If the sendmode is buffered then the message must be buffered if there is no pending receive.
发送完成函数在数据已经被全部拷贝出发送缓冲区后返回。它也许会附带额外的信息,根据发送模式。
2
Wire the send work item event between the custom step completion widget and the ECM step completion widget so that the custom widget can obtain the work item to render in its view mode.