LogReader.cpp revision 9fc9edf95a308f5884bf541cac81ce1f41aba0ba 
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 */
16
17#include "logd/LogReader.h"
18
19#include <log/log_read.h>
20
21#include <utils/Errors.h>
22
23#include <time.h>
24#include <unistd.h>
25
26using namespace android;
27using namespace std;
28
29namespace android {
30namespace os {
31namespace statsd {
32
33#define SNOOZE_INITIAL_MS 100
34#define SNOOZE_MAX_MS (10 * 60 * 1000)  // Ten minutes
35
36LogReader::LogReader(const sp<LogListener>& listener) : mListener(listener) {
37}
38
39LogReader::~LogReader() {
40}
41
42void LogReader::Run() {
43    int nextSnoozeMs = SNOOZE_INITIAL_MS;
44
45    // In an ideal world, this outer loop will only ever run one iteration, but it
46    // exists to handle crashes in logd.  The inner loop inside connect_and_read()
47    // reads from logd forever, but if that read fails, we fall out to the outer
48    // loop, do the backoff (resetting the backoff timeout if we successfully read
49    // something), and then try again.
50    while (true) {
51        // Connect and read
52        int lineCount = connect_and_read();
53
54        // Figure out how long to sleep.
55        if (lineCount > 0) {
56            // If we managed to read at least one line, reset the backoff
57            nextSnoozeMs = SNOOZE_INITIAL_MS;
58        } else {
59            // Otherwise, expontial backoff
60            nextSnoozeMs *= 1.5f;
61            if (nextSnoozeMs > 10 * 60 * 1000) {
62                // Don't wait for toooo long.
63                nextSnoozeMs = SNOOZE_MAX_MS;
64            }
65        }
66
67        // Sleep
68        timespec ts;
69        timespec rem;
70        ts.tv_sec = nextSnoozeMs / 1000;
71        ts.tv_nsec = (nextSnoozeMs % 1000) * 1000000L;
72        while (nanosleep(&ts, &rem) == -1) {
73            if (errno == EINTR) {
74                ts = rem;
75            }
76            // other errors are basically impossible
77        }
78    }
79}
80
81int LogReader::connect_and_read() {
82    int lineCount = 0;
83    status_t err;
84    logger_list* loggers;
85    logger* eventLogger;
86
87    // Prepare the logging context
88    loggers = android_logger_list_alloc(ANDROID_LOG_RDONLY,
89                                        /* don't stop after N lines */ 0,
90                                        /* no pid restriction */ 0);
91
92    // Open the buffer(s)
93    eventLogger = android_logger_open(loggers, LOG_ID_STATS);
94
95    // Read forever
96    if (eventLogger) {
97        while (true) {
98            log_msg msg;
99
100            // Read a message
101            err = android_logger_list_read(loggers, &msg);
102            if (err < 0) {
103                fprintf(stderr, "logcat read failure: %s\n", strerror(err));
104                break;
105            }
106
107            // Record that we read one (used above to know how to snooze).
108            lineCount++;
109
110            // Call the listener
111            mListener->OnLogEvent(msg);
112        }
113    }
114
115    // Free the logger list and close the individual loggers
116    android_logger_list_free(loggers);
117
118    return lineCount;
119}
120
121}  // namespace statsd
122}  // namespace os
123}  // namespace android
124