Android12系统源码分析：NativeTombstoneManager 概述
android12新增的system_server进程（LocalService）本地服务，用于管理native tombstones。
该服务在开机Systemerver初始化流程启动，添加到LocalService，然后启动一个ServiceThread线程用于（mHandler.post）处理本服务的业务。
NativeTombstoneManager的功能主要是：
监听/data/tombstones目录文件变动，解析为TombstoneFile对象保存，通知dropbox
特定tombstones文件删除
特定tombstones文件检索
值得关注的是AMS对该服务的使用，也是Android11新增API：getHistoricalProcessExitReasons()
软件架构如图：
图：NativeTombstoneManager类图
启动流程图：NativeTombstoneManager服务启动时序图
服务比较简单，和其他SystemServer启动的服务一样，
frameworks/base/services/core/java/com/android/server/os/NativeTombstoneManagerService.java
public class NativeTombstoneManagerService extends SystemService { private NativeTombstoneManager mManager; @Override public void onStart() { mManager = new NativeTombstoneManager(getContext()); //仅添加本地服务，没有binder服务 LocalServices.addService(NativeTombstoneManager.class, mManager); } @Override public void onBootPhase(int phase) { if (phase == SystemService.PHASE_ACTIVITY_MANAGER_READY) { mManager.onSystemReady(); } } }本服务也是SystemService工具类的子类，通过重写onStart、onBootPhase获得代码流程
在onStart中初始化真正的服务实现NativeTombstoneManager，实例化后添加到LocalServices
frameworks/base/services/core/java/com/android/server/os/NativeTombstoneManager.java
public final class NativeTombstoneManager { NativeTombstoneManager(Context context) { //启动handler线程，用于后续处理本服务的业务 final ServiceThread thread = new ServiceThread(TAG + ":tombstoneWatcher", THREAD_PRIORITY_BACKGROUND, true /* allowIo */); thread.start(); mHandler = thread.getThreadHandler(); //启动文件监听/data/tombstones mWatcher = new TombstoneWatcher(); mWatcher.startWatching(); } void onSystemReady() { registerForUserRemoval(); registerForPackageRemoval(); // 开机阶段先扫描一次/data/tombstones目录 mHandler.post(() -> { final File[] tombstoneFiles = TOMBSTONE_DIR.listFiles(); for (int i = 0; tombstoneFiles != null && i < tombstoneFiles.length; i++) { if (tombstoneFiles[i].isFile()) { handleTombstone(tombstoneFiles[i]);开机流程有三个动作
启动handler线程，用于后续处理本服务的业务
TombstoneWatcher启动文件监听/data/tombstones
开机阶段先扫描一次/data/tombstones目录
看一下handleTombstone
frameworks/base/services/core/java/com/android/server/os/NativeTombstoneManager.java
private void handleTombstone(File path) { final String filename = path.getName(); if (!filename.startsWith("tombstone_")) { return; } if (filename.endsWith(".pb")) { handleProtoTombstone(path); BootReceiver.addTombstoneToDropBox(mContext, path, true); } else { BootReceiver.addTombstoneToDropBox(mContext, path, false);如果是以pb结尾的原型文件，则handleProtoTombstone方法中为该文件生成TombstoneFile对象，并添加到数据结构
private final SparseArray<TombstoneFile> mTombstones;
并且，每个新生成的tombstone文件都会同步给dropbox
新文件的监听frameworks/base/services/core/java/com/android/server/os/NativeTombstoneManager.java
class TombstoneWatcher extends FileObserver { TombstoneWatcher() { super(TOMBSTONE_DIR, FileObserver.CREATE | FileObserver.MOVED_TO); } @Override public void onEvent(int event, @Nullable String path) { mHandler.post(() -> { handleTombstone(new File(TOMBSTONE_DIR, path)); });内部类TombstoneWatcher，当目录/data/tombstones有文件生成时，回调到onEvent，然后通过handleTombstone方法做处理
AciivtyManager#getHistoricalProcessExitReasons图：getHistoricalProcessExitReasons方法时序图
需要注意返回的数据结构的处理ApplicationExitInfo。
frameworks/base/services/core/java/com/android/server/os/NativeTombstoneManager.java
public void collectTombstones(ArrayList<ApplicationExitInfo> output, int callingUid, int pid, int maxNum) { CompletableFuture<Object> future = new CompletableFuture<>(); if (!UserHandle.isApp(callingUid)) { return; } final int userId = UserHandle.getUserId(callingUid); final int appId = UserHandle.getAppId(callingUid); mHandler.post(() -> { boolean appendedTombstones = false; synchronized (mLock) { final int tombstonesSize = mTombstones.size(); tombstoneIter: //遍历所有已知tombstoe， //如果userid和appid和reason匹配 //则返回请求的数量的tombstone for (int i = 0; i < tombstonesSize; ++i) { TombstoneFile tombstone = mTombstones.valueAt(i); if (tombstone.matches(Optional.of(userId), Optional.of(appId))) { if (pid != 0 && tombstone.mPid != pid) { continue; } //reason判断 // Try to attach to an existing REASON_CRASH_NATIVE. final int outputSize = output.size(); for (int j = 0; j < outputSize; ++j) { ApplicationExitInfo exitInfo = output.get(j); if (tombstone.matches(exitInfo)) { exitInfo.setNativeTombstoneRetriever(tombstone.getPfdRetriever()); continue tombstoneIter; } } //请求数量判断 if (output.size() < maxNum) { appendedTombstones = true; output.add(tombstone.toAppExitInfo()); } } } } //如果超过一个则按时间戳排序 if (appendedTombstones) { Collections.sort(output, (lhs, rhs) -> { // Reports should be ordered with newest reports first. long diff = rhs.getTimestamp() - lhs.getTimestamp(); if (diff < 0) { return -1; } else if (diff == 0) { return 0; } else { return 1; } }); } future.complete(null); }); try { future.get();遍历所有已知tombstoe，如果userid和appid和reason匹配则返回请求的数量的tombstone
如果数量超过一个则按时间戳排序