DropBoxManager启动篇 - Gityuan博客 | 袁辉辉的技术博客

一、启动流程

DropBoxManagerService(简称DBMS) 记录着系统关键log信息，主要功能用于Debug调试。 Android系统启动过程SystemServer进程时，在startOtherServices()过程会启动DBMS服务，如下：

1.1 启动DBMS

[-> SystemServer.java]

private void startOtherServices() {
    //初始化DBMS，并登记该服务【见小节1.2】
    ServiceManager.addService(Context.DROPBOX_SERVICE,
            new DropBoxManagerService(context, new File("/data/system/dropbox")));
    ...
}

其中DROPBOX_SERVICE = “dropbox”, DBMS工作目录位于”/data/system/dropbox”，这个过程向ServiceManager 登记名为“dropbox”的服务。那么可通过dumpsys dropbox来查看该dropbox服务信息。

1.2 初始化DBMS

[-> DropBoxManagerService.java]

public final class DropBoxManagerService extends IDropBoxManagerService.Stub {

    public DropBoxManagerService(final Context context, File path) {
        mDropBoxDir = path;  // 目录/data/system/dropbox
        mContext = context;
        mContentResolver = context.getContentResolver();

        IntentFilter filter = new IntentFilter();
        // 监听存储设备可用空间低的广播
        filter.addAction(Intent.ACTION_DEVICE_STORAGE_LOW);
        // 监听开机完毕的广播
        filter.addAction(Intent.ACTION_BOOT_COMPLETED);
        context.registerReceiver(mReceiver, filter);

        // Settings数据库变化时则回调广播接收者的onReceive方法,此处CONTENT_URI=content://settings/global"
        mContentResolver.registerContentObserver(
            Settings.Global.CONTENT_URI, true,
            new ContentObserver(new Handler()) {
                public void onChange(boolean selfChange) {
                    mReceiver.onReceive(context, (Intent) null);
                }
            });

        mHandler = new Handler() {
            public void handleMessage(Message msg) {
                // 发送广播
                if (msg.what == MSG_SEND_BROADCAST) {
                    mContext.sendBroadcastAsUser((Intent)msg.obj, UserHandle.OWNER,
                            android.Manifest.permission.READ_LOGS);
                }
            }
        };
    }
}

该方法主要功能是给dropbox目录所对应的存储空间进行瘦身:

存储设备可用空间低；
开机完毕；
Settings数据库变化；

当发生任一以上情况都会触发触发执行mReceiver的onReceive方法,接下来看看该onReceive()过程.

1.3 mReceiver.onReceive

[-> DropBoxManagerService.java]

private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
    public void onReceive(Context context, Intent intent) {
        if (intent != null && Intent.ACTION_BOOT_COMPLETED.equals(intent.getAction())) {
            mBooted = true;
            return;
        }

        //收到ACTION_DEVICE_STORAGE_LOW，则强制重新check存储空间
        mCachedQuotaUptimeMillis = 0; 

        //创建工作线程来执行init和trim操作
        new Thread() {
            public void run() {
                try {
                    init(); //【见小节1.3.1】
                    trimToFit(); //【见小节1.3.2】
                } catch (IOException e) {
                    ...
                }
            }
        }.start();
    }
};

1.3.1 init

private synchronized void init() throws IOException {
    if (mStatFs == null) {
        if (!mDropBoxDir.isDirectory() && !mDropBoxDir.mkdirs()) {
            ...
        }
        mStatFs = new StatFs(mDropBoxDir.getPath());
        mBlockSize = mStatFs.getBlockSize(); //mBlockSize=4096
    }

    if (mAllFiles == null) {
        File[] files = mDropBoxDir.listFiles();
        // 列举所有的dropbox文件
        mAllFiles = new FileList();
        mFilesByTag = new HashMap<String, FileList>();

        for (File file : files) {
            if (file.getName().endsWith(".tmp")) {
                file.delete(); //删除后缀为.tmp文件
                continue;
            }
            // 创建dropbox的实体文件对象, 根据文件名来获取相应的时间戳
            EntryFile entry = new EntryFile(file, mBlockSize);
            if (entry.tag == null) {
                continue; //忽略tag为空的文件
            } else if (entry.timestampMillis == 0) {
                file.delete(); //删除时间戳为0的文件
                continue;
            }
            //将entry加入到mAllFiles对象
            enrollEntry(entry);
        }
    }
}

