应用程序的入口
当启动应用程序时会由ActivityMangerService孵化一个进程，并且实例化一个ActivityThread对象，该类为fianl类型，并不是一个线程类，该类mian()方法实现了常说的消息循环
public static void main(String[] args) {
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SamplingProfilerIntegration.start();
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// CloseGuard defaults to true and can be quite spammy. We
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// disable it here, but selectively enable it later (via
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// StrictMode) on debug builds, but using DropBox, not logs.
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CloseGuard.setEnabled(false);
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Environment.initForCurrentUser();
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// Set the reporter for event logging in libcore
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EventLogger.setReporter(new EventLoggingReporter());
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Security.addProvider(new AndroidKeyStoreProvider());
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// Make sure TrustedCertificateStore looks in the right place for CA certificates
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final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
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TrustedCertificateStore.setDefaultUserDirectory(configDir);
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Process.setArgV0("<pre-initialized>");
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Looper.prepareMainLooper();
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ActivityThread thread = new ActivityThread();
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thread.attach(false);
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if (sMainThreadHandler == null) {
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sMainThreadHandler = thread.getHandler();
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}
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AsyncTask.init();
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if (false) {
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Looper.myLooper().setMessageLogging(new
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LogPrinter(Log.DEBUG, "ActivityThread"));
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}
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Looper.loop();
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throw new RuntimeException("Main thread loop unexpectedly exited");
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}
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}
该类中还有一个内部类ApplicationThread该类可以说是ActivityMangerService和应用程序通信的桥梁，private class ApplicationThread extends ApplicationThreadNative 该类是一个Binder类型结构的，用于通信，可以说是操作应用程序的命令的发送者。