Android DropBoxManagerService解析

文字说明部分转载自http://gityuan.com/2016/06/12/DropBoxManagerService/

最后的源码文件注释自己完成

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/dropboxmContext = 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restatif (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itemsfor (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/OThread worker = new Thread("Error dump: " + dropboxTag) {@Overridepublic 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256KBsb.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logcatif (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sbwhile ((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.tmptemp = 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bufferdo {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trimlastTrim = 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_BROADCASTmHandler.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

[ -> DropBoxManagerService.java]

private synchronized long createEntry(File temp, String tag, int flags) throws IOException {long t = System.currentTimeMillis(); //当当前时间作为dropbox文件的时间戳...if (temp == null) {enrollEntry(new EntryFile(mDropBoxDir, tag, t));} else {enrollEntry(new EntryFile(temp, mDropBoxDir, tag, t, flags, mBlockSize));}return t;
}

关于时间戳问题:

EntryFile(File file, int blockSize) : 从file文件获取时间戳,并保存到EntryFile.timestampMillis. init()过程使用.
其他的构造方法则都会在创建时,将当前时间保存到EntryFile.timestampMillis.比如EntryFile(File dir, String tag, long timestampMillis)

三. 总结

DBMS服务的数据保存目录为/data/system/dropbox。

当出现crash, anr, wtf，lowmem，以及开机完成时都会通过DropBoxManager，收集系统的重要信息： Process,flags, package等头信息和logcat信息。另外就是根据不同场景输出相应的信息，例如：

CRASH：输出发生crash时的当前线程的调用栈信息；
ANR：输出Cpuinfo，以及重要进程的各个线程的traces文件(kill -3)；
Watchdog: 也输出重要进程的各个线程的traces文件(kill -3)

