因为CLR是一个托管环境，所以运行时中有几个组件需要在执行任何代码之前初始化。本文将介绍EE（执行引擎）启动程序，并详细检查初始化过程。68只是一个粗略的指南，它取决于您使用的运行时版本、启用了哪些功能以及其他一些东西。
样例代码
假设你有一个最简单的C#程序，在CLR将“Hello World”输出到控制台之前会发生什么？
using System;
namespace ConsoleApplication
{
public class Program
{
public static void Main(string[] args)
{
Console.WriteLine("Hello World!");
}
}
}
进入EE（执行引擎）的代码路径
当.NET可执行文件运行时，通过以下代码路径进入EE：
- _CorExeMain() (the external entry point)
- call to _CorExeMainInternal()
- _CorExeMainInternal()
- call to EnsureEEStarted()
- EnsureEEStarted()
- EEStartup()
- call to EEStartupHelper()
- EEStartupHelper()
因此，我们在EEStartupHelper（）中结束，它在高层执行以下操作（来自ceemain.cpp中的注释）---EEStartup负责运行时的所有一次性初始化：
- 创建默认和共享的appdomains。
- 加载mscorlib.dll并加载基本类型（System.Object…）
EE（执行引擎）启动程序的主要阶段
下面的列表包含了从EEStartupHelper（）调用的所有单独函数（~500 L.O.C）。为了使它们更容易理解，我们将它们分为不同的阶段：
- 第1阶段-在运行其他任何东西之前，设置需要到位的基础设施
- 第2阶段-初始化核心低层组件
- 第3阶段-启动低级组件，即错误处理、Profiling API、调试
- 阶段4-启动主要组件，即垃圾收集器（GC）、AppDomains、安全性
- 第5阶段-最终设置，然后通知其他组件EE已启动
注意：下面列表中的某些项仅在生成时定义了特定功能时才包含，这些项由ifdef语句中的包含来指示。还要注意的是，这些链接指向要调用的函数的代码，而不是EEStartupHelper（）中的代码行。
第1阶段-在运行其他任何东西之前，设置需要到位的基础设施
- Wire-up console handling - SetConsoleCtrlHandler(..) (
ifndef FEATURE_PAL)
- Initialise the internal
SString class (everything uses strings!) - SString::Startup()
- Make sure the configuration is set-up, so settings that control run-time options can be accessed - EEConfig::Set-up() and InitializeHostConfigFile() (
#if !defined(CROSSGEN_COMPILE))
- Initialize Numa and CPU group information - NumaNodeInfo::InitNumaNodeInfo() and CPUGroupInfo::EnsureInitialized() (
#ifndef CROSSGEN_COMPILE)
- Initialize global configuration settings based on startup flags - InitializeStartupFlags()
- Set-up the Thread Manager that gives the runtime access to the OS threading functionality (
StartThread(), Join(), SetThreadPriority() etc) - InitThreadManager()
- Initialize Event Tracing (ETW) and fire off the CLR startup events - InitializeEventTracing() and ETWFireEvent(EEStartupStart_V1) (
#ifdef FEATURE_EVENT_TRACE)
- Set-up the GS Cookie (Buffer Security Check) to help prevent buffer overruns - InitGSCookie()
- Create the data-structures needed to hold the ‘frames’ used for stack-traces - Frame::Init()
- Ensure initialization of Apphacks environment variables - GetGlobalCompatibilityFlags() (
#ifndef FEATURE_CORECLR)
- Create the diagnostic and performance logs used by the runtime - InitializeLogging() (
#ifdef LOGGING) and PerfLog::PerfLogInitialize() (#ifdef ENABLE_PERF_LOG)
第2阶段-初始化核心低层组件
- Write to the log
===================EEStartup Starting===================
- Ensure that the Runtime Library functions (that interact with ntdll.dll) are enabled - EnsureRtlFunctions() (
#ifndef FEATURE_PAL)
- Set-up the global store for events (mutexes, semaphores) used for synchronisation within the runtime - InitEventStore()
- Create the Assembly Binding logging mechanism a.k.a Fusion - InitializeFusion() (
#ifdef FEATURE_FUSION)
- Then initialize the actual Assembly Binder infrastructure - CCoreCLRBinderHelper::Init() which in turn calls AssemblyBinder::Startup() (
#ifdef FEATURE_FUSION is NOT defined)
- Set-up the heuristics used to control Monitors, Crsts, and SimpleRWLocks - InitializeSpinConstants()
- Initialize the InterProcess Communication with COM (IPC) - InitializeIPCManager() (
#ifdef FEATURE_IPCMAN)
- Set-up and enable Performance Counters - PerfCounters::Init() (
#ifdef ENABLE_PERF_COUNTERS)
- Set-up the CLR interpreter - Interpreter::Initialize() (
#ifdef FEATURE_INTERPRETER), turns out that the CLR has a mode where your code is interpreted instead of compiled!
