SystemServer process

android12-release
Android The system starts
Zygote process

---

Zygote process fork And come

init process -> Zygote process -> system_server process

frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
frameworks/base/core/java/com/android/internal/os/Zygote.java
frameworks/base/core/jni/com_android_internal_os_Zygote.cpp
art/runtime/native/dalvik_system_ZygoteHooks.cc

forkSystemServer().run() -> pid = Zygote.forkSystemServer() -> nativeForkSystemServer() -> com_android_internal_os_Zygote_nativeForkSystemServer -> pid = zygote::ForkCommon() -> pid = fork() -> SpecializeCommon()

/* 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,"
                + "1024,1032,1065,3001,3002,3003,3006,3007,3009,3010,3011",
        "--capabilities=" + capabilities + "," + capabilities,
        "--nice-name=system_server",
        "--runtime-args",
        "--target-sdk-version=" + VMRuntime.SDK_VERSION_CUR_DEVELOPMENT,
        "com.android.server.SystemServer",
};
ZygoteArguments parsedArgs;

1. SystemServer The process parameter information is uid=1000,gid=1000, The process name is sytem_server

2. Zygote.forkSystemServer() fork Out system_server process
   

3. com_android_internal_os_Zygote_nativeForkSystemServer JNI zygote::ForkCommon() Call to fork() Create a new process , use copy on write The way , This is a linux Standard method for creating processes , There will be two return. The return value is 3 Types ： In parent process ,fork Returns the... Of the newly created child process pid; In subprocess ,fork return 0; When an error occurs ,fork Return negative .
   
   When system_server After the process dies , restart zygote process .

4. New creation system_server The process is complete ,pid == 0 Then enter handleSystemServerProcess() Method
   

handleSystemServerProcess

fork() Here we are system_server The process has completed all the work created , Here we go system_server The real work of the process

1. handleSystemServerProcess(parsedArgs) complete system_server Process remaining work , Running on the system_server process
2. Process.setArgV0(parsedArgs.mNiceName) Current process name "system_server"
3. performSystemServerDexOpt() perform dex Optimize operation , from installd To complete
4. system_server perform ZygoteInit.zygoteInit()

/** * Finish remaining work for the newly forked system server process. */
private static Runnable handleSystemServerProcess(ZygoteArguments parsedArgs) {
    
    // set umask to 0077 so new files and directories will default to owner-only permissions.
    Os.umask(S_IRWXG | S_IRWXO);

    if (parsedArgs.mNiceName != null) {
    
        Process.setArgV0(parsedArgs.mNiceName);
    }

    final String systemServerClasspath = Os.getenv("SYSTEMSERVERCLASSPATH");
    if (systemServerClasspath != null) {
    
        performSystemServerDexOpt(systemServerClasspath);
        // Capturing profiles is only supported for debug or eng builds since selinux normally
        // prevents it.
        if (shouldProfileSystemServer() && (Build.IS_USERDEBUG || Build.IS_ENG)) {
    
            try {
    
                Log.d(TAG, "Preparing system server profile");
                prepareSystemServerProfile(systemServerClasspath);
            } catch (Exception e) {
    
                Log.wtf(TAG, "Failed to set up system server profile", e);
            }
        }
    }

    if (parsedArgs.mInvokeWith != null) {
    
        String[] args = parsedArgs.mRemainingArgs;
        // 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.mInvokeWith,
                parsedArgs.mNiceName, parsedArgs.mTargetSdkVersion,
                VMRuntime.getCurrentInstructionSet(), null, args);

        throw new IllegalStateException("Unexpected return from WrapperInit.execApplication");
    } else {
    
        ClassLoader cl = getOrCreateSystemServerClassLoader();
        if (cl != null) {
    
            Thread.currentThread().setContextClassLoader(cl);
        }

        /* * Pass the remaining arguments to SystemServer. */
        return ZygoteInit.zygoteInit(parsedArgs.mTargetSdkVersion,
                parsedArgs.mDisabledCompatChanges,
                parsedArgs.mRemainingArgs, cl);
    }

    /* should never reach here */
}

ZygoteInit.zygoteInit()

1. ZygoteInit.nativeZygoteInit() stay AndroidRuntime.cpp in , the jni mapping
2. RuntimeInit.applicationInit() Meso endomorph MethodAndArgsCaller.run function mMethod.invoke() start-up SystemServer.main()
   

SystemServer.main

4.2 system service ： from SystemServer.java Be responsible for starting and managing the whole Java framework In the service startBootstrapServices、startCoreServices、startOtherServices

Sequence diagram