zygote进程（三）_process_name_ptr

注：此文章主要基于展锐Android R代码加上学习总结自IngresGe大佬的分析

zygote进程

由*.rc文件配置启动

---

zygote重启条件(grep “restart zygote” 查找):

inputflinger 进程被杀 （onrestart）
servicemanager 进程被杀 （onrestart）
surfaceflinger 进程被杀 （onrestart）
netd 进程被杀 （onrestart）
zygote进程被杀 (oneshot=false)
system_server进程被杀（waitpid）
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Zygote启动流程:
代码入口为:frameworks/base/cmds/app_process/app_main.cpp
app_main.cpp
刚开始进程名称为app_process改名为zygote,最后通过runtime的start()方法启动java虚拟机,进入java世界

/*
 * Main entry of app process.
 *
 * Starts the interpreted runtime, then starts up the application.
 *
 */

#define LOG_TAG "appproc"

#include <stdio.h>
#include <stdlib.h>
#include <sys/prctl.h>
#include <sys/stat.h>
#include <unistd.h>

#include <android-base/macros.h>
#include <binder/IPCThreadState.h>
#include <hwbinder/IPCThreadState.h>
#include <utils/Log.h>
#include <cutils/memory.h>
#include <cutils/properties.h>
#include <cutils/trace.h>
#include <android_runtime/AndroidRuntime.h>
#include <private/android_filesystem_config.h>  // for AID_SYSTEM

namespace android {

static void app_usage()
{
    fprintf(stderr,
        "Usage: app_process [java-options] cmd-dir start-class-name [options]\n");
}

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

        AndroidRuntime::onExit(code);
    }


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

}

using namespace android;

static size_t computeArgBlockSize(int argc, char* const argv[]) {
    // TODO: This assumes that all arguments are allocated in
    // contiguous memory. There isn't any documented guarantee
    // that this is the case, but this is how the kernel does it
    // (see fs/exec.c).
    //
    // Also note that this is a constant for "normal" android apps.
    // Since they're forked from zygote, the size of their command line
    // is the size of the zygote command line.
    //
    // We change the process name of the process by over-writing
    // the start of the argument block (argv[0]) with the new name of
    // the process, so we'd mysteriously start getting truncated process
    // names if the zygote command line decreases in size.
    uintptr_t start = reinterpret_cast<uintptr_t>(argv[0]);
    uintptr_t end = reinterpret_cast<uintptr_t>(argv[argc - 1]);
    end += strlen(argv[argc - 1]) + 1;
    return (end - start);
}

static void maybeCreateDalvikCache() {
    const char* androidRoot = getenv("ANDROID_DATA");
    LOG_ALWAYS_FATAL_IF(androidRoot == NULL, "ANDROID_DATA environment variable unset");

    char dalvikCacheDir[PATH_MAX];
    const int numChars = snprintf(dalvikCacheDir, PATH_MAX,
            "%s/dalvik-cache/" ABI_STRING, androidRoot);
    LOG_ALWAYS_FATAL_IF((numChars >= PATH_MAX || numChars < 0),
            "Error constructing dalvik cache : %s", strerror(errno));

    int result = mkdir(dalvikCacheDir, 0711);
    LOG_ALWAYS_FATAL_IF((result < 0 && errno != EEXIST),
            "Error creating cache dir %s : %s", dalvikCacheDir, strerror(errno));

    // We always perform these steps because the directory might
    // already exist, with wider permissions and a different owner
    // than we'd like.
    result = chown(dalvikCacheDir, AID_ROOT, AID_ROOT);
    LOG_ALWAYS_FATAL_IF((result < 0), "Error changing dalvik-cache ownership : %s", strerror(errno));

    result = chmod(dalvikCacheDir, 0711);
    LOG_ALWAYS_FATAL_IF((result < 0),
            "Error changing dalvik-cache permissions : %s", strerror(errno));
}

#if defined(__LP64__)
static const char ABI_LIST_PROPERTY[] = "ro.product.cpu.abilist64";
static const char ZYGOTE_NICE_NAME[] = "zygote64";
#else
static const char ABI_LIST_PROPERTY[] = "ro.product.cpu.abilist32";
static const char ZYGOTE_NICE_NAME[] = "zygote";
#endif