DropBoxManagerService源码注释

/** Copyright (C) 2009 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.*/package com.android.server;import android.content.BroadcastReceiver;
import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.pm.PackageManager;
import android.database.ContentObserver;
import android.net.Uri;
import android.os.Binder;
import android.os.Debug;
import android.os.DropBoxManager;
import android.os.FileUtils;
import android.os.Handler;
import android.os.Message;
import android.os.StatFs;
import android.os.SystemClock;
import android.os.UserHandle;
import android.provider.Settings;
import android.text.format.Time;
import android.util.Slog;import libcore.io.IoUtils;import com.android.internal.os.IDropBoxManagerService;import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.zip.GZIPOutputStream;/*** Implementation of {@link IDropBoxManagerService} using the filesystem.* Clients use {@link DropBoxManager} to access this service.* 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*/
public final class DropBoxManagerService extends SystemService {private static final String TAG = "DropBoxManagerService";private static final int DEFAULT_AGE_SECONDS = 3 * 86400;//72小时，3天private static final int DEFAULT_MAX_FILES = 1000;private static final int DEFAULT_QUOTA_KB = 5 * 1024;//分配dropbox空间的最大值5Mprivate static final int DEFAULT_QUOTA_PERCENT = 10;//dropbox目录最多可占用空间比例10%private static final int DEFAULT_RESERVE_PERCENT = 10;//dropbox不可使用的存储空间比例10%private static final int QUOTA_RESCAN_MILLIS = 5000;// mHandler 'what' value.private static final int MSG_SEND_BROADCAST = 1;private static final boolean PROFILE_DUMP = false;// TODO: This implementation currently uses one file per entry, which is// inefficient for smallish entries -- consider using a single queue file// per tag (or even globally) instead.// The cached context and derived objectsprivate final ContentResolver mContentResolver;private final File mDropBoxDir;// Accounting of all currently written log files (set in init()).private FileList mAllFiles = null;private HashMap<String, FileList> mFilesByTag = null;// Various bits of disk information//保存文件系统的信息，这个类是对Unix statvfs()的封装private StatFs mStatFs = null;private int mBlockSize = 0;private int mCachedQuotaBlocks = 0;  // Space we can use: computed from free space, etc.private long mCachedQuotaUptimeMillis = 0;private volatile boolean mBooted = false;// Provide a way to perform sendBroadcast asynchronously to avoid deadlocks.private final Handler mHandler;/** Receives events that might indicate a need to clean up files. */private final BroadcastReceiver mReceiver = new BroadcastReceiver() {@Overridepublic void onReceive(Context context, Intent intent) {// For ACTION_DEVICE_STORAGE_LOW:mCachedQuotaUptimeMillis = 0;  // Force a re-check of quota size// Run the initialization in the background (not this main thread).// The init() and trimToFit() methods are synchronized, so they still// block other users -- but at least the onReceive() call can finish.//在设备存储空间不足时，异步清理文件new Thread() {public void run() {try {init();trimToFit();} catch (IOException e) {Slog.e(TAG, "Can't init", e);}}}.start();}};private final IDropBoxManagerService.Stub mStub = new IDropBoxManagerService.Stub() {@Overridepublic void add(DropBoxManager.Entry entry) {DropBoxManagerService.this.add(entry);}@Overridepublic boolean isTagEnabled(String tag) {return DropBoxManagerService.this.isTagEnabled(tag);}@Overridepublic DropBoxManager.Entry getNextEntry(String tag, long millis) {return DropBoxManagerService.this.getNextEntry(tag, millis);}@Overridepublic void dump(FileDescriptor fd, PrintWriter pw, String[] args) {DropBoxManagerService.this.dump(fd, pw, args);}};/*** Creates an instance of managed drop box storage using the default dropbox* directory.** @param context to use for receiving free space & gservices intents* /data/system/dropbox目录是dropbox的超作目录，文件都保存在这个目录下*/public DropBoxManagerService(final Context context) {this(context, new File("/data/system/dropbox"));}/*** Creates an instance of managed drop box storage.  Normally there is one of these* run by the system, but others can be created for testing and other purposes.