Re: RE : RE : Multi-threading
Patrick van Beem wrote: Hello Carl, It sounds like you would like to free resources on a per-call basis. Is that right? I'm quite new to the Axis2/C architecture so perhaps a more experienced person could suggest a mechanism that would fit into the existing methodology and provide this extra feature. My impression is that the design philosophy so far is to free resources after all calls are completed. I'm only in it myself for about a month too. But you're right on the design philosophy. Only: that's not the usage pattern of our application. We've got a (very) large client - server application where the user can write his own code (using a custom declarative / constraint programming language). Some interfaces available in this server programming environment perform calls to the outside world using soap. It's up to the user when and how to use it. So our framework must be flexible. We do not know in advance what the end-user is going to write. I was hoping to be able to re-use axis structures for each (parallel) call. Or cloning them. But indeed, this is not the design philosophy of axis. I'm now on the road of using thread local storage (TLS) to store the thread-specific structures, so I don't have to allocate / free them for each thread (my threads are worker threads that can do anything. Not just soap calls. So I can't (don't want) to design them for a set of specific soap calls). With the fd_set in winsock and the select() function, you can wait at a maximum of 64 (current implementation) sockets at once. With I/O Completion Ports you can use one thread for an infinite number of ports... But I think they don't fit well in the modular (transportation) design of axis That's very interesting. I'm curious as to more of the details of how this functions... If you have one thread waiting on 12 sockets and want to make a new call, can this thread begin the next call, or does a second thread open the socket and pass the job of waiting on it to the first thread? The 'problem' is that the waiting thread can only wait on sockets. Not also on, for example, a job queue. So the waiting thread is mostly implemented as some round-robin algorithm: Wait on the sockets with a time-out of a few milliseconds, check a job queue and optionally perform a few tasks (open more sockets, accept a socket another thread opened, ...) and start waiting again on the new set of sockets. So this uses slightly more CPU then strictly necessary. The IO completion ports use a call-back strategy when IO on a socket is completed. This is a much nicer concept. If you're programming C++, you might be interested in the asio classes of the boost project, where the used IO completion for their windows implementation of the asio (asynchronous IO). But we're running out of context :-) I think we would all agree that your use case would benefit from adding this capability to Axis2/C. You mention a potential conflict with the modular design of Axis; there is also the idea that making such a powerful feature accessible to the average programmer using Axis could be a challenge. Maybe the solution would be to add a new communication mode instead of changing all asynchronous communication to one-thread-multi-socket. I wish I understood the Axis2/C architecture more fully because this would be an interesting area to contribute. I'm not 'deep' into the details of axis too (the idea was to use an existing toolkit to save on development time for soap, so I'm not planning to go into much detail for now either). But one implementation might be to add another 'configuration structure' (like the allocator and thread pool) for socket IO and make that responsible for all IO. That implementation can then decide to use one or multiple threads for IO. It can use call-backs to signal the completion (or failure or timeout) of the IO. The async calls can then be implemented as writing data (by the new io struct) and exiting that start-call. Finished. Nothing more to do. No extra thread, nothing. Then, when finished, the call-back can be used to parse the result and call the user call-back for the result. The io struct (module) should probably use a (real!) thread pool for this to prevent one time-consuming call to block other calls. But a simple implementation might to for the 'average' user. This pattern mimics the io completion port / boost interface, so users of axis can easily use these for their async IO. May be implementing a new transport using Proactor pattern(1) possibly using boost library is a good solution. This is possible since new transports could be plugged into Axis2/C by design. However this will need some changes in op_client implementation because currently for async calls it execute on new threads. However adding this functionality through environment structure seems inappropriate. Also it is not clear to me how to implement it in that way. WDYT?.
