ART虚拟机启动的流程非常复杂，这里先将涉及到的各个模块列个提纲。后续再详细分析各个子模块。

总之，看虚拟机的启动流程，紧紧抓住下面这条主线即可。

vm_startup.jpg

init

init.rc

• source

  • system/core/rootdir/init.rc

• import zygote的资源文件

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

• angler board的值如下

  • ${ro.zygote}在build/target/product/core_64_bit.mk中定义

    # Set the zygote property to select the 64-bit primary, 32-bit secondary script
    
    # This line must be parsed before the one in core_minimal.mk
    
    PRODUCT_DEFAULT_PROPERTY_OVERRIDES += ro.zygote=zygote64_32
    

  • 获取ro.zygote属性

    angler:/ # getprop ro.zygote
    zygote64_32
    

init.zygote*.rc

• source
  • system/core/rootdir/init.zygote64_32.rc
• 内容

  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
    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
    socket zygote_secondary stream 660 root system
    onrestart restart zygote
    writepid /dev/cpuset/foreground/tasks
  

app_process

source

• frameworks/base/cmds/app_process/app_main.cpp
• Android.mk

  LOCAL_MODULE:= app_process
  LOCAL_MULTILIB := both
  LOCAL_MODULE_STEM_32 := app_process32
  LOCAL_MODULE_STEM_64 := app_process64
  

流程

• 创建AppRuntime对象

  AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
  

• 解析参数
• runtime.start
  • runtime.start("com.android.internal.os.ZygoteInit", args, zygote)
  • runtime.start("com.android.internal.os.RuntimeInit", args, zygote)

AndroidRuntime

source

• frameworks/base/core/jni/include/android_runtime/AndroidRuntime.h
• frameworks/base/core/jni/AndroidRuntime.cpp

AndroidRuntime::start()流程

• 初始化JNI

  JniInvocation jni_invocation;
  jni_invocation.Init(NULL);
  

• startVm(&mJavaVM, &env, zygote)

  • 构造ART VM参数(dalvik property)
  • JNI_CreateJavaVM(pJavaVM, pEnv, &initArgs)
    • 通过JNI创建ART虚拟机

• onVmCreated()

  • AppRuntime::onVmCreated()

• startReg()

  • androidSetCreateThreadFunc()
  • env->PushLocalFrame(200)
  • register_jni_procs()
    • register_com_android_internal_os_RuntimeInit()
    • register_com_android_internal_os_ZygoteInit()
    • ... ...
  • env->PopLocalFrame(NULL)

• 进入Java main()

  • env->FindClass(slashClassName)
  • env->GetStaticMethodID()
  • env->CallStaticVoidMethod(startClass, startMeth, strArray);

libnativehelper

source

• libnativehelper/include/nativehelper/jni.h
• libnativehelper/include/nativehelper/JniInvocation.h
• libnativehelper/JniInvocation.cpp

代码

• JniInvocation::Init()

  • dlopen("libart.so")
  • JniInvocation::FindSymbol()
    • JNI_GetDefaultJavaVMInitArgs_(JNI_GetDefaultJavaVMInitArgs)
    • JNI_CreateJavaVM_(JNI_CreateJavaVM)
    • JNI_GetCreatedJavaVMs_(JNI_GetCreatedJavaVMs)

• JniInvocation::JNI_CreateJavaVM

  jint JniInvocation::JNI_CreateJavaVM(JavaVM** p_vm, JNIEnv** p_env, void* vm_args) {
    return JNI_CreateJavaVM_(p_vm, p_env, vm_args);
  }
  

ART

source

• art/runtime/java_vm_ext.cc
• art/runtime/runtime.cc

流程

art::JNI_CreateJavaVM()

Runtime::Create()

• Runtime::ParseOptions()

  • ParsedOptions::Parse()
    • ParsedOptions::Parse()
      • ParsedOptions::DoParse()
        • ParsedOptions::ProcessSpecialOptions()
        • parser->Parse(argv_list)
        • 设置BootClassPath/Image等

• Runtime::Create()

  • instance_ = new Runtime()
  • Runtime::Init()
    • MemMap::Init()
    • QuasiAtomic::Startup()
    • oat_file_manager_ = new OatFileManager
    • monitor相关
      • Monitor::Init()
      • monitor_list_ = new MonitorList
      • monitor_pool_ = MonitorPool::Create()
    • thread_list_ = new ThreadList()
    • intern_table_ = new InternTable
    • heap_ = new gc::Heap()
    • jit_options_.reset()
    • fault_manager
      • BlockSignals()
      • InitPlatformSignalHandlers()
      • fault_manager.Init()
      • new StackOverflowHandler(&fault_manager)
      • new NullPointerHandler(&fault_manager)
    • java_vm_ = JavaVMExt::Create()
    • Thread::Startup()
    • Thread::Attach("main")
    • class_linker_
      • class_linker_ = new ClassLinker(intern_table_)
      • GetHeap()->HasBootImageSpace()
        • InitFromBootImage()
        • InitWithoutImage()
    • verifier::MethodVerifier::Init()
    • plugin.Load()
    • agent.Load()

• Thread::Attach()

  • new Thread()
  • Thread::Init()
    • JNIEnvExt::Create()
      • new JNIEnvExt()
        • GetFunctionTable()
        • GetJniNativeInterface()
          • gJniNativeInterface
            • JNI::FindClass()
            • JNI::RegisterNatives()
            • ... ...
  • self->InitStringEntryPoints()
  • SetState(kNative)

