Android系统启动——4 zyogte进程 (C篇)

import /init.${ro.zygote}.rc

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
    class main
    socket zygote stream 660 root system
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart media
    onrestart restart netd
    writepid /dev/cpuset/foreground/tasks

service zygote /system/bin/app_process32 -Xzygote /system/bin --zygote --start-system-server --socket-name=zygote
    class main
    socket zygote stream 660 root system
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart media
    onrestart restart netd
    writepid /dev/cpuset/foreground/tasks

service zygote_secondary /system/bin/app_process64 -Xzygote /system/bin --zygote --socket-name=zygote_secondary
    class main
    socket zygote_secondary stream 660 root system
    onrestart restart zygote
    writepid /dev/cpuset/foreground/tasks

    socket zygote stream 660 root system

void service_start(struct service *svc, const char *dynamic_args)
{
    //*****************  第1步 ***********************
    // Starting a service removes it from the disabled or reset state and
    // immediately takes it out of the restarting state if it was in there.
     // 状态重置
    svc->flags &= (~(SVC_DISABLED|SVC_RESTARTING|SVC_RESET|SVC_RESTART|SVC_DISABLED_START));

    // 初始化启动时间，开始计时
    svc->time_started = 0;

    // Running processes require no additional work --- if they're in the
    // process of exiting, we've ensured that they will immediately restart
    // on exit, unless they are ONESHOT.
    // 排除正在运行的service
    if (svc->flags & SVC_RUNNING) {
        return;
    }

    //*****************  第2步 ***********************
    // 如果是需要控制台的环境，但是还没有控制台，则设置SVC_DISABLED标志，后返回
    bool needs_console = (svc->flags & SVC_CONSOLE);
    if (needs_console && !have_console) {
        ERROR("service '%s' requires console\n", svc->name);
        svc->flags |= SVC_DISABLED;
        return;
    }

   //*****************  第3步 ***********************
    struct stat s;

     // 在parse_service中构建service的过程中，会将配置文件中的service文件路径名赋值给svc->args  
     //然后这个李判断可执行文件是否存在
    if (stat(svc->args[0], &s) != 0) {
        ERROR("cannot find '%s', disabling '%s'\n", svc->args[0], svc->name);
        svc->flags |= SVC_DISABLED;
        return;
    }

   //*****************  第4步 ***********************
    // 如果是SVC_ONESHOT 则表示该service退出后，不能再次运行
    if ((!(svc->flags & SVC_ONESHOT)) && dynamic_args) {
        ERROR("service '%s' must be one-shot to use dynamic args, disabling\n",
               svc->args[0]);
        svc->flags |= SVC_DISABLED;
        return;
    }

   //*****************  第5步 ***********************
    char* scon = NULL;

   // 是否开启了selinux
    if (is_selinux_enabled() > 0) {
       // 如果 init.rc中已经制定了安全上下文
        if (svc->seclabel) {
            // 复制一份
            scon = strdup(svc->seclabel);
            if (!scon) {
                ERROR("Out of memory while starting '%s'\n", svc->name);
                return;
            }
        } else {
            char *mycon = NULL, *fcon = NULL;

            INFO("computing context for service '%s'\n", svc->args[0]);

            // 获取当前init进程的安全上下文
            int rc = getcon(&mycon);
            if (rc < 0) {
                ERROR("could not get context while starting '%s'\n", svc->name);
                return;
            }

            // 获取可执行文件的安全上下文
            rc = getfilecon(svc->args[0], &fcon);
            if (rc < 0) {
                ERROR("could not get context while starting '%s'\n", svc->name);
                freecon(mycon);
                return;
            }

            // 计算守护进程的安全上下文
            rc = security_compute_create(mycon, fcon, string_to_security_class("process"), &scon);
            if (rc == 0 && !strcmp(scon, mycon)) {
                ERROR("Warning!  Service %s needs a SELinux domain defined; please fix!\n", svc->name);
            }
            freecon(mycon);
            freecon(fcon);
            if (rc < 0) {
                ERROR("could not get context while starting '%s'\n", svc->name);
                return;
            }
        }
    }

    NOTICE("Starting service '%s'...\n", svc->name);

   //*****************  第6步 ***********************
    // fork一个新进程 
    pid_t pid = fork();

    // pid为0 表示子进程运行空间
    if (pid == 0) {
        struct socketinfo *si;
        struct svcenvinfo *ei;
        char tmp[32];
        int fd, sz;

        umask(077);

         //*****************  第7步 ***********************
        //如果 属性已经被初始化了
        if (properties_initialized()) {
 
            // 增加一个property属性，用文件描述符做key，大小做value
            get_property_workspace(&fd, &sz);
            snprintf(tmp, sizeof(tmp), "%d,%d", dup(fd), sz);

            // 增加一个环境变量
            add_environment("ANDROID_PROPERTY_WORKSPACE", tmp);
        }

        // 在配置文件中，service 通过setenv设置envvars
        for (ei = svc->envvars; ei; ei = ei->next)
            add_environment(ei->name, ei->value);

         //*****************  第8步 ***********************

        // 在init.rc配置文件中，通过sokcet关键字 设置service的socket
        for (si = svc->sockets; si; si = si->next) {
             int socket_type = (
                    !strcmp(si->type, "stream") ? SOCK_STREAM :
                        (!strcmp(si->type, "dgram") ? SOCK_DGRAM : SOCK_SEQPACKET));

            // 创建socket
            int s = create_socket(si->name, socket_type,
                                  si->perm, si->uid, si->gid, si->socketcon ?: scon);
            if (s >= 0) {
                // 调用add_environment，ANDROID_SOCKET_%s(name)，s为文件描述符
                 // Zygote的socket的key 为ANDROID_SOCKET_zygote，就是这么创建的
                publish_socket(si->name, s);
            }
        }

        freecon(scon);
        scon = NULL;

        if (svc->writepid_files_) {
            std::string pid_str = android::base::StringPrintf("%d", pid);
            for (auto& file : *svc->writepid_files_) {
                if (!android::base::WriteStringToFile(pid_str, file)) {
                    ERROR("couldn't write %s to %s: %s\n",
                          pid_str.c_str(), file.c_str(), strerror(errno));
                }
            }
        }

        if (svc->ioprio_class != IoSchedClass_NONE) {
            if (android_set_ioprio(getpid(), svc->ioprio_class, svc->ioprio_pri)) {
                ERROR("Failed to set pid %d ioprio = %d,%d: %s\n",
                      getpid(), svc->ioprio_class, svc->ioprio_pri, strerror(errno));
            }
        }

         //*****************  第9步 ***********************
       // 如果还是用新的控制台
        if (needs_console) {
            setsid();
            // 打开设备文件"/dev/sonsole"
            open_console();
        } else {
            //重定向到设备文件"/dev/null"
            zap_stdio();
        }

        if (false) {
            for (size_t n = 0; svc->args[n]; n++) {
                INFO("args[%zu] = '%s'\n", n, svc->args[n]);
            }
            for (size_t n = 0; ENV[n]; n++) {
                INFO("env[%zu] = '%s'\n", n, ENV[n]);
            }
        }

        // 因为第一个参数为0，所以将当前进程的pgid设置成自己的pid
        setpgid(0, getpid());

        // As requested, set our gid, supplemental gids, and uid.
        if (svc->gid) {
            if (setgid(svc->gid) != 0) {
                ERROR("setgid failed: %s\n", strerror(errno));
                _exit(127);
            }
        }
        if (svc->nr_supp_gids) {
            if (setgroups(svc->nr_supp_gids, svc->supp_gids) != 0) {
                ERROR("setgroups failed: %s\n", strerror(errno));
                _exit(127);
            }
        }
        if (svc->uid) {
            if (setuid(svc->uid) != 0) {
                ERROR("setuid failed: %s\n", strerror(errno));
                _exit(127);
            }
        }
        if (svc->seclabel) {
            if (is_selinux_enabled() > 0 && setexeccon(svc->seclabel) < 0) {
                ERROR("cannot setexeccon('%s'): %s\n", svc->seclabel, strerror(errno));
                _exit(127);
            }
        }

