Android SystemServer进程解析
SystemServer进程在android系统中占了举足轻重的地位，系统的所有服务和SystemUI都是由它启动。
一、SystemServer进程主函数流程
1、主函数三部曲
//frameworks/base/services/java/com/android/server/SystemServer.java
/** * The main entry point from zygote. */
public static void main(String[] args) {
new SystemServer().run();
}SystemServer的入口函数同样是main，调用顺序先是构造函数，再是run，构造函数没有什么重点地方后文dump详细介绍，主要流程主要还是run方法。run里面哦流程其实还是遵循普遍的三部曲：初始化上下文->启动服务->进入loop循环
1）初始化上下文
//frameworks/base/services/java/com/android/server/SystemServer.java
private void run() {
TimingsTraceAndSlog t = new TimingsTraceAndSlog();
try {
t.traceBegin("InitBeforeStartServices");
//.....一些属性的初始化....
// The system server should never make non-oneway calls
Binder.setWarnOnBlocking(true);
// The system server should always load safe labels
PackageItemInfo.forceSafeLabels();
// Default to FULL within the system server.
SQLiteGlobal.sDefaultSyncMode = SQLiteGlobal.SYNC_MODE_FULL;
// Deactivate SQLiteCompatibilityWalFlags until settings provider is initialized
SQLiteCompatibilityWalFlags.init(null);
// Here we go!
Slog.i(TAG, "Entered the Android system server!");
final long uptimeMillis = SystemClock.elapsedRealtime(); //记录开始启动的时间错，调试系统启动时间的时候需要关注
// Mmmmmm... more memory!
VMRuntime.getRuntime().clearGrowthLimit();
// Some devices rely on runtime fingerprint generation, so make sure we've defined it before booting further.
Build.ensureFingerprintProperty();
// Within the system server, it is an error to access Environment paths without explicitly specifying a user.
Environment.setUserRequired(true);
// Within the system server, any incoming Bundles should be defused to avoid throwing BadParcelableException.
BaseBundle.setShouldDefuse(true);
// Within the system server, when parceling exceptions, include the stack trace
Parcel.setStackTraceParceling(true);
// Ensure binder calls into the system always run at foreground priority.
BinderInternal.disableBackgroundScheduling(true);
// Increase the number of binder threads in system_server
BinderInternal.setMaxThreads(sMaxBinderThreads);
// Prepare the main looper thread (this thread).
android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_FOREGROUND);
android.os.Process.setCanSelfBackground(false);
Looper.prepareMainLooper();
Looper.getMainLooper().setSlowLogThresholdMs(SLOW_DISPATCH_THRESHOLD_MS, SLOW_DELIVERY_THRESHOLD_MS);
SystemServiceRegistry.sEnableServiceNotFoundWtf = true;
// Initialize native services.
System.loadLibrary("android_servers");
// Allow heap / perf profiling.
initZygoteChildHeapProfiling();
// Check whether we failed to shut down last time we tried. This call may not return.
performPendingShutdown();
// Initialize the system context.
createSystemContext();
// Call per-process mainline module initialization.
ActivityThread.initializeMainlineModules();
} finally {
t.traceEnd(); // InitBeforeStartServices
}2）启动系统所有服务
//frameworks/base/services/java/com/android/server/SystemServer.java
// Start services.
try {
t.traceBegin("StartServices");
startBootstrapServices(t); //启动BOOT服务（即没有这些服务系统无法运行）
startCoreServices(t); //启动核心服务
startOtherServices(t); //启动其他服务
startApexServices(t); //启动APEX服务，此服务必现要在前面的所有服务启动之后才能启动，为了防止OTA相关问题
// Only update the timeout after starting all the services so that we use
// the default timeout to start system server.
updateWatchdogTimeout(t);
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
t.traceEnd(); // StartServices
}
/**
* Starts system services defined in apexes.
* <p>Apex services must be the last category of services to start. No other service must be
* starting after this point. This is to prevent unnecessary stability issues when these apexes
* are updated outside of OTA; and to avoid breaking dependencies from system into apexes.
