android.os.Build#IS_USERDEBUG源码实例Demo

@Override
public boolean isRuntimeProfilingEnabled(@ProfileType int profileType, String callingPackage) {
    int callingUid = Binder.getCallingUid();
    if (callingUid != Process.SHELL_UID && !checkAndroidPermissions(callingUid, callingPackage)) {
        return false;
    }

    switch (profileType) {
        case ArtManager.PROFILE_APPS :
            return SystemProperties.getBoolean("dalvik.vm.usejitprofiles", false);
        case ArtManager.PROFILE_BOOT_IMAGE:
            return (Build.IS_USERDEBUG || Build.IS_ENG) &&
                    SystemProperties.getBoolean("dalvik.vm.usejitprofiles", false) &&
                    SystemProperties.getBoolean("dalvik.vm.profilebootimage", false);
        default:
            throw new IllegalArgumentException("Invalid profile type:" + profileType);
    }
}
 

private static boolean isDisabled() {
    // Check if we're explicitly enabled for testing
    if (SystemProperties.getBoolean(PROP_ENABLE_RESCUE, false)) {
        return false;
    }

    // We're disabled on all engineering devices
    if (Build.IS_ENG) {
        Slog.v(TAG, "Disabled because of eng build");
        return true;
    }

    // We're disabled on userdebug devices connected over USB, since that's
    // a decent signal that someone is actively trying to debug the device,
    // or that it's in a lab environment.
    if (Build.IS_USERDEBUG && isUsbActive()) {
        Slog.v(TAG, "Disabled because of active USB connection");
        return true;
    }

    // One last-ditch check
    if (SystemProperties.getBoolean(PROP_DISABLE_RESCUE, false)) {
        Slog.v(TAG, "Disabled because of manual property");
        return true;
    }

    return false;
}
 

/**
 * Finish remaining work for the newly forked system server process.
 */
private static Runnable handleSystemServerProcess(ZygoteConnection.Arguments parsedArgs) {
    // set umask to 0077 so new files and directories will default to owner-only permissions.
    // umask一般是用在你初始创建一个目录或者文件的时候赋予他们的权限
    Os.umask(S_IRWXG | S_IRWXO);

    // 设置当前进程名为 "system_server"
    if (parsedArgs.niceName != null) { 
        Process.setArgV0(parsedArgs.niceName);
    }

    final String systemServerClasspath = Os.getenv("SYSTEMSERVERCLASSPATH");
    if (systemServerClasspath != null) {
        // dex 优化操作
        performSystemServerDexOpt(systemServerClasspath);
        // Capturing profiles is only supported for debug or eng builds since selinux normally
        // prevents it.
        boolean profileSystemServer = SystemProperties.getBoolean(
                "dalvik.vm.profilesystemserver", false);
        if (profileSystemServer && (Build.IS_USERDEBUG || Build.IS_ENG)) {
            try {
                prepareSystemServerProfile(systemServerClasspath);
            } catch (Exception e) {
                Log.wtf(TAG, "Failed to set up system server profile", e);
            }
        }
    }

    if (parsedArgs.invokeWith != null) { // invokeWith 一般为空
        String[] args = parsedArgs.remainingArgs;
        // If we have a non-null system server class path, we'll have to duplicate the
        // existing arguments and append the classpath to it. ART will handle the classpath
        // correctly when we exec a new process.
        if (systemServerClasspath != null) {
            String[] amendedArgs = new String[args.length + 2];
            amendedArgs[0] = "-cp";
            amendedArgs[1] = systemServerClasspath;
            System.arraycopy(args, 0, amendedArgs, 2, args.length);
            args = amendedArgs;
        }

        WrapperInit.execApplication(parsedArgs.invokeWith,
                parsedArgs.niceName, parsedArgs.targetSdkVersion,
                VMRuntime.getCurrentInstructionSet(), null, args);

        throw new IllegalStateException("Unexpected return from WrapperInit.execApplication");
    } else {
        ClassLoader cl = null;
        if (systemServerClasspath != null) {
            // 创建类加载器，并赋给当前线程
            cl = createPathClassLoader(systemServerClasspath, parsedArgs.targetSdkVersion);
            
            Thread.currentThread().setContextClassLoader(cl);
        }

        /*
         * Pass the remaining arguments to SystemServer.
         */
        return ZygoteInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);
    }

    /* should never reach here */
}