>>**//主函数入口main**<<
>>==
int main(int argc, char* const argv[])
{
    if (!LOG_NDEBUG) {
      String8 argv_String;
      for (int i = 0; i < argc; ++i) {
        argv_String.append("\"");
        argv_String.append(argv[i]);
        argv_String.append("\" ");
      }
      ALOGV("app_process main with argv: %s", argv_String.string());
    }

    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.
    //
    // As an exception to the above rule, anything in "spaced commands"
    // goes to the vm even though it has a space in it.
    const char* spaced_commands[] = { "-cp", "-classpath" };
    // Allow "spaced commands" to be succeeded by exactly 1 argument (regardless of -s).
    bool known_command = false;

    int i;
    for (i = 0; i < argc; i++) {
        if (known_command == true) {
          runtime.addOption(strdup(argv[i]));
          // The static analyzer gets upset that we don't ever free the above
          // string. Since the allocation is from main, leaking it doesn't seem
          // problematic. NOLINTNEXTLINE
          ALOGV("app_process main add known option '%s'", argv[i]);
          known_command = false;
          continue;
        }

        for (int j = 0;
             j < static_cast<int>(sizeof(spaced_commands) / sizeof(spaced_commands[0]));
             ++j) {
          if (strcmp(argv[i], spaced_commands[j]) == 0) {
            known_command = true;
            ALOGV("app_process main found known command '%s'", argv[i]);
          }
        }

        if (argv[i][0] != '-') {
            break;
        }
        if (argv[i][1] == '-' && argv[i][2] == 0) {
            ++i; // Skip --.
            break;
        }

        runtime.addOption(strdup(argv[i]));
        // The static analyzer gets upset that we don't ever free the above
        // string. Since the allocation is from main, leaking it doesn't seem
        // problematic. NOLINTNEXTLINE
        ALOGV("app_process main add option '%s'", argv[i]);
    }

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

    ++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;
        }
    }

    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);

        if (!LOG_NDEBUG) {
          String8 restOfArgs;
          char* const* argv_new = argv + i;
          int argc_new = argc - i;
          for (int k = 0; k < argc_new; ++k) {
            restOfArgs.append("\"");
            restOfArgs.append(argv_new[k]);
            restOfArgs.append("\" ");
          }
          ALOGV("Class name = %s, args = %s", className.string(), restOfArgs.string());
        }
    } 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]));
        }
    }

    if (!niceName.isEmpty()) {
        runtime.setArgv0(niceName.string(), true /* setProcName */);
    }

    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.");
    }
}
==<<
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AndroidRuntime.cpp
路径:frameworks/base/core/jni/AndroidRuntime.cpp

