android8.1启动过程(七) SystemServer

最新推荐文章于 2023-11-15 16:14:23 发布

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最新推荐文章于 2023-11-15 16:14:23 发布 · 599 阅读

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#framework #android

本文详细解析了Android系统启动过程中，Zygote进程如何孵化SystemServer进程的过程。从ZygoteInit.java的forkSystemServer方法开始，通过参数解析创建SystemServer进程，接着调用nativeZygoteInit启动Binder线程池，最终通过反射调用SystemServer的main方法，启动系统服务。

本文承接上一篇文章android8.1启动过程(六) zygote进程分析2_we1less的博客-优快云博客

SystemServer进程主要用于创建系统服务，AMS、WMS、PMS都是由它来创建的

在上一篇说道启动systemserver

启动systemserver AOSP/frameworks/base/core/java/com/android/internal/os/ZygoteInit.java

if (startSystemServer) {
    Runnable r = forkSystemServer(abiList, socketName, zygoteServer);
 
    // {@code r == null} in the parent (zygote) process, and {@code r != null} in the
    // child (system_server) process.
    if (r != null) {
        r.run();
        return;
    }
}

forkSystemServer

private static Runnable forkSystemServer(String abiList, String socketName,
            ZygoteServer zygoteServer) {
        ...

        /* Hardcoded command line to start the system server */
        String args[] = {
            "--setuid=1000",
            "--setgid=1000",
            "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,1032,3001,3002,3003,3006,3007,3009,3010",
            "--capabilities=" + capabilities + "," + capabilities,
            "--nice-name=system_server",
            "--runtime-args",
            "com.android.server.SystemServer",
        };
        ZygoteConnection.Arguments parsedArgs = null;

        int pid;

        try {
            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) {
            if (hasSecondZygote(abiList)) {
                waitForSecondaryZygote(socketName);
            }

            zygoteServer.closeServerSocket();
            return handleSystemServerProcess(parsedArgs);
        }

        return null;
    }

【1】ZygoteConnection.Arguments(args); AOSP/frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java 里面的一个静态内部类它将上述String数组中的参数传递进去

class ZygoteConnection {
    private static final String TAG = "Zygote";
    ...
    static class Arguments {
        ...
        Arguments(String args[]) throws IllegalArgumentException {
            parseArgs(args);
        }
        ...      
    }  
}

parseArgs 传递的参数就是

String args[] = {
            "--setuid=1000",
            "--setgid=1000",
            "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,1032,3001,3002,3003,3006,3007,3009,3010",
            "--capabilities=" + capabilities + "," + capabilities,
            "--nice-name=system_server",
            "--runtime-args",
&nb