源码
</frameworks/base/services/java/com/android/server/SystemServer.java>
上面的文章中我们知道了怎么通过zygote来启动SystemServer进程，接下来我们来具体分析SystemServer里面的细节
3.1 main
在zygote里面会通过反射来调用到main方法
public static void main(String[] args) {
294 new SystemServer().run();
295 }
3.2 SystemServer run
private void run() {
308 try {
309 traceBeginAndSlog("InitBeforeStartServices");
310 // If a device's clock is before 1970 (before 0), a lot of
311 // APIs crash dealing with negative numbers, notably
312 // java.io.File#setLastModified, so instead we fake it and
313 // hope that time from cell towers or NTP fixes it shortly.
如果时间比1970年早, 设置为1970年
314 if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {
315 Slog.w(TAG, "System clock is before 1970; setting to 1970.");
316 SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
317 }
318
319 //
320 // Default the timezone property to GMT if not set.
321 //
322 String timezoneProperty = SystemProperties.get("persist.sys.timezone");
323 if (timezoneProperty == null || timezoneProperty.isEmpty()) {
324 Slog.w(TAG, "Timezone not set; setting to GMT.");
325 SystemProperties.set("persist.sys.timezone", "GMT");
326 }
327
328 // If the system has "persist.sys.language" and friends set, replace them with
329 // "persist.sys.locale". Note that the default locale at this point is calculated
330 // using the "-Duser.locale" command line flag. That flag is usually populated by
331 // AndroidRuntime using the same set of system properties, but only the system_server
332 // and system apps are allowed to set them.
333 //
334 // NOTE: Most changes made here will need an equivalent change to
335 // core/jni/AndroidRuntime.cpp
336 if (!SystemProperties.get("persist.sys.language").isEmpty()) {
337 final String languageTag = Locale.getDefault().toLanguageTag();
338
339 SystemProperties.set("persist.sys.locale", languageTag);
340 SystemProperties.set("persist.sys.language", "");
341 SystemProperties.set("persist.sys.country", "");
342 SystemProperties.set("persist.sys.localevar", "");
343 }
344
345 // The system server should never make non-oneway calls
346 Binder.setWarnOnBlocking(true);
347 // The system server should always load safe labels
348 PackageItemInfo.setForceSafeLabels(true);
349 // Deactivate SQLiteCompatibilityWalFlags until settings provider is initialized
350 SQLiteCompatibilityWalFlags.init(null);
351
352 // Here we go!
353 Slog.i(TAG, "Entered the Android system server!");
354 int uptimeMillis = (int) SystemClock.elapsedRealtime();
355 EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN, uptimeMillis);
356 if (!mRuntimeRestart) {
357 MetricsLogger.histogram(null, "boot_system_server_init", uptimeMillis);
358 }
359
360 // In case the runtime switched since last boot (such as when
361 // the old runtime was removed in an OTA), set the system
362 // property so that it is in sync. We can | xq oqi't do this in
363 // libnativehelper's JniInvocation::Init code where we already
364 // had to fallback to a different runtime because it is
365 // running as root and we need to be the system user to set
366 // the property. http://b/11463182
367 SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());
368
369 // Mmmmmm... more memory!
370 VMRuntime.getRuntime().clearGrowthLimit();
371
372 // The system server has to run all of the time, so it needs to be
373 // as efficient as possible with its memory usage.
374 VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);
375
376 // Some devices rely on runtime fingerprint generation, so make sure
377 // we've defined it before booting further.
378 Build.ensureFingerprintProperty();
379
380 // Within the system server, it is an error to access Environment paths without
381 // explicitly specifying a user.
382 Environment.setUserRequired(true);
383
384 // Within the system server, any incoming Bundles should be defused
385 // to avoid throwing BadParcelableException.
386 BaseBundle.setShouldDefuse(true);
387
388 // Within the system server, when parceling exceptions, include the stack trace
389 Parcel.setStackTraceParceling(true);
390
391 // Ensure binder calls into the system always run at foreground priority.
392 BinderInternal.disableBackgroundScheduling(true);
393
394 // Increase the number of binder threads in system_server
395 BinderInternal.setMaxThreads(sMaxBinderThreads);
396
397 // Prepare the main looper thread (this thread).
398 android.os.Process.setThreadPriority(
399 android.os.Process.THREAD_PRIORITY_FOREGROUND);
400 android.os.Process.setCanSelfBackground(false);
401 Looper.prepareMainLooper();
402 Looper.getMainLooper().setSlowLogThresholdMs(
403 SLOW_DISPATCH_THRESHOLD_MS, SLOW_DELIVERY_THRESHOLD_MS);
404
405 // Initialize native services.
406 System.loadLibrary("android_servers");
407
408 // Check whether we failed to shut down last time we tried.
409 // This call may not return.
410 performPendingShutdown();
411
412 // Initialize the system context.
//创建系统的上下文
413 createSystemContext();
414
415 // Create the system service manager.
//系统服务管理者
416 mSystemServiceManager = new SystemServiceManager(mSystemContext);
417 mSystemServiceManager.setStartInfo(mRuntimeRestart,
418 mRuntimeStartElapsedTime, mRuntimeStartUptime);
419 LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
420 // Prepare the thread pool for init tasks that can be parallelized
421 SystemServerInitThreadPool.get();
422 } finally {
423 traceEnd(); // InitBeforeStartServices
424 }
425
426 // Start services.
427 try {
428 traceBeginAndSlog("StartServices");
429 startBootstrapServices(); // 启动引导服务
430 startCoreServices(); //核心服务
431 startOtherServices(); //一些其它的服务
432 SystemServerInitThreadPool.shutdown();
433 } catch (Throwable ex) {
434 Slog.e("System", "******************************************");
435 Slog.e("System", "************ Failure starting system services", ex);
436 throw ex;
437 } finally {
438 traceEnd();
439 }
440
441 StrictMode.initVmDefaults(null);
442
443 if (!mRuntimeRestart && !isFirstBootOrUpgrade()) {
444 int uptimeMillis = (int) SystemClock.elapsedRealtime();
445 MetricsLogger.histogram(null, "boot_system_server_ready", uptimeMillis);
446 final int MAX_UPTIME_MILLIS = 60 * 1000;
447 if (uptimeMillis > MAX_UPTIME_MILLIS) {
448 Slog.wtf(SYSTEM_SERVER_TIMING_TAG,
449 "SystemServer init took too long. uptimeMillis=" + uptimeMillis);
450 }
451 }
452 //保证SystemServer进程一直存活
453 // Loop forever.
454 Looper.loop();
455 throw new RuntimeException("Main thread loop unexpectedly exited");
456 }
3.3 createSystemContext
private void createSystemContext() {
//创建ActivityThread, 在systemMain函数里面调用ActivityThread的构造函数
//ActivityThread thread = new ActivityThread();
522 ActivityThread activityThread = ActivityThread.systemMain();
523 mSystemContext = activityThread.getSystemContext();
524 mSystemContext.setTheme(DEFAULT_SYSTEM_THEME);
525
526 final Context systemUiContext = activityThread.getSystemUiContext();
527 systemUiContext.setTheme(DEFAULT_SYSTEM_THEME);
528 }
529
当然在SystemServer里面启动了好多的java层的service，他们内部通过binder 来进行通信，这个地方就暂时不说了
以后会专门开一篇来说SystemServer里面启动的服务，以及怎么通过binder来进行通信的。到这个地方我们的SystemServer
算是启动完成了，那下面是怎么启动到launcher呢，继续看下一篇文章。