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。
1.1 注册DBMS
当系统启动过程中SystemServer.java中的startOtherServices()方法中启动：
[-> SystemServer.java]
private void startOtherServices() { try {
ServiceManager.addService(Context.DROPBOX_SERVICE, new DropBoxManagerService(context, new File("/data/system/dropbox")));
} catch (Throwable e) {
reportWtf("starting DropBoxManagerService", e);
}
...
}其中DROPBOX_SERVICE = “dropbox”, DBMS工作目录位于”/data/system/dropbox”。
1.2 创建DBMS
[-> DropBoxManagerService.java]
public final class DropBoxManagerService extends IDropBoxManagerService.Stub {
... public DropBoxManagerService(final Context context, File path) {
mDropBoxDir = path; //保存工作目录
mContext = context;
mContentResolver = context.getContentResolver();
IntentFilter filter = new IntentFilter(); //注册存储设备可用空间低的广播
filter.addAction(Intent.ACTION_DEVICE_STORAGE_LOW); //注册开机完毕的广播
filter.addAction(Intent.ACTION_BOOT_COMPLETED);
context.registerReceiver(mReceiver, filter); //当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()) { @Override
public void onChange(boolean selfChange) {
mReceiver.onReceive(context, (Intent) null);
}
});
mHandler = new Handler() { @Override
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);
}
}
};
}
}当下面3种情况任一发生：
存储设备可用空间低；
开机完毕；
Settings数据库变化；
则会都触发执行mReceiver的onReceive方法，该方法主要功能是给dropbox目录所对应的存储空间进行搜身，接下来再说说这个搜身过程。
1.3 广播接收者
DBMS中的mReceiver定义如下：
private final BroadcastReceiver mReceiver = new BroadcastReceiver() { @Override
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; // 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.
new Thread() { public void run() { try {
init(); //【见小节1.3.1】
trimToFit(); //【见小节1.3.2】
} catch (IOException e) {
Slog.e(TAG, "Can't init", e);
}
}
}.start();
}
};1.3.1 init
private synchronized void init() throws IOException { if (mStatFs == null) { if (!mDropBoxDir.isDirectory() && !mDropBoxDir.mkdirs()) { throw new IOException("Can't mkdir: " + mDropBoxDir);
}
mStatFs = new StatFs(mDropBoxDir.getPath());
mBlockSize = mStatFs.getBlockSize(); //mBlockSize=4096
} if (mAllFiles == null) {
File[] files = mDropBoxDir.listFiles(); //创建mAllFiles对象，记录所有的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
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);
}
}
}dropbox文件格式为tag@时间戳.txt或者tag@时间戳.txt.gz，例如system_server_wtf@1465650845355.txt
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：
文件有效时长超过3天；
最大文件数超过1000；
剩余可用存储设备过低；
二、处理流程
当应用出现Crash时，调用ActivityManagerService的handleApplicationCrash方法，在该方法内部会调用addErrorToDropBox
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) { //如果是普通App崩溃，则dropboxTag为data_app_crash
final String dropboxTag = processClass(process) + "_" + eventType; //获取dropbox服务的客户端
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
appendDropBoxProcessHeaders(process, processName, sb);
...
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) {
sb.append(report);
} if (logFile != null) { //当logFile不为空，则添加log信息到dropbox，最大上限为256KB
sb.append(FileUtils.readTextFile(logFile, DROPBOX_MAX_SIZE, "\n\n[[TRUNCATED]]"));
} if (crashInfo != null && crashInfo.stackTrace != null) { //当栈信息不为空，则添加stacktrace到dropbox
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) {
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]; while ((num = input.read(buf)) > 0) sb.append(buf, 0, num);
} catch (IOException e) {
Slog.e(TAG, "Error running logcat", e);
} finally { if (input != null) try { input.close(); } catch (IOException e) {}
}
} //将logcat的evets/system/main/crash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();
}
}(1). dropbox文件输出内容项：
Process,flags, package等头信息；
当logFile不为空，则添加log信息到dropbox，最大上限为256KB；
当stack不为空，则添加stacktrace到dropbox；
当dropboxTag所对应的settings项不等于0，则输出logcat的events/system/main/crash信息。
(2). dropbox文件名
dropbox文件名为dropboxTag@xxx.txt
dropboxTag = processClass(process) + “_” + eventType;
processClass：分为
system_server,system_app,data_app;eventType：分为
crash,anr,wtf等
xxx代表的是时间戳;
后缀除了
.txt，还可以是.txt.gz压缩格式。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”; } }
例如system_server_crash@1465650845355.txt，代表的是system_server进程出现crash，记录该文件时间戳为1465650845355。
2.2 DBM.addText
[-> DropBoxManager.java]
public void addText(String tag, String data) { //data数据封装到Entry对象实例，再调用DBMS中的方法。
try { 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
public void add(DropBoxManager.Entry entry) {
File temp = null;
OutputStream output = null; final String tag = entry.getTag(); try { int flags = entry.getFlags(); if ((flags & DropBoxManager.IS_EMPTY) != 0) throw new IllegalArgumentException();
init(); // 初始化【见小节1.3.1】
if (!isTagEnabled(tag)) return; long max = trimToFit(); // 压缩空间【见小节1.3.2】
long lastTrim = System.currentTimeMillis(); //mBlockSize等于4096
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) {
Slog.w(TAG, "Dropping: " + tag + " (" + temp.length() + " > " + max + " bytes)");
temp.delete();
temp = null; break;
}
} 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);
} //发送广播MSG_SEND_BROADCAST
mHandler.sendMessage(mHandler.obtainMessage(MSG_SEND_BROADCAST, dropboxIntent));
} catch (IOException e) {
Slog.e(TAG, "Can't write: " + tag, e);
} finally { try { if (output != null) output.close(); } catch (IOException e) {}
entry.close(); if (temp != null) temp.delete();
}
}小结
当应用出现Crash时，调用AMS的handleApplicationCrash方法，该方法最终会调用DBMS，将数据保存在目录/data/system/dropbox，当出现crash, anr, wtf或者存储设备可用空间低，以及开机完成时利用DropBoxManager，再通过binder向DBMS发出请求，完成信息的收集工作。 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。