // read the log to find the most recent event.
89        read(0L);
90        // any queued event is now too old, so drop them.
91        mEventQueue.clear();
92        mCheckpointMs = mLastEventMs;
93    }
94
95    /**
96     * Rewind the session to the beginning of time and read all available logs.
97     *
98     * A prior call to {@link #checkpoint()} will cause the reader to ignore
99     * any event with a timestamp before the time of that call.
100     *
101     * The underlying log buffer is live: between calls to {@link #reset()}, older
102     * events may be lost from the beginning of the session, and new events may
103     * appear at the end.
104     */
105    public void reset() {
106        read(0l);
107    }
108
109    /* Does the current log session have another entry? */
110    public boolean hasNext() {
111        return !mEventQueue.isEmpty();
112    }
113
114    /* Return the next entry in the current log session. */
115    public LogMaker next() {
116        return mEventQueue.poll();
117    }
118
119}
120