[Ace-users] [ace-users] Race condition between handle_input() & handle_timeout() in ACE_Svc_Handler ?
Douglas C. Schmidt
schmidt at dre.vanderbilt.edu
Fri Nov 16 07:56:55 CST 2007
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>ACE VERSION: 5.4
ACE 5.4 is ancient. Please upgrade to ACE+TAO+CIAO x.6.1 (i.e., ACE
5.6.1, TAO 1.6.1, and CIAO 0.6.1), which you can download from
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Thus, if you need more "predictable" help for earlier versions of
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>HOST MACHINE and OPERATING SYSTEM:
> Windows XP sp2
>COMPILER NAME AND VERSION (AND PATCHLEVEL):
> MSVC6 SP6
>CONTENTS OF $ACE_ROOT/ace/config.h:
> TP_Reactor, ACE_Svc_Handler
>DOES THE PROBLEM AFFECT:
> Application crashes randomly if a handler is handling the
>request and at the same time it's expired by timer.
> Hi all ACE experts,
>I'm newbie to ACE. Now I'm struggle with a nasty crash in my
>application, and it's seems caused by race condition between the
>handle_timout() and handle_input()
>This is a service application, using ACE5.4, running under windows XP
>I used TPReactor, and extended ACE_Svc_Handler to handle incoming tcp
>In order to recycle/close idle connections, we also registered a timer
>and in our Svc_Handler::handle_timeout(), if detected that handler is
>idle, then we'll return -1 to release the handle.
>But I found an interesting problem by this *timeout* mechanism, that
>is, if a request come in at the *exact* time when *timeout* is fired,
>ACE might crash.
>To reproduce this problem, I changed the server idle timeout interval
>to 5s, and write a client app to send request to server every 5s, soon
>the service application crashed.
>By analysising the log and call stack trace and the thread states, I
>found that there seems to be a race condition.
>Request -> come in -> Handler ctor called and timer is registered ->
>back to the ACE -> OS Switch to another thread -> ACE trigger the
>timer and spawn a new thread to call the handle_timeout on this newly
>created handler -> handle_timeout return -1(detected the busy/active
>state, but got idle information) -> back to ACE -> handler destructor
>called -> OS switch back to the first thread -> crash...
>Any ideas ? or Could anyone give me some advice about how to close the
>handler gracefully & thread-safely when idle timeout is triggered ?
If you're using ACE_TP_Reactor you probably need to use an
ACE_Thread_Mutex to serialize the processing between the various
ACE_Svc_Handler methods. There are some examples of how to do this
sort of thing in the C++NP books <www.cs.wustl.edu/~schmidt/ACE/>.
Dr. Douglas C. Schmidt Professor and Associate Chair
Electrical Engineering and Computer Science TEL: (615) 343-8197
Vanderbilt University WEB: www.dre.vanderbilt.edu/~schmidt
Nashville, TN 37203 NET: d.schmidt at vanderbilt.edu
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