Handling exceptions in Socket Callbacks

[faktujaa]

Hi,
I am having some problem with callback used in socket implementation.
private static void Connect(string strPrtrIPAddr, int intPrtrPort, ref
Socket rsocClient)
{
try
{
// Create remote end point.
System.Net.IPAd dress IPAddress = System.Net.IPAd dress.Parse(str PrtrIPAddr);
System.Net.IPEn dPoint IPEndPoint = new System.Net.IPEn dPoint(IPAddres s,
intPrtrPort);

// Create a TCP/IP socket.
rsocClient = new Socket(AddressF amily.InterNetw ork, SocketType.Stre am,
ProtocolType.Tc p);

// Connect to the remote end point.
rsocClient.Begi nConnect(IPEndP oint, new AsyncCallback(C onnectCallback) ,
rsocClient);

// Signal the connection event to wait.
mevtConnectDone .WaitOne();
}
catch(Exception objException)
{
throw objException;
}
}

private static void ConnectCallback (IAsyncResult IResult)
{
try
{
// Retrieve the socket from the state object.
Socket socClient = (Socket) IResult.AsyncSt ate;

// Complete the connection.
socClient.EndCo nnect(IResult);

// Signal that the connection has been made.
mevtConnectDone .Set();
}
catch(Exception objException)
{
mevtConnectDone .Set();
throw objException;
}
}

Please check the above two methods. Callback throws an error at EndConnect
but it is not propogated to the parent function. How to solve this problem.
Please help me asap. Thanks in advance.

[RockinFewl]

Re: Handling exceptions in Socket Callbacks

faktujaa,

The exception propagation doesn't work because, in contrary to what you
think, your Connect() method is NOT a parent function of your
ConnectCallback (). The asynchronous Delegate mechanism uses an other
thread to eventually run the callback on, so basically your two
functions are highly independent, and surely not on the same call stack.

In your case the solution is simple though.
I see you use asynchronous methods, yet try to mimic a synchronous
behaviour (with the mevtConnectDone event). This makes everything
unnecessary complex, and induces also your particular problem. I don't
know what your future plans with this code are, but I'd ditch the
asynchronous approach here. You'd get this:

private static void Connect(string strPrtrIPAddr, int intPrtrPort, ref
socket rsocClient)
{
try
{
// Create remote end point.
System.Net.IPAd dress IPAddress = System.Net.IPAd dress.Parse(str PrtrIPAddr);
System.Net.IPEn dPoint IPEndPoint = new System.Net.IPEn dPoint(IPAddres s,
intPrtrPort);

// Create a TCP/IP socket.
rsocClient = new Socket(AddressF amily.InterNetw ork, SocketType.Stre am,
ProtocolType.Tc p);

// Connect to the remote end point SYNCHRONOUSLY.
rsocClient.Conn ect(IPEndPoint) ;
}

catch(Exception objException)
{
throw objException;
}

}

No callback applies.

Code goes untested, so forgive me the occasional typo.

Hope his helps,
Koen.


faktujaa wrote:
[color=blue]
> Hi,
> I am having some problem with callback used in socket implementation.
> private static void Connect(string strPrtrIPAddr, int intPrtrPort, ref
> Socket rsocClient)
> {
> try
> {
> // Create remote end point.
> System.Net.IPAd dress IPAddress = System.Net.IPAd dress.Parse(str PrtrIPAddr);
> System.Net.IPEn dPoint IPEndPoint = new System.Net.IPEn dPoint(IPAddres s,
> intPrtrPort);
>
> // Create a TCP/IP socket.
> rsocClient = new Socket(AddressF amily.InterNetw ork, SocketType.Stre am,
> ProtocolType.Tc p);
>
> // Connect to the remote end point.
> rsocClient.Begi nConnect(IPEndP oint, new AsyncCallback(C onnectCallback) ,
> rsocClient);
>
> // Signal the connection event to wait.
> mevtConnectDone .WaitOne();
> }
> catch(Exception objException)
> {
> throw objException;
> }
> }
>
> private static void ConnectCallback (IAsyncResult IResult)
> {
> try
> {
> // Retrieve the socket from the state object.
> Socket socClient = (Socket) IResult.AsyncSt ate;
>
> // Complete the connection.
> socClient.EndCo nnect(IResult);
>
> // Signal that the connection has been made.
> mevtConnectDone .Set();
> }
> catch(Exception objException)
> {
> mevtConnectDone .Set();
> throw objException;
> }
> }
>
> Please check the above two methods. Callback throws an error at EndConnect
> but it is not propogated to the parent function. How to solve this problem.
> Please help me asap. Thanks in advance.[/color]


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[RockinFewl]

Re: Handling exceptions in Socket Callbacks


Hi faktujaa,

You're correct the asynchronous socket methods give more opportunities
in creating performant code. There aren't many occasions I use
synchronous ones myself.
However, I'd consider this particular Microsoft article as example code.
Using an asynchrounous BeginConnect() to avoid blocking, yet
immediately do a WaitOne to _do_ blocking, doesn't make much sense.
Typically, you'd do other, useful things instead of just blocking
waiting for a completion event: you may attempt to begin some more
connections, or handle existing ones for instance.

Anyway, I see you feel intuitively your Connect() method can't possibly
be the place to catch exceptions thrown in ConnectCallback (). If you
remove the WaitOne in you original code, it's expectable Connect()
finishes BEFORE ConnectCallback () finishes (or even starts perhaps).
Again, this illustrates that the two method calls are not on the same
call stack.