       //*****************  第10步 ***********************
        if (!dynamic_args) {
            // 静态调用execve函数
            if (execve(svc->args[0], (char**) svc->args, (char**) ENV) < 0) {
                ERROR("cannot execve('%s'): %s\n", svc->args[0], strerror(errno));
            }
        } else {
            // 动态调用execve函数
            char *arg_ptrs[INIT_PARSER_MAXARGS+1];
            int arg_idx = svc->nargs;
            char *tmp = strdup(dynamic_args);
            char *next = tmp;
            char *bword;

            /* Copy the static arguments */
            memcpy(arg_ptrs, svc->args, (svc->nargs * sizeof(char *)));

            while((bword = strsep(&next, " "))) {
                arg_ptrs[arg_idx++] = bword;
                if (arg_idx == INIT_PARSER_MAXARGS)
                    break;
            }
            arg_ptrs[arg_idx] = NULL;
            execve(svc->args[0], (char**) arg_ptrs, (char**) ENV);
        }
        _exit(127);
    }

    freecon(scon);

    // 如果子进程创建失败
    if (pid < 0) {
        ERROR("failed to start '%s'\n", svc->name);
        svc->pid = 0;
        return;
    }

    //*****************  第11步 ***********************
    // init程序作为父进程，则设置相应service的几个属性：启动时间、pid、RUNNING标志
    svc->time_started = gettime();
    svc->pid = pid;
    svc->flags |= SVC_RUNNING;

    if ((svc->flags & SVC_EXEC) != 0) {
        INFO("SVC_EXEC pid %d (uid %d gid %d+%zu context %s) started; waiting...\n",
             svc->pid, svc->uid, svc->gid, svc->nr_supp_gids,
             svc->seclabel ? : "default");
        waiting_for_exec = true;
    }

    // 设置状态为running
    svc->NotifyStateChange("running");
}

int main(int argc, char* const argv[])
{

    // ******************** 第一部分 *********************
    if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0) {
        // Older kernels don't understand PR_SET_NO_NEW_PRIVS and return
        // EINVAL. Don't die on such kernels.
        if (errno != EINVAL) {
            LOG_ALWAYS_FATAL("PR_SET_NO_NEW_PRIVS failed: %s", strerror(errno));
            return 12;
        }
    }

    // ******************** 第二部分 *********************
    AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
    // Process command line arguments
    // ignore argv[0]
    argc--;
    argv++;

    // Everything up to '--' or first non '-' arg goes to the vm.
    //
    // The first argument after the VM args is the "parent dir", which
    // is currently unused.
    //
    // After the parent dir, we expect one or more the following internal
    // arguments :
    //
    // --zygote : Start in zygote mode
    // --start-system-server : Start the system server.
    // --application : Start in application (stand alone, non zygote) mode.
    // --nice-name : The nice name for this process.
    //
    // For non zygote starts, these arguments will be followed by
    // the main class name. All remaining arguments are passed to
    // the main method of this class.
    //
    // For zygote starts, all remaining arguments are passed to the zygote.
    // main function.
    //
    // Note that we must copy argument string values since we will rewrite the
    // entire argument block when we apply the nice name to argv0.


     // ******************** 第三部分 *********************  
    int i;
    for (i = 0; i < argc; i++) {
        if (argv[i][0] != '-') {
            break;
        }
        if (argv[i][1] == '-' && argv[i][2] == 0) {
            ++i; // Skip --.
            break;
        }
        runtime.addOption(strdup(argv[i]));
    }

    // Parse runtime arguments.  Stop at first unrecognized option.
    bool zygote = false;
    bool startSystemServer = false;
    bool application = false;
    String8 niceName;
    String8 className;

     // ******************** 第四部分 *********************  
    ++i;  // Skip unused "parent dir" argument.
    while (i < argc) {
        const char* arg = argv[i++];
        if (strcmp(arg, "--zygote") == 0) {
            zygote = true;
            niceName = ZYGOTE_NICE_NAME;
        } else if (strcmp(arg, "--start-system-server") == 0) {
            startSystemServer = true;
        } else if (strcmp(arg, "--application") == 0) {
            application = true;
        } else if (strncmp(arg, "--nice-name=", 12) == 0) {
            niceName.setTo(arg + 12);
        } else if (strncmp(arg, "--", 2) != 0) {
            className.setTo(arg);
            break;
        } else {
            --i;
            break;
        }
    }


     // ******************** 第五部分 *********************  
    Vector<String8> args;
    if (!className.isEmpty()) {
        // We're not in zygote mode, the only argument we need to pass
        // to RuntimeInit is the application argument.
        //
        // The Remainder of args get passed to startup class main(). Make
        // copies of them before we overwrite them with the process name.
        args.add(application ? String8("application") : String8("tool"));
        runtime.setClassNameAndArgs(className, argc - i, argv + i);
    } else {
        // We're in zygote mode.
        maybeCreateDalvikCache();

        if (startSystemServer) {
            args.add(String8("start-system-server"));
        }

        char prop[PROP_VALUE_MAX];
        if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {
            LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.",
                ABI_LIST_PROPERTY);
            return 11;
        }

        String8 abiFlag("--abi-list=");
        abiFlag.append(prop);
        args.add(abiFlag);

        // In zygote mode, pass all remaining arguments to the zygote
        // main() method.
        for (; i < argc; ++i) {
            args.add(String8(argv[i]));
        }
    }

     // ******************** 第六部分 *********************  
    if (!niceName.isEmpty()) {
        runtime.setArgv0(niceName.string());
        set_process_name(niceName.string());
    }

     // ******************** 第七部分 *********************  
    if (zygote) {
        runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
    } else if (className) {
        runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
    } else {
        fprintf(stderr, "Error: no class name or --zygote supplied.\n");
        app_usage();
        LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
        return 10;
    }
}

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
    class main
    socket zygote stream 660 root system
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart media
    onrestart restart netd
    writepid /dev/cpuset/foreground/tasks

class AppRuntime : public AndroidRuntime
{
public:
    AppRuntime(char* argBlockStart, const size_t argBlockLength)
        : AndroidRuntime(argBlockStart, argBlockLength)
        , mClass(NULL)
    {
    }

    void setClassNameAndArgs(const String8& className, int argc, char * const *argv) {
        mClassName = className;
        for (int i = 0; i < argc; ++i) {
             mArgs.add(String8(argv[i]));
        }
    }

    virtual void onVmCreated(JNIEnv* env)
    {
        if (mClassName.isEmpty()) {
            return; // Zygote. Nothing to do here.
        }

        /*
         * This is a little awkward because the JNI FindClass call uses the
         * class loader associated with the native method we're executing in.
         * If called in onStarted (from RuntimeInit.finishInit because we're
         * launching "am", for example), FindClass would see that we're calling
         * from a boot class' native method, and so wouldn't look for the class
         * we're trying to look up in CLASSPATH. Unfortunately it needs to,
         * because the "am" classes are not boot classes.
         *
         * The easiest fix is to call FindClass here, early on before we start
         * executing boot class Java code and thereby deny ourselves access to
         * non-boot classes.
         */
        char* slashClassName = toSlashClassName(mClassName.string());
        mClass = env->FindClass(slashClassName);
        if (mClass == NULL) {
            ALOGE("ERROR: could not find class '%s'\n", mClassName.string());
        }
        free(slashClassName);

        mClass = reinterpret_cast<jclass>(env->NewGlobalRef(mClass));
    }

    virtual void onStarted()
    {
        sp<ProcessState> proc = ProcessState::self();
        ALOGV("App process: starting thread pool.\n");
        proc->startThreadPool();

        AndroidRuntime* ar = AndroidRuntime::getRuntime();
        ar->callMain(mClassName, mClass, mArgs);

        IPCThreadState::self()->stopProcess();
    }

    virtual void onZygoteInit()
    {
        sp<ProcessState> proc = ProcessState::self();
        ALOGV("App process: starting thread pool.\n");
        proc->startThreadPool();
    }

    virtual void onExit(int code)
    {
        if (mClassName.isEmpty()) {
            // if zygote
            IPCThreadState::self()->stopProcess();
        }

        AndroidRuntime::onExit(code);
    }


    String8 mClassName;
    Vector<String8> mArgs;
    jclass mClass;
};

AndroidRuntime::AndroidRuntime(char* argBlockStart, const size_t argBlockLength) :
        mExitWithoutCleanup(false),
        mArgBlockStart(argBlockStart),
        mArgBlockLength(argBlockLength)
{
    SkGraphics::Init();
    // There is also a global font cache, but its budget is specified by
    // SK_DEFAULT_FONT_CACHE_COUNT_LIMIT and SK_DEFAULT_FONT_CACHE_LIMIT.

