C# Discussion Boards - CodeProject

17-Jul-07 1:38

Hi all
I am new to MSMQ.I have an application which sends a message.This message will be recieved by another application and stores in a MSMQ.And then it will read from the msmq and sends to some other process.Now the thing i am facing is that i have a recieve thread which starts at the application_start event .inside this thread i am calling the receive method of msmq.and i am using the follwing code with timespan
msg = mq.Receive(new TimeSpan(0,0,100));
now i know after 100 ms it will show MessageQueueException.my doubt is that what should i do after i catch the exception,because i want the thread to abort only at the application_end.so what should i do if a exception occurs.
Thanks in advance.

Regards
DilipRam

Jimmanuel17-Jul-07 3:55

17-Jul-07 3:55

ramdil wrote:
what should i do if a exception

What do you want your app to do? wait for another message? do nothing until the app exits?

ramdil17-Jul-07 4:24

17-Jul-07 4:24

Yes it should wait for message to arrive.
actually since i have started my thread on application , then the recieve method will get time out after the span of time ,it will throw messaging exception..so my doubt is in this exception section, i again need to wait until message comes

Regards
DilipRam

Jimmanuel17-Jul-07 4:35

17-Jul-07 4:35

so catch the exception inside of a while loop:

while (listenForMessages)
{
    try
    {
        msg = mq.Receive(new TimeSpan(0,0,100));
        
        // parse the message here . . .

        // if you don't want to listen for more messages then set
        listenForMessages = false;
    }
    catch (MessageQueueException ex)
    {
        // log the error somewhere
    }
}

ramdil17-Jul-07 5:35

17-Jul-07 5:35

Thanks for the reply. i dont want to catch the exception.i want it to listen again..so what should i do..if i move a thread to sleep(100) in exception, will it serve my purpose. i am pasting my code section.
while (IsMessageRecieved)
{
try
{
mq = new MessageQueue(XMLMSMQRecievePath);
msg = mq.Receive(new TimeSpan(0,0,100));
XMLMSMQFileName = msg.Body.ToString();
}
catch (System.Messaging.MessageQueueException ex)
{
Logging.TraceError(ex.Message);
mq.Purge();
Thread.Sleep(100);
}

Regards
DilipRam

Jimmanuel17-Jul-07 6:10

17-Jul-07 6:10

I'm not quite sure that I fully understand you. If you don't catch the exception then the program will explode. From the code segment posted, it looks like you want to read the first available message from the MSMQ and store the body of it in the variable "XMLMSMQFileName" and for each 100 ms that no message is received log an error . . . is this correct?

If so there are a few things to note:
1) there's no need to set mq to a new MessageQueue in each iteration of the loop. setting it once before the loop should be sufficient
2) if the timeout expires and the exception is thrown that means there are no messages in the queue, so calling Purge() is unnecessary
3) IsMessageRecieved needs to be set to true or else it will keep reading messages from the queue

ramdil17-Jul-07 6:23

Re: MSMQ Error Handling [modified]

17-Jul-07 6:23

Thanks for the reply.yes..it will wait for 100ms then not will go to exception.but i dont want to set the flag value to change,because what i want is that if the error occurs, then it should again wait unitl message comes..
so i am asking that if i am adding thread.sleep(100) will serve my purpose
..that means what actually i want is that on exception i dont want to exit the loop but should wait for the mssage to arrive..

will my code will satisfy if do sleep(100).hope i am clear with my requirement

Thanks in advance

Regards
DilipRam

Jimmanuel17-Jul-07 6:45

17-Jul-07 6:45

no, Thread.Sleep won't do what you want, all it'll accomplish is to make the Thread wait for 100 more ms before it executes the next iteration of the loop. The way that it is currently written it will accomplish what you're describing, but you still need to add the line "IsMessageRecieved = false;" into the try block after the message has successfully been read like this:

try
{
   msg = mq.Receive(new TimeSpan(0,0,100));
   XMLMSMQFileName = msg.Body.ToString();
   IsMessageRecieved = false;
}
catch . . .

this will make it so that if a message is received successfully then IsMessageRecieved will be set to false and the while loop will be exited but if the Receive method times out then the line IsMessageRecieved = false; is skipped and the loop is repeated

Last modified: 10mins after originally posted -- corrected IsMessageRecieved = true; to IsMessageRecieved = false;

ramdil17-Jul-07 7:15

17-Jul-07 7:15

Hi first of all thanks for detailed description,i understand what you are telling me but the think here is that i calling this method in a thread.thread starts at appn_start and thread stops at appn_end and here only i setting the variable value IsMessageRecieved=false..so that when ever my application is running mode, it will always check whether any message is in msmq then it will read..if i am setting flag variable inside the iteration, then once it is read then it will not listen...hope u understand my requriment.in this context ,will my code work with out any problem..this is my doubt

Regards
DilipRam

Jimmanuel17-Jul-07 7:27

17-Jul-07 7:27

You're absolutely correct! I was thinking that you were reading only one message; the way you've described it sounds like you have it set up correctly to continue reading messages until the application ends, so it should work fine.

Just like before though, it's probably a good idea to set the IsBackground property to true on the Thread object so that it doesn't hang up you application when it's closing. Things should work fine even if you don't do this, but it probably won't hurt to throw this in just in case. Smile | :)

ramdil17-Jul-07 22:28