** @param context to use for receiving free space & gservices intents* @param path to store drop box entries in*/public DropBoxManagerService(final Context context, File path) {super(context);mDropBoxDir = path;mContentResolver = getContext().getContentResolver();/*DropBoxManagerService在SystemServer进程中的线程中运行，而此线程已经调用了Looper的prepaer()方法*/mHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {if (msg.what == MSG_SEND_BROADCAST) {getContext().sendBroadcastAsUser((Intent)msg.obj, UserHandle.SYSTEM,android.Manifest.permission.READ_LOGS);}}};}/* onStart在DropBoxManagerService构造函数后调用*/@Overridepublic void onStart() {// Set up intent receiversIntentFilter filter = new IntentFilter();filter.addAction(Intent.ACTION_DEVICE_STORAGE_LOW);//接收设备存储空间不足广播getContext().registerReceiver(mReceiver, filter);//监听settings的uri,一旦有变化调用onReceivemContentResolver.registerContentObserver(Settings.Global.CONTENT_URI, true,new ContentObserver(new Handler()) {@Overridepublic void onChange(boolean selfChange) {mReceiver.onReceive(getContext(), (Intent) null);}});//发布binder可以被调用publishBinderService(Context.DROPBOX_SERVICE, mStub);// The real work gets done lazily in init() -- that way service creation always// succeeds, and things like disk problems cause individual method failures.}@Overridepublic void onBootPhase(int phase) {switch (phase) {//系统启动完成case PHASE_BOOT_COMPLETED:mBooted = true;break;}}/** Retrieves the binder stub -- for test instances */public IDropBoxManagerService getServiceStub() {return mStub;}/*** Entry存放在drop box日志的一个索引* @param entry*/public void add(DropBoxManager.Entry entry) {File temp = null;InputStream input = null;OutputStream output = null;final String tag = entry.getTag();try {int flags = entry.getFlags();//如果entry是空，抛出异常if ((flags & DropBoxManager.IS_EMPTY) != 0) throw new IllegalArgumentException();//方法里有判断，基本上只被初始化一次init();//从settings.globle判断tag对应的drop box是否使能if (!isTagEnabled(tag)) return;long max = trimToFit();//获取目录可用的空间long lastTrim = System.currentTimeMillis();byte[] buffer = new byte[mBlockSize];input = entry.getInputStream();// First, accumulate up to one block worth of data in memory before// deciding whether to compress the data or not.//读取一个块大小的数据，当文件数据小于一个块大小时，全部读取int read = 0;while (read < buffer.length) {int n = input.read(buffer, read, buffer.length - read);if (n <= 0) break;read += n;}// If we have at least one block, compress it -- otherwise, just write// the data in uncompressed form.//只有写入文件的数据大于块的长度时，才压缩，要不然，直接写入数据//先写入临时文件"drop"+线程id+".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);if (read == buffer.length && ((flags & DropBoxManager.IS_GZIPPED) == 0)) {output = new GZIPOutputStream(output);flags = flags | DropBoxManager.IS_GZIPPED;}do {output.write(buffer, 0, read);long now = System.currentTimeMillis();if (now - lastTrim > 30 * 1000) {//写文件的时间超过30s,执行trimToFit()max = trimToFit();  // In case data dribbles in slowlylastTrim = now;}read = input.read(buffer);if (read <= 0) {FileUtils.sync(foutput);output.close();  // Get a final size measurementoutput = null;} else {output.flush();  // So the size measurement is pseudo-reasonable}long len = temp.length();//如果临时文件大于可用的size，删除临时文件，cteat entry时只创建一个空文件if (len > max) {Slog.w(TAG, "Dropping: " + tag + " (" + temp.length() + " > " + max + " bytes)");temp.delete();temp = null;  // Pass temp = null to createEntry() to leave a tombstonebreak;}} while (read > 0);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);}// Call sendBroadcast after returning from this call to avoid deadlock. In particular// the caller may be holding the WindowManagerService lock but sendBroadcast requires a// lock in ActivityManagerService. ActivityManagerService has been caught holding that// very lock while waiting for the WindowManagerService lock.mHandler.sendMessage(mHandler.obtainMessage(MSG_SEND_BROADCAST, dropboxIntent));} catch (IOException e) {Slog.e(TAG, "Can't write: " + tag, e);} finally {IoUtils.closeQuietly(output);IoUtils.closeQuietly(input);entry.close();if (temp != null) temp.delete();}}public boolean isTagEnabled(String tag) {final long token = Binder.clearCallingIdentity();try {return !"disabled".equals(Settings.Global.getString(mContentResolver, Settings.Global.DROPBOX_TAG_PREFIX + tag));} finally {Binder.restoreCallingIdentity(token);}}public synchronized DropBoxManager.Entry getNextEntry(String tag, long millis) {if (getContext().checkCallingOrSelfPermission(android.Manifest.permission.READ_LOGS)!= PackageManager.PERMISSION_GRANTED) {throw new SecurityException("READ_LOGS permission required");}try {init();} catch (IOException e) {Slog.e(TAG, "Can't init", e);return null;}FileList list = tag == null ? mAllFiles : mFilesByTag.get(tag);if (list == null) return null;for (EntryFile entry : list.contents.tailSet(new EntryFile(millis + 1))) {if (entry.tag == null) continue;if ((entry.flags & DropBoxManager.IS_EMPTY) != 0) {return new DropBoxManager.Entry(entry.tag, entry.timestampMillis);}try {return new DropBoxManager.Entry(entry.tag, entry.timestampMillis, entry.file, entry.flags);} catch (IOException e) {Slog.e(TAG, "Can't read: " + entry.file, e);// Continue to next file}}return null;}public synchronized void dump(FileDescriptor fd, PrintWriter pw, String[] args) {if (getContext().checkCallingOrSelfPermission(android.Manifest.permission.DUMP)!