Android Zygote介绍

著论准过秦，作赋拟子虚。这篇文章主要讲述Android Zygote介绍相关的知识，希望能为你提供帮助。
1. 介绍 Zygote是android系统创建新进程的核心进程，负责启动Dalvik虚拟机，加载一些必要的系统资源和系统类，启动system_server进程，随后进入等待处理app应用请求
Zygote涉及的主要代码如下

frameworks/base/cmds/app_process/App_main.cpp frameworks/base/core/jni/AndroidRuntime.cppframeworks/base/core/java/com/android/internal/os/ - Zygote.java - ZygoteInit.java - ZygoteServer.java - ZygoteConnection.java

2. 启动Zygote进程由init启动，在笔者开发板上是以app_process64为主模式，app_process为辅

# /vendor/default.prop ro.zygote=zygote64_32# /init.rc import /init.${ro.zygote}.rc on zygote-start & & property:ro.crypto.state=... # A/B update verifier that marks a successful boot. exec_start update_verifier_nonencrypted start netd start zygote start zygote_secondary# /init.zygote64_32.rc service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server --socket-name=zygote class main priority -20 user root group root readproc reserved_disk socket zygote stream 660 root system onrestart write /sys/android_power/request_state wake onrestart write /sys/power/state on onrestart restart audioserver onrestart restart cameraserver onrestart restart media onrestart restart netd onrestart restart wificond writepid /dev/cpuset/foreground/tasksservice zygote_secondary /system/bin/app_process32 -Xzygote /system/bin --zygote --socket-name=zygote_secondary --enable-lazy-preload class main priority -20 user root group root readproc reserved_disk socket zygote_secondary stream 660 root system onrestart restart zygote writepid /dev/cpuset/foreground/tasks

属性 ro.zygote 的值包括zygote32、zygote64、zygote32_64、zygote64_32，对应区别如下：
- init.zygote32.rc：zygote进程对应的执行程序是app_process(纯32bit模式)
- init.zygote64.rc：zygote进程对应的执行程序是app_process64(纯64bit模式)
- init.zygote32_64.rc：启动两个zygote进程，对应的执行程序分别是app_process32(主模式)、app_process64
- init.zygote64_32.rc：启动两个zygote进程，对应的执行程序分别是app_process64(主模式)、app_process32
3. app_processzygote和zygote_secondary其实大同小异，都是执行/system/bin/app_process，其执行的的应用及参数如下

app_process64 -Xzygote /system/bin --zygote --start-system-server --socket-name=zygote

这里以app_process作为切入点来看看其主要流程

文章图片

main() AppRuntime::AppRuntime() AndroidRuntime::AndroidRuntime() SkGraphics::Init() // 创建Dalvik缓存 maybeCreateDalvikCache() AndroidRuntime::start("com.android.internal.os.ZygoteInit", args, ) // JniInvocation位于libnativehelper JniInvocation::JniInvocation() /* * 初始化虚拟机环境 * - 加载libart.so, 由art/runtime生成 * - 导出JNI_GetDefaultJavaVMInitArgs * - 导出JNI_CreateJavaVM * - 导出JNI_GetCreatedJavaVMs */ JniInvocation::Init(NULL) AndroidRuntime::startVm(JavaVM, JNIEnv,) // 获取虚拟机参数 AndroidRuntime::parseRuntimeOption() // 位于libnativehelper ??? JNI_CreateJavaVM() JniInvocation::JNI_CreateJavaVM() AppRuntime::onVmCreated() // 向VM注册native函数 AndroidRuntime::startReg() /* * 依次注册预定义的gRegJNI列表, 包括 *frameworks/base/core/jni/android_xxx.cpp *frameworks/base/core/jni/com_xxx.cpp * 下面以android_util_Process.cpp为例 */ register_jni_procs(gRegJNI) register_android_os_Process() /* * 注册 android.os.Process 类 * 注册 android.os.Process.setUid 方法 * ... * * static const JNINativeMethod methods[] = { *... *{"setUid", "(I)I", (void*)android_os_Process_setUid}, *... * }; */ RegisterMethodsOrDie(env, "android/os/Process", methods,) AndroidRuntime::registerNativeMethods(env, className, methods, ) jniRegisterNativeMethods() JNINativeInterface::RegisterNatives() /* * 找到入口com.android.internal.os.ZygoteInit(在register_jni_procs中注册) */ JNIEnv::FindClass("com/android/internal/os/ZygoteInit") // 找到入口类的main函数 JNIEnv::GetStaticMethodID(jclass, "main") // 执行com.android.internal.os.ZygoteInit.main() JNIEnv::CallStaticVoidMethod(jclass, jmethodID, jobjectArray)

