SystemServer.main
SystemServer通过ZygoteInit.java反射启动，首先会进入main方法，main会构造一个新的SystemServer，然后运行run()方法
/frameworks/base/services/java/com/android/server/SystemServer.java
public final class SystemServer {
/**
* The main entry point from zygote.
*/
public static void main(String[] args) {
new SystemServer().run();
}
}
SystemServer.run
private void run() {
try {
traceBeginAndSlog("InitBeforeStartServices");
// 如果一个设备时间在1970年之前，很多API会crash，所以会将时间统一设置为1970年起
if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {
Slog.w(TAG, "System clock is before 1970; setting to 1970.");
SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
}
// Default the timezone property to GMT if not set.
String timezoneProperty = SystemProperties.get("persist.sys.timezone");
if (timezoneProperty == null || timezoneProperty.isEmpty()) {
Slog.w(TAG, "Timezone not set; setting to GMT.");
SystemProperties.set("persist.sys.timezone", "GMT");
}
// If the system has "persist.sys.language" and friends set, replace them with
// "persist.sys.locale". Note that the default locale at this point is calculated
// using the "-Duser.locale" command line flag. That flag is usually populated by
// AndroidRuntime using the same set of system properties, but only the system_server
// and system apps are allowed to set them.
//
// NOTE: Most changes made here will need an equivalent change to
// core/jni/AndroidRuntime.cpp
if (!SystemProperties.get("persist.sys.language").isEmpty()) {
final String languageTag = Locale.getDefault().toLanguageTag();
SystemProperties.set("persist.sys.locale", languageTag);
SystemProperties.set("persist.sys.language", "");
SystemProperties.set("persist.sys.country", "");
SystemProperties.set("persist.sys.localevar", "");
}
// The system server should never make non-oneway calls
Binder.setWarnOnBlocking(true);
// Here we go! 正式进入system server
Slog.i(TAG, "Entered the Android system server!");
int uptimeMillis = (int) SystemClock.elapsedRealtime();
EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN, uptimeMillis);
if (!mRuntimeRestart) {
MetricsLogger.histogram(null, "boot_system_server_init", uptimeMillis);
}
// In case the runtime switched since last boot (such as when
// the old runtime was removed in an OTA), set the system
// property so that it is in sync. We can | xq oqi't do this in
// libnativehelper's JniInvocation::Init code where we already
// had to fallback to a different runtime because it is
// running as root and we need to be the system user to set
// the property. http://b/11463182
// 变更虚拟机的库文件
SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());
// Enable the sampling profiler.
if (SamplingProfilerIntegration.isEnabled()) {
SamplingProfilerIntegration.start();
mProfilerSnapshotTimer = new Timer();
mProfilerSnapshotTimer.schedule(new TimerTask() {
@Override
public void run() {
SamplingProfilerIntegration.writeSnapshot("system_server", null);
}
}, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL);
}
// Mmmmmm... more memory!
// 因为启动过程需要较多的虚拟机内存空间，清除vm内存增长上限
VMRuntime.getRuntime().clearGrowthLimit();
// The system server has to run all of the time, so it needs to be
// as efficient as possible with its memory usage.
// 设置内存利用率0.8
VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);
// Some devices rely on runtime fingerprint generation, so make sure
// we've defined it before booting further.
// 部分机型依赖于运行时就产生指纹信息，因此需要在开机完成前定义
Build.ensureFingerprintProperty();
// Within the system server, it is an error to access Environment paths without
// explicitly specifying a user.
// 指定访问环境变量的用户
Environment.setUserRequired(true);
// Within the system server, any incoming Bundles should be defused
// to avoid throwing BadParcelableException.
BaseBundle.setShouldDefuse(true);
// Ensure binder calls into the system always run at foreground priority.
// 确保进入系统的binder调用运行高优先级
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();
// Initialize native services.
// 加载native 库
System.loadLibrary("android_servers");
// Check whether we failed to shut down last time we tried.
