cmds/statsd/src/LogReader.cpp

/*
 * Copyright (C) 2017 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.
 */

#include "LogReader.h"

#include <log/log_read.h>

#include <utils/Errors.h>

#include <time.h>
#include <unistd.h>

using namespace android;
using namespace std;

#define SNOOZE_INITIAL_MS 100
#define SNOOZE_MAX_MS (10 * 60 * 1000) // Ten minutes


// ================================================================================
LogListener::LogListener()
{
}

LogListener::~LogListener()
{
}


// ================================================================================
LogReader::LogReader()
{
}

LogReader::~LogReader()
{
}

void
LogReader::AddListener(const sp<LogListener>& listener)
{
    m_listeners.push_back(listener);
}

void
LogReader::Run()
{
    int nextSnoozeMs = SNOOZE_INITIAL_MS;

    // In an ideal world, this outer loop will only ever run one iteration, but it
    // exists to handle crashes in logd.  The inner loop inside connect_and_read()
    // reads from logd forever, but if that read fails, we fall out to the outer
    // loop, do the backoff (resetting the backoff timeout if we successfully read
    // something), and then try again.
    while (true) {
        // Connect and read
        int lineCount = connect_and_read();

        // Figure out how long to sleep.
        if (lineCount > 0) {
            // If we managed to read at least one line, reset the backoff
            nextSnoozeMs = SNOOZE_INITIAL_MS;
        } else {
            // Otherwise, expontial backoff
            nextSnoozeMs *= 1.5f;
            if (nextSnoozeMs > 10 * 60 * 1000) {
                // Don't wait for toooo long.
                nextSnoozeMs = SNOOZE_MAX_MS;
            }
        }

        // Sleep
        timespec ts;
        timespec rem;
        ts.tv_sec = nextSnoozeMs / 1000;
        ts.tv_nsec = (nextSnoozeMs % 1000) * 1000000L;
        while (nanosleep(&ts, &rem) == -1) {
            if (errno == EINTR) {
                ts = rem;
            }
            // other errors are basically impossible
        }
    }
}

int
LogReader::connect_and_read()
{
    int lineCount = 0;
    status_t err;
    logger_list* loggers;
    logger* eventLogger;

    // Prepare the logging context
    loggers = android_logger_list_alloc(ANDROID_LOG_RDONLY,
            /* don't stop after N lines */ 0,
            /* no pid restriction */ 0);

    // Open the buffer(s)
    eventLogger = android_logger_open(loggers, LOG_ID_EVENTS);

    // Read forever
    if (eventLogger) {
        while (true) {
            log_msg msg;

            // Read a message
            err = android_logger_list_read(loggers, &msg);
            if (err < 0) {
                fprintf(stderr, "logcat read failure: %s\n", strerror(err));
                break;
            }

            // Record that we read one (used above to know how to snooze).
            lineCount++;

            // Call the listeners
            for (vector<sp<LogListener> >::iterator it = m_listeners.begin();
                    it != m_listeners.end(); it++) {
                (*it)->OnLogEvent(msg);
            }
        }
    }

    // Free the logger list and close the individual loggers
    android_logger_list_free(loggers);

    return lineCount;
}