    // Pre-allocate enough space to hold a fair number of options.    
    mOptions.setCapacity(20);
    

    assert(gCurRuntime == NULL);        // one per process
    gCurRuntime = this;
}

/*
 * Start the Android runtime.  This involves starting the virtual machine
 * and calling the "static void main(String[] args)" method in the class
 * named by "className".
 *
 * Passes the main function two arguments, the class name and the specified
 * options string.
 */
void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
    //******************* 第一部分**********************
    ALOGD(">>>>>> START %s uid %d <<<<<<\n",
            className != NULL ? className : "(unknown)", getuid());

    static const String8 startSystemServer("start-system-server");

    /*
     * 'startSystemServer == true' means runtime is obsolete and not run from
     * init.rc anymore, so we print out the boot start event here.
     */
    for (size_t i = 0; i < options.size(); ++i) {
        if (options[i] == startSystemServer) {
           /* track our progress through the boot sequence */
           const int LOG_BOOT_PROGRESS_START = 3000;
           LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START,  ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));
        }
    }

     //******************* 第二部分**********************
    const char* rootDir = getenv("ANDROID_ROOT");
    if (rootDir == NULL) {
        rootDir = "/system";
        if (!hasDir("/system")) {
            LOG_FATAL("No root directory specified, and /android does not exist.");
            return;
        }
        setenv("ANDROID_ROOT", rootDir, 1);
    }

    //const char* kernelHack = getenv("LD_ASSUME_KERNEL");
    //ALOGD("Found LD_ASSUME_KERNEL='%s'\n", kernelHack);


    //******************* 第三部分**********************
    /* start the virtual machine */
    JniInvocation jni_invocation;
    jni_invocation.Init(NULL);
    JNIEnv* env;
    if (startVm(&mJavaVM, &env, zygote) != 0) {
        return;
    }

    //******************* 第四部分**********************
    onVmCreated(env);


    //******************* 第五部分**********************
    /*
     * Register android functions.
     */
    if (startReg(env) < 0) {
        ALOGE("Unable to register all android natives\n");
        return;
    }

   //******************* 第六部分**********************
    /*
     * We want to call main() with a String array with arguments in it.
     * At present we have two arguments, the class name and an option string.
     * Create an array to hold them.
     */
    jclass stringClass;
    jobjectArray strArray;
    jstring classNameStr;

    stringClass = env->FindClass("java/lang/String");
    assert(stringClass != NULL);
    strArray = env->NewObjectArray(options.size() + 1, stringClass, NULL);
    assert(strArray != NULL);
    classNameStr = env->NewStringUTF(className);
    assert(classNameStr != NULL);
    env->SetObjectArrayElement(strArray, 0, classNameStr);

    for (size_t i = 0; i < options.size(); ++i) {
        jstring optionsStr = env->NewStringUTF(options.itemAt(i).string());
        assert(optionsStr != NULL);
        env->SetObjectArrayElement(strArray, i + 1, optionsStr);
    }


   //******************* 第七部分**********************
    /*
     * Start VM.  This thread becomes the main thread of the VM, and will
     * not return until the VM exits.
     */
    char* slashClassName = toSlashClassName(className);
    jclass startClass = env->FindClass(slashClassName);
    if (startClass == NULL) {
        ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);
        /* keep going */
    } else {
        jmethodID startMeth = env->GetStaticMethodID(startClass, "main",
            "([Ljava/lang/String;)V");
        if (startMeth == NULL) {
            ALOGE("JavaVM unable to find main() in '%s'\n", className);
            /* keep going */
        } else {
            env->CallStaticVoidMethod(startClass, startMeth, strArray);

#if 0
            if (env->ExceptionCheck())
                threadExitUncaughtException(env);
#endif
        }
    }
    free(slashClassName);

    ALOGD("Shutting down VM\n");
    if (mJavaVM->DetachCurrentThread() != JNI_OK)
        ALOGW("Warning: unable to detach main thread\n");
    if (mJavaVM->DestroyJavaVM() != 0)
        ALOGW("Warning: VM did not shut down cleanly\n");
}

    virtual void onVmCreated(JNIEnv* env)
    {
        if (mClassName.isEmpty()) {
            return; // Zygote. Nothing to do here.
        }

        /*
         * This is a little awkward because the JNI FindClass call uses the
         * class loader associated with the native method we're executing in.
         * If called in onStarted (from RuntimeInit.finishInit because we're
         * launching "am", for example), FindClass would see that we're calling
         * from a boot class' native method, and so wouldn't look for the class
         * we're trying to look up in CLASSPATH. Unfortunately it needs to,
         * because the "am" classes are not boot classes.
         *
         * The easiest fix is to call FindClass here, early on before we start
         * executing boot class Java code and thereby deny ourselves access to
         * non-boot classes.
         */
        char* slashClassName = toSlashClassName(mClassName.string());
        mClass = env->FindClass(slashClassName);
        if (mClass == NULL) {
            ALOGE("ERROR: could not find class '%s'\n", mClassName.string());
        }
        free(slashClassName);

        mClass = reinterpret_cast<jclass>(env->NewGlobalRef(mClass));
    }

bool JniInvocation::Init(const char* library) {
#ifdef HAVE_ANDROID_OS
  char buffer[PROPERTY_VALUE_MAX];
#else
  char* buffer = NULL;
#endif
  // 我们知道传入的library是null，所以最后应该是library是libart.so
  library = GetLibrary(library, buffer);

  // 通过dlopen加载libdvm.so，libdvm.so是dalvik vm的核心库
  handle_ = dlopen(library, RTLD_NOW);

  if (handle_ == NULL) {
    // 如果打开libart.so失败，则直接返回。如果打开其他library失败在，额尝试打开libart.so
    if (strcmp(library, kLibraryFallback) == 0) {
      // Nothing else to try.
      ALOGE("Failed to dlopen %s: %s", library, dlerror());
      return false;
    }
    // Note that this is enough to get something like the zygote
    // running, we can't property_set here to fix this for the future
    // because we are root and not the system user. See
    // RuntimeInit.commonInit for where we fix up the property to
    // avoid future fallbacks. http://b/11463182
    ALOGW("Falling back from %s to %s after dlopen error: %s",
          library, kLibraryFallback, dlerror());
    library = kLibraryFallback;
    handle_ = dlopen(library, RTLD_NOW);
    if (handle_ == NULL) {
      ALOGE("Failed to dlopen %s: %s", library, dlerror());
      return false;
    }
  }

   // 寻找并导出JNI_GetDefaultJavaVMInitArgs_
  if (!FindSymbol(reinterpret_cast<void**>(&JNI_GetDefaultJavaVMInitArgs_),
                  "JNI_GetDefaultJavaVMInitArgs")) {
    return false;
  }

   // 寻找并导出JNI_CreateJavaVM_
  if (!FindSymbol(reinterpret_cast<void**>(&JNI_CreateJavaVM_),
                  "JNI_CreateJavaVM")) {
    return false;
  }

  // 寻找并导出JNI_GetCreatedJavaVMs_
  if (!FindSymbol(reinterpret_cast<void**>(&JNI_GetCreatedJavaVMs_),
                  "JNI_GetCreatedJavaVMs")) {
    return false;
  }
  return true;
}