- Initialise the stubs that are used by the CLR for calling methods and triggering the JIT - StubManager::InitializeStubManagers(), also Stub::Init() and StubLinkerCPU::Init()
- Set up the core handle map, used to load assemblies into memory - PEImage::Startup()
- Startup the access checks options, used for granting/denying security demands on method calls - AccessCheckOptions::Startup()
- Startup the mscorlib binder (used for loading “known” types from mscorlib.dll) - MscorlibBinder::Startup()
- Initialize remoting, which allows out-of-process communication - CRemotingServices::Initialize() (
#ifdef FEATURE_REMOTING)
- Set-up the data structures used by the GC for weak, strong and no-pin references - Ref_Initialize()
- Set-up the contexts used to proxy method calls across App Domains - Context::Initialize()
- Wire-up events that allow the EE to synchronise shut-down -
g_pEEShutDownEvent->CreateManualEvent(FALSE)
- Initialise the process-wide data structures used for reader-writer lock implementation - CRWLock::ProcessInit() (
#ifdef FEATURE_RWLOCK)
- Initialize the debugger manager - CCLRDebugManager::ProcessInit() (
#ifdef FEATURE_INCLUDE_ALL_INTERFACES)
- Initialize the CLR Security Attribute Manager - CCLRSecurityAttributeManager::ProcessInit() (
#ifdef FEATURE_IPCMAN)
- Set-up the manager for Virtual call stubs - VirtualCallStubManager::InitStatic()
- Initialise the lock that that GC uses when controlling memory pressure - GCInterface::m_MemoryPressureLock.Init(CrstGCMemoryPressure)
- Initialize Assembly Usage Logger - InitAssemblyUsageLogManager() (
#ifndef FEATURE_CORECLR)
第3阶段-启动低级组件，即错误处理、Profiling API、调试
- Set-up the App Domains used by the CLR - SystemDomain::Attach() (also creates the DefaultDomain and the SharedDomain by calling SystemDomain::CreateDefaultDomain() and SharedDomain::Attach())
- Start up the ECall interface, a private native calling interface used within the CLR - ECall::Init()
- Set-up the caches for the stubs used by
delegates - COMDelegate::Init()
- Set-up all the global/static variables used by the EE itself - ExecutionManager::Init()
- Initialise Watson, for windows error reporting - InitializeWatson(fFlags) (
#ifndef FEATURE_PAL)
- Initialize the debugging services, this must be done before any EE thread objects are created, and before any classes or modules are loaded - InitializeDebugger() (
#ifdef DEBUGGING_SUPPORTED)
- Activate the Managed Debugging Assistants that the CLR provides - ManagedDebuggingAssistants::EEStartupActivation() (
ifdef MDA_SUPPORTED)
- Initialise the Profiling API - ProfilingAPIUtility::InitializeProfiling() (
#ifdef PROFILING_SUPPORTED)
- Initialise the exception handling mechanism - InitializeExceptionHandling()
- Install the CLR global exception filter - InstallUnhandledExceptionFilter()
- Ensure that the initial runtime thread is created - SetupThread() in turn calls SetupThread(..)
