android8.1启动过程(十) SystemServer启动FallbackHome2

Android跨进程通信及相关方法调用分析

最新推荐文章于 2024-07-15 00:24:45 发布

原创

最新推荐文章于 2024-07-15 00:24:45 发布 · 2.2k 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#android

本文结合相关文章，详细分析了Android利用Socket进行跨进程通信的过程。涉及startViaZygote、zygoteSendArgsAndGetResult等方法调用，还阐述了反射调用android.app.ActivityThread的main函数，以及后续双向通信、消息发送等操作，最终实现Activity的启动调度。

本篇结合上一篇https://blog.youkuaiyun.com/we1less/article/details/117485532?spm=1001.2014.3001.5501

上一篇方法最后调用了

startViaZygote(processClass, niceName, uid, gid, gids, debugFlags, mountExternal, targetSdkVersion, seInfo, abi, instructionSet, appDataDir, invokeWith, zygoteArgs);

startViaZygote() frameworks/base/core/java/android/os/ZygoteProcess.java

最后调用了 zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);

注意这块在函数参数部分调用了openZygoteSocketIfNeeded(abi)

    private Process.ProcessStartResult startViaZygote(final String processClass,
                                                      final String niceName,
                                                      final int uid, final int gid,
                                                      final int[] gids,
                                                      int debugFlags, int mountExternal,
                                                      int targetSdkVersion,
                                                      String seInfo,
                                                      String abi,
                                                      String instructionSet,
                                                      String appDataDir,
                                                      String invokeWith,
                                                      String[] extraArgs)
                                                      throws ZygoteStartFailedEx {
        ArrayList<String> argsForZygote = new ArrayList<String>();

        // --runtime-args, --setuid=, --setgid=,
        // and --setgroups= must go first
        argsForZygote.add("--runtime-args");
        argsForZygote.add("--setuid=" + uid);
        argsForZygote.add("--setgid=" + gid);
        ...//以下省略配置参数

        synchronized(mLock) {
            return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);
        }
    }

zygoteSendArgsAndGetResult() frameworks/base/core/java/android/os/ZygoteProcess.java

见名知其意发送参数(就是上面方法配置的)、返回结果在这里就指代与Socket通信

    @GuardedBy("mLock")
    private static Process.ProcessStartResult zygoteSendArgsAndGetResult(
            ZygoteState zygoteState, ArrayList<String> args)
            throws ZygoteStartFailedEx {
        try {
            ...
            final BufferedWriter writer = zygoteState.writer;
            final DataInputStream inputStream = zygoteState.inputStream;

            writer.write(Integer.toString(args.size()));
            writer.newLine();

            for (int i = 0; i < sz; i++) {
                String arg = args.get(i);
                writer.write(arg);
                writer.newLine();
            }

            writer.flush();
            ...
            result.pid = inputStream.readInt();
            result.usingWrapper = inputStream.readBoolean();

            if (result.pid < 0) {
                throw new ZygoteStartFailedEx("fork() failed");
            }
            return result;
        } catch (IOException ex) {
            zygoteState.close();
            throw new ZygoteStartFailedEx(ex);
        }
    }

上面代码中的zygoteState.writer是被封装在frameworks/base/core/java/android/os/ZygoteProcess.java类

里面的一个静态内部类public static class ZygoteState

其构造器是这样的

private ZygoteState(LocalSocket socket, DataInputStream inputStream,
                BufferedWriter writer, List<String> abiList) {
            this.socket = socket;
            this.i