"Connection closed gracefully" problem
Hi, I have two Delphi applications, which communicate with Indy / Http. The client runs in a loop and sends several hundred times a request to the server. Requests are sent one by one (all from the same thread). Sometimes the server app needs up to one minute to prepare the response (time in OnCommandGet event). In this case (at least I think so), the client gets a "Connection closed gracefully" exception. If I run the server app in the debugger and stop it in the OnCommandGet event, I can stop it for 2-3 minutes. In this case, the client app is just blocked and resumes with no problem, once I continue the server application. So I think at some point the TIdHttpServer just discards a long running request thread and sends an error back to the client. Is this correct? How can I ensure that a request is not closed, even if it takes a long time to complete it? I found the TerminateWaitTime property but noticed, that this is never used in the Indy code. I'm using Delphi XE2 prof. with preinstalled Indy. cu Christian
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Christian
5/23/2012 6:54:19 AM
embarcadero.delphi.winsock
1874 articles. 
2 followers.
5 Replies
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Christian wrote:
> In this case (at least I think so), the client gets a "Connection
> closed gracefully" exception.
That means the connection is being intentionally and gracefully closed on
the other end. By default, Indy uses infinite timeouts and no TCP/IP keepalives.
If the server itself is not closing the connection, but the connection passes
through a network router to reach the server, the router may be closing the
connection if it is idle for too long.
> So I think at some point the TIdHttpServer just discards a long
> running request thread and sends an error back to the client.
No, it does not.
> How can I ensure that a request is not closed, even if it takes a long
> time to complete it?
I would suggest enabling TCP/IP keepalives to see if it makes a difference.
Since TIdHTTP uses dynamic connections and thus may have to re-connect between
requests, you will have to use its OnConnected event to re-enable the keepalive
on each new connection, eg:
{code}
procedure TForm1.IdHTTP1Connected(ASender: TObject);
begin
// send a keepalive every 1s after 15s of being idle...
IdHTTP1.Socket.Binding.SetKeepAliveValues(True, 15000, 1000);
end;
{code}
> I found the TerminateWaitTime property but noticed, that this is never
> used in the Indy code.
That is used only during server shutdown, but is currently disabled. When
it was enabled, it specified the timeout used when waiting for client threads
to terminate.
--
Remy Lebeau (TeamB)
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Remy
3/5/2013 6:24:15 PM
>That means the connection is being intentionally and gracefully closed on >the other end. By default, Indy uses infinite timeouts and no TCP/IP keepalives. > If the server itself is not closing the connection, but the connection passes >through a network router to reach the server, the router may be closing the >connection if it is idle for too long. OK. But why does it happen when the server app is running and a request has a long timeout, but it doesn't happen if I cause the long timeout with a debugger breakpoint in the thread? > I would suggest enabling TCP/IP keepalives to see if it makes a difference. I added SetKeepAliveValues(). So far my first tests show, that it seems to help. Thanks. cu Christian
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Christian
3/5/2013 7:51:55 PM
Christian wrote: > OK. But why does it happen when the server app is running and a > request has a long timeout, but it doesn't happen if I cause the > long timeout with a debugger breakpoint in the thread? The particular error you are seeing is caused by the other party disconnecting. Since it only happens when TIdHTTPServer is not frozen by the debugger, the only possibility that makes sense is that the long-running thread is encountering an uncaught exception (verify that with the server's OnException event). If TIdHTTPServer catches an uncaught exception, it will close the socket. TIdHTTPServer itself does not close long-running threads in general. -- Remy Lebeau (TeamB)
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Remy
3/5/2013 8:28:39 PM
> Since it only happens when TIdHTTPServer is not frozen by the debugger, >the only possibility that makes sense is that the long-running thread is >encountering an uncaught exception (verify that with the server's OnException In my HandleRequest event I have a try except block. So I hardly can imagine, that an uncaught exception can happen. But I wil verify that. cu Christian
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Christian
3/5/2013 9:06:44 PM
Christian wrote: > In my HandleRequest event I have a try except block. Make sure you are not throwing away any Indy-specific exceptions. If you catch an EIdException-derived exception, you should re-raise it after you have processed it. This is important for TIdHTTPServer to detect client-side disconnects in particularly, especially during server shutdown if clients are still connected. -- Remy Lebeau (TeamB)
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Remy
3/5/2013 11:05:05 PM
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