// This call may not return.
performPendingShutdown();
// Initialize the system context.
createSystemContext();
// Create the system service manager.
mSystemServiceManager = new SystemServiceManager(mSystemContext);
mSystemServiceManager.setRuntimeRestarted(mRuntimeRestart);
// 添加mSystemServiceManager到本地服务成员sLocalServiceObjects 见LocalServices.java
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
// Prepare the thread pool for init tasks that can be parallelized
SystemServerInitThreadPool.get();
} finally {
traceEnd(); // InitBeforeStartServices
}
// Start services.
try {
traceBeginAndSlog("StartServices");
startBootstrapServices(); // 启动引导服务
startCoreServices(); // 启动核心服务
startOtherServices(); // 启动其他服务
SystemServerInitThreadPool.shutdown();
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
traceEnd();
}
// For debug builds, log event loop stalls to dropbox for analysis.
if (StrictMode.conditionallyEnableDebugLogging()) {
Slog.i(TAG, "Enabled StrictMode for system server main thread.");
}
if (!mRuntimeRestart && !isFirstBootOrUpgrade()) {
int uptimeMillis = (int) SystemClock.elapsedRealtime();
MetricsLogger.histogram(null, "boot_system_server_ready", uptimeMillis);
final int MAX_UPTIME_MILLIS = 60 * 1000;
if (uptimeMillis > MAX_UPTIME_MILLIS) {
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");
}
下面看一下run函数用到的本地私有方法
SystemServer.performPendingShutdown
private void performPendingShutdown() {
// 通过检查ShutdownThread.SHUTDOWN_ACTION_PROPERTY来判断上次关机是否失败
final String shutdownAction = SystemProperties.get(
ShutdownThread.SHUTDOWN_ACTION_PROPERTY, "");
if (shutdownAction != null && shutdownAction.length() > 0) {
boolean reboot = (shutdownAction.charAt(0) == '1');
final String reason;
if (shutdownAction.length() > 1) {
reason = shutdownAction.substring(1, shutdownAction.length());
} else {
reason = null;
}
// If it's a pending reboot into recovery to apply an update,
// always make sure uncrypt gets executed properly when needed.
// If '/cache/recovery/block.map' hasn't been created, stop the
// reboot which will fail for sure, and get a chance to capture a
// bugreport when that's still feasible. (Bug: 26444951)
if (reason != null && reason.startsWith(PowerManager.REBOOT_RECOVERY_UPDATE)) {
File packageFile = new File(UNCRYPT_PACKAGE_FILE);
if (packageFile.exists()) {
String filename = null;
try {
filename = FileUtils.readTextFile(packageFile, 0, null);
} catch (IOException e) {
Slog.e(TAG, "Error reading uncrypt package file", e);
}
if (filename != null && filename.startsWith("/data")) {
if (!new File(BLOCK_MAP_FILE).exists()) {
Slog.e(TAG, "Can't find block map file, uncrypt failed or " +
"unexpected runtime restart?");
return;
}
}
}
}
ShutdownThread.rebootOrShutdown(null, reboot, reason);
}
}
SystemServer.createSystemContext
private void createSystemContext() {
// 创建系统上下文并设置主题
ActivityThread activityThread = ActivityThread.systemMain();
mSystemContext = activityThread.getSystemContext();
mSystemContext.setTheme(DEFAULT_SYSTEM_THEME);
final Context systemUiContext = activityThread.getSystemUiContext();
systemUiContext.setTheme(DEFAULT_SYSTEM_THEME);
}
SystemServer.startBootstrapServices
/**
* Starts the small tangle of critical services that are needed to get
* the system off the ground. These services have complex mutual dependencies
* which is why we initialize them all in one place here. Unless your service
* is also entwined in these dependencies, it should be initialized in one of
* the other functions.
* 这里的服务都是有复杂的依赖性，所以放在这里统一初始化。如果有与这些服务不相关的服务需要启动，应该放在其他地方去做
*/
private void startBootstrapServices() {
Slog.i(TAG, "Reading configuration...");
final String TAG_SYSTEM_CONFIG = "ReadingSystemConfig";
traceBeginAndSlog(TAG_SYSTEM_CONFIG);
SystemServerInitThreadPool.get().submit(SystemConfig::getInstance, TAG_SYSTEM_CONFIG);
traceEnd();
// Wait for installd to finish starting up so that it has a chance to
// create critical directories such as /data/user with the appropriate
// permissions. We need this to complete before we initialize other services.
traceBeginAndSlog("StartInstaller");
// 等待installd启动，使其有时间建立正确权限的目录。之后才可以初始化其他服务
Installer installer = mSystemServiceManager.startService(Installer.class);
traceEnd();
// In some cases after launching an app we need to access device identifiers,
// therefore register the device identifier policy before the activity manager.
traceBeginAndSlog("DeviceIdentifiersPolicyService");
mSystemServiceManager.startService(DeviceIdentifiersPolicyService.class);
traceEnd();
// Activity manager runs the show.
traceBeginAndSlog("StartActivityManager");
// 启动ActivityManagerService
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
traceEnd();
// Power manager needs to be started early because other services need it.