该方法主要功能：

创建目录/data/system/dropbox;
列举该目录下所有文件,并对其进行:
- 将每一个dropbox文件都对应于一个EntryFile对象,根据文件名来获取相应的时间戳
- 删除后缀为.tmp的文件;
- 删除时间戳为0的文件.

1.3.2 trimToFit

private synchronized long trimToFit() {

    int ageSeconds = Settings.Global.getInt(mContentResolver,
            Settings.Global.DROPBOX_AGE_SECONDS, DEFAULT_AGE_SECONDS);
    int maxFiles = Settings.Global.getInt(mContentResolver,
            Settings.Global.DROPBOX_MAX_FILES, DEFAULT_MAX_FILES);
    long cutoffMillis = System.currentTimeMillis() - ageSeconds * 1000;
    
    while (!mAllFiles.contents.isEmpty()) {
        EntryFile entry = mAllFiles.contents.first();
        //当最老的文件时间戳在3天之内，且文件个数低于1000，则跳出循环
        if (entry.timestampMillis > cutoffMillis 
            && mAllFiles.contents.size() < maxFiles) break;
        FileList tag = mFilesByTag.get(entry.tag);
        if (tag != null && tag.contents.remove(entry)) tag.blocks -= entry.blocks;
        if (mAllFiles.contents.remove(entry)) mAllFiles.blocks -= entry.blocks;
        if (entry.file != null) entry.file.delete(); //删除文件
    }

    long uptimeMillis = SystemClock.uptimeMillis();
    //除非接收设备存储低的广播，否则间隔5s才能再次执行restat
    if (uptimeMillis > mCachedQuotaUptimeMillis + QUOTA_RESCAN_MILLIS) {
        int quotaPercent = Settings.Global.getInt(mContentResolver,
                Settings.Global.DROPBOX_QUOTA_PERCENT, DEFAULT_QUOTA_PERCENT);
        int reservePercent = Settings.Global.getInt(mContentResolver,
                Settings.Global.DROPBOX_RESERVE_PERCENT, DEFAULT_RESERVE_PERCENT);
        int quotaKb = Settings.Global.getInt(mContentResolver,
                Settings.Global.DROPBOX_QUOTA_KB, DEFAULT_QUOTA_KB);
        //重新统计文件
        mStatFs.restat(mDropBoxDir.getPath());
        int available = mStatFs.getAvailableBlocks();
        int nonreserved = available - mStatFs.getBlockCount() * reservePercent / 100;
        int maximum = quotaKb * 1024 / mBlockSize;
        //可用的块数量
        mCachedQuotaBlocks = Math.min(maximum, Math.max(0, nonreserved * quotaPercent / 100));
        mCachedQuotaUptimeMillis = uptimeMillis;
    }

    if (mAllFiles.blocks > mCachedQuotaBlocks) {
        //公平地限制所有tag的空间
        int unsqueezed = mAllFiles.blocks, squeezed = 0;
        TreeSet<FileList> tags = new TreeSet<FileList>(mFilesByTag.values());
        for (FileList tag : tags) {
            if (squeezed > 0 && tag.blocks <= (mCachedQuotaBlocks - unsqueezed) / squeezed) {
                break;
            }
            unsqueezed -= tag.blocks;
            squeezed++;
        }
        int tagQuota = (mCachedQuotaBlocks - unsqueezed) / squeezed;

