c# - How the property isCompleted of IAsyncResult is updated? -

when call method asynchronously (using pattern beginxxx/endxxx), iasyncresult result after calling beginxxx. how property "iscompleted" (in returning result variable) updated if neither method beginxxxx or endxxx have reference result variable?

ex:

// create delegate. asyncmethodcaller caller = new asyncmethodcaller(ad.testmethod);  // initiate asychronous call. iasyncresult result = caller.begininvoke(3000, out threadid, null, null);  // poll while simulating work. while(result.iscompleted == false) {     thread.sleep(250);     console.write("."); } 

begininvoke returning iasyncresult have reference it. internally created , sent you.

for example, beginread in filestream creates filestreamasyncresult , returns it:

private unsafe filestreamasyncresult beginreadcore(byte[] bytes, int offset, int numbytes, asynccallback usercallback, object stateobject, int numbufferedbytesread) {     nativeoverlapped* overlappedptr;     filestreamasyncresult ar = new filestreamasyncresult {         _handle = this._handle,         _usercallback = usercallback,         _userstateobject = stateobject,         _iswrite = false,         _numbufferedbytes = numbufferedbytesread     };     manualresetevent event2 = new manualresetevent(false);     ar._waithandle = event2;      .....      if (hr == 0x6d)     {         overlappedptr->internallow = intptr.zero;         ar.callusercallback();         return ar;     }