/*
 * 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.
 */
 >>**
 启动java虚拟机,并进行一些配置,主要操作:
 一调用startVm开启虚拟机
 二调用startReg注册JNI方法
 三就是使用JNI把Zygote进程启动起来
**<<

```c++
/*
 * 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)
{
    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)));
        }
    }

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

    const char* runtimeRootDir = getenv("ANDROID_RUNTIME_ROOT");
    if (runtimeRootDir == NULL) {
        LOG_FATAL("No runtime directory specified with ANDROID_RUNTIME_ROOT environment variable.");
        return;
    }

    const char* tzdataRootDir = getenv("ANDROID_TZDATA_ROOT");
    if (tzdataRootDir == NULL) {
        LOG_FATAL("No tz data directory specified with ANDROID_TZDATA_ROOT environment variable.");
        return;
    }

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

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

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

    /*
     * 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);
    }

    /*
     * Start VM.  This thread becomes the main thread of the VM, and will
     * not return until the VM exits.
     */
    char* slashClassName = toSlashClassName(className != NULL ? 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");
}
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alps/libnativehelper/JniInvocation.cpp
Init函数主要作用是初始化JNI，具体工作是首先通过dlopen加载libart.so获得其句柄，然后调用dlsym从libart.so中找到
JNI_GetDefaultJavaVMInitArgs、JNI_CreateJavaVM、JNI_GetCreatedJavaVMs三个函数地址，赋值给对应成员属性，这三个函数会在后续虚拟机创建中调用.

bool JniInvocationImpl::Init(const char* library) {
#ifdef __ANDROID__
  char buffer[PROP_VALUE_MAX];
#else
  char* buffer = NULL;
#endif
  library = GetLibrary(library, buffer);
  handle_ = OpenLibrary(library);
  if (handle_ == NULL) {
    if (strcmp(library, kLibraryFallback) == 0) {
      // Nothing else to try.
      ALOGE("Failed to dlopen %s: %s", library, GetError().c_str());
      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, GetError().c_str());
    library = kLibraryFallback;
    handle_ = OpenLibrary(library);
    if (handle_ == NULL) {
      ALOGE("Failed to dlopen %s: %s", library, GetError().c_str());
      return false;
    }
  }
  if (!FindSymbol(reinterpret_cast<FUNC_POINTER*>(&JNI_GetDefaultJavaVMInitArgs_),
                  "JNI_GetDefaultJavaVMInitArgs")) {
    return false;
  }
  if (!FindSymbol(reinterpret_cast<FUNC_POINTER*>(&JNI_CreateJavaVM_),
                  "JNI_CreateJavaVM")) {
    return false;
  }
  if (!FindSymbol(reinterpret_cast<FUNC_POINTER*>(&JNI_GetCreatedJavaVMs_),
                  "JNI_GetCreatedJavaVMs")) {
    return false;
  }
  return true;
}
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配置虚拟机相关参数,再调用之前 JniInvocation初始化得到的 JNI_CreateJavaVM_来启动虚拟机。

int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv, bool zygote)
{
    JavaVMInitArgs initArgs;
    char propBuf[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 jitpthreadpriorityOptsBuf[sizeof("-Xjitpthreadpriority:")-1 + PROPERTY_VALUE_MAX];
    char jitmaxsizeOptsBuf[sizeof("-Xjitmaxsize:")-1 + PROPERTY_VALUE_MAX];
    char jitinitialsizeOptsBuf[sizeof("-Xjitinitialsize:")-1 + PROPERTY_VALUE_MAX];
    char jitthresholdOptsBuf[sizeof("-Xjitthreshold:")-1 + PROPERTY_VALUE_MAX];
    char useJitProfilesOptsBuf[sizeof("-Xjitsaveprofilinginfo:")-1 + PROPERTY_VALUE_MAX];
    char jitprithreadweightOptBuf[sizeof("-Xjitprithreadweight:")-1 + PROPERTY_VALUE_MAX];
    char jittransitionweightOptBuf[sizeof("-Xjittransitionweight:")-1 + PROPERTY_VALUE_MAX];
    char hotstartupsamplesOptsBuf[sizeof("-Xps-hot-startup-method-samples:")-1 + PROPERTY_VALUE_MAX];
    char madviseRandomOptsBuf[sizeof("-XX:MadviseRandomAccess:")-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 foregroundHeapGrowthMultiplierOptsBuf[
            sizeof("-XX:ForegroundHeapGrowthMultiplier=")-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 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 corePlatformApiPolicyBuf[sizeof("-Xcore-platform-api-policy:") + PROPERTY_VALUE_MAX];
    char methodTraceFileBuf[sizeof("-Xmethod-trace-file:") + PROPERTY_VALUE_MAX];
    char methodTraceFileSizeBuf[sizeof("-Xmethod-trace-file-size:") + PROPERTY_VALUE_MAX];
    std::string fingerprintBuf;
    char jdwpProviderBuf[sizeof("-XjdwpProvider:") - 1 + PROPERTY_VALUE_MAX];
    char bootImageBuf[sizeof("-Ximage:") - 1 + PROPERTY_VALUE_MAX];

    std::string use_apex_image =
        server_configurable_flags::GetServerConfigurableFlag(RUNTIME_NATIVE_BOOT_NAMESPACE,
                                                             ENABLE_APEX_IMAGE,
                                                             /*default_value=*/ "");
    if (use_apex_image == "true") {
