System.IO.FileStream.InitFromHandle C# (CSharp) Method

        private void InitFromHandle(SafeFileHandle handle)
        {
            int handleType = Interop.Kernel32.GetFileType(_fileHandle);
            Debug.Assert(handleType == Interop.Kernel32.FileTypes.FILE_TYPE_DISK || handleType == Interop.Kernel32.FileTypes.FILE_TYPE_PIPE || handleType == Interop.Kernel32.FileTypes.FILE_TYPE_CHAR, "FileStream was passed an unknown file type!");

            _canSeek = handleType == Interop.Kernel32.FileTypes.FILE_TYPE_DISK;
            _isPipe = handleType == Interop.Kernel32.FileTypes.FILE_TYPE_PIPE;

            // This is necessary for async IO using IO Completion ports via our 
            // managed Threadpool API's.  This calls the OS's 
            // BindIoCompletionCallback method, and passes in a stub for the 
            // LPOVERLAPPED_COMPLETION_ROUTINE.  This stub looks at the Overlapped
            // struct for this request and gets a delegate to a managed callback 
            // from there, which it then calls on a threadpool thread.  (We allocate
            // our native OVERLAPPED structs 2 pointers too large and store EE 
            // state & a handle to a delegate there.)
            // 
            // If, however, we've already bound this file handle to our completion port,
            // don't try to bind it again because it will fail.  A handle can only be
            // bound to a single completion port at a time.
            if (_useAsyncIO && !GetSuppressBindHandle(handle))
            {
                try
                {
                    _fileHandle.ThreadPoolBinding = ThreadPoolBoundHandle.BindHandle(_fileHandle);
                }
                catch (Exception ex)
                {
                    // If you passed in a synchronous handle and told us to use
                    // it asynchronously, throw here.
                    throw new ArgumentException(SR.Arg_HandleNotAsync, nameof(handle), ex);
                }
            }
            else if (!_useAsyncIO)
            {
                if (handleType != Interop.Kernel32.FileTypes.FILE_TYPE_PIPE)
                    VerifyHandleIsSync();
            }

            if (_canSeek)
                SeekCore(0, SeekOrigin.Current);
            else
                _filePosition = 0;
        }