android sharedUserId 使用知识盲点解析

private void initializeJavaContextClassLoader() {
	IPackageManager pm = ActivityThread.getPackageManager();
	android.content.pm.PackageInfo pi =
			PackageManager.getPackageInfoAsUserCached(
					mPackageName,
					PackageManager.MATCH_DEBUG_TRIAGED_MISSING,
					UserHandle.myUserId());
	if (pi == null) {
		throw new IllegalStateException("Unable to get package info for "
				+ mPackageName + "; is package not installed?");
	}
	/*
	 * Two possible indications that this package could be
	 * sharing its virtual machine with other packages:
	 *
	 * 1.) the sharedUserId attribute is set in the manifest,
	 *     indicating a request to share a VM with other
	 *     packages with the same sharedUserId.
	 *
	 * 2.) the application element of the manifest has an
	 *     attribute specifying a non-default process name,
	 *     indicating the desire to run in another packages VM.
	 */
	boolean sharedUserIdSet = (pi.sharedUserId != null);
	boolean processNameNotDefault =
		(pi.applicationInfo != null &&
		 !mPackageName.equals(pi.applicationInfo.processName));
	boolean sharable = (sharedUserIdSet || processNameNotDefault);
	ClassLoader contextClassLoader =
		(sharable)
		? new WarningContextClassLoader()
		: mClassLoader;
	Thread.currentThread().setContextClassLoader(contextClassLoader);
}
private static class WarningContextClassLoader extends ClassLoader {
	private static boolean warned = false;
	private void warn(String methodName) {
		if (warned) {
			return;
		}
		warned = true;
		Thread.currentThread().setContextClassLoader(getParent());
		Slog.w(ActivityThread.TAG, "ClassLoader." + methodName + ": " +
			  "The class loader returned by " +
			  "Thread.getContextClassLoader() may fail for processes " +
			  "that host multiple applications. You should explicitly " +
			  "specify a context class loader. For example: " +
			  "Thread.setContextClassLoader(getClass().getClassLoader());");
	}
	...
}