Android DropBoxManager服务分析
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();
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 tags = new TreeSet(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[email protected] xxx代表时间戳,例如[email protected],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}
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
[ -> 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)这里写代码片