上面的类中还出现了一个很重要的类型AsyncMethodBuilderCore，简单的了解一下这个类型也很有必要。

namespace System.Runtime.CompilerServices {     internal struct AsyncMethodBuilderCore     {         internal sealed class MoveNextRunner         {             private readonly ExecutionContext m_context;             internal IAsyncStateMachine m_stateMachine;             [SecurityCritical]             private static ContextCallback s_invokeMoveNext;             [SecurityCritical]             internal MoveNextRunner(ExecutionContext context, IAsyncStateMachine stateMachine)             {                 this.m_context = context;                 this.m_stateMachine = stateMachine;             }             [SecuritySafeCritical]             internal void Run()             {                 //这个方法被包装为“继续执行”委托实际执行的代码                 //这个方法最终要的作用是给继续执行的代码设置正确的ExecutionContext             }             [SecurityCritical]             private static void InvokeMoveNext(object stateMachine)             {                 ((IAsyncStateMachine)stateMachine).MoveNext();             }         }         private class ContinuationWrapper         {             internal readonly Action m_continuation;             private readonly Action m_invokeAction;             internal readonly Task m_innerTask;             internal ContinuationWrapper(Action continuation, Action invokeAction, Task innerTask)             {                 if (innerTask == null)                 {                     innerTask = AsyncMethodBuilderCore.TryGetContinuationTask(continuation);                 }                 this.m_continuation = continuation;                 this.m_innerTask = innerTask;                 this.m_invokeAction = invokeAction;             }             internal void Invoke()             {                 this.m_invokeAction();             }         }         internal IAsyncStateMachine m_stateMachine;         internal Action m_defaultContextAction;         public void SetStateMachine(IAsyncStateMachine stateMachine)         {                      }         //上文提到的获取“继续执行”委托的方法         //方法通过包装内部类MoveNextRunner的Run方法来实现         [SecuritySafeCritical]         internal Action GetCompletionAction(Task taskForTracing, ref AsyncMethodBuilderCore.MoveNextRunner runnerToInitialize)         {             Debugger.NotifyOfCrossThreadDependency();             ExecutionContext executionContext = ExecutionContext.FastCapture();             Action action;             AsyncMethodBuilderCore.MoveNextRunner moveNextRunner;             if (executionContext != null && executionContext.IsPreAllocatedDefault)             {                 action = this.m_defaultContextAction;                 if (action != null)                 {                     return action;                 }                 moveNextRunner = new AsyncMethodBuilderCore.MoveNextRunner(executionContext, this.m_stateMachine);                 action = new Action(moveNextRunner.Run);                 if (taskForTracing != null)                 {                     action = (this.m_defaultContextAction = this.OutputAsyncCausalityEvents(taskForTracing, action));                 }                 else                 {                     this.m_defaultContextAction = action;                 }             }             else             {                 moveNextRunner = new AsyncMethodBuilderCore.MoveNextRunner(executionContext, this.m_stateMachine);                 action = new Action(moveNextRunner.Run);                 if (taskForTracing != null)                 {                     action = this.OutputAsyncCausalityEvents(taskForTracing, action);                 }             }             if (this.m_stateMachine == null)             {                 runnerToInitialize = moveNextRunner;             }             return action;         }         private Action OutputAsyncCausalityEvents(Task innerTask, Action continuation)         {                      }         internal void PostBoxInitialization(IAsyncStateMachine stateMachine, AsyncMethodBuilderCore.MoveNextRunner runner, Task builtTask)         {             //初始化AsyncMethodBuilderCore中的状态机变量。这里发生装箱操作。         }         internal static void ThrowAsync(Exception exception, SynchronizationContext targetContext)         {             //将异常与SynchronizationContext相关联         }         internal static Action CreateContinuationWrapper(Action continuation, Action invokeAction, Task innerTask = null)         {             return new Action(new AsyncMethodBuilderCore.ContinuationWrapper(continuation, invokeAction, innerTask).Invoke);         }         internal static Action TryGetStateMachineForDebugger(Action action)         {             //获取用于调试目的的“继续执行”委托         }         internal static Task TryGetContinuationTask(Action action)         {             //获取“继续执行”的Task         }     } }