Re: Asynchronous socket operations and threadpool

"William Stacey [MVP]" <william.stacey@xxxxxxxxx> wrote
| The scenario I keep seeing is:
|
| 0 - You get the Socket.BeginRead callback, and get your data. You're now
on
| an IOCP thread.
| 1 - Perform an async operation (say, lookup MX or SRV records in the
DNS).
| Pass in a delegate for the callback.
| 2 - While that operation is under way, your IOCP thread keeps going
doing
| whatever it can do.
| 3 - Eventually the IOCP thread hits a WaitHandle and has to sync up with
the
| async operation you kicked off.

I thought we are talking about a pure async server? This is more like a
thread per connection server because your blocking on a Wait.

The wait is on a WaitHandle for an operation performed during a callback.
For example, you get a big chunk of data for the user (via the async call)
and realize you need to perform a database lookup to satisfy the reqeust.
You kick off the DB Request async, do as much more of the user request as
you can, then wait for the DB Request to complete. Once it's done, you send
the user back his data, and put the socket back into BeginRead.

I tend do either this, or just do everything synchronous once I'm on the
IOCP thread in my callback.

At various times, I've tried doing this a number of other ways and always
come back to this approach.

In a full async server, you would not block at all (or for very short
times).
In Socket.EndRead, you would get data, update state, and Begin your
next async operation, and on down the line like walking a "virtual" task
list
controlled by state.

An additional complication is that your socket is back in BeginRead mode so
you may get another request in on that socket. Now you need to decide which
request to process first - is it key requests are processed in order? If so,
then more logic is needed (a state machine, as you allude to).

One thing I'm not clear on, given what you describe - when you get data from
a socket, and realize you have something signifigant to do (and you want to
do it async), how do you do it? You can't just post it to the ThreadPool, as
there aren't enough threads in there. You don't want to manage a ton of
threads manually if you can help it...

So most the time, your system will be waiting on BeginReceives and
EndReceives to fire.

Agreed - if you have 10K connected TCP sockets, almost all of them are going
to be stuck in "BeginReceive" at any particular moment in time.This is by
design and one of the biggest strenghts of the IOCP infrastructure - it
manages which threads are awake, what processors they run on, what socket
data they have, and all of the other good stuff.

--
Chris Mullins


.

Relevant Pages

  • Re: Question on Socket disconnect handling
    ... static void SendCallback ... // simulate timing that can cause callback ... SafeSocket socket = new SafeSocket( ... private class SendCallBackArgs ...
    (microsoft.public.dotnet.languages.csharp)
  • Re: Handling exceptions in Socket Callbacks
    ... You're correct the asynchronous socket methods give more opportunities ... I always handle exceptions in callbacks in the callback itself. ... why im using this complicated method of socket communication - ...
    (microsoft.public.dotnet.general)
  • [3/4] Distributed storage. Algorithms.
    ... * GNU General Public License for more details. ... * This callback is invoked when node is removed from storage. ... * request processing. ... * This function reads or writes node's private data from underlying media. ...
    (Linux-Kernel)
  • Async callbacks with Global.asax
    ... ICallbackEventHandler and RaiseCallbackEvent) and a regular GET request ... And here is the page that handles the callback request. ... the callback handler in _Default page. ... includeStagesBeforeAsyncPoint = true, bool includeStagesAfterAsyncPoint ...
    (microsoft.public.dotnet.framework.aspnet)
  • Re: block, end, async read/write cause delay?
    ... Client could send data once few seconds of minutes. ... The stream you get from a TCP socket will only reach the end when the connection is closed. ... It works by having a pool of threads waiting on i/o completions. ... They are scheduled according to the normal round-robin rotation, so once the first runnable IOCP thread gets to run, it dequeues the completion and processes it. ...
    (microsoft.public.dotnet.languages.csharp)