// Native daemons may be watching for it to be registered so it must be ready
// to handle incoming binder calls immediately (including being able to verify
// the permissions for those calls).
// 启动PowerManagerService，因为其他服务需要使用它，所以需要早期创建
traceBeginAndSlog("StartPowerManager");
mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
traceEnd();
// Now that the power manager has been started, let the activity manager
// initialize power management features.
traceBeginAndSlog("InitPowerManagement");
mActivityManagerService.initPowerManagement();
traceEnd();
// Bring up recovery system in case a rescue party needs a reboot
// 如果一个rescure party需要重启，则启动recovery
// rescure party是Android O的新特性，代码位于/services/core/java/com/android/server/RescueParty.java
if (!SystemProperties.getBoolean("config.disable_noncore", false)) {
traceBeginAndSlog("StartRecoverySystemService");
mSystemServiceManager.startService(RecoverySystemService.class);
traceEnd();
}
// Now that we have the bare essentials of the OS up and running, take
// note that we just booted, which might send out a rescue party if
// we're stuck in a runtime restart loop.
// 正常启动系统做一个标记，如果开机重启循环，就会发出一个rescure party
RescueParty.noteBoot(mSystemContext);
// Manages LEDs and display backlight so we need it to bring up the display.
// 点亮display
traceBeginAndSlog("StartLightsService");
mSystemServiceManager.startService(LightsService.class);
traceEnd();
// Display manager is needed to provide display metrics before package manager
// starts up.
// 要在package manager之前启动display manager，这样可以提供display metrics数据下去
traceBeginAndSlog("StartDisplayManager");
mDisplayManagerService = mSystemServiceManager.startService(DisplayManagerService.class);
traceEnd();
// We need the default display before we can initialize the package manager.
// 初始化package manager前需要default display
traceBeginAndSlog("WaitForDisplay");
mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);
traceEnd();
// Only run "core" apps if we're encrypting the device.
// 设备在加密时，运行核心app
String cryptState = SystemProperties.get("vold.decrypt");
if (ENCRYPTING_STATE.equals(cryptState)) {
Slog.w(TAG, "Detected encryption in progress - only parsing core apps");
mOnlyCore = true;
} else if (ENCRYPTED_STATE.equals(cryptState)) {
Slog.w(TAG, "Device encrypted - only parsing core apps");
mOnlyCore = true;
}
// Start the package manager.
// 开始启动PMS
if (!mRuntimeRestart) {
MetricsLogger.histogram(null, "boot_package_manager_init_start",
(int) SystemClock.elapsedRealtime());
}
traceBeginAndSlog("StartPackageManagerService");
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
mFirstBoot = mPackageManagerService.isFirstBoot();
mPackageManager = mSystemContext.getPackageManager();
traceEnd();
if (!mRuntimeRestart && !isFirstBootOrUpgrade()) {
MetricsLogger.histogram(null, "boot_package_manager_init_ready",
(int) SystemClock.elapsedRealtime());
}
// Manages A/B OTA dexopting. This is a bootstrap service as we need it to rename
// A/B artifacts after boot, before anything else might touch/need them.
// Note: this isn't needed during decryption (we don't have /data anyways).
if (!mOnlyCore) {
boolean disableOtaDexopt = SystemProperties.getBoolean("config.disable_otadexopt",
false);
if (!disableOtaDexopt) {
traceBeginAndSlog("StartOtaDexOptService");
try {
OtaDexoptService.main(mSystemContext, mPackageManagerService);
} catch (Throwable e) {
reportWtf("starting OtaDexOptService", e);
} finally {
traceEnd();
}
}
}
traceBeginAndSlog("StartUserManagerService");
// UserManagerService 新建目录/data/user/
mSystemServiceManager.startService(UserManagerService.LifeCycle.class);
traceEnd();
// Initialize attribute cache used to cache resources from packages.
traceBeginAndSlog("InitAttributerCache");
AttributeCache.init(mSystemContext);
traceEnd();
// Set up the Application instance for the system process and get started.