Runtime::Start()

• self->TransitionFromRunnableToSuspended(kNative)

• InitNativeMethods()

  • JniConstants::init(env)
  • RegisterRuntimeNativeMethods(env)
    • register_dalvik_system_DexFile(env)
    • register_dalvik_system_VMRuntime(env)
    • register_dalvik_system_ZygoteHooks(env)
    • ... ...
  • WellKnownClasses::Init(env)
    • CacheClass()
    • CacheMethod()
    • CacheField()
    • CachePrimitiveBoxingMethod()
  • java_vm_->LoadNativeLibrary("libjavacore.so")
  • java_vm_->LoadNativeLibrary("libopenjdk.so")
  • WellKnownClasses::LateInit(env)

• InitThreadGroups(self)

• Thread::FinishStartup()

• !IsZygote()

  • T: CreateJit()
  • F: jit::Jit::LoadCompilerLibrary(&error_msg)

• system_class_loader_ = CreateSystemClassLoader(this);

• !is_zygote_

  • InitNonZygoteOrPostFork()

• StartDaemonThreads()

  • env->CallStaticVoidMethod()
    • ReferenceQueueDaemon.INSTANCE.start()
    • FinalizerDaemon.INSTANCE.start()
    • FinalizerWatchdogDaemon.INSTANCE.start()
    • HeapTaskDaemon.INSTANCE.start()

Runtime::InitNonZygoteOrPostFork()

非Zygote或zygote fork后的子进程，走到这里会创建和启动jit/signalcatcher/jdwp三个线程。

• Runtime::InitNonZygoteOrPostFork()
  • Heap::CreateThreadPool()
  • Heap::ResetGcPerformanceInfo()
  • CreateJit()
  • StartSignalCatcher()
  • Dbg::StartJdwp()

ZygoteInit

source

• frameworks/base/core/java/com/android/internal/os/ZygoteInit.java

• frameworks/base/core/java/com/android/internal/os/ZygoteServer.java

• frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java

• frameworks/base/core/java/com/android/internal/os/Zygote.java

• frameworks/base/core/jni/com_android_internal_os_Zygote.cpp

• libcore/dalvik/src/main/java/dalvik/system/ZygoteHooks.java

  ZygoteInit最终会编译到framework.jar

main()

• new ZygoteServer()

• registerZygoteSocket()

• preload()

  • beginIcuCachePinning()

  • preloadClasses()

    • 主要是预加载preloaded-classes
      • preloaded-classes在代码库的位置:frameworks/base/preloaded-classes
      • preloaded-classes在手机中的位置:/system/etc/preloaded-classes
      • Android 8.1版本在frameworks/base/config/preloaded-classes
    • new FileInputStream(PRELOADED_CLASSES)
    • new BufferedReader(new InputStreamReader(is), 256)
    • line = br.readLine()
    • Class.forName(line, true, null)
      • classForName()
        • art::Class_classForName()
          • ClassLinker::FindClass()

  • preloadResources()

  • preloadOpenGL()

  • preloadSharedLibraries()

  • preloadTextResources()

• startSystemServer()

  • Zygote.forkSystemServer()

    • VM_HOOKS.preFork()
      • Daemons.stop()
      • waitUntilAllThreadsStopped()
      • nativePreFork()
    • nativeForkSystemServer()
      • com_android_internal_os_Zygote_nativeForkSystemServer()
        • ForkAndSpecializeCommon()
    • VM_HOOKS.postForkCommon()
      • Daemons.startPostZygoteFork()
        • ReferenceQueueDaemon.INSTANCE.startPostZygoteFork()
        • FinalizerDaemon.INSTANCE.startPostZygoteFork()
        • FinalizerWatchdogDaemon.INSTANCE.startPostZygoteFork()
        • HeapTaskDaemon.INSTANCE.startPostZygoteFork()

  • handleSystemServerProcess()

    • performSystemServerDexOpt()
    • ZygoteInit.zygoteInit()
      • RuntimeInit.commonInit()
      • ZygoteInit.nativeZygoteInit()
        • com_android_internal_os_ZygoteInit_nativeZygoteInit()
          • AppRuntime::onZygoteInit()
            • ProcessState::self()
            • startThreadPool()
      • RuntimeInit.applicationInit()
        • invokeStaticMain()
          • 获取指定类的main()方法
          • throw new Zygote.MethodAndArgsCaller(m, argv)
          • caller.run()
            • mMethod.invoke()

• zygoteServer.runSelectLoop()

  • runOnce()

    • Zygote.forkAndSpecialize()

      • VM_HOOKS.preFork()
      • nativeForkAndSpecialize()
        • com_android_internal_os_Zygote_nativeForkAndSpecialize()
          • ForkAndSpecializeCommon()

    • VM_HOOKS.postForkCommon()

    • 子进程: handleChildProc()

      这里和前面system_server的处理类似。

      • closeSocket()
      • ZygoteInit.zygoteInit()

    • 父进程: handleParentProc()

ForkAndSpecializeCommon()

• ForkAndSpecializeCommon()
  • fork()

子进程

• UnsetSigChldHandler()
• env->CallStaticVoidMethod(gZygoteClass, gCallPostForkChildHooks, ...)
  • callPostForkChildHooks()
    • VM_HOOKS.postForkChild()
      • nativePostForkChild()
        • ZygoteHooks_nativePostForkChild()
          • Runtime::InitNonZygoteOrPostFork()

父进程

• sigprocmask(SIG_UNBLOCK, &sigchld, nullptr)