DropBoxManager简介

介绍 Android DropBoxManager Service

什么是 DropBoxManager ?

Enqueues chunks of data (from various sources – application crashes, kernel log records, etc.). The queue is size bounded and will drop old data if the enqueued data exceeds the maximum size. You can think of this as a persistent, system-wide, blob-oriented “logcat”.

DropBoxManager 是 Android 在 Froyo(API level 8) 引入的用来持续化存储系统数据的机制, 主要用于记录Android 运行过程中, 内核, 系统进程, 用户进程等出现严重问题时的 log, 可以认为这是一个可持续存储的系统级别的logcat.

我们可以通过用参数 DROPBOX_SERVICE调用 getSystemService(String)来获得这个服务, 并查询出所有存储在 DropBoxManager 里的系统错误记录.

Android 缺省能记录哪些系统错误 ?

我没有在官方的网站上找到关于哪些系统错误会被记录到 DropBoxManager 中的文档, 但我们可以查看源代码来找到相关信息.从源代码中可以查找到记录到 DropBoxManager 中各种tag(类似于 logcat 的 tag).

crash (应用程序强制关闭, Force Close)

当Java层遇到未被 catch 的例外时, ActivityManagerService 会记录一次 crash 到 DropBoxManager中, 并弹出Force Close 对话框提示用户.

ActivityManagerServicelink

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public void handleApplicationCrash(IBinder app, ApplicationErrorReport.CrashInfo crashInfo) {    ProcessRecord r = findAppProcess(app, "Crash");    final String processName = app == null ? "system_server"            : (r == null ? "unknown" : r.processName);    EventLog.writeEvent(EventLogTags.AM_CRASH, Binder.getCallingPid(),            UserHandle.getUserId(Binder.getCallingUid()), processName,            r == null ? -1 : r.info.flags,            crashInfo.exceptionClassName,            crashInfo.exceptionMessage,            crashInfo.throwFileName,            crashInfo.throwLineNumber);    addErrorToDropBox("crash", r, processName, null, null, null, null, null, crashInfo);    crashApplication(r, crashInfo);}

anr (应用程序没响应, Application Not Responding, ANR)

当应用程序的主线程(UI线程)长时间未能得到响应时, ActivityManagerService 会记录一次 anr 到 DropBoxManager中, 并弹出Application Not Responding 对话框提示用户.

ActivityManagerServicelink

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final void appNotResponding(ProcessRecord app, ActivityRecord activity,        ActivityRecord parent, boolean aboveSystem, final String annotation) {    //......    addErrorToDropBox("anr", app, app.processName, activity, parent, annotation,            cpuInfo, tracesFile, null);    //......}

wtf (What a Terrible Failure)

‘android.util.Log’ 类提供了静态的 wtf 函数, 应用程序可以在代码中用来主动报告一个不应当发生的情况. 依赖于系统设置,这个函数会通过 ActivityManagerService 增加一个wtf 记录到 DropBoxManager中, 并/或终止当前应用程序进程.

ActivityManagerServicelink

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public boolean handleApplicationWtf(IBinder app, String tag,        ApplicationErrorReport.CrashInfo crashInfo) {    ProcessRecord r = findAppProcess(app, "WTF");    final String processName = app == null ? "system_server"            : (r == null ? "unknown" : r.processName);    EventLog.writeEvent(EventLogTags.AM_WTF,            UserHandle.getUserId(Binder.getCallingUid()), Binder.getCallingPid(),            processName,            r == null ? -1 : r.info.flags,            tag, crashInfo.exceptionMessage);    addErrorToDropBox("wtf", r, processName, null, null, tag, null, null, crashInfo);    if (r != null && r.pid != Process.myPid() &&            Settings.Global.getInt(mContext.getContentResolver(),                    Settings.Global.WTF_IS_FATAL, 0) != 0) {        crashApplication(r, crashInfo);        return true;    } else {        return false;    }}

strict_mode (StrictMode Violation)

StrictMode (严格模式), 顾名思义, 就是在比正常模式检测得更严格, 通常用来监测不应当在主线程执行的网络, 文件等操作.任何 StrictMode 违例都会被 ActivityManagerService 在 DropBoxManager 中记录为一次strict_mode 违例.

ActivityManagerServicelink

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public void handleApplicationStrictModeViolation(        IBinder app,        int violationMask,        StrictMode.ViolationInfo info) {    ProcessRecord r = findAppProcess(app, "StrictMode");    if (r == null) {        return;    }    if ((violationMask & StrictMode.PENALTY_DROPBOX) != 0) {        Integer stackFingerprint = info.hashCode();        boolean logIt = true;        synchronized (mAlreadyLoggedViolatedStacks) {            if (mAlreadyLoggedViolatedStacks.contains(stackFingerprint)) {                logIt = false;                // TODO: sub-sample into EventLog for these, with                // the info.durationMillis?  Then we'd get                // the relative pain numbers, without logging all                // the stack traces repeatedly.  We'd want to do                // likewise in the client code, which also does                // dup suppression, before the Binder call.            } else {                if (mAlreadyLoggedViolatedStacks.size() >= MAX_DUP_SUPPRESSED_STACKS) {                    mAlreadyLoggedViolatedStacks.clear();                }                mAlreadyLoggedViolatedStacks.add(stackFingerprint);            }        }        if (logIt) {            logStrictModeViolationToDropBox(r, info);        }    }    //......}

lowmem (低内存)

在内存不足的时候, Android 会终止后台应用程序来释放内存, 但如果没有后台应用程序可被释放时, ActivityManagerService 就会在 DropBoxManager 中记录一次lowmem.

