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进程由init启动：
# /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/tasks
service 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
zygote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
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()
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
Zygote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.javaSystemServer(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();
/* * 启动其他服务, 太多了, 这里不一一列举 */ startOtherServices();
/*
* 进入循环
*/
Looper.loop();
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