接下来就是ZygoteInit的执行过程

ZygoteInit.main() /* * 在init.zygote*.rc中注册了zygote套接字 * init进程在启动service时会添加环境变量 * 环境变量: "ANDROID_SOCKET_zygote" * * 从环境变量中获取socket的fd * 通过LocalServerSocket()创建服务端 */ ZygoteServer::registerServerSocketFromEnv("zygote") // FIXME: Add More ZygoteInit::preload() // 主动进行GC操作 ZygoteInit::gcAndFinalize() Zygote::nativeSecurityInit() com_android_internal_os_Zygote_nativeSecurityInit() Zygote::nativeUnmountStorageOnInit() com_android_internal_os_Zygote_nativeUnmountStorageOnInit() /* * 启动SystemServer, 重命名为system_server */ ZygoteInit::forkSystemServer() Zygote::forkSystemServer() Zygote::nativeForkSystemServer() com_android_internal_os_Zygote_nativeForkSystemServer() ForkAndSpecializeCommon() fork() // 子进程: com.android.internal.os.Zygote JNIENV::CallStaticVoidMethod("com/android/internal/os/Zygote") // 子进程: FIXME: Add More ZygoteInit::handleSystemServerProcess() ZygoteInit::zygoteInit(, "com.android.server.SystemServer", ) RuntimeInit::commonInit() ZygoteInit::nativeZygoteInit() com_android_internal_os_ZygoteInit_nativeZygoteInit() AppRuntime::onZygoteInit() RuntimeInit::applicationInit() RuntimeInit::findStaticMain("com.android.server.SystemServer", , ) // 执行com.android.server.SystemServer.main() MethodAndArgsCaller.run() /* * 监听zygote socket * 等待客户端消息并处理 * ZygoteConnection用于表示和客户端的连接 */ ZygoteServer::runSelectLoop() ZygoteConnection::processOneCommand()

TIP: app_process有两种启动模式，都是调用AppRuntime::start()，加载ZygoteInit或RuntimeInit两个Java类
- Zygote模式: 即初始化zygote进程，也即上面分析的流程
- Application模式: 即启动普通应用程序，传递的参数有class名字以及class带的参数
4. SystemServerZygote启动过程中fork了一个新进程用于启动com.android.server.SystemServer，即SystemServer，文件路径如下

frameworks/base/services/java/com/android/server/SystemServer.java

SystemServer(进程名为system_server)是android服务的提供者，所有service运行在该进程中，主要流程如下

SystemServer::main() SystemServer::run() /* * 一些准备工作 */ Looper.prepareMainLooper() /* * 初始化native服务 *libandroid_servers *< - libservices.core *由[frameworks/base/services/core/jni/*]编译生成 */ System::loadLibrary("android_servers"); // 位于frameworks/base/services/core/jni/onload.cpp JNI_OnLoad() register_android_server_broadcastradio_BroadcastRadioService() register_android_server_broadcastradio_Tuner() register_android_server_PowerManagerService() /* * 向com.android.server.power.PowerManagerService注册native方法 *2rd参数: "com/android/server/power/PowerManagerService" *3rd参数: gPowerManagerServiceMethods *4rd参数: NELEM(gPowerManagerServiceMethods) */ jniRegisterNativeMethods(JNIEnv, , ,) register_android_server_SerialService() ... // FIXME SystemServer::performPendingShutdown() // 初始化系统上下文 SystemServer::createSystemContext() ActivityThread::systemMain() new ActivityThread() // FIXME: a lot thing seems done ActivityThread::attach(true, 0) ActivityThread::getSystemContext() mSystemServiceManager = new SystemServiceManager() /* * 区别于BinderService, Localservice只在本进程使用 */ LocalServices.addService(SystemServiceManager.class, mSystemServiceManager)/* * 启动关键服务 */ startBootstrapServices(); // FIXME: 读取系统配置 SystemServerInitThreadPool.get().submit(SystemConfig::getInstance, ) /* * 启动[Installer]服务并连接至installd * installd为native服务, 位于frameworks/native/cmds/installd/ */ SystemServiceManager::startService(Installer.class) new Installer() & & Installer::onStart()

// 启动[设备标识符]服务

SystemServiceManager::startService(DeviceIdentifiersPolicyService.class) new DeviceIdentifiersPolicyService() DeviceIdentifiersPolicyService::onStart()

// 启动[AMS]服务

SystemServiceManager::startService(ActivityManagerService.Lifecycle.class) new ActivityManagerService() ActivityManagerService::onStart()

// 启动[电源管理服务]

SystemServiceManager::startService(PowerManagerService.class) new PowerManagerService() PowerManagerService::onStart() publishBinderService(Context.POWER_SERVICE, new BinderService()); // 向servicemanager注册服务 ServiceManager.addService( , , , ) publishLocalService(PowerManagerInternal.class, new LocalService()); LocalServices.addService( , )

// 初始化电源管理功能

ActivityManagerService::initPowerManagement()SystemServiceManager::startService(RecoverySystemService.class) SystemServiceManager::startService(LightsService.class)

// 启动[显示管理服务]

SystemServiceManager::startService(DisplayManagerService.class)// 等待默认显示器 SystemServiceManager::startBootPhase(SystemService.PHASE_WAIT_FOR_DE~T_DISPLAY); DisplayManagerService::onBootPhase(SystemService.PHASE_WAIT_FOR_DE~T_DISPLAY)

// 启动[PackageManagerService, PMS]服务

PackageManagerService::main(mSystemContext, installer, , ) ActivityManagerService::setSystemProcess() new OverlayManagerService(mSystemContext, installer) SystemServiceManager::startService(mOverlayManagerService) startSensorService() /* * 启动必要服务 */ startCoreServices(); SystemServiceManager::startService(BatteryService.class) SystemServiceManager::startService(UsageStatsService.class) BinderCallsStatsService.start();