Re: GetStream.Read behavior changed in .Net 2.0 with respect to ReceiveTimeout

On Jul 31, 11:56 pm, Peter Duniho <NpOeStPe...@xxxxxxxxxxxxxxxx>
wrote:
Keith Langer wrote:
Could you show me some code which uses these alternatives for checking
if data has arrived?

For the record, I only mentioned alternatives to implementing a timeout.
Alternatives for "checking if data has arrived" is a somewhat
different topic.

The only other way I know to check for data on
the socket is to keep checking the DataAvailable property and sleeping
for a small period of time, then exit out when my timeout period has
elapsed without receiving data.

I guess at this point it may be helpful to take a step back and look at
the bigger picture. From the sounds of it, you are using a timeout for
something other than an actual timeout. It might be helpful to be more
clear about why it is you are using a timeout in the first place. Most
socket i/o code does not bother with a timeout at all.

For simple socket-based applications, in .NET or otherwise, generally
the design either assigns a dedicated thread to each socket for
receiving, or uses the function/method named "select" or "Select"
(Winsock and .NET Socket, respetively). The thread-per-socket model
works fine for very small numbers of sockets, while the select model
works fine for slightly larger numbers of sockets, but less than 64 (in
Winsock, there's a limit of 64 sockets that can be passed to
select...I'm not sure if the same limit exists in the .NET version, but
it may).

In .NET specifically, one would normally use the async paradigm. That
is, using the BeginXXX/EndXXX methods for i/o. These are the most
efficient, and for very large numbers of sockets they are the only
practical way to produce scalable network i/o code. (In Winsock, there
are other alternatives to deal with larger numbers of sockets, one of
them being to use i/o completion ports, which is what the .NET async
paradigm is built on when run on platforms that support it).

IMHO, even if you have just one socket, the async paradigm makes a lot
of sense. It is easily extended if you wind up needing to do so in the
future, it has no additional issues beyond that which would normally be
present in a dedicated-thread implementation, and personally I just like
the way it works. Via a BeginXXX method you tell .NET to call a
specific method when the i/o completes, and when it completes, your
method is called. You do in there whatever you want to process the i/o
(such as calling Socket.EndReceive() for a receive operation), and then
you call the BeginXXX method again to repeat the sequence.

In _any_ of these mechanisms, there is no need for a timeout. You don't
do your i/o on a thread that needs to do something else. Using
Socket.Select(), you can in fact provide a timeout value, but that
shouldn't be used just so that you can mix your i/o code in the same
thread with code that does something else.

Anyway, that's all a long way of saying that, from the limited amount of
information you've posted so far, it sounds to me as though even though
you are asking how to get the timeout to do what you want, the more
basic issue is that using a timeout isn't the appropriate solution in
the first place.

So, if after reading the above you still think it is, maybe the next
step here is for you to explain in more detail why you need the timeout.
That would help with respect to answering the question regarding how
to implement a timeout.

If instead the question remains "Could you show me some code which uses
these alternatives for checking if data has arrived", then hopefully the
above at least begins to answer that question (the code is on MSDN, as
sample code for the various methods and other members of the Socket class).

Finally, yes...I realize you asked about GetStream.Read() (which is a
little confusing itself...I know you really mean Stream.Read(), but
since there's not actually any GetStream class, saying
"GetStream.Read()" seems a little odd out of context), but clearly
what's really going on is related to the socket itself, not the stream
wrapped around it, I think it's more useful to discuss the socket
specifically. You can implement the above either by manipulating the
socket directly, or in the case of the BeginXXX/EndXXX method, the
Stream class does have the async i/o methods in it, so you can operate
on the stream directly in that case.

Pete


Pete,

This application runs a number of signs (serial devices) connected to
several device servers. Each device server has a dedicated thread and
TcpClient associated with it in my application. There could be
anywhere from 1 to 150 of these device servers, and each device server
could have 1 to 100 signs (a typical site might have anywhere from 10
to 500 signs in total). Some of the signs respond to messages sent,
but there is no guarantee that all signs are functional. So for each
device server, I must send a message to sign 1, wait for a response or
for a timeout period of X seconds to elapse, then send the next
message to that sign or the next sign. Hence, this is my need for
some sort of timeout. I either need to keep checking the
DataAvailable property for several seconds, or implement a blocking
operation for several seconds until data is available.

Keith

.

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