        addOption(kApexImageOption);
        ALOGI("Using Apex boot image: '%s'\n", kApexImageOption);
    } else if (parseRuntimeOption("dalvik.vm.boot-image", bootImageBuf, "-Ximage:")) {
        ALOGI("Using dalvik.vm.boot-image: '%s'\n", bootImageBuf);
    } else {
        ALOGI("Using default boot image");
    }

    std::string disable_lock_profiling =
        server_configurable_flags::GetServerConfigurableFlag(RUNTIME_NATIVE_BOOT_NAMESPACE,
                                                             DISABLE_LOCK_PROFILING,
                                                             /*default_value=*/ "");
    if (disable_lock_profiling == "true") {
        addOption(kLockProfThresholdRuntimeOption);
        ALOGI("Disabling lock profiling: '%s'\n", kLockProfThresholdRuntimeOption);
    } else {
        ALOGI("Leaving lock profiling enabled");
    }

    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;
        }
    }
    ALOGV("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");
    }

    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;
    }

    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");

    /*
     * 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=");

    /* Foreground heap growth multiplier option */
    parseRuntimeOption("dalvik.vm.foreground-heap-growth-multiplier",
                       foregroundHeapGrowthMultiplierOptsBuf,
                       "-XX:ForegroundHeapGrowthMultiplier=");

    /*
     * JIT related options.
     */
    parseRuntimeOption("dalvik.vm.usejit", usejitOptsBuf, "-Xusejit:");
    parseRuntimeOption("dalvik.vm.jitmaxsize", jitmaxsizeOptsBuf, "-Xjitmaxsize:");
    parseRuntimeOption("dalvik.vm.jitinitialsize", jitinitialsizeOptsBuf, "-Xjitinitialsize:");
    parseRuntimeOption("dalvik.vm.jitthreshold", jitthresholdOptsBuf, "-Xjitthreshold:");
    parseRuntimeOption("dalvik.vm.jitpthreadpriority",
                       jitpthreadpriorityOptsBuf,
                       "-Xjitpthreadpriority:");
    property_get("dalvik.vm.usejitprofiles", useJitProfilesOptsBuf, "");
    if (strcmp(useJitProfilesOptsBuf, "true") == 0) {
        addOption("-Xjitsaveprofilinginfo");
    }

    parseRuntimeOption("dalvik.vm.jitprithreadweight",
                       jitprithreadweightOptBuf,
                       "-Xjitprithreadweight:");

    parseRuntimeOption("dalvik.vm.jittransitionweight",
                       jittransitionweightOptBuf,
                       "-Xjittransitionweight:");

    property_get("dalvik.vm.profilebootimage", propBuf, "");
    if (strcmp(propBuf, "true") == 0) {
        addOption("-Xps-profile-boot-class-path");
        addOption("-Xps-profile-aot-code");
    }

    /*
     * Madvise related options.
     */
    parseRuntimeOption("dalvik.vm.madvise-random", madviseRandomOptsBuf, "-XX:MadviseRandomAccess:");

    /*
     * Profile related options.
     */
    parseRuntimeOption("dalvik.vm.hot-startup-method-samples", hotstartupsamplesOptsBuf,
            "-Xps-hot-startup-method-samples:");

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

    /*
     * Garbage-collection related options.
     */
    parseRuntimeOption("dalvik.vm.gctype", gctypeOptsBuf, "-Xgc:");

    // If it set, honor the "enable_generational_cc" device configuration;
    // otherwise, let the runtime use its default behavior.
    std::string enable_generational_cc =
        server_configurable_flags::GetServerConfigurableFlag(RUNTIME_NATIVE_BOOT_NAMESPACE,
                                                             ENABLE_GENERATIONAL_CC,
                                                             /*default_value=*/ "");
    if (enable_generational_cc == "true") {
        addOption(kGenerationalCCRuntimeOption);
    } else if (enable_generational_cc == "false") {
        addOption(kNoGenerationalCCRuntimeOption);
    }

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

    /*
     * Enable debugging only for apps forked from zygote.
     */
    if (zygote) {
      // Set the JDWP provider and required arguments. By default let the runtime choose how JDWP is
      // implemented. When this is not set the runtime defaults to not allowing JDWP.
      addOption("-XjdwpOptions:suspend=n,server=y");
      parseRuntimeOption("dalvik.vm.jdwp-provider",
                         jdwpProviderBuf,
                         "-XjdwpProvider:",
                         "default");
    }

    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=assume-verified");
    } else {
        parseCompilerOption("dalvik.vm.image-dex2oat-filter", dex2oatImageCompilerFilterBuf,
                            "--compiler-filter=", "-Ximage-compiler-option");
    }