ActivityManagerServicelink

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    public void handleMessage(Message msg) {        switch (msg.what) {        //...        case REPORT_MEM_USAGE: {            //......            Thread thread = new Thread() {                @Override public void run() {                    StringBuilder dropBuilder = new StringBuilder(1024);                    StringBuilder logBuilder = new StringBuilder(1024);                    //......                    addErrorToDropBox("lowmem", null, "system_server", null,                            null, tag.toString(), dropBuilder.toString(), null, null);                    //......                }            };            thread.start();            break;        }        //......    }

watchdog

如果 WatchDog 监测到系统进程(system_server)出现问题, 会增加一条 watchdog 记录到 DropBoxManager 中, 并终止系统进程的执行.

Watchdoglink

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/** This class calls its monitor every minute. Killing this process if they don't return **/public class Watchdog extends Thread {    //......    @Override    public void run() {        boolean waitedHalf = false;        while (true) {            //......            // If we got here, that means that the system is most likely hung.            // First collect stack traces from all threads of the system process.            // Then kill this process so that the system will restart.            //......            // Try to add the error to the dropbox, but assuming that the ActivityManager            // itself may be deadlocked.  (which has happened, causing this statement to            // deadlock and the watchdog as a whole to be ineffective)            Thread dropboxThread = new Thread("watchdogWriteToDropbox") {                    public void run() {                        mActivity.addErrorToDropBox(                                "watchdog", null, "system_server", null, null,                                name, null, stack, null);                    }                };            dropboxThread.start();            try {                dropboxThread.join(2000);  // wait up to 2 seconds for it to return.            } catch (InterruptedException ignored) {}            //......        }    }    //......}

netstats_error

NetworkStatsService 负责收集并持久化存储网络状态的统计数据, 当遇到明显的网络状态错误时, 它会增加一条 netstats_error 记录到 DropBoxManager.

BATTERY_DISCHARGE_INFO

BatteryService 负责检测充电状态, 并更新手机电池信息. 当遇到明显的 discharge 事件, 它会增加一条 BATTERY_DISCHARGE_INFO 记录到 DropBoxManager.

系统服务(System Serve)启动完成后的检测

系统服务(System Serve)启动完成后会进行一系列自检, 包括:

• 开机

  每次开机都会增加一条 SYSTEM_BOOT 记录.

• System Server 重启

  如果系统服务(System Server)不是开机后的第一次启动, 会增加一条 SYSTEM_RESTART 记录, 正常情况下系统服务(System Server)在一次开机中只会启动一次,启动第二次就意味着 bug.

• Kernel Panic (内核错误)

  发生 Kernel Panic 时, Kernel 会记录一些 log 信息到文件系统, 因为 Kernel 已经挂掉了, 当然这时不可能有其他机会来记录错误信息了. 唯一能检测 Kernel Panic的办法就是在手机启动后检查这些 log 文件是否存在, 如果存在则意味着上一次手机是因为 Kernel Panic 而宕机, 并记录这些日志到 DropBoxManager 中.DropBoxManager 记录 TAG 名称和对应的文件名分别是:

  • SYSTEM_LAST_KMSG, 如果 /proc/last_kmsg 存在.
  • APANIC_CONSOLE, 如果 /data/dontpanic/apanic_console 存在.
  • APANIC_THREADS, 如果 /data/dontpanic/apanic_threads 存在.

• 系统恢复(System Recovery)

  通过检测文件 /cache/recovery/log 是否存在来检测设备是否因为系统恢复而重启, 并增加一条 SYSTEM_RECOVERY_LOG 记录到 DropBoxManager 中.