#ifdef HAVE_ANDROID_OS
static const char* kLibrarySystemProperty = "persist.sys.dalvik.vm.lib.2";
static const char* kDebuggableSystemProperty = "ro.debuggable";
static const char* kDebuggableFallback = "0";  // Not debuggable.
#endif
static const char* kLibraryFallback = "libart.so";

template<typename T> void UNUSED(const T&) {}

const char* JniInvocation::GetLibrary(const char* library, char* buffer) {
#ifdef HAVE_ANDROID_OS
  const char* default_library;

  char debuggable[PROPERTY_VALUE_MAX];
  property_get(kDebuggableSystemProperty, debuggable, kDebuggableFallback);

  if (strcmp(debuggable, "1") != 0) {
    // Not a debuggable build.
    // Do not allow arbitrary library. Ignore the library parameter. This
    // will also ignore the default library, but initialize to fallback
    // for cleanliness.
    library = kLibraryFallback;
    default_library = kLibraryFallback;
  } else {
    // Debuggable build.
    // Accept the library parameter. For the case it is NULL, load the default
    // library from the system property.
    if (buffer != NULL) {
      property_get(kLibrarySystemProperty, buffer, kLibraryFallback);
      default_library = buffer;
    } else {
      // No buffer given, just use default fallback.
      default_library = kLibraryFallback;
    }
  }
#else
  UNUSED(buffer);
  const char* default_library = kLibraryFallback;
#endif
  if (library == NULL) {
    library = default_library;
  }

  return library;
}

/*
 * Start the Dalvik Virtual Machine.
 *
 * Various arguments, most determined by system properties, are passed in.
 * The "mOptions" vector is updated.
 *
 * CAUTION: when adding options in here, be careful not to put the
 * char buffer inside a nested scope.  Adding the buffer to the
 * options using mOptions.add() does not copy the buffer, so if the
 * buffer goes out of scope the option may be overwritten.  It's best
 * to put the buffer at the top of the function so that it is more
 * unlikely that someone will surround it in a scope at a later time
 * and thus introduce a bug.
 *
 * Returns 0 on success.
 */
int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv, bool zygote)
{

    //******************* 第1部分**********************
    JavaVMInitArgs initArgs;
    char propBuf[PROPERTY_VALUE_MAX];
    char stackTraceFileBuf[sizeof("-Xstacktracefile:")-1 + PROPERTY_VALUE_MAX];
    char jniOptsBuf[sizeof("-Xjniopts:")-1 + PROPERTY_VALUE_MAX];
    char heapstartsizeOptsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
    char heapsizeOptsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
    char heapgrowthlimitOptsBuf[sizeof("-XX:HeapGrowthLimit=")-1 + PROPERTY_VALUE_MAX];
    char heapminfreeOptsBuf[sizeof("-XX:HeapMinFree=")-1 + PROPERTY_VALUE_MAX];
    char heapmaxfreeOptsBuf[sizeof("-XX:HeapMaxFree=")-1 + PROPERTY_VALUE_MAX];
    char usejitOptsBuf[sizeof("-Xusejit:")-1 + PROPERTY_VALUE_MAX];
    char jitcodecachesizeOptsBuf[sizeof("-Xjitcodecachesize:")-1 + PROPERTY_VALUE_MAX];
    char jitthresholdOptsBuf[sizeof("-Xjitthreshold:")-1 + PROPERTY_VALUE_MAX];
    char gctypeOptsBuf[sizeof("-Xgc:")-1 + PROPERTY_VALUE_MAX];
    char backgroundgcOptsBuf[sizeof("-XX:BackgroundGC=")-1 + PROPERTY_VALUE_MAX];
    char heaptargetutilizationOptsBuf[sizeof("-XX:HeapTargetUtilization=")-1 + PROPERTY_VALUE_MAX];
    char cachePruneBuf[sizeof("-Xzygote-max-boot-retry=")-1 + PROPERTY_VALUE_MAX];
    char dex2oatXmsImageFlagsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
    char dex2oatXmxImageFlagsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
    char dex2oatXmsFlagsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
    char dex2oatXmxFlagsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
    char dex2oatCompilerFilterBuf[sizeof("--compiler-filter=")-1 + PROPERTY_VALUE_MAX];
    char dex2oatImageCompilerFilterBuf[sizeof("--compiler-filter=")-1 + PROPERTY_VALUE_MAX];
    char dex2oatThreadsBuf[sizeof("-j")-1 + PROPERTY_VALUE_MAX];
    char dex2oatThreadsImageBuf[sizeof("-j")-1 + PROPERTY_VALUE_MAX];
    char dex2oat_isa_variant_key[PROPERTY_KEY_MAX];
    char dex2oat_isa_variant[sizeof("--instruction-set-variant=") -1 + PROPERTY_VALUE_MAX];
    char dex2oat_isa_features_key[PROPERTY_KEY_MAX];
    char dex2oat_isa_features[sizeof("--instruction-set-features=") -1 + PROPERTY_VALUE_MAX];
    char dex2oatFlagsBuf[PROPERTY_VALUE_MAX];
    char dex2oatImageFlagsBuf[PROPERTY_VALUE_MAX];
    char extraOptsBuf[PROPERTY_VALUE_MAX];
    char voldDecryptBuf[PROPERTY_VALUE_MAX];
    enum {
      kEMDefault,
      kEMIntPortable,
      kEMIntFast,
      kEMJitCompiler,
    } executionMode = kEMDefault;
    char profilePeriod[sizeof("-Xprofile-period:")-1 + PROPERTY_VALUE_MAX];
    char profileDuration[sizeof("-Xprofile-duration:")-1 + PROPERTY_VALUE_MAX];
    char profileInterval[sizeof("-Xprofile-interval:")-1 + PROPERTY_VALUE_MAX];
    char profileBackoff[sizeof("-Xprofile-backoff:")-1 + PROPERTY_VALUE_MAX];
    char profileTopKThreshold[sizeof("-Xprofile-top-k-threshold:")-1 + PROPERTY_VALUE_MAX];
    char profileTopKChangeThreshold[sizeof("-Xprofile-top-k-change-threshold:")-1 +
                                    PROPERTY_VALUE_MAX];
    char profileType[sizeof("-Xprofile-type:")-1 + PROPERTY_VALUE_MAX];
    char profileMaxStackDepth[sizeof("-Xprofile-max-stack-depth:")-1 + PROPERTY_VALUE_MAX];
    char localeOption[sizeof("-Duser.locale=") + PROPERTY_VALUE_MAX];
    char lockProfThresholdBuf[sizeof("-Xlockprofthreshold:")-1 + PROPERTY_VALUE_MAX];
    char nativeBridgeLibrary[sizeof("-XX:NativeBridge=") + PROPERTY_VALUE_MAX];
    char cpuAbiListBuf[sizeof("--cpu-abilist=") + PROPERTY_VALUE_MAX];
    char methodTraceFileBuf[sizeof("-Xmethod-trace-file:") + PROPERTY_VALUE_MAX];
    char methodTraceFileSizeBuf[sizeof("-Xmethod-trace-file-size:") + PROPERTY_VALUE_MAX];
    char fingerprintBuf[sizeof("-Xfingerprint:") + PROPERTY_VALUE_MAX];


    //******************* 第2部分**********************
    bool checkJni = false;
    property_get("dalvik.vm.checkjni", propBuf, "");
    if (strcmp(propBuf, "true") == 0) {
        checkJni = true;
    } else if (strcmp(propBuf, "false") != 0) {
        /* property is neither true nor false; fall back on kernel parameter */
        property_get("ro.kernel.android.checkjni", propBuf, "");
        if (propBuf[0] == '1') {
            checkJni = true;
        }
    }

    ALOGD("CheckJNI is %s\n", checkJni ? "ON" : "OFF");
    if (checkJni) {
        /* extended JNI checking */
        addOption("-Xcheck:jni");

        /* with -Xcheck:jni, this provides a JNI function call trace */
        //addOption("-verbose:jni");
    }


    //******************* 第3部分**********************
    property_get("dalvik.vm.execution-mode", propBuf, "");
    if (strcmp(propBuf, "int:portable") == 0) {
        executionMode = kEMIntPortable;
    } else if (strcmp(propBuf, "int:fast") == 0) {
        executionMode = kEMIntFast;
    } else if (strcmp(propBuf, "int:jit") == 0) {
        executionMode = kEMJitCompiler;
    }


    //******************* 第4部分**********************
    parseRuntimeOption("dalvik.vm.stack-trace-file", stackTraceFileBuf, "-Xstacktracefile:");

    //******************* 第5部分**********************
    strcpy(jniOptsBuf, "-Xjniopts:");
    if (parseRuntimeOption("dalvik.vm.jniopts", jniOptsBuf, "-Xjniopts:")) {
        ALOGI("JNI options: '%s'\n", jniOptsBuf);
    }

    /* route exit() to our handler */
    addOption("exit", (void*) runtime_exit);

    /* route fprintf() to our handler */
    addOption("vfprintf", (void*) runtime_vfprintf);

