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Here,wo is a local variable of type Win32Com.OVERLAPPED,and ptrUWO is a private class variable of type IntPtr.Marshal is a static object in System.Runtime.InteropServices that provides access to the interop marshaler.In this code,i am doing manually what the marshaler normally does automatically when an external function is called.The first step is to allocate an appropriately sized block of unmanaged memory, christian louboutin sale then copy the contents of the managed structure into it,remapping the memory layout as required.After the function call,the marshaler would normally use Marshal.PtrToStructure to perform the reverse copy,then Marshal.FreeHGlobal to release the memory.I perform this operation manually because of the special way the API uses the OVERLAPPED structure.I will specify it in a WriteFile call,but then the operating system will continue to use it after the call returns.Programmers bring RS232 device communications into the. christian louboutin booties Once the port is opened and configured.Open invokes a virtual method AfterOpen,which may be overridden to check the status of the connection to the remote device and possibly also to configure it.If this returns false,the port will be closed again and Open itself will return false.There is also a BeforeClose method for shutting down the remote devi Before sending new data,the result of any pvious Send should be checked, enabling the detection of error conditions or timeouts.Strangely,the API treats a pending operation as an error, christian louboutin boots sale but a timeout as perfectly normal—the only way of detecting it is that fewer bytes are sent than were queued.Ironing out this kind of anomaly is one of the hidden pleasures of writing a wrapper library!Although I could allow multiple pending sends,each with its own OVERLAPPED structure,it would add a lot of complexity.Instead,I have blocked a subsequent Send until the pvious one completes.If this blocking is a problem,it can be disabled by setting the checkAllSends member to false,in which case the OVERLAPPED structure is reused and there is no guarantee that errors or timeouts will be caught.Figure 6 shows a simplified version of ReceiveThread.SetCommMask indicates that I want to be notified when a new byte arrives. christian louboutin on sale WaitCommEvent may return true,in which case there is already one or more bytes waiting.If it returns false with error code ERROR_IO_PENDING, I can suspend the thread until a byte arrives.The OVERLAPPED structure that was passed to WaitCommEvent includes the handle to an AutoResetEvent,which will be signaled when the byte arrives.When I execute the AutoResetEvent's WaitOne method,execution is suspended until the event is signaled.
Error handling and exceptions need to be carefully considered when using worker threads.Any unhandled exceptions that occur in ReceiveThread,any of the virtual methods called from it,and any methods or events called or fired from any of these will propagate up and be handled by the catch clause.If the exception is not ThreadAbortException.ykl