        //移除每个tags中的旧items
        for (FileList tag : tags) {
            if (mAllFiles.blocks < mCachedQuotaBlocks) break;
            while (tag.blocks > tagQuota && !tag.contents.isEmpty()) {
                EntryFile entry = tag.contents.first();
                if (tag.contents.remove(entry)) tag.blocks -= entry.blocks;
                if (mAllFiles.contents.remove(entry)) mAllFiles.blocks -= entry.blocks;

                try {
                    if (entry.file != null) entry.file.delete();
                    enrollEntry(new EntryFile(mDropBoxDir, entry.tag, entry.timestampMillis));
                } catch (IOException e) {
                    Slog.e(TAG, "Can't write tombstone file", e);
                }
            }
        }
    }

    return mCachedQuotaBlocks * mBlockSize;
}

trimToFit过程中触发条件是：当文件有效时长超过3天，或者最大文件数超过1000，再或者剩余可用存储设备过低；

DBMS有很多常量参数：

DEFAULT_AGE_SECONDS = 3 * 86400：文件最长可存活时长为3天
DEFAULT_MAX_FILES = 1000：最大dropbox文件个数为1000
DEFAULT_QUOTA_KB = 5 * 1024：分配dropbox空间的最大值5M
DEFAULT_QUOTA_PERCENT = 10：是指dropbox目录最多可占用空间比例10%
DEFAULT_RESERVE_PERCENT = 10：是指dropbox不可使用的存储空间比例10%
QUOTA_RESCAN_MILLIS = 5000：重新扫描retrim时长为5s

当然上面这些都是默认值，完全可以通过设置content://settings/global数据库中相应项来设定值。

二、DropBox工作

当发生以下任一场景，都会调用AMS.addErrorToDropBox()来触发DBMS工作。

crash: 文章理解Android Crash处理流程 [小节4]的AMS.handleApplicationCrashInner过程
anr: 文章android ANR原理分析[小节3.1]的AMS.appNotResponding()过程；
watchdog: 文章WatchDog工作原理 [小节3.1]的Watchdog.run()过程;
native_crash: 当调用NativeCrashReporter.run()的过程;
wtf: 当调用Log.wtf()或者Log.wtfQuiet()的过程；
lowmem: 当内存较低时，触发AMS.reportMemUsage()过程；
…

2.1 AMS.addErrorToDropBox

[–>ActivityManagerService.java]

public void addErrorToDropBox(String eventType,
        ProcessRecord process, String processName, ActivityRecord activity,
        ActivityRecord parent, String subject,
        final String report, final File logFile,
        final ApplicationErrorReport.CrashInfo crashInfo) {

    //创建dropbox标签名【见小节2.1.1】
    final String dropboxTag = processClass(process) + "_" + eventType;
    //获取dropbox服务的代理端
    final DropBoxManager dbox = (DropBoxManager)
            mContext.getSystemService(Context.DROPBOX_SERVICE);

    //当不需要输出dropbox报告则直接返回
    if (dbox == null || !dbox.isTagEnabled(dropboxTag)) return;

    final StringBuilder sb = new StringBuilder(1024);
    //输出Process,flags,以及进程中所有package 【见小节2.1.2】
    appendDropBoxProcessHeaders(process, processName, sb);
    ...
    if (subject != null) {
        sb.append("Subject: ").append(subject).append("\n");
    }
    sb.append("Build: ").append(Build.FINGERPRINT).append("\n");
    sb.append("\n");

    //创建新线程，避免将调用者阻塞在I/O
    Thread worker = new Thread("Error dump: " + dropboxTag) {
        @Override
        public void run() {
            if (report != null) {
                //比如ANR时输出Cpuinfo，或者lowmem时输出的内存信息
                sb.append(report); 
            }
            if (logFile != null) {
                //比如anr或者Watchdog时输出的traces文件(kill -3)，最大上限为256KB
                sb.append(FileUtils.readTextFile(logFile, DROPBOX_MAX_SIZE,
                            "\n\n[[TRUNCATED]]"));
            }
            if (crashInfo != null && crashInfo.stackTrace != null) {
                // 比如crash时输出的调用栈
                sb.append(crashInfo.stackTrace);
            }