Re: RE : Multi-threading
Patrick van Beem wrote: Hello Carl, What Axis does well is freeing resources (once we figure out how to set everything up right!) so I am a little confused as to where exactly the limitations are. You say the callback system provided is not good in terms of freeing resources, but have you tried freeing your resources from another function which itself waits for the callback to occur? (either error callback or success callback) I think this is the way Axis was designed with as implied by Dimuthu: wait in a loop in your main thread while the callbacks are outstanding, do no cleanup in the callback itself, let that thread exit completely and after it is done, then from your main thread detect that the callback ocurred and do the cleanup there. Correct. But I think the design is missing one thing. If I allocate the stub and env and then do an async call, I'm not allowed to free those two resources in the callback, because they're used by the axis framework. But if I signal the main thread from the callback, to free the resources, the callback might be switched out directly after this signal, and the main thread might free the resources before the callback ended and the axis framework used them. As you indicate, the only safe way is to wait until the thread is finished. But the axis framework does not provide an api to find out which thread is processing you request. And it shouldn't, because the thread mechanism is an implementation detail of the axis framework. Future versions might re-use the thread or even use no threading at all for asynchronous calls. So the only safe way to free resources is for the axis framework to signal the caller that the resources are no longer needed. A (second?) callback is the most used (elegant) way to do this. Yes, this problem exists in the current implementation. A second callback as you said is the ideal solution. thanks, Damitha Right now, the framework does not provide a safe way of freeing resources in async calls. My reason for responding though is really to comment on this phrase: Threads are a rather expensive resource to use for just waiting on an IO completion. It may be my lack of understanding, but I am pretty sure that -- at least in the win32 tcp/ip stack -- once your thread goes into asynchronous communication on a socket, you do not see it again until there is some result. This means if there is a timeout your thread is inactive for a long time. Correct. So if I've got a couple of hundred outstanding calls, they all consume precious memory. In our case, this is a lot of memory, since we have a heavy server applications with a greedy memory allocation strategy per thread (for performance) and a rather large default stacks. Of course, both can be optimized for the 'just waiting on io-completion'-threads... CPU-wise, it's no problem. How can one thread wait on more than one asychronous communication? I admit this would be a far better solution, however from my understanding of winsock2 it is not possible. With the fd_set in winsock and the select() function, you can wait at a maximum of 64 (current implementation) sockets at once. With I/O Completion Ports you can use one thread for an infinite number of ports (though a pool of threads might be a good idea if the number of sockets grows large). This is also used by the well known boost (C++) library. Mechanisms like these would be a much better implementation. But I think they don't fit well in the modular (transportation) design of axis, since they require knowledge about the lower level transportation on a higher level. Seen this way, one thread per socket communication is maybe expensive in resources, but it is the only way to ensure your main thread continues to operate in a timely fashion. But prone to explode with a log of async calls. As a 'workaround' I've now my own static-sized thread pool that perform synchronous calls. If there are more async calls then threads in the pool, they're queued. Thank you for your input. -- __ Damitha Kumarage http://people.apache.org/ __
Re: RE : RE : Multi-threading
Hi, Hello Patrick, But if I signal the main thread from the callback, to free the resources, the callback might be switched out directly after this signal, and the main thread might free the resources before the callback ended and the axis framework used them. Yes, this is a pretty serious limitation. I have been trying to find out if Axis2/C provides a way to either know the thread id of the communication threads created internally or to be notified exactly when the threads exit. As you suggest, this is treated as an implementation detail and we are expected to code without a precise notification of when these threads finishes their tasks. It sounds like you would like to free resources on a per-call basis. Is that right? I'm quite new to the Axis2/C architecture so perhaps a more experienced person could suggest a mechanism that would fit into the existing methodology and provide this extra feature. My impression is that the design philosophy so far is to free resources after all calls are completed. Current implementation does not provide a way to free resources on a per-call basis. I agree with Patrick, we should provide a callback to free the resources. Regards, Shankar With the fd_set in winsock and the select() function, you can wait at a maximum of 64 (current implementation) sockets at once. With I/O Completion Ports you can use one thread for an infinite number of ports... But I think they don't fit well in the modular (transportation) design of axis That's very interesting. I'm curious as to more of the details of how this functions... If you have one thread waiting on 12 sockets and want to make a new call, can this thread begin the next call, or does a second thread open the socket and pass the job of waiting on it to the first thread? I think we would all agree that your use case would benefit from adding this capability to Axis2/C. You mention a potential conflict with the modular design of Axis; there is also the idea that making such a powerful feature accessible to the average programmer using Axis could be a challenge. Maybe the solution would be to add a new communication mode instead of changing all asynchronous communication to one-thread-multi-socket. I wish I understood the Axis2/C architecture more fully because this would be an interesting area to contribute. The pleasure is all mine in this conversation. So far I am learning more about winsock :) _ Ce message est confidentiel, a l'usage exclusif du destinataire ci-dessus et son contenu ne represente en aucun cas un engagement de la part de AXA, sauf en cas de stipulation expresse et par ecrit de la part de AXA. Toute publication, utilisation ou diffusion, meme partielle, doit etre autorisee prealablement. Si vous n'etes pas destinataire de ce message, merci d'en avertir immediatement l'expediteur. This e-mail message is confidential, for the exclusive use of the addressee and its contents shall not constitute a commitment by AXA, except as otherwise specifically provided in writing by AXA. Any unauthorized disclosure, use or dissemination, either whole or partial, is prohibited. If you are not the intended recipient of the message, please notify the sender immediately. -- S.Uthaiyashankar Software Architect WSO2 Inc. http://wso2.com/ - The Open Source SOA Company
RE : RE : Multi-threading
Hello Patrick, But if I signal the main thread from the callback, to free the resources, the callback might be switched out directly after