Android O系统启动流程--SystemServer篇一

private static Runnable forkSystemServer(String abiList, String socketName,
            ZygoteServer zygoteServer) {
        ..
        try {
            //将上面准备的参数，按照ZygoteConnection的风格进行封装
            parsedArgs = new ZygoteConnection.Arguments(args);
            ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);
            ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);

            /* Request to fork the system server process */
            pid = Zygote.forkSystemServer(
                    parsedArgs.uid, parsedArgs.gid,
                    parsedArgs.gids,
                    parsedArgs.debugFlags,
                    null,
                    parsedArgs.permittedCapabilities,
                    parsedArgs.effectiveCapabilities);
        } catch (IllegalArgumentException ex) {
            throw new RuntimeException(ex);
        }

        /* For child process */
        if (pid == 0) {
            //处理32_64和64_32的情况
            if (hasSecondZygote(abiList)) {
                waitForSecondaryZygote(socketName);
            }
            // fork时会copy socket，system server需要主动关闭
            zygoteServer.closeServerSocket();
            return handleSystemServerProcess(parsedArgs);
        }

        return null;
}

public static int forkSystemServer(int uid, int gid, int[] gids, int debugFlags,
            int[][] rlimits, long permittedCapabilities, long effectiveCapabilities) {
        VM_HOOKS.preFork();
        // Resets nice priority for zygote process.
        resetNicePriority();
        // 调用native方法fork system_server
        int pid = nativeForkSystemServer(
                uid, gid, gids, debugFlags, rlimits, permittedCapabilities, effectiveCapabilities);
        // Enable tracing as soon as we enter the system_server.
        if (pid == 0) {
            Trace.setTracingEnabled(true, debugFlags);
        }
        VM_HOOKS.postForkCommon();
        return pid;
}

private static Runnable handleSystemServerProcess(ZygoteConnection.Arguments parsedArgs) {
        // set umask to 0077 so new files and directories will default to owner-only permissions.
        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) {
            //执行dex优化操作
            performSystemServerDexOpt(systemServerClasspath);
        ...
        if (parsedArgs.invokeWith != null) {
            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;
            }
            //启动应用进程
            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，并赋予当前线程
                cl = createPathClassLoader(systemServerClasspath, parsedArgs.targetSdkVersion);

                Thread.currentThread().setContextClassLoader(cl);
            }

            /*
             * Pass the remaining arguments to SystemServer.
             */
            //system_server故进入此分支，初始化zygoteInit
            return ZygoteInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);
        }

        /* should never reach here */
}

private static void performSystemServerDexOpt(String classPath) {
    final String[] classPathElements = classPath.split(":");
    final IInstalld installd = IInstalld.Stub
                .asInterface(ServiceManager.getService("installd"));
            ...
            if (dexoptNeeded != DexFile.NO_DEXOPT_NEEDED) {
                final String packageName = "*";
                final String outputPath = null;
                final int dexFlags = 0;
                final String compilerFilter = systemServerFilter;
                final String uuid = StorageManager.UUID_PRIVATE_INTERNAL;
                final String seInfo = null;
                final String classLoaderContext =
                        getSystemServerClassLoaderContext(classPathForElement);
                try {
                    //以system权限，执行dex文件优化
                    installd.dexopt(classPathElement, Process.SYSTEM_UID, packageName,
                            instructionSet, dexoptNeeded, outputPath, dexFlags, compilerFilter,
                            uuid, classLoaderContext, seInfo, false /* downgrade */);
                } catch (RemoteException | ServiceSpecificException e) {
                    // Ignore (but log), we need this on the classpath for fallback mode.
                    Log.w(TAG, "Failed compiling classpath element for system server: "
                            + classPathElement, e);
                }
            }

            classPathForElement = encodeSystemServerClassPath(
                    classPathForElement, classPathElement);
        }
}

public static final Runnable zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) {
        if (RuntimeInit.DEBUG) {
            Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote");
        }

        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");
        RuntimeInit.redirectLogStreams();
        //通用的一些初始化
        RuntimeInit.commonInit();
        //启动Binder线程池
        ZygoteInit.nativeZygoteInit();
        //执行SystemServer的main方法
        return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);
}

protected static Runnable applicationInit(int targetSdkVersion, String[] argv,
            ClassLoader classLoader) {
        // If the application calls System.exit(), terminate the process
        // immediately without running any shutdown hooks.  It is not possible to
        // shutdown an Android application gracefully.  Among other things, the
        // Android runtime shutdown hooks close the Binder driver, which can cause
        // leftover running threads to crash before the process actually exits.
        nativeSetExitWithoutCleanup(true);

        // We want to be fairly aggressive about heap utilization, to avoid
        // holding on to a lot of memory that isn't needed.
        VMRuntime.getRuntime().setTargetHeapUtilization(0.75f);
        VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion);

        final Arguments args = new Arguments(argv);

        // The end of of the RuntimeInit event (see #zygoteInit).
        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

        // Remaining arguments are passed to the start class's static main
        return findStaticMain(args.startClass, args.startArgs, classLoader);
}

private static Runnable findStaticMain(String className, String[] argv,
            ClassLoader classLoader) {
        Class<?> cl;

        try {
            cl = Class.forName(className, true, classLoader);
        } catch (ClassNotFoundException ex) {
            throw new RuntimeException(
                    "Missing class when invoking static main " + className,
                    ex);
        }

        Method m;
        try {
            //通过反射，获取SystemServer类的main方法
            m = cl.getMethod("main", new Class[] { String[].class });
        } catch (NoSuchMethodException ex) {
            throw new RuntimeException(
                    "Missing static main on " + className, ex);
        } catch (SecurityException ex) {
            throw new RuntimeException(
                    "Problem getting static main on " + className, ex);
        }

        int modifiers = m.getModifiers();
        if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
            throw new RuntimeException(
                    "Main method is not public and static on " + className);
        }

        /*
         * This throw gets caught in ZygoteInit.main(), which responds
         * by invoking the exception's run() method. This arrangement
         * clears up all the stack frames that were required in setting
         * up the process.
         */
        return new MethodAndArgsCaller(m, argv);
}

static class MethodAndArgsCaller implements Runnable {
        /** method to call */
        private final Method mMethod;

        /** argument array */
        private final String[] mArgs;

        public MethodAndArgsCaller(Method method, String[] args) {
            mMethod = method;
            mArgs = args;
        }

        public void run() {
            try {
                mMethod.invoke(null, new Object[] { mArgs });
            } catch (IllegalAccessException ex) {
                throw new RuntimeException(ex);
            } catch (InvocationTargetException ex) {
                Throwable cause = ex.getCause();
                if (cause instanceof RuntimeException) {
                    throw (RuntimeException) cause;
                } else if (cause instanceof Error) {
                    throw (Error) cause;
                }
                throw new RuntimeException(ex);
            }
        }
}