- Initialise the PreStub manager (PreStub’s trigger the JIT) - InitPreStubManager() and the corresponding helpers StubHelpers::Init()
- Initialise the COM Interop layer - InitializeComInterop() (
#ifdef FEATURE_COMINTEROP)
- Initialise NDirect method calls (lazy binding of unmanaged P/Invoke targets) - NDirect::Init()
- Set-up the JIT Helper functions, so they are in place before the execution manager runs - InitJITHelpers1() and InitJITHelpers2()
- Initialise and set-up the SyncBlock cache - SyncBlockCache::Attach() and SyncBlockCache::Start()
- Create the cache used when walking/unwinding the stack - StackwalkCache::Init()
阶段4-启动主要组件，即垃圾收集器（GC）、AppDomains、安全性
- Start up security system, that handles Code Access Security (CAS) - Security::Start() which in turn calls SecurityPolicy::Start()
- Wire-up an event to allow synchronisation of AppDomain unloads - AppDomain::CreateADUnloadStartEvent()
- Initialise the ‘Stack Probes’ used to setup stack guards InitStackProbes() (
#ifdef FEATURE_STACK_PROBE)
- Initialise the GC and create the heaps that it uses - InitializeGarbageCollector()
- Initialise the tables used to hold the locations of pinned objects - InitializePinHandleTable()
- Inform the debugger about the DefaultDomain, so it can interact with it - SystemDomain::System()->PublishAppDomainAndInformDebugger(..) (
#ifdef DEBUGGING_SUPPORTED)
- Initialise the existing OOB Assembly List (no idea?) - ExistingOobAssemblyList::Init() (
#ifndef FEATURE_CORECLR)
- Actually initialise the System Domain (which contains mscorlib), so that it can start executing - SystemDomain::System()->Init()
第5阶段最终设置，然后通知其他组件EE已经启动了第4阶段-启动主要组件，即垃圾收集器（GC）、AppDomains、Security
- Tell the profiler we’ve stated up - SystemDomain::NotifyProfilerStartup() (
#ifdef PROFILING_SUPPORTED)
- Pre-create a thread to handle AppDomain unloads - AppDomain::CreateADUnloadWorker() (
#ifndef CROSSGEN_COMPILE)
- Set a flag to confirm that ‘initialisation’ of the EE succeeded -
g_fEEInit = false
- Load the System Assemblies (‘mscorlib’) into the Default Domain - SystemDomain::System()->DefaultDomain()->LoadSystemAssemblies()
- Set-up all the shared static variables (and
String.Empty) in the Default Domain - SystemDomain::System()->DefaultDomain()->SetupSharedStatics(), they are all contained in the internal class SharedStatics.cs
- Set-up the stack sampler feature, that identifies ‘hot’ methods in your code - StackSampler::Init() (
#ifdef FEATURE_STACK_SAMPLING)
- Perform any once-only SafeHandle initialization - SafeHandle::Init() (
#ifndef CROSSGEN_COMPILE)
- Set flags to indicate that the CLR has successfully started -
g_fEEStarted = TRUE, g_EEStartupStatus = S_OK and hr = S_OK
- Write to the log
===================EEStartup Completed===================
一旦这些都完成了，CLR现在就可以执行您的代码了！
执行用户代码
您的代码将通过以下代码流执行（在第一次被“JITted”之后）：
- CorHost2::ExecuteAssembly()
- calling ExecuteMainMethod()
- Assembly::ExecuteMainMethod()
- RunMain() (in assembly.cpp)
- eventually calling into you main() method
- full explanation of the ‘call’ process
转自：https://mattwarren.org/2017/02/07/The-68-things-the-CLR-does-before-executing-a-single-line-of-your-code/
在执行一行代码之前CLR做的68件事
原文：https://www.cnblogs.com/yilang/p/12063822.html