    /* register the framework-specific "is sensitive thread" hook */
    addOption("sensitiveThread", (void*) runtime_isSensitiveThread);

    /* enable verbose; standard options are { jni, gc, class } */
    //addOption("-verbose:jni");
    addOption("-verbose:gc");
    //addOption("-verbose:class");


    //******************* 第6部分**********************
    /*
     * The default starting and maximum size of the heap.  Larger
     * values should be specified in a product property override.
     */
    parseRuntimeOption("dalvik.vm.heapstartsize", heapstartsizeOptsBuf, "-Xms", "4m");
    parseRuntimeOption("dalvik.vm.heapsize", heapsizeOptsBuf, "-Xmx", "16m");

    parseRuntimeOption("dalvik.vm.heapgrowthlimit", heapgrowthlimitOptsBuf, "-XX:HeapGrowthLimit=");
    parseRuntimeOption("dalvik.vm.heapminfree", heapminfreeOptsBuf, "-XX:HeapMinFree=");
    parseRuntimeOption("dalvik.vm.heapmaxfree", heapmaxfreeOptsBuf, "-XX:HeapMaxFree=");
    parseRuntimeOption("dalvik.vm.heaptargetutilization",
                       heaptargetutilizationOptsBuf,
                       "-XX:HeapTargetUtilization=");



    //******************* 第7部分**********************
    /*
     * JIT related options.
     */
    parseRuntimeOption("dalvik.vm.usejit", usejitOptsBuf, "-Xusejit:");
    parseRuntimeOption("dalvik.vm.jitcodecachesize", jitcodecachesizeOptsBuf, "-Xjitcodecachesize:");
    parseRuntimeOption("dalvik.vm.jitthreshold", jitthresholdOptsBuf, "-Xjitthreshold:");

    property_get("ro.config.low_ram", propBuf, "");
    if (strcmp(propBuf, "true") == 0) {
      addOption("-XX:LowMemoryMode");
    }

    parseRuntimeOption("dalvik.vm.gctype", gctypeOptsBuf, "-Xgc:");
    parseRuntimeOption("dalvik.vm.backgroundgctype", backgroundgcOptsBuf, "-XX:BackgroundGC=");

   //******************* 第8部分**********************
    /*
     * Enable debugging only for apps forked from zygote.
     * Set suspend=y to pause during VM init and use android ADB transport.
     */
    if (zygote) {
      addOption("-agentlib:jdwp=transport=dt_android_adb,suspend=n,server=y");
    }

    parseRuntimeOption("dalvik.vm.lockprof.threshold",
                       lockProfThresholdBuf,
                       "-Xlockprofthreshold:");

    if (executionMode == kEMIntPortable) {
        addOption("-Xint:portable");
    } else if (executionMode == kEMIntFast) {
        addOption("-Xint:fast");
    } else if (executionMode == kEMJitCompiler) {
        addOption("-Xint:jit");
    }

    // If we are booting without the real /data, don't spend time compiling.
    property_get("vold.decrypt", voldDecryptBuf, "");
    bool skip_compilation = ((strcmp(voldDecryptBuf, "trigger_restart_min_framework") == 0) ||
                             (strcmp(voldDecryptBuf, "1") == 0));

    // Extra options for boot.art/boot.oat image generation.
    parseCompilerRuntimeOption("dalvik.vm.image-dex2oat-Xms", dex2oatXmsImageFlagsBuf,
                               "-Xms", "-Ximage-compiler-option");
    parseCompilerRuntimeOption("dalvik.vm.image-dex2oat-Xmx", dex2oatXmxImageFlagsBuf,
                               "-Xmx", "-Ximage-compiler-option");
    if (skip_compilation) {
        addOption("-Ximage-compiler-option");
        addOption("--compiler-filter=verify-none");
    } else {
        parseCompilerOption("dalvik.vm.image-dex2oat-filter", dex2oatImageCompilerFilterBuf,
                            "--compiler-filter=", "-Ximage-compiler-option");
    }


   //******************* 第9部分**********************
    // Make sure there is a preloaded-classes file.
    if (!hasFile("/system/etc/preloaded-classes")) {
        ALOGE("Missing preloaded-classes file, /system/etc/preloaded-classes not found: %s\n",
              strerror(errno));
        return -1;
    }
    addOption("-Ximage-compiler-option");
    addOption("--image-classes=/system/etc/preloaded-classes");

     //******************* 第10部分**********************
    // If there is a compiled-classes file, push it.
    if (hasFile("/system/etc/compiled-classes")) {
        addOption("-Ximage-compiler-option");
        addOption("--compiled-classes=/system/etc/compiled-classes");
    }

    property_get("dalvik.vm.image-dex2oat-flags", dex2oatImageFlagsBuf, "");
    parseExtraOpts(dex2oatImageFlagsBuf, "-Ximage-compiler-option");

    // Extra options for DexClassLoader.
    parseCompilerRuntimeOption("dalvik.vm.dex2oat-Xms", dex2oatXmsFlagsBuf,
                               "-Xms", "-Xcompiler-option");
    parseCompilerRuntimeOption("dalvik.vm.dex2oat-Xmx", dex2oatXmxFlagsBuf,
                               "-Xmx", "-Xcompiler-option");
    if (skip_compilation) {
        addOption("-Xcompiler-option");
        addOption("--compiler-filter=verify-none");

        // We skip compilation when a minimal runtime is brought up for decryption. In that case
        // /data is temporarily backed by a tmpfs, which is usually small.
        // If the system image contains prebuilts, they will be relocated into the tmpfs. In this
        // specific situation it is acceptable to *not* relocate and run out of the prebuilts
        // directly instead.
        addOption("--runtime-arg");
        addOption("-Xnorelocate");
    } else {
        parseCompilerOption("dalvik.vm.dex2oat-filter", dex2oatCompilerFilterBuf,
                            "--compiler-filter=", "-Xcompiler-option");
    }
    parseCompilerOption("dalvik.vm.dex2oat-threads", dex2oatThreadsBuf, "-j", "-Xcompiler-option");
    parseCompilerOption("dalvik.vm.image-dex2oat-threads", dex2oatThreadsImageBuf, "-j",
                        "-Ximage-compiler-option");

    // The runtime will compile a boot image, when necessary, not using installd. Thus, we need to
    // pass the instruction-set-features/variant as an image-compiler-option.
    // TODO: Find a better way for the instruction-set.
#if defined(__arm__)
    constexpr const char* instruction_set = "arm";
#elif defined(__aarch64__)
    constexpr const char* instruction_set = "arm64";
#elif defined(__mips__) && !defined(__LP64__)
    constexpr const char* instruction_set = "mips";
#elif defined(__mips__) && defined(__LP64__)
    constexpr const char* instruction_set = "mips64";
#elif defined(__i386__)
    constexpr const char* instruction_set = "x86";
#elif defined(__x86_64__)
    constexpr const char* instruction_set = "x86_64";
#else
    constexpr const char* instruction_set = "unknown";
#endif
    // Note: it is OK to reuse the buffer, as the values are exactly the same between
    //       * compiler-option, used for runtime compilation (DexClassLoader)
    //       * image-compiler-option, used for boot-image compilation on device

    // Copy the variant.
    sprintf(dex2oat_isa_variant_key, "dalvik.vm.isa.%s.variant", instruction_set);
    parseCompilerOption(dex2oat_isa_variant_key, dex2oat_isa_variant,
                        "--instruction-set-variant=", "-Ximage-compiler-option");
    parseCompilerOption(dex2oat_isa_variant_key, dex2oat_isa_variant,
                        "--instruction-set-variant=", "-Xcompiler-option");
    // Copy the features.
    sprintf(dex2oat_isa_features_key, "dalvik.vm.isa.%s.features", instruction_set);
    parseCompilerOption(dex2oat_isa_features_key, dex2oat_isa_features,
                        "--instruction-set-features=", "-Ximage-compiler-option");
    parseCompilerOption(dex2oat_isa_features_key, dex2oat_isa_features,
                        "--instruction-set-features=", "-Xcompiler-option");


    property_get("dalvik.vm.dex2oat-flags", dex2oatFlagsBuf, "");
    parseExtraOpts(dex2oatFlagsBuf, "-Xcompiler-option");