    // If there is a boot profile, it takes precedence over the image and preloaded classes.
    if (hasFile("/system/etc/boot-image.prof")) {
        addOption("-Ximage-compiler-option");
        addOption("--profile-file=/system/etc/boot-image.prof");
        addOption("-Ximage-compiler-option");
        addOption("--compiler-filter=speed-profile");
    } else {
        // 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");

        // If there is a dirty-image-objects file, push it.
        if (hasFile("/system/etc/dirty-image-objects")) {
            addOption("-Ximage-compiler-option");
            addOption("--dirty-image-objects=/system/etc/dirty-image-objects");
        }
    }

    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=assume-verified");

        // 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.
    // 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", ABI_STRING);
    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", ABI_STRING);
    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);
    }

    // Trace files are stored in /data/misc/trace which is writable only in debug mode.
    property_get("ro.debuggable", propBuf, "0");
    if (strcmp(propBuf, "1") == 0) {
        property_get("dalvik.vm.method-trace", propBuf, "false");
        if (strcmp(propBuf, "true") == 0) {
            addOption("-Xmethod-trace");
            parseRuntimeOption("dalvik.vm.method-trace-file",
                               methodTraceFileBuf,startVm
                               "-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.
    //
    // Note: bridging is only enabled for the zygote. Other runs of
    //       app_process may not have the permissions to mount etc.
    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 (zygote && 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");
    }

    // The mini-debug-info makes it possible to backtrace through JIT code.
    if (property_get_bool("dalvik.vm.minidebuginfo", 0)) {
        addOption("-Xcompiler-option");
        addOption("--generate-mini-debug-info");
    }

    // If set, the property below can be used to enable core platform API violation reporting.
    property_get("persist.debug.dalvik.vm.core_platform_api_policy", propBuf, "");
    if (propBuf[0] != '\0') {
      snprintf(corePlatformApiPolicyBuf,
               sizeof(corePlatformApiPolicyBuf),
               "-Xcore-platform-api-policy:%s",
               propBuf);
      addOption(corePlatformApiPolicyBuf);
    }

    /*
     * Retrieve the build fingerprint and provide it to the runtime. That way, ANR dumps will
     * contain the fingerprint and can be parsed.
     * Fingerprints are potentially longer than PROPERTY_VALUE_MAX, so parseRuntimeOption() cannot
     * be used here.
     * Do not ever re-assign fingerprintBuf as its c_str() value is stored in mOptions.
     */
    std::string fingerprint = GetProperty("ro.build.fingerprint", "");
    if (!fingerprint.empty()) {
        fingerprintBuf = "-Xfingerprint:" + fingerprint;
        addOption(fingerprintBuf.c_str());
    }

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

    /*
     * 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;
}
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/*
 1. Register android native functions with the VM.
 */
/*static*/ int AndroidRuntime::startReg(JNIEnv* env)
{
    ATRACE_NAME("RegisterAndroidNatives");
    /*
     * This hook causes all future threads created in this process to be
     * attached to the JavaVM.  (This needs to go away in favor of JNI
     * Attach calls.)
     */
    androidSetCreateThreadFunc((android_create_thread_fn) javaCreateThreadEtc);

    ALOGV("--- registering native functions ---\n");

    /*
     * Every "register" function calls one or more things that return
     * a local reference (e.g. FindClass).  Because we haven't really
     * started the VM yet, they're all getting stored in the base frame
     * and never released.  Use Push/Pop to manage the storage.
     */
    env->PushLocalFrame(200);

    if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {
        env->PopLocalFrame(NULL);
        return -1;
    }
    env->PopLocalFrame(NULL);

    //createJavaThread("fubar", quickTest, (void*) "hello");

    return 0;
}
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进入java层

代码路径:frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
main的主要工作:

1. 调用preload()来预加载类和资源
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2. 调用ZygoteServer()创建两个Server端的Socket--/dev/socket/zygote 和 /dev/socket/zygote_secondary，Socket用来等待ActivityManagerService来请求Zygote来创建新的应用程序进程。
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3. 调用forkSystemServer 来启动SystemServer进程，这样系统的关键服务也会由SystemServer进程启动起来。
