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Java Forum / CORBA / November 2007Event dispatch in OrbixWeb: single threaded or multi-threaded?
I have just found a nasty race condition in my java servant which can only be explained if the CORBA event dispatching in OrbixWeb occurs using multiple threads. Does it? Can any OrbixWeb/IONA expert comment please? This servant is a rewrite of one in C++. In Orbix it looks like by default the event loop is single threaded but this can be changed with a small amount of code. I assumed that this default behaviour would also apply to OrbixWeb. It seems like I am wrong. Regards, Andrew Marlow > I have just found a nasty race condition in my java servant which can > only be explained if the CORBA event dispatching in OrbixWeb occurs > using multiple threads. That is according the standard unless the servant is registered under single-threaded POA. The default threading policy for POA is multithreaded and in Orbix 2000 and Orbix 6.3 it is so. I never worked with OrbixWeb, but I see no reason to implement something against the standard. May be you should check the policies of the POA on which your servant is registered. > > I have just found a nasty race condition in my java servant which can > > only be explained if the CORBA event dispatching in OrbixWeb occurs [quoted text clipped - 7 lines] > May be you should check the policies of the POA on which your servant > is registered. OrbixWeb 3.0.x is ancient and quite different to the other IONA products. On page 408 of the OrbixWeb programmers guide in the section titled "multithreaded servers" it says (and I quote): Where parallism is not required, there is no need to make a server multi-threaded. The way I read this is that by default a server is single-threaded, you have to write some extra code (e.g using thread filters) to make it multi-threaded. I have discussed this with an IONA consultant, who reads this the same way I do. But our OrbixWeb setup seems to dispatching CORBA requests from more than one thread. I am using the apache commons logger which reports the thread name in each logging record. When I log the incoming CORBA request I see two thread names, one is "main" which I expect since that is where my call to processEvents is, the other is called "Request Processor". I don't know where that thread comes from. It's not one of mine. -Andrew M. On Nov 28, 6:32 am, ap...@student.open.ac.uk wrote: > > > I have just found a nasty race condition in my java servant which can > > > only be explained if the CORBA event dispatching in OrbixWeb occurs [quoted text clipped - 28 lines] > > -Andrew M. Don't confuse event dispatching with POA threading policies. The ROOT POA is single threaded by default. If you want to have multiple servants processing messages concurrently, you have to define your own POA with a multi-threaded policy. I don't believe the CORBA specs says anything about how an orb delivers the message to the POA. The processEvents operation is part of the orb, not the POA. It's possible that the orb itself is using 2 or more threads to process incoming messages: one that reads the socket and enqueues the message, and one or more other threads that are associated with the processEvents function. Those thread(s) would check the message queue, and dispatch the call to the appropriate POA. Thus, it's possible that multiple threads in the orb layer would block if multiple calls were send to an object associated with a single- threaded POA. Mark > On Nov 28, 6:32 am, ap...@student.open.ac.uk wrote: > > > > I have just found a nasty race condition in my java servant which can [quoted text clipped - 3 lines] > > > That is according the standard unless the servant is registered under > > > single-threaded POA. > > OrbixWeb 3.0.x is ancient and quite different to the other IONA > > products. > Don't confuse event dispatching with POA threading policies. I should have mentioned earlier that OrbixWeb 3.0.x is so ancient it is before the POA was invented. The code in question has no choice but to use the BOA. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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