            String setting = Settings.Global.ERROR_LOGCAT_PREFIX + dropboxTag;
            int lines = Settings.Global.getInt(mContext.getContentResolver(), setting, 0);
            //当dropboxTag所对应的settings项不等于0，则输出logcat
            if (lines > 0) {
              //输出evets/system/main/crash这些log信息
              java.lang.Process logcat = new ProcessBuilder("/system/bin/logcat",
                      "-v", "time", "-b", "events", "-b", "system", "-b", "main",
                      "-b", "crash",
                      "-t", String.valueOf(lines)).redirectErrorStream(true).start();

              input = new InputStreamReader(logcat.getInputStream());

              int num;
              char[] buf = new char[8192];
              //不断读取input中的log内容，并添加到sb
              while ((num = input.read(buf)) > 0) sb.append(buf, 0, num);
              ...
            }
            //将log信息输出到DropBox 【见小节2.2】
            dbox.addText(dropboxTag, sb.toString());
        }
    };

    if (process == null) {
        //当进程为空，意味着system_server进程崩溃，系统可能很快就要挂了,
        //那么不再创建新线程，而是直接在system_server进程中同步运行
        worker.run();
    } else {
        //启动新线程
        worker.start();
    }
}

该方法主要功能是输出以下内容项：

Process,flags, package等头信息；
当report不为空，则比如ANR时输出Cpuinfo，或者lowmem时输出的内存信息
当logFile不为空，则比如anr或者Watchdog时输出的traces文件(kill -3)，最大上限为256KB；
当stack不为空，则比如crash时输出的调用栈；
输出logcat的events/system/main/crash信息。

2.1.1 AMS.processClass

private static String processClass(ProcessRecord process) {
    //MY_PID代表的是当前进程pid，正是system_server进程
    if (process == null || process.pid == MY_PID) {
        return "system_server";
    } else if ((process.info.flags & ApplicationInfo.FLAG_SYSTEM) != 0) {
        return "system_app";
    } else {
        return "data_app";
    }
}

dropbox文件名格式为dropboxTag@xxx.txt xxx代表时间戳,例如system_server_crash@1465650845355.txt,则记录该文件时间戳为1465650845355. 文件后缀除了.txt，还有压缩格式.txt.gz. 对于dropboxTag是由processClass + eventType组合而成.

processClass分为system_server, system_app, data_app;
eventType：分为crash,anr,wtf,native_cras,lowmem, watchdog

列举部分常见tags以及含义:

dropboxTag	含义
system_server_anr	system进程无响应
system_server_watchdog	system进程发生watchdog
system_server_crash	system进程崩溃
system_server_native_crash	system进程native出现崩溃
system_server_wtf	system进程发生严重错误
system_server_lowmem	system进程内存不足

当然除了system_server进程, 还有system_app, data_app类型的进程, 以上所有类型都适用,列举部分:

system_app_crash	系统app崩溃
system_app_anr	系统app无响应
data_app_crash	普通app崩溃
data_app_anr	普通app无响应

2.1.2 AMS.appendDropBoxProcessHeaders

private void appendDropBoxProcessHeaders(ProcessRecord process, String processName,
        StringBuilder sb) {
    if (process == null) {
        sb.append("Process: ").append(processName).append("\n");
        return;
    }

    synchronized (this) {
        sb.append("Process: ").append(processName).append("\n");
        int flags = process.info.flags;
        IPackageManager pm = AppGlobals.getPackageManager();
        sb.append("Flags: 0x").append(Integer.toString(flags, 16)).append("\n");
        for (int ip=0; ip<process.pkgList.size(); ip++) {
            String pkg = process.pkgList.keyAt(ip);
            sb.append("Package: ").append(pkg);
            try {
                PackageInfo pi = pm.getPackageInfo(pkg, 0, UserHandle.getCallingUserId());
                if (pi != null) {
                    sb.append(" v").append(pi.versionCode);
                    if (pi.versionName != null) {
                        sb.append(" (").append(pi.versionName).append(")");
                    }
                }
            } catch (RemoteException e) {
                ...
            }
            sb.append("\n");
        }
    }
}