    /* extra options; parse this late so it overrides others */
    property_get("dalvik.vm.extra-opts", extraOptsBuf, "");
    parseExtraOpts(extraOptsBuf, NULL);

    /* Set the properties for locale */
    {
        strcpy(localeOption, "-Duser.locale=");
        const std::string locale = readLocale();
        strncat(localeOption, locale.c_str(), PROPERTY_VALUE_MAX);
        addOption(localeOption);
    }

    /*
     * Set profiler options
     */
    // Whether or not the profiler should be enabled.
    property_get("dalvik.vm.profiler", propBuf, "0");
    if (propBuf[0] == '1') {
        addOption("-Xenable-profiler");
    }

    // Whether the profile should start upon app startup or be delayed by some random offset
    // (in seconds) that is bound between 0 and a fixed value.
    property_get("dalvik.vm.profile.start-immed", propBuf, "0");
    if (propBuf[0] == '1') {
        addOption("-Xprofile-start-immediately");
    }

    // Number of seconds during profile runs.
    parseRuntimeOption("dalvik.vm.profile.period-secs", profilePeriod, "-Xprofile-period:");

    // Length of each profile run (seconds).
    parseRuntimeOption("dalvik.vm.profile.duration-secs",
                       profileDuration,
                       "-Xprofile-duration:");

    // Polling interval during profile run (microseconds).
    parseRuntimeOption("dalvik.vm.profile.interval-us", profileInterval, "-Xprofile-interval:");

    // Coefficient for period backoff.  The the period is multiplied
    // by this value after each profile run.
    parseRuntimeOption("dalvik.vm.profile.backoff-coeff", profileBackoff, "-Xprofile-backoff:");

    // Top K% of samples that are considered relevant when
    // deciding if the app should be recompiled.
    parseRuntimeOption("dalvik.vm.profile.top-k-thr",
                       profileTopKThreshold,
                       "-Xprofile-top-k-threshold:");

    // The threshold after which a change in the structure of the
    // top K% profiled samples becomes significant and triggers
    // recompilation. A change in profile is considered
    // significant if X% (top-k-change-threshold) of the top K%
    // (top-k-threshold property) samples has changed.
    parseRuntimeOption("dalvik.vm.profile.top-k-ch-thr",
                       profileTopKChangeThreshold,
                       "-Xprofile-top-k-change-threshold:");

    // Type of profile data.
    parseRuntimeOption("dalvik.vm.profiler.type", profileType, "-Xprofile-type:");

    // Depth of bounded stack data
    parseRuntimeOption("dalvik.vm.profile.stack-depth",
                       profileMaxStackDepth,
                       "-Xprofile-max-stack-depth:");

    /*
     * Tracing options.
     */
    property_get("dalvik.vm.method-trace", propBuf, "false");
    if (strcmp(propBuf, "true") == 0) {
        addOption("-Xmethod-trace");
        parseRuntimeOption("dalvik.vm.method-trace-file",
                           methodTraceFileBuf,
                           "-Xmethod-trace-file:");
        parseRuntimeOption("dalvik.vm.method-trace-file-siz",
                           methodTraceFileSizeBuf,
                           "-Xmethod-trace-file-size:");
        property_get("dalvik.vm.method-trace-stream", propBuf, "false");
        if (strcmp(propBuf, "true") == 0) {
            addOption("-Xmethod-trace-stream");
        }
    }

    // Native bridge library. "0" means that native bridge is disabled.
    property_get("ro.dalvik.vm.native.bridge", propBuf, "");
    if (propBuf[0] == '\0') {
        ALOGW("ro.dalvik.vm.native.bridge is not expected to be empty");
    } else if (strcmp(propBuf, "0") != 0) {
        snprintf(nativeBridgeLibrary, sizeof("-XX:NativeBridge=") + PROPERTY_VALUE_MAX,
                 "-XX:NativeBridge=%s", propBuf);
        addOption(nativeBridgeLibrary);
    }

#if defined(__LP64__)
    const char* cpu_abilist_property_name = "ro.product.cpu.abilist64";
#else
    const char* cpu_abilist_property_name = "ro.product.cpu.abilist32";
#endif  // defined(__LP64__)
    property_get(cpu_abilist_property_name, propBuf, "");
    if (propBuf[0] == '\0') {
        ALOGE("%s is not expected to be empty", cpu_abilist_property_name);
        return -1;
    }
    snprintf(cpuAbiListBuf, sizeof(cpuAbiListBuf), "--cpu-abilist=%s", propBuf);
    addOption(cpuAbiListBuf);

    // Dalvik-cache pruning counter.
    parseRuntimeOption("dalvik.vm.zygote.max-boot-retry", cachePruneBuf,
                       "-Xzygote-max-boot-retry=");

    /*
     * When running with debug.generate-debug-info, add --generate-debug-info to
     * the compiler options so that the boot image, if it is compiled on device,
     * will include native debugging information.
     */
    property_get("debug.generate-debug-info", propBuf, "");
    if (strcmp(propBuf, "true") == 0) {
        addOption("-Xcompiler-option");
        addOption("--generate-debug-info");
        addOption("-Ximage-compiler-option");
        addOption("--generate-debug-info");
    }

    /*
     * Retrieve the build fingerprint and provide it to the runtime. That way, ANR dumps will
     * contain the fingerprint and can be parsed.
     */
    parseRuntimeOption("ro.build.fingerprint", fingerprintBuf, "-Xfingerprint:");

    initArgs.version = JNI_VERSION_1_4;
    initArgs.options = mOptions.editArray();
    initArgs.nOptions = mOptions.size();
    initArgs.ignoreUnrecognized = JNI_FALSE;


    //******************* 第11部分**********************
    /*
     * Initialize the VM.
     *
     * The JavaVM* is essentially per-process, and the JNIEnv* is per-thread.
     * If this call succeeds, the VM is ready, and we can start issuing
     * JNI calls.
     */
    if (JNI_CreateJavaVM(pJavaVM, pEnv, &initArgs) < 0) {
        ALOGE("JNI_CreateJavaVM failed\n");
        return -1;
    }

    return 0;
}

// JNI Invocation interface.

extern "C" jint JNI_CreateJavaVM(JavaVM** p_vm, JNIEnv** p_env, void* vm_args) {
  ATRACE_BEGIN(__FUNCTION__);
  const JavaVMInitArgs* args = static_cast<JavaVMInitArgs*>(vm_args);
  
  //***************  第一步 ***************
  if (IsBadJniVersion(args->version)) {
    LOG(ERROR) << "Bad JNI version passed to CreateJavaVM: " << args->version;
    ATRACE_END();
    return JNI_EVERSION;
  }

  //***************  第二步 ***************
  RuntimeOptions options;
  for (int i = 0; i < args->nOptions; ++i) {
    JavaVMOption* option = &args->options[i];
    options.push_back(std::make_pair(std::string(option->optionString), option->extraInfo));
  }
  bool ignore_unrecognized = args->ignoreUnrecognized;

  //***************  第三步 ***************
  if (!Runtime::Create(options, ignore_unrecognized)) {
    ATRACE_END();
    return JNI_ERR;
  }
  Runtime* runtime = Runtime::Current();


  //***************  第四步 ***************
  bool started = runtime->Start();

  //***************  第五步 ***************
  if (!started) {
    delete Thread::Current()->GetJniEnv();
    delete runtime->GetJavaVM();
    LOG(WARNING) << "CreateJavaVM failed";
    ATRACE_END();
    return JNI_ERR;
  }

  //***************  第六步 ***************
  *p_env = Thread::Current()->GetJniEnv();
  *p_vm = runtime->GetJavaVM();
  ATRACE_END();
  return JNI_OK;
}

bool Runtime::Create(const RuntimeOptions& options, bool ignore_unrecognized) {
  // TODO: acquire a static mutex on Runtime to avoid racing.
  // 单例判断
  if (Runtime::instance_ != nullptr) {
    return false;
  }

  //log 初始化
  InitLogging(nullptr);  // Calls Locks::Init() as a side effect.