// 设置AMS
traceBeginAndSlog("SetSystemProcess");
mActivityManagerService.setSystemProcess();
traceEnd();
// DisplayManagerService needs to setup android.display scheduling related policies
// since setSystemProcess() would have overridden policies due to setProcessGroup
// 配置displayManagerService
mDisplayManagerService.setupSchedulerPolicies();
// Manages Overlay packages
// 启动OverlayManagerService
traceBeginAndSlog("StartOverlayManagerService");
mSystemServiceManager.startService(new OverlayManagerService(mSystemContext, installer));
traceEnd();
// The sensor service needs access to package manager service, app ops
// service, and permissions service, therefore we start it after them.
// Start sensor service in a separate thread. Completion should be checked
// before using it.
// sensor service需要访问PMS,app ops service和permission service。所以基本上在最后启动。
// sensor在线程启动，访问前需要检查是否启动完成
mSensorServiceStart = SystemServerInitThreadPool.get().submit(() -> {
BootTimingsTraceLog traceLog = new BootTimingsTraceLog(
SYSTEM_SERVER_TIMING_ASYNC_TAG, Trace.TRACE_TAG_SYSTEM_SERVER);
traceLog.traceBegin(START_SENSOR_SERVICE);
startSensorService();
traceLog.traceEnd();
}, START_SENSOR_SERVICE);
}
BootstrapService整理：
Installer.class
等待installd启动，使其有时间建立正确权限的目录。之后才可以初始化其他服务。
DeviceIdentifiersPolicyService.class
在activity manager之前启动该服务，提供app访问设备identifier。
ActivityManagerService.Lifecycle.class
启动AMS
PowerManagerService.class
启动PowerManagerService，因为其他服务需要使用它，所以需要早期创建。
mActivityManagerService.initPowerManagement();
由AMS初始化PowerManagerService
RecoverySystemService.class
准备rescue party相关
LightsService.class
点亮display
DisplayManagerService.class
上一步点亮屏幕后，启动displayManagerService，准备display metrics数据
mSystemServiceManager.startBootPhase(SystemService.PHASE_WAIT_FOR_DEFAULT_DISPLAY);
systemServiceManager等待display
PackageManagerService.main
启动PMS
UserManagerService.LifeCycle.class
启动UserManagerService，管理多用户，创建/data/user目录
AttributeCache.init(mSystemContext);
初始化attribute cache，用来缓存从packages拿到的资源
mActivityManagerService.setSystemProcess();
设置AMS
mDisplayManagerService.setupSchedulerPolicies();
设置DisplayManagerService的schedule
new OverlayManagerService
启动OverlayManagerService
startSensorService();
启动sensor服务，最后启动它，而且是在线程中启动，所以使用时需要检查完整性
SystemServer.startCoreServices
来了解一下核心服务，核心的也就是最基本的。这些服务不会和启动阶段的进程产生影响。
/**
* Starts some essential services that are not tangled up in the bootstrap process.
*/
private void startCoreServices() {
// Records errors and logs, for example wtf()
// 记录error和log的服务，经典的wtf的log...
traceBeginAndSlog("StartDropBoxManager");
mSystemServiceManager.startService(DropBoxManagerService.class);
traceEnd();
traceBeginAndSlog("StartBatteryService");
// Tracks the battery level. Requires LightService.
// 统计电池的服务，需要LightService
mSystemServiceManager.startService(BatteryService.class);
traceEnd();
// Tracks application usage stats.
// 统计应用使用情况的服务
traceBeginAndSlog("StartUsageService");
mSystemServiceManager.startService(UsageStatsService.class);
mActivityManagerService.setUsageStatsManager(
LocalServices.getService(UsageStatsManagerInternal.class));
traceEnd();
// Tracks whether the updatable WebView is in a ready state and watches for update installs.
traceBeginAndSlog("StartWebViewUpdateService");
mWebViewUpdateService = mSystemServiceManager.startService(WebViewUpdateService.class);
traceEnd();
}
DropBoxManagerService.class
记录error和log的服务
BatteryService.class
记录电池使用的服务
UsageStatsService.class
应用使用情况的服务
WebViewUpdateService.class
WebView更新的服务
SystemServer.startOtherServices
启动一些没有被重构和管理的杂项。
这个代码很长，有一千多行就不贴了。基本上如果遇到一些前面过程没提到的服务，就可以到这里面找。
这个方法内最后的代码是：
// We now tell the activity manager it is okay to run third party
// code. It will call back into us once it has gotten to the state
// where third party code can really run (but before it has actually
// started launching the initial applications), for us to complete our
// initialization.
mActivityManagerService.systemReady(() -> {
...
}
这时候AMS已经启动完成，可以运行三方代码了。
参考
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