*/
private void startApexServices(@NonNull TimingsTraceAndSlog t) {
t.traceBegin("startApexServices");
// TODO(b/192880996): get the list from "android" package, once the manifest entries are migrated to system manifest.
List<ApexSystemServiceInfo> services = ApexManager.getInstance().getApexSystemServices();
for (ApexSystemServiceInfo info : services) {
String name = info.getName();
String jarPath = info.getJarPath();
t.traceBegin("starting " + name);
if (TextUtils.isEmpty(jarPath)) {
mSystemServiceManager.startService(name);
} else {
mSystemServiceManager.startServiceFromJar(name, jarPath);
}
t.traceEnd();
}
// make sure no other services are started after this point
mSystemServiceManager.sealStartedServices();
t.traceEnd(); // startApexServices
}如上代码大体启动了四类服务：
- startBootstrapServices：启动一些关键引导服务，这些服务耦合到一起
- startCoreServices：启动一些关键引导服务，这些服务没有耦合到一起
- startOtherServices：启动其他一些杂七杂八的服务
- startApexServices：启动apex类的服务，其实就是mainline那些东西，详情参考请点击我
3）进入loop循环
//frameworks/base/services/java/com/android/server/SystemServer.java
StrictMode.initVmDefaults(null);
if (!mRuntimeRestart && !isFirstBootOrUpgrade()) {
final long uptimeMillis = SystemClock.elapsedRealtime();
final long maxUptimeMillis = 60 * 1000;
if (uptimeMillis > maxUptimeMillis) {
Slog.wtf(SYSTEM_SERVER_TIMING_TAG, "SystemServer init took too long. uptimeMillis=" + uptimeMillis);
}
}
// Loop forever.
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");和之前讲的binder一样，基本上所有的进程最后都会进入loop进行循环，轮询主线程相关的handle消息和binder消息，如下日志堆栈，表示handle消息处理过程中发生异常：
2、顺序启动服务
二、SystemServer正常启动日志
1、SystemServerTiming日志封装
2、SystemServer启动阶段OnBootPhase
3、SystemServer无法找到服务
4、Slow operation
三、SystemServer dumpsys解读
1、SystemServer的dump
2、其他服务的dump
SystemServer:
Runtime restart: false
Start count: 1
Runtime start-up time: +8s0ms
Runtime start-elapsed time: +8s0ms
SystemServiceManager:
Current phase: 1000
Current user not set!
1 target users: 0(full)
172 started services:
com.transsion.hubcore.server.TranBootstrapServiceManagerService
com.android.server.security.FileIntegrityService
com.android.server.pm.Installer
com.android.server.os.DeviceIdentifiersPolicyService
com.android.server.uri.UriGrantsManagerService.Lifecycle
com.android.server.powerstats.PowerStatsService
com.android.server.permission.access.AccessCheckingService
com.android.server.wm.ActivityTaskManagerService.Lifecycle
com.android.server.am.ActivityManagerService.Lifecycle
......
com.android.server.Watchdog:
WatchdogTimeoutMillis=60000
SystemServerInitThreadPool:
has instance: false
number of threads: 8
service: java.util.concurrent.ThreadPoolExecutor@7bf04fb[Terminated, pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 351]
is shutdown: true
no pending tasks
AdServices:
mAdServicesModuleName: com.google.android.adservices
mAdServicesModuleVersion: 341131050
mHandlerThread: Thread[AdServicesManagerServiceHandler,5,main]
mAdServicesPackagesRolledBackFrom: {}
mAdServicesPackagesRolledBackTo: {}
ShellCmd enabled: false
UserInstanceManager
mAdServicesBaseDir: /data/system/adservices
mConsentManagerMapLocked: {}
mAppConsentManagerMapLocked: {}
mRollbackHandlingManagerMapLocked: {}
mBlockedTopicsManagerMapLocked={}
TopicsDbHelper
CURRENT_DATABASE_VERSION: 1
mDbFile: /data/system/adservices_topics.db
mDbVersion: 1