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4. 最后调用runSelectLoop函数来等待客户端请求
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    public static void main(String argv[]) {
       ZygoteServer zygoteServer = null;

       // Mark zygote start. This ensures that thread creation will throw
       // an error.
       ZygoteHooks.startZygoteNoThreadCreation();

       // Zygote goes into its own process group.
       try {
           Os.setpgid(0, 0);
       } catch (ErrnoException ex) {
           throw new RuntimeException("Failed to setpgid(0,0)", ex);
       }

       Runnable caller;
       try {
           // Report Zygote start time to tron unless it is a runtime restart
           if (!"1".equals(SystemProperties.get("sys.boot_completed"))) {
               MetricsLogger.histogram(null, "boot_zygote_init",
                       (int) SystemClock.elapsedRealtime());
           }

           String bootTimeTag = Process.is64Bit() ? "Zygote64Timing" : "Zygote32Timing";
           TimingsTraceLog bootTimingsTraceLog = new TimingsTraceLog(bootTimeTag,
                   Trace.TRACE_TAG_DALVIK);
           bootTimingsTraceLog.traceBegin("ZygoteInit");
           RuntimeInit.enableDdms();

           boolean startSystemServer = false;
           String zygoteSocketName = "zygote";
           String abiList = null;
           boolean enableLazyPreload = false;
           for (int i = 1; i < argv.length; i++) {
               if ("start-system-server".equals(argv[i])) {
                   startSystemServer = true;
               } else if ("--enable-lazy-preload".equals(argv[i])) {
                   enableLazyPreload = true;
               } else if (argv[i].startsWith(ABI_LIST_ARG)) {
                   abiList = argv[i].substring(ABI_LIST_ARG.length());
               } else if (argv[i].startsWith(SOCKET_NAME_ARG)) {
                   zygoteSocketName = argv[i].substring(SOCKET_NAME_ARG.length());
               } else {
                   throw new RuntimeException("Unknown command line argument: " + argv[i]);
               }
           }

           final boolean isPrimaryZygote = zygoteSocketName.equals(Zygote.PRIMARY_SOCKET_NAME);

           if (abiList == null) {
               throw new RuntimeException("No ABI list supplied.");
           }

           // In some configurations, we avoid preloading resources and classes eagerly.
           // In such cases, we will preload things prior to our first fork.
           if (!enableLazyPreload) {
               bootTimingsTraceLog.traceBegin("ZygotePreload");
               EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
                       SystemClock.uptimeMillis());
               preload(bootTimingsTraceLog);
               EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
                       SystemClock.uptimeMillis());
               bootTimingsTraceLog.traceEnd(); // ZygotePreload
           } else {
               Zygote.resetNicePriority();
           }

           // Do an initial gc to clean up after startup
           bootTimingsTraceLog.traceBegin("PostZygoteInitGC");
           gcAndFinalize();
           bootTimingsTraceLog.traceEnd(); // PostZygoteInitGC

           bootTimingsTraceLog.traceEnd(); // ZygoteInit
           // Disable tracing so that forked processes do not inherit stale tracing tags from
           // Zygote.
           Trace.setTracingEnabled(false, 0);


           Zygote.initNativeState(isPrimaryZygote);

           ZygoteHooks.stopZygoteNoThreadCreation();

           zygoteServer = new ZygoteServer(isPrimaryZygote);

           if (startSystemServer) {
               Runnable r = forkSystemServer(abiList, zygoteSocketName, 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;
               }
           }

           Log.i(TAG, "Accepting command socket connections");

           // The select loop returns early in the child process after a fork and
           // loops forever in the zygote.
           caller = zygoteServer.runSelectLoop(abiList);
       } catch (Throwable ex) {
           Log.e(TAG, "System zygote died with exception", ex);
           throw ex;
       } finally {
           if (zygoteServer != null) {
               zygoteServer.closeServerSocket();
           }
       }

       // We're in the child process and have exited the select loop. Proceed to execute the
       // command.
       if (caller != null) {
           caller.run();
       }
   }
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总结

Zygote进程共做了如下几件事：

1. 解析init.zygotexxx.rc，创建AppRuntime并调用其start方法，启动Zygote进程。
2. 创建JavaVM并为JavaVM注册JNI.
3. 通过JNI调用ZygoteInit的main函数进入Zygote的Java框架层。
4. 通过ZygoteServer创建服务端Socket，预加载类和资源，并通过runSelectLoop函数等待如AMS等的请求。
5. 启动SystemServer进程。