= PackageManager.PERMISSION_GRANTED) {pw.println("Permission Denial: Can't dump DropBoxManagerService");return;}try {init();} catch (IOException e) {pw.println("Can't initialize: " + e);Slog.e(TAG, "Can't init", e);return;}if (PROFILE_DUMP) Debug.startMethodTracing("/data/trace/dropbox.dump");StringBuilder out = new StringBuilder();boolean doPrint = false, doFile = false;ArrayList<String> searchArgs = new ArrayList<String>();for (int i = 0; args != null && i < args.length; i++) {if (args[i].equals("-p") || args[i].equals("--print")) {doPrint = true;} else if (args[i].equals("-f") || args[i].equals("--file")) {doFile = true;} else if (args[i].startsWith("-")) {out.append("Unknown argument: ").append(args[i]).append("\n");} else {searchArgs.add(args[i]);}}out.append("Drop box contents: ").append(mAllFiles.contents.size()).append(" entries\n");if (!searchArgs.isEmpty()) {out.append("Searching for:");for (String a : searchArgs) out.append(" ").append(a);out.append("\n");}int numFound = 0, numArgs = searchArgs.size();Time time = new Time();out.append("\n");for (EntryFile entry : mAllFiles.contents) {time.set(entry.timestampMillis);String date = time.format("%Y-%m-%d %H:%M:%S");boolean match = true;for (int i = 0; i < numArgs && match; i++) {String arg = searchArgs.get(i);match = (date.contains(arg) || arg.equals(entry.tag));}if (!match) continue;numFound++;if (doPrint) out.append("========================================\n");out.append(date).append(" ").append(entry.tag == null ? "(no tag)" : entry.tag);if (entry.file == null) {out.append(" (no file)\n");continue;} else if ((entry.flags & DropBoxManager.IS_EMPTY) != 0) {out.append(" (contents lost)\n");continue;} else {out.append(" (");if ((entry.flags & DropBoxManager.IS_GZIPPED) != 0) out.append("compressed ");out.append((entry.flags & DropBoxManager.IS_TEXT) != 0 ? "text" : "data");out.append(", ").append(entry.file.length()).append(" bytes)\n");}if (doFile || (doPrint && (entry.flags & DropBoxManager.IS_TEXT) == 0)) {if (!doPrint) out.append("    ");out.append(entry.file.getPath()).append("\n");}if ((entry.flags & DropBoxManager.IS_TEXT) != 0 && (doPrint || !doFile)) {DropBoxManager.Entry dbe = null;InputStreamReader isr = null;try {dbe = new DropBoxManager.Entry(entry.tag, entry.timestampMillis, entry.file, entry.flags);if (doPrint) {isr = new InputStreamReader(dbe.getInputStream());char[] buf = new char[4096];boolean newline = false;for (;;) {int n = isr.read(buf);if (n <= 0) break;out.append(buf, 0, n);newline = (buf[n - 1] == '\n');// Flush periodically when printing to avoid out-of-memory.if (out.length() > 65536) {pw.write(out.toString());out.setLength(0);}}if (!newline) out.append("\n");} else {String text = dbe.getText(70);out.append("    ");if (text == null) {out.append("[null]");} else {boolean truncated = (text.length() == 70);out.append(text.trim().replace('\n', '/'));if (truncated) out.append(" ...");}out.append("\n");}} catch (IOException e) {out.append("*** ").append(e.toString()).append("\n");Slog.e(TAG, "Can't read: " + entry.file, e);} finally {if (dbe != null) dbe.close();if (isr != null) {try {isr.close();} catch (IOException unused) {}}}}if (doPrint) out.append("\n");}if (numFound == 0) out.append("(No entries found.)\n");if (args == null || args.length == 0) {if (!doPrint) out.append("\n");out.append("Usage: dumpsys dropbox [--print|--file] [YYYY-mm-dd] [HH:MM:SS] [tag]\n");}pw.write(out.toString());if (PROFILE_DUMP) Debug.stopMethodTracing();}////////////////////////////////////////////////////////////////////////////*** Chronologically sorted list of {@link EntryFile}* */private static final class FileList implements Comparable<FileList> {public int blocks = 0;public final TreeSet<EntryFile> contents = new TreeSet<EntryFile>();/** Sorts bigger FileList instances before smaller ones. */public final int compareTo(FileList o) {if (blocks != o.blocks) return o.blocks - blocks;if (this == o) return 0;if (hashCode() < o.hashCode()) return -1;if (hashCode() > o.hashCode()) return 1;return 0;}}/** Metadata describing an on-disk log file. */private static final class EntryFile implements Comparable<EntryFile> {public final String tag;/*** 1,从文件获取时间戳* 2,构造方法在创建时，将当前时间保存为时间戳*/public final long timestampMillis;public final int flags;public final File file;public final int blocks;/** Sorts earlier EntryFile instances before later ones. */public final int compareTo(EntryFile o) {if (timestampMillis < o.timestampMillis) return -1;if (timestampMillis > o.timestampMillis) return 1;if (file != null && o.file != null) return file.compareTo(o.file);if (o.file != null) return -1;if (file != null) return 1;if (this == o) return 0;if (hashCode() < o.hashCode()) return -1;if (hashCode() > o.hashCode()) return 1;return 0;}/*** Moves an existing temporary file to a new log filename.