Removing a handle from a I/O completion port and other questions about IOCP

The CreateIoCompletionPort function allows the creation of a new I/O completion port and the registration of file handles to an existing I/O completion port.

Then, I can use any function, like a recv on a socket or a ReadFile on a file with a OVERLAPPED structure to start an asynchronous operation.

I have to check whether the function call returned synchronously although it was called with an OVERLAPPED structure and in this case handle it directly. In the other case, when ERROR_IO_PENDING is returned, I can use the GetQueuedCompletionStatus function to be notified when the operation completes.

The question which arise are:

• How can I remove a handle from the I/O completion port? For example, when I add sockets to the IOCP, how can I remove closed ones? Should I just re-register another socket with the same completion key?

• Also, is there a way to make the calls ALWAYS go over the I/O completion port and don't return synchronously?

• And finally, is it possible for example to recv asynchronously but to send synchronously? For example when a simple echo service is implemented: Can I wait with an asynchronous recv for new data but send the response in a synchronous way so that code complexity is reduced? In my case, I wouldn't recv a second time anyways before the first request was processed.

• What happens if an asynchronous ReadFile has been requested, but before it completes, a WriteFile to the same file should be processed. Will the ReadFile be cancelled with an error message and I have to restar