C#筆記 – 線程及異步（三）異步函數

• 值得注意的是，每個await都有一個TaskAwaiter類型的字段

  • 在任何時候，都只有其中一個是重要的，這一個引用了最近執行、以異步方式完成的await

• 然後這是異步方法的核心流程概要IL

.method private hidebysig newslot virtual final 
        instance void  MoveNext() cil managed
{
  .override [System.Runtime]System.Runtime.CompilerServices.IAsyncStateMachine::MoveNext
  // 程式碼大小       448 (0x1c0)
  //...
    .try
    {
      .try
      {
        //調用Method1Async並獲得其Awaiter
        IL_0030:  call       class [System.Runtime]System.Threading.Tasks.Task`1<class CLR_Ch28.Program/Type1> CLR_Ch28.Program::Method1Async()
        IL_0035:  callvirt   instance valuetype [System.Runtime]System.Runtime.CompilerServices.TaskAwaiter`1<!0> class [System.Runtime]System.Threading.Tasks.Task`1<class CLR_Ch28.Program/Type1>::GetAwaiter()
        //...
        //如果還沒完成，使用異步方式完成
        IL_003d:  call       instance bool valuetype [System.Runtime]System.Runtime.CompilerServices.TaskAwaiter`1<class CLR_Ch28.Program/Type1>::get_IsCompleted()
        IL_0042:  brtrue.s   IL_0087
        IL_0048:  stfld      int32 CLR_Ch28.Program/'<MyMethodAsync>d__5'::'<>1__state'
        //...
        //保存awaiter以便將來返回
        IL_004f:  stfld      valuetype [System.Runtime]System.Runtime.CompilerServices.TaskAwaiter`1<class CLR_Ch28.Program/Type1> CLR_Ch28.Program/'<MyMethodAsync>d__5'::'<>u__1'
        //...
        IL_0057:  ldflda     valuetype [System.Threading.Tasks]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<string> CLR_Ch28.Program/'<MyMethodAsync>d__5'::'<>t__builder'
        //...
        //await操作完成時調用MoveNext
        IL_0060:  call       instance void valuetype [System.Threading.Tasks]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<string>::AwaitUnsafeOnCompleted<valuetype [System.Runtime]System.Runtime.CompilerServices.TaskAwaiter`1<class CLR_Ch28.Program/Type1>,class CLR_Ch28.Program/'<MyMethodAsync>d__5'>(!!0&,!!1&)
        //...
        //第一個await的結果捕捉
        IL_008a:  call       instance !0 valuetype [System.Runtime]System.Runtime.CompilerServices.TaskAwaiter`1<class CLR_Ch28.Program/Type1>::GetResult()
        //...
        //啟動循環
        IL_00ae:  br         IL_0148
        //內部邏輯，與第一個await流程類似
        //...
        //結束循環
        IL_00ec:  leave      IL_01bf
        //第二個await的結果
        IL_010f:  ldloca.s   V_4
        IL_0111:  call       instance !0 valuetype [System.Runtime]System.Runtime.CompilerServices.TaskAwaiter`1<class CLR_Ch28.Program/Type2>::GetResult()
        //...
      }  // end .try
      catch [System.Runtime]System.Exception 
      {
        //...
        IL_0166:  ldstr      "Catch"
        //...
        }  // end handler
      IL_0174:  leave.s    IL_0188
    }  // end .try
    finally
    {
      //...
      IL_017b:  ldstr      "Finally"
      //...
      IL_0187:  endfinally
    }  // end handler
    IL_0188:  ldstr      "Done"
    //...
  }  // end .try
  catch [System.Runtime]System.Exception 
  {
    //狀態機異常處理部分
    //...
    IL_01a2:  call       instance void valuetype [System.Threading.Tasks]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<string>::SetException(class [System.Runtime]System.Exception)
    IL_01a7:  nop
    IL_01a8:  leave.s    IL_01bf
  }  // end handler
  //...
  //無異常，返回結果
  IL_01b9:  call       instance void valuetype [System.Threading.Tasks]System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<string>::SetResult(!0)
  IL_01be:  nop
  IL_01bf:  ret
} // end of method '<MyMethodAsync>d__5'::MoveNext

• 書中把IL編譯回C#的MoveNext概要