* @param temp file to rename* @param dir to store file in* @param tag to use for new log file name* @param timestampMillis of log entry* @param flags for the entry data* @param blockSize to use for space accounting* @throws IOException if the file can't be moved*/public EntryFile(File temp, File dir, String tag,long timestampMillis,int flags, int blockSize) throws IOException {if ((flags & DropBoxManager.IS_EMPTY) != 0) throw new IllegalArgumentException();this.tag = tag;this.timestampMillis = timestampMillis;this.flags = flags;this.file = new File(dir, Uri.encode(tag) + "@" + timestampMillis +((flags & DropBoxManager.IS_TEXT) != 0 ? ".txt" : ".dat") +((flags & DropBoxManager.IS_GZIPPED) != 0 ? ".gz" : ""));if (!temp.renameTo(this.file)) {throw new IOException("Can't rename " + temp + " to " + this.file);}this.blocks = (int) ((this.file.length() + blockSize - 1) / blockSize);}/*** Creates a zero-length tombstone for a file whose contents were lost.* @param dir to store file in* @param tag to use for new log file name* @param timestampMillis of log entry* @throws IOException if the file can't be created.*/public EntryFile(File dir, String tag, long timestampMillis) throws IOException {this.tag = tag;this.timestampMillis = timestampMillis;this.flags = DropBoxManager.IS_EMPTY;this.file = new File(dir, Uri.encode(tag) + "@" + timestampMillis + ".lost");this.blocks = 0;new FileOutputStream(this.file).close();}/*** Extracts metadata from an existing on-disk log filename.* @param file name of existing log file* @param blockSize to use for space accounting*/public EntryFile(File file, int blockSize) {this.file = file;this.blocks = (int) ((this.file.length() + blockSize - 1) / blockSize);String name = file.getName();int at = name.lastIndexOf('@');if (at < 0) {this.tag = null;this.timestampMillis = 0;this.flags = DropBoxManager.IS_EMPTY;return;}int flags = 0;this.tag = Uri.decode(name.substring(0, at));if (name.endsWith(".gz")) {flags |= DropBoxManager.IS_GZIPPED;name = name.substring(0, name.length() - 3);}if (name.endsWith(".lost")) {flags |= DropBoxManager.IS_EMPTY;name = name.substring(at + 1, name.length() - 5);} else if (name.endsWith(".txt")) {flags |= DropBoxManager.IS_TEXT;name = name.substring(at + 1, name.length() - 4);} else if (name.endsWith(".dat")) {name = name.substring(at + 1, name.length() - 4);} else {this.flags = DropBoxManager.IS_EMPTY;this.timestampMillis = 0;return;}this.flags = flags;long millis;try { millis = Long.valueOf(name); } catch (NumberFormatException e) { millis = 0; }this.timestampMillis = millis;}/*** Creates a EntryFile object with only a timestamp for comparison purposes.* @param millis to compare with.*/public EntryFile(long millis) {this.tag = null;this.timestampMillis = millis;this.flags = DropBoxManager.IS_EMPTY;this.file = null;this.blocks = 0;}}////////////////////////////////////////////////////////////////////////////** If never run before, scans disk contents to build in-memory tracking data. */private synchronized void init() throws IOException {if (mStatFs == null) {//目录/data/system/dropbox不存在并且创建失败，抛出异常if (!mDropBoxDir.isDirectory() && !mDropBoxDir.mkdirs()) {throw new IOException("Can't mkdir: " + mDropBoxDir);}try {mStatFs = new StatFs(mDropBoxDir.getPath());mBlockSize = mStatFs.getBlockSize();} catch (IllegalArgumentException e) {  // StatFs throws this on errorthrow new IOException("Can't statfs: " + mDropBoxDir);}}if (mAllFiles == null) {//listFiles()返回的是目录下面的文件和目录数组，返回的是文件和目录的绝对路径//如果mDropBoxDir目录下没有文件或目录，则files不为null，files.length为0File[] files = mDropBoxDir.listFiles();if (files == null) throw new IOException("Can't list files: " + mDropBoxDir);mAllFiles = new FileList();mFilesByTag = new HashMap<String, FileList>();// Scan pre-existing files.for (File file : files) {//清除.tmp结尾的文件if (file.getName().endsWith(".tmp")) {Slog.i(TAG, "Cleaning temp file: " + file);file.delete();continue;}//为每个日志文件创建一个entry对象进行跟踪EntryFile entry = new EntryFile(file, mBlockSize);if (entry.tag == null) {Slog.w(TAG, "Unrecognized file: " + file);continue;} else if (entry.timestampMillis == 0) {Slog.w(TAG, "Invalid filename: " + file);//删除时间戳为0的文件file.delete();continue;}enrollEntry(entry);}}}/*** Adds a disk log file to in-memory tracking for accounting and enumeration.