Using HttpApi with I/O Completion Ports

问题:

I've just stumbled upon Microsoft's HTTP Server API. The introduction states:

The HTTP Server API enables applications to communicate over HTTP without using Microsoft Internet Information Server (IIS). Applications can register to receive HTTP requests for particular URLs, receive HTTP requests, and send HTTP responses. The HTTP Server API includes SSL support so that applications can exchange data over secure HTTP connections without IIS. It is also designed to work with I/O completion ports.

Finding this cool, I took a long hard look at the list of functions for both versions of the API. Now, the only other part of the documentation that mentions I/O completion ports is the HttpReceiveHttpRequest() function. The last parameter is an optional OVERLAPPED structure with the following description:

For asynchronous calls, set pOverlapped to point to an OVERLAPPED structure; for synchronous calls, set it to NULL. A synchronous call blocks until a request has arrived in the specified queue and some or all of it has been retrieved, whereas an asynchronous call immediately returns ERROR_IO_PENDING and the calling application then uses GetOverlappedResult() or I/O completion ports to determine when the operation is completed. For more information about using OVERLAPPED structures for synchronization, see Synchronization and Overlapped Input and Output.

There is no other information, and all structures are opaque and deliberately hide connection information. Also notice that the Synchronization and Overlapped Input and Output subject makes no mention of the HTTP API.

Does anyone have any idea on how to connect the HTTP API's queue to an I/O completion port?

回答1:

Using IO completion ports is trivially simple in theory, but abomnible in practice :P

the "normal" usage is:

1. Call CreateIOCompletionPort to create a IO completion port handle.
2. Create a bunch of threads, and get each thread to loop, on a call to GetOverlappedResult. GetOverlappedResult will return when an overlapped operation associated with the port completes, with structures indicating which handle, and operation, was completed.
3. As your program runs, and creates objects that it wishes to handle asynchronously, it associates each HANDLE with the IO CompletionPort handle by calling CreateIOCompletionPort again.

Now, each time the application issues an asynchronous operation on the HANDLE (which is signalled by passing in an OVERLAPPED struct) the notification of the completed operation will be indicated by one of the threads thats waiting on GetOverlappedResult returning.

The clear implication is that the HANDLE returned by HttpCreateRequestQueue can be associated with an IO Completion port and subsequent asynchronous operations will result in GetOverlappedResult's returning the result of the operation.