该方法输出的信息:

进程名;
进程的ApplicationInfo的flags信息;
进程中所有的包名以及版本信息;

这里列举头信息实例:

2016-11-11 22:22:22 system_app_anr (compressed text, 26165 bytes)
Process: com.android.systemui
Flags: 0x40d83e0d
Package: com.android.systemui v21 (5.0.2)
Subject: Broadcast of Intent { act=android.intent.action.TIME_TICK flg=0x50000014 (has extras) }

2.2 DBM.addText

[-> DropBoxManager.java]

public void addText(String tag, String data) {
    try { 
        //data数据封装到Entry对象实例 【见小节2.3】
        mService.add(new Entry(tag, 0, data)); 
    } catch (RemoteException e) {
        ...
    }
}

在DropBoxManager中有addText, addData, addFile方法，三分归一统，对应于DBMS的add()方法。

2.3 DBMS.add

[ -> DropBoxManagerService.java]

public void add(DropBoxManager.Entry entry) {
    File temp = null;
    OutputStream output = null;
    final String tag = entry.getTag();
    try {
        int flags = entry.getFlags();
        ...
        init(); // 初始化【见小节1.3.1】
        long max = trimToFit(); // 压缩空间【见小节1.3.2】
        long lastTrim = System.currentTimeMillis();
        byte[] buffer = new byte[mBlockSize];
        InputStream input = entry.getInputStream();

        int read = 0;
        while (read < buffer.length) {
            int n = input.read(buffer, read, buffer.length - read);
            if (n <= 0) break;
            read += n;
        }
        //创建临时文件，例如tid=1234的对应文件drop1234.tmp
        temp = new File(mDropBoxDir, "drop" + Thread.currentThread().getId() + ".tmp");
        int bufferSize = mBlockSize;
        if (bufferSize > 4096) bufferSize = 4096;
        if (bufferSize < 512) bufferSize = 512;
        FileOutputStream foutput = new FileOutputStream(temp);
        output = new BufferedOutputStream(foutput, bufferSize);
        //创建gzip压缩文件
        if (read == buffer.length && ((flags & DropBoxManager.IS_GZIPPED) == 0)) {
            output = new GZIPOutputStream(output);
            flags = flags | DropBoxManager.IS_GZIPPED;
        }

        //不断将temp文件数据写入buffer
        do {
            output.write(buffer, 0, read);
            long now = System.currentTimeMillis();
            if (now - lastTrim > 30 * 1000) {
                max = trimToFit(); //执行时间超过30s则执行trim
                lastTrim = now;
            }

            read = input.read(buffer);
            if (read <= 0) {
                FileUtils.sync(foutput);
                output.close();
                output = null;
            } else {
                output.flush();
            }

            long len = temp.length();
            if (len > max) {
                temp.delete();
                temp = null;
                break;
            }
        } while (read > 0);
        
        //[见小节2.3.1]
        long time = createEntry(temp, tag, flags);
        temp = null;

        final Intent dropboxIntent = new Intent(DropBoxManager.ACTION_DROPBOX_ENTRY_ADDED);
        dropboxIntent.putExtra(DropBoxManager.EXTRA_TAG, tag);
        dropboxIntent.putExtra(DropBoxManager.EXTRA_TIME, time);
        if (!mBooted) {
            dropboxIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
        }
        //发送广播MSG_SEND_BROADCAST
        mHandler.sendMessage(mHandler.obtainMessage(MSG_SEND_BROADCAST, dropboxIntent));
    } catch (IOException e) {
        ...
    } finally {
        if (output != null) output.close();
        entry.close();
        if (temp != null) temp.delete();
    }
}

2.3.1 DBMS.createEntry