System Server BootReceiverlink

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private void logBootEvents(Context ctx) throws IOException {    final DropBoxManager db = (DropBoxManager) ctx.getSystemService(Context.DROPBOX_SERVICE);    final SharedPreferences prefs = ctx.getSharedPreferences("log_files", Context.MODE_PRIVATE);    final String headers = new StringBuilder(512)        .append("Build: ").append(Build.FINGERPRINT).append("\n")        .append("Hardware: ").append(Build.BOARD).append("\n")        .append("Revision: ")        .append(SystemProperties.get("ro.revision", "")).append("\n")        .append("Bootloader: ").append(Build.BOOTLOADER).append("\n")        .append("Radio: ").append(Build.RADIO).append("\n")        .append("Kernel: ")        .append(FileUtils.readTextFile(new File("/proc/version"), 1024, "...\n"))        .append("\n").toString();    String recovery = RecoverySystem.handleAftermath();    if (recovery != null && db != null) {        db.addText("SYSTEM_RECOVERY_LOG", headers + recovery);    }    if (SystemProperties.getLong("ro.runtime.firstboot", 0) == 0) {        String now = Long.toString(System.currentTimeMillis());        SystemProperties.set("ro.runtime.firstboot", now);        if (db != null) db.addText("SYSTEM_BOOT", headers);        // Negative sizes mean to take the *tail* of the file (see FileUtils.readTextFile())        addFileToDropBox(db, prefs, headers, "/proc/last_kmsg",                -LOG_SIZE, "SYSTEM_LAST_KMSG");        addFileToDropBox(db, prefs, headers, "/cache/recovery/log",                -LOG_SIZE, "SYSTEM_RECOVERY_LOG");        addFileToDropBox(db, prefs, headers, "/data/dontpanic/apanic_console",                -LOG_SIZE, "APANIC_CONSOLE");        addFileToDropBox(db, prefs, headers, "/data/dontpanic/apanic_threads",                -LOG_SIZE, "APANIC_THREADS");    } else {        if (db != null) db.addText("SYSTEM_RESTART", headers);    }    // Scan existing tombstones (in case any new ones appeared)    File[] tombstoneFiles = TOMBSTONE_DIR.listFiles();    for (int i = 0; tombstoneFiles != null && i < tombstoneFiles.length; i++) {        addFileToDropBox(db, prefs, headers, tombstoneFiles[i].getPath(),                LOG_SIZE, "SYSTEM_TOMBSTONE");    }    // Start watching for new tombstone files; will record them as they occur.    // This gets registered with the singleton file observer thread.    sTombstoneObserver = new FileObserver(TOMBSTONE_DIR.getPath(), FileObserver.CLOSE_WRITE) {        @Override        public void onEvent(int event, String path) {            try {                String filename = new File(TOMBSTONE_DIR, path).getPath();                addFileToDropBox(db, prefs, headers, filename, LOG_SIZE, "SYSTEM_TOMBSTONE");            } catch (IOException e) {                Slog.e(TAG, "Can't log tombstone", e);            }        }    };    sTombstoneObserver.startWatching();}

SYSTEM_TOMBSTONE (Native 进程的崩溃)

Tombstone 是 Android 用来记录 native 进程崩溃的 core dump 日志, 系统服务在启动完成后会增加一个 Observer 来侦测 tombstone 日志文件的变化,每当生成新的tombstone 文件, 就会增加一条 SYSTEM_TOMBSTONE 记录到 DropBoxManager 中.

DropBoxManager 如何存储记录数据 ?

DropBoxManager 使用的是文件存储, 所有的记录都存储在 /data/system/dropbox 目录中, 一条记录就是一个文件, 当文本文件的尺寸超过文件系统的最小区块尺寸后,DropBoxManager 还会自动压缩该文件, 通常文件名以调用 DropBoxManager 的 TAG 参数开头.

System Server BootReceiverlink

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$ adb shell ls -l /data/system/dropbox-rw------- system   system        258 2012-11-21 11:36 [e-mail]-rw------- system   system         39 2012-11-21 11:40 [e-mail]-rw------- system   system         39 2012-11-21 12:10 [e-mail]-rw------- system   system         34 2012-11-21 18:10 [e-mail]-rw------- system   system         34 2012-11-21 18:40 [e-mail]-rw------- system   system         34 2012-11-22 10:10 [e-mail]-rw------- system   system       1528 2012-11-21 22:54 [e-mail]-rw------- system   system       1877 2012-11-21 11:36 [e-mail]-rw------- system   system       3724 2012-11-21 11:36 [e-mail]

如何利用 DropBoxManager ?

• 利用 DropBoxManager 来记录需要持久化存储的错误日志信息

  DropBoxManager 提供了 logcat 之外的另外一种错误日志记录机制, 程序可以在出错的时候自动将相关信息记录到 DropBoxManager 中. 相对于 logcat,DropBoxManager 更适合于程序的自动抓错, 避免人为因素而产生的错误遗漏. 并且 DropBoxManager 是 Android 系统的公开服务, 相对于很多私有实现,出现兼容性问题的几率会大大降低.

• 错误自动上报

  可以将 DropBoxManager 和设备的 BugReport 结合起来, 实现自动上报错误到服务器. 每当生成新的记录, DropBoxManager 就会广播一个DropBoxManager.ACTION_DROPBOX_ENTRY_ADDED Intent, 设备的 BugReport 服务需要侦听这个 Intent, 然后触发错误的自动上报.

参考

• Android Official Site
• DropBoxManager Overview
• ActivityManager Service Overview
• Android StrictMode Overview

参考链接：http://xiaocong.github.io/blog/2012/11/21/to-introduce-android-dropboxmanager-service/