** 把日志文件对应的对象加入到内存集合中，以方便计数和查询* */private synchronized void enrollEntry(EntryFile entry) {//所有文件的集合mAllFiles.contents.add(entry);mAllFiles.blocks += entry.blocks;// mFilesByTag is used for trimming, so don't list empty files.// (Zero-length/lost files are trimmed by date from mAllFiles.)if (entry.tag != null && entry.file != null && entry.blocks > 0) {FileList tagFiles = mFilesByTag.get(entry.tag);if (tagFiles == null) {tagFiles = new FileList();mFilesByTag.put(entry.tag, tagFiles);}//以tag为Key,FileList为value的map;把相同tag的文件作为一个集合tagFiles.contents.add(entry);tagFiles.blocks += entry.blocks;}}/** Moves a temporary file to a final log filename and enrolls it. */private synchronized long createEntry(File temp, String tag, int flags) throws IOException {long t = System.currentTimeMillis();// Require each entry to have a unique timestamp; if there are entries// >10sec in the future (due to clock skew), drag them back to avoid// keeping them around forever.//每个entry有唯一的时间戳，如果在未来的10s内已经有entry,则删除此，重新加入//tailSet : 返回此 set 的部分视图，其元素大于等于 fromElementSortedSet<EntryFile> tail = mAllFiles.contents.tailSet(new EntryFile(t + 10000));EntryFile[] future = null;if (!tail.isEmpty()) {future = tail.toArray(new EntryFile[tail.size()]);tail.clear();  // Remove from mAllFiles}if (!mAllFiles.contents.isEmpty()) {t = Math.max(t, mAllFiles.contents.last().timestampMillis + 1);}if (future != null) {for (EntryFile late : future) {mAllFiles.blocks -= late.blocks;FileList tagFiles = mFilesByTag.get(late.tag);if (tagFiles != null && tagFiles.contents.remove(late)) {tagFiles.blocks -= late.blocks;}if ((late.flags & DropBoxManager.IS_EMPTY) == 0) {enrollEntry(new EntryFile(late.file, mDropBoxDir, late.tag, t++, late.flags, mBlockSize));} else {enrollEntry(new EntryFile(mDropBoxDir, late.tag, t++));}}}if (temp == null) {enrollEntry(new EntryFile(mDropBoxDir, tag, t));} else {enrollEntry(new EntryFile(temp, mDropBoxDir, tag, t, flags, mBlockSize));}return t;}/*** Trims the files on disk to make sure they aren't using too much space.* 整理日志文件，节省空间* @return the overall quota for storage (in bytes)*/private synchronized long trimToFit() {// Expunge aged items (including tombstones marking deleted data).//删除时间长的文件//获取过期时间int ageSeconds = Settings.Global.getInt(mContentResolver,Settings.Global.DROPBOX_AGE_SECONDS, DEFAULT_AGE_SECONDS);//获取文件最大数int maxFiles = Settings.Global.getInt(mContentResolver,Settings.Global.DROPBOX_MAX_FILES, DEFAULT_MAX_FILES);//截止点，也就是和entry的时间戳进行比较，long cutoffMillis = System.currentTimeMillis() - ageSeconds * 1000;while (!mAllFiles.contents.isEmpty()) {EntryFile entry = mAllFiles.contents.first();if (entry.timestampMillis > cutoffMillis && mAllFiles.contents.size() < maxFiles) break;//entry的时间戳小于等于截止点，或者是文件书大于等于1000,删除日志文件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();}// Compute overall quota (a fraction of available free space) in blocks.// The quota changes dynamically based on the amount of free space;// that way when lots of data is available we can use it, but we'll get// out of the way if storage starts getting tight.//获取开机到现在的毫秒long uptimeMillis = SystemClock.uptimeMillis();//除非接收到了低存储空间的广播，否者隔5s才能执行一次此动作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);//重启统计文件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 we're using too much space, delete old items to make room.//// We trim each tag independently (this is why we keep per-tag lists).// Space is "fairly" shared between tags -- they are all squeezed// equally until enough space is reclaimed.//// A single circular buffer (a la logcat) would be simpler, but this// way we can handle fat/bursty data (like 1MB+ bugreports, 300KB+// kernel crash dumps, and 100KB+ ANR reports) without swamping small,// well-behaved data streams (event statistics, profile data, etc).//// Deleted files are replaced with zero-length tombstones to mark what// was lost.  Tombstones are expunged by age (see above).//日志文件占用的块数大于可用的块数量if (mAllFiles.blocks > mCachedQuotaBlocks) {// Find a fair share amount of space to limit each tagint unsqueezed = mAllFiles.blocks,/*未压缩块数*/ squeezed = 0;//已压缩tag的个数TreeSet<FileList> tags = new TreeSet<FileList>(mFilesByTag.values());for (FileList tag : tags) {//算法？？？if (squeezed > 0 && tag.blocks <= (mCachedQuotaBlocks - unsqueezed) / squeezed) {break;}unsqueezed -= tag.blocks;squeezed++;}int tagQuota = (mCachedQuotaBlocks - unsqueezed) / squeezed;// Remove old items from each tag until it meets the per-tag quota.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;}
}