  //创建Runtime实例
  instance_ = new Runtime;

  //调用Init函数来进行初始化
  if (!instance_->Init(options, ignore_unrecognized)) {
    // TODO: Currently deleting the instance will abort the runtime on destruction. Now This will
    // leak memory, instead. Fix the destructor. b/19100793.
    // delete instance_;
    instance_ = nullptr;
    return false;
  }
  return true;
}

bool Runtime::Init(const RuntimeOptions& raw_options, bool ignore_unrecognized) {
  ATRACE_BEGIN("Runtime::Init");
  CHECK_EQ(sysconf(_SC_PAGE_SIZE), kPageSize);

  //****************** 第一步 ****************** 
  MemMap::Init();

  //****************** 第二步 ****************** 
  using Opt = RuntimeArgumentMap;
  RuntimeArgumentMap runtime_options;
  std::unique_ptr<ParsedOptions> parsed_options(
      ParsedOptions::Create(raw_options, ignore_unrecognized, &runtime_options));
  if (parsed_options.get() == nullptr) {
    LOG(ERROR) << "Failed to parse options";
    ATRACE_END();
    return false;
  }
  VLOG(startup) << "Runtime::Init -verbose:startup enabled";

  //****************** 第三步 ****************** 
  QuasiAtomic::Startup();

  //****************** 第四步 ****************** 
  Monitor::Init(runtime_options.GetOrDefault(Opt::LockProfThreshold),
                runtime_options.GetOrDefault(Opt::HookIsSensitiveThread));


  //****************** 第五步 ****************** 
  boot_class_path_string_ = runtime_options.ReleaseOrDefault(Opt::BootClassPath);
  class_path_string_ = runtime_options.ReleaseOrDefault(Opt::ClassPath);
  properties_ = runtime_options.ReleaseOrDefault(Opt::PropertiesList);

  compiler_callbacks_ = runtime_options.GetOrDefault(Opt::CompilerCallbacksPtr);
  patchoat_executable_ = runtime_options.ReleaseOrDefault(Opt::PatchOat);
  must_relocate_ = runtime_options.GetOrDefault(Opt::Relocate);
  is_zygote_ = runtime_options.Exists(Opt::Zygote);
  is_explicit_gc_disabled_ = runtime_options.Exists(Opt::DisableExplicitGC);
  dex2oat_enabled_ = runtime_options.GetOrDefault(Opt::Dex2Oat);
  image_dex2oat_enabled_ = runtime_options.GetOrDefault(Opt::ImageDex2Oat);

  vfprintf_ = runtime_options.GetOrDefault(Opt::HookVfprintf);
  exit_ = runtime_options.GetOrDefault(Opt::HookExit);
  abort_ = runtime_options.GetOrDefault(Opt::HookAbort);

  default_stack_size_ = runtime_options.GetOrDefault(Opt::StackSize);
  stack_trace_file_ = runtime_options.ReleaseOrDefault(Opt::StackTraceFile);

  compiler_executable_ = runtime_options.ReleaseOrDefault(Opt::Compiler);
  compiler_options_ = runtime_options.ReleaseOrDefault(Opt::CompilerOptions);
  image_compiler_options_ = runtime_options.ReleaseOrDefault(Opt::ImageCompilerOptions);
  image_location_ = runtime_options.GetOrDefault(Opt::Image);

  max_spins_before_thin_lock_inflation_ =
      runtime_options.GetOrDefault(Opt::MaxSpinsBeforeThinLockInflation);

  monitor_list_ = new MonitorList;
  monitor_pool_ = MonitorPool::Create();
  thread_list_ = new ThreadList;
  intern_table_ = new InternTable;

  verify_ = runtime_options.GetOrDefault(Opt::Verify);
  allow_dex_file_fallback_ = !runtime_options.Exists(Opt::NoDexFileFallback);

  Split(runtime_options.GetOrDefault(Opt::CpuAbiList), ',', &cpu_abilist_);

  fingerprint_ = runtime_options.ReleaseOrDefault(Opt::Fingerprint);

  if (runtime_options.GetOrDefault(Opt::Interpret)) {
    GetInstrumentation()->ForceInterpretOnly();
  }

  zygote_max_failed_boots_ = runtime_options.GetOrDefault(Opt::ZygoteMaxFailedBoots);

  XGcOption xgc_option = runtime_options.GetOrDefault(Opt::GcOption);
  ATRACE_BEGIN("CreateHeap");

  //****************** 第六步 ****************** 
  heap_ = new gc::Heap(runtime_options.GetOrDefault(Opt::MemoryInitialSize),
                       runtime_options.GetOrDefault(Opt::HeapGrowthLimit),
                       runtime_options.GetOrDefault(Opt::HeapMinFree),
                       runtime_options.GetOrDefault(Opt::HeapMaxFree),
                       

runtime_options.GetOrDefault(Opt::HeapTargetUtilization),
                       runtime_options.GetOrDefault(Opt::ForegroundHeapGrowthMultiplier),
                       runtime_options.GetOrDefault(Opt::MemoryMaximumSize),
                       runtime_options.GetOrDefault(Opt::NonMovingSpaceCapacity),
                       runtime_options.GetOrDefault(Opt::Image),
                       runtime_options.GetOrDefault(Opt::ImageInstructionSet),
                       xgc_option.collector_type_,
                       runtime_options.GetOrDefault(Opt::BackgroundGc),
                       runtime_options.GetOrDefault(Opt::LargeObjectSpace),
                       runtime_options.GetOrDefault(Opt::LargeObjectThreshold),
                       runtime_options.GetOrDefault(Opt::ParallelGCThreads),
                       runtime_options.GetOrDefault(Opt::ConcGCThreads),
                       runtime_options.Exists(Opt::LowMemoryMode),
                       runtime_options.GetOrDefault(Opt::LongPauseLogThreshold),
                       runtime_options.GetOrDefault(Opt::LongGCLogThreshold),
                       runtime_options.Exists(Opt::IgnoreMaxFootprint),
                       runtime_options.GetOrDefault(Opt::UseTLAB),
                       xgc_option.verify_pre_gc_heap_,
                       xgc_option.verify_pre_sweeping_heap_,
                       xgc_option.verify_post_gc_heap_,
                       xgc_option.verify_pre_gc_rosalloc_,
                       xgc_option.verify_pre_sweeping_rosalloc_,
                       xgc_option.verify_post_gc_rosalloc_,
                       xgc_option.gcstress_,
                       runtime_options.GetOrDefault(Opt::EnableHSpaceCompactForOOM),
                       runtime_options.GetOrDefault(Opt::HSpaceCompactForOOMMinIntervalsMs));
  ATRACE_END();

  if (heap_->GetImageSpace() == nullptr && !allow_dex_file_fallback_) {
    LOG(ERROR) << "Dex file fallback disabled, cannot continue without image.";
    ATRACE_END();
    return false;
  }

 //****************** 第七步 ****************** 
  dump_gc_performance_on_shutdown_ = runtime_options.Exists(Opt::DumpGCPerformanceOnShutdown);

  if (runtime_options.Exists(Opt::JdwpOptions)) {
    Dbg::ConfigureJdwp(runtime_options.GetOrDefault(Opt::JdwpOptions));
  }

  jit_options_.reset(jit::JitOptions::CreateFromRuntimeArguments(runtime_options));
  if (IsAotCompiler()) {
    // If we are already the compiler at this point, we must be dex2oat. Don't create the jit in
    // this case.
    // If runtime_options doesn't have UseJIT set to true then CreateFromRuntimeArguments returns
    // null and we don't create the jit.
    jit_options_->SetUseJIT(false);
  }

  // Use MemMap arena pool for jit, malloc otherwise. Malloc arenas are faster to allocate but
  // can't be trimmed as easily.
  const bool use_malloc = IsAotCompiler();
  arena_pool_.reset(new ArenaPool(use_malloc, false));
  if (IsCompiler() && Is64BitInstructionSet(kRuntimeISA)) {
    // 4gb, no malloc. Explanation in header.
    low_4gb_arena_pool_.reset(new ArenaPool(false, true));
    linear_alloc_.reset(new LinearAlloc(low_4gb_arena_pool_.get()));
  } else {
    linear_alloc_.reset(new LinearAlloc(arena_pool_.get()));
  }


 //****************** 第八步 ****************** 
  BlockSignals();
  InitPlatformSignalHandlers();


 //****************** 第九步 ****************** 
  // Change the implicit checks flags based on runtime architecture.
  switch (kRuntimeISA) {
    case kArm:
    case kThumb2:
    case kX86:
    case kArm64:
    case kX86_64:
    case kMips:
    case kMips64:
      implicit_null_checks_ = true;
      // Installing stack protection does not play well with valgrind.
      implicit_so_checks_ = (RUNNING_ON_VALGRIND == 0);
      break;
    default:
      // Keep the defaults.
      break;
  }


 //****************** 第九步 ****************** 
  // Always initialize the signal chain so that any calls to sigaction get
  // correctly routed to the next in the chain regardless of whether we
  // have claimed the signal or not.
  InitializeSignalChain();


 //****************** 第十步 ****************** 
  if (implicit_null_checks_ || implicit_so_checks_ || implicit_suspend_checks_) {
    fault_manager.Init();

    // These need to be in a specific order.  The null point check handler must be
    // after the suspend check and stack overflow check handlers.
    //
    // Note: the instances attach themselves to the fault manager and are handled by it. The manager
    //       will delete the instance on Shutdown().
    if (implicit_suspend_checks_) {
      new SuspensionHandler(&fault_manager);
    }

    if (implicit_so_checks_) {
      new StackOverflowHandler(&fault_manager);
    }

    if (implicit_null_checks_) {
      new NullPointerHandler(&fault_manager);
    }

    if (kEnableJavaStackTraceHandler) {
      new JavaStackTraceHandler(&fault_manager);
    }
  }


 //****************** 第十一步 ****************** 
  java_vm_ = new JavaVMExt(this, runtime_options);


 //****************** 第十二步 ****************** 
  Thread::Startup();



  // ClassLinker needs an attached thread, but we can't fully attach a thread without creating
  // objects. We can't supply a thread group yet; it will be fixed later. Since we are the main
  // thread, we do not get a java peer.
  Thread* self = Thread::Attach("main", false, nullptr, false);
  CHECK_EQ(self->GetThreadId(), ThreadList::kMainThreadId);
  CHECK(self != nullptr);

  // Set us to runnable so tools using a runtime can allocate and GC by default
  self->TransitionFromSuspendedToRunnable();

 //****************** 第十三步 ****************
  // Now we're attached, we can take the heap locks and validate the heap.
  GetHeap()->EnableObjectValidation();

  CHECK_GE(GetHeap()->GetContinuousSpaces().size(), 1U);

 //****************** 第十四步 ****************
  class_linker_ = new ClassLinker(intern_table_);
  if (GetHeap()->HasImageSpace()) {
    ATRACE_BEGIN("InitFromImage");
    class_linker_->InitFromImage();
    ATRACE_END();
    if (kIsDebugBuild) {
      GetHeap()->GetImageSpace()->VerifyImageAllocations();
    }
    if (boot_class_path_string_.empty()) {
      // The bootclasspath is not explicitly specified: construct it from the loaded dex files.
      const std::vector<const DexFile*>& boot_class_path = GetClassLinker()->GetBootClassPath();
      std::vector<std::string> dex_locations;
      dex_locations.reserve(boot_class_path.size());
      for (const DexFile* dex_file : boot_class_path) {
        dex_locations.push_back(dex_file->GetLocation());
      }
      boot_class_path_string_ = Join(dex_locations, ':');
    }
  } else {
    std::vector<std::string> dex_filenames;
    Split(boot_class_path_string_, ':', &dex_filenames);

    std::vector<std::string> dex_locations;
    if (!runtime_options.Exists(Opt::BootClassPathLocations)) {
      dex_locations = dex_filenames;
    } else {
      dex_locations = runtime_options.GetOrDefault(Opt::BootClassPathLocations);
      CHECK_EQ(dex_filenames.size(), dex_locations.size());
    }

    std::vector<std::unique_ptr<const DexFile>> boot_class_path;
    OpenDexFiles(dex_filenames,
                 dex_locations,
                 runtime_options.GetOrDefault(Opt::Image),
                 &boot_class_path);
    instruction_set_ = runtime_options.GetOrDefault(Opt::ImageInstructionSet);
    class_linker_->InitWithoutImage(std::move(boot_class_path));

    // TODO: Should we move the following to InitWithoutImage?
    SetInstructionSet(instruction_set_);
    for (int i = 0; i < Runtime::kLastCalleeSaveType; i++) {
      Runtime::CalleeSaveType type = Runtime::CalleeSaveType(i);
      if (!HasCalleeSaveMethod(type)) {
        SetCalleeSaveMethod(CreateCalleeSaveMethod(), type);
      }
    }
  }

  CHECK(class_linker_ != nullptr);

  //****************** 第十五步 ****************
  // Initialize the special sentinel_ value early.
  sentinel_ = GcRoot<mirror::Object>(class_linker_->AllocObject(self));
  CHECK(sentinel_.Read() != nullptr);

  verifier::MethodVerifier::Init();

 //****************** 第十六步 ****************
  if (runtime_options.Exists(Opt::MethodTrace)) {
    trace_config_.reset(new TraceConfig());
    trace_config_->trace_file = runtime_options.ReleaseOrDefault(Opt::MethodTraceFile);
    trace_config_->trace_file_size = runtime_options.ReleaseOrDefault(Opt::MethodTraceFileSize);
    trace_config_->trace_mode = Trace::TraceMode::kMethodTracing;
    trace_config_->trace_output_mode = runtime_options.Exists(Opt::MethodTraceStreaming) ?
        Trace::TraceOutputMode::kStreaming :
        Trace::TraceOutputMode::kFile;
  }


 //****************** 第十七步 ****************
  {
    auto&& profiler_options = runtime_options.ReleaseOrDefault(Opt::ProfilerOpts);
    profile_output_filename_ = profiler_options.output_file_name_;

    // TODO: Don't do this, just change ProfilerOptions to include the output file name?
    ProfilerOptions other_options(
        profiler_options.enabled_,
        profiler_options.period_s_,
        profiler_options.duration_s_,
        profiler_options.interval_us_,
        profiler_options.backoff_coefficient_,
        profiler_options.start_immediately_,
        profiler_options.top_k_threshold_,
        profiler_options.top_k_change_threshold_,
        profiler_options.profile_type_,
        profiler_options.max_stack_depth_);

    profiler_options_ = other_options;
  }

  // TODO: move this to just be an Trace::Start argument
  Trace::SetDefaultClockSource(runtime_options.GetOrDefault(Opt::ProfileClock));


 //****************** 第十八步 ****************
  // Pre-allocate an OutOfMemoryError for the double-OOME case.
  self->ThrowNewException("Ljava/lang/OutOfMemoryError;",
                          "OutOfMemoryError thrown while trying to throw OutOfMemoryError; "
                          "no stack trace available");
  pre_allocated_OutOfMemoryError_ = GcRoot<mirror::Throwable>(self->GetException());
  self->ClearException();

  // Pre-allocate a NoClassDefFoundError for the common case of failing to find a system class
  // ahead of checking the application's class loader.
  self->ThrowNewException("Ljava/lang/NoClassDefFoundError;",
                          "Class not found using the boot class loader; no stack trace available");
  pre_allocated_NoClassDefFoundError_ = GcRoot<mirror::Throwable>(self->GetException());
  self->ClearException();

  // Look for a native bridge.
  //
  // The intended flow here is, in the case of a running system:
  //
  // Runtime::Init() (zygote):
  //   LoadNativeBridge -> dlopen from cmd line parameter.
  //  |
  //  V
  // Runtime::Start() (zygote):
  //   No-op wrt native bridge.
  //  |
  //  | start app
  //  V
  // DidForkFromZygote(action)
  //   action = kUnload -> dlclose native bridge.
  //   action = kInitialize -> initialize library
  //
  //
  // The intended flow here is, in the case of a simple dalvikvm call:
  //
  // Runtime::Init():
  //   LoadNativeBridge -> dlopen from cmd line parameter.
  //  |
  //  V
  // Runtime::Start():
  //   DidForkFromZygote(kInitialize) -> try to initialize any native bridge given.
  //   No-op wrt native bridge.


 //****************** 第十九步 ****************
  {
    std::string native_bridge_file_name = runtime_options.ReleaseOrDefault(Opt::NativeBridge);
    is_native_bridge_loaded_ = LoadNativeBridge(native_bridge_file_name);
  }

  VLOG(startup) << "Runtime::Init exiting";

  ATRACE_END();

  return true;
}