I always handle exceptions in callbacks in the callback itself. Apart
from some complicated (unseen) approach to transfer exceptions as
objects to another thread and rethrowing it there, I see no other option.

Koen.






faktujaa wrote:[color=blue]
> Hi Koen,
> Thanks for the help.
> First of all, why im using this complicated method of socket communication -
> actually what i understood from most of the articles is that synchronous way
> of communication does not go well in performance as compared to asyncronous
> in real world applications (multiple clients) as all the synchronous method
> operates in the blocking mode. They have to poll for the data being received
> and wait untill it is actually received whereas in asynchronous
> communication, callback function will automatically notify the completion of
> operation.
> Secondly im using ManulaResetEven t to block the parent thread till the
> callbak thread indicates its completion - this is nothing but im again using
> synchronous way of communication (i agree with u) but microsoft has really
> confused me by giving readymade asynchronous socket client example that im
> using in my application. Please check the link -
> http://msdn.microsoft.com/library/de...ketexample.asp.
> Can u explain this to me as im now totally confused.
> Lastly but the most impostant one say what if i use this example code
> without ManualResetEven ts then the code becomes truely asynchronous but still
> there remains the problem of propogating the error generated in the callback
> function as it is executed by a seperate thread. I know for sure that i have
> to use asynchronous way of communication but how do i resolve this
> problem????????
> Now to give brief idea abt what im doing - Im using this client socket to
> send print data to a third party print server - Hematrax.
> Thanx in advance.
>
>
> "RockinFewl " wrote:
>
>[color=green]
>>faktujaa,
>>
>>The exception propagation doesn't work because, in contrary to what you
>>think, your Connect() method is NOT a parent function of your
>>ConnectCallba ck(). The asynchronous Delegate mechanism uses an other
>>thread to eventually run the callback on, so basically your two
>>functions are highly independent, and surely not on the same call stack.
>>
>>In your case the solution is simple though.
>>I see you use asynchronous methods, yet try to mimic a synchronous
>>behaviour (with the mevtConnectDone event). This makes everything
>>unnecessary complex, and induces also your particular problem. I don't
>>know what your future plans with this code are, but I'd ditch the
>>asynchronou s approach here. You'd get this:
>>
>>private static void Connect(string strPrtrIPAddr, int intPrtrPort, ref
>>socket rsocClient)
>>{
>>try
>>{
>>// Create remote end point.
>>System.Net.IP Address IPAddress = System.Net.IPAd dress.Parse(str PrtrIPAddr);
>>System.Net.IP EndPoint IPEndPoint = new System.Net.IPEn dPoint(IPAddres s,
>>intPrtrPort );
>>
>>// Create a TCP/IP socket.
>>rsocClient = new Socket(AddressF amily.InterNetw ork, SocketType.Stre am,
>>ProtocolType. Tcp);
>>
>>// Connect to the remote end point SYNCHRONOUSLY.
>>rsocClient.Co nnect(IPEndPoin t);
>>}
>>
>>catch(Excepti on objException)
>>{
>>throw objException;
>>}
>>
>>}
>>
>>No callback applies.
>>
>>Code goes untested, so forgive me the occasional typo.
>>
>>Hope his helps,
>>Koen.
>>
>>
>>faktujaa wrote:
>>
>>[color=darkred]
>>>Hi,
>>>I am having some problem with callback used in socket implementation.
>>>private static void Connect(string strPrtrIPAddr, int intPrtrPort, ref
>>>Socket rsocClient)
>>>{
>>>try
>>>{
>>>// Create remote end point.
>>>System.Net.I PAddress IPAddress = System.Net.IPAd dress.Parse(str PrtrIPAddr);
>>>System.Net.I PEndPoint IPEndPoint = new System.Net.IPEn dPoint(IPAddres s,
>>>intPrtrPort) ;
>>>
>>>// Create a TCP/IP socket.
>>>rsocClient = new Socket(AddressF amily.InterNetw ork, SocketType.Stre am,
>>>ProtocolType .Tcp);
>>>
>>>// Connect to the remote end point.
>>>rsocClient.B eginConnect(IPE ndPoint, new AsyncCallback(C onnectCallback) ,
>>>rsocClient );
>>>
>>>// Signal the connection event to wait.
>>>mevtConnectD one.WaitOne();
>>>}
>>>catch(Except ion objException)
>>>{
>>>throw objException;
>>>}
>>>}
>>>
>>>private static void ConnectCallback (IAsyncResult IResult)
>>>{
>>>try
>>>{
>>>// Retrieve the socket from the state object.
>>>Socket socClient = (Socket) IResult.AsyncSt ate;
>>>
>>>// Complete the connection.
>>>socClient.En dConnect(IResul t);
>>>
>>>// Signal that the connection has been made.
>>>mevtConnectD one.Set();
>>>}
>>>catch(Except ion objException)
>>>{
>>>mevtConnectD one.Set();
>>>throw objException;
>>>}
>>>}
>>>
>>>Please check the above two methods. Callback throws an error at EndConnect
>>>but it is not propogated to the parent function. How to solve this problem.
>>>Please help me asap. Thanks in advance.[/color]
>>
>>
>>--
>>Notice: Remove all packaging [from e-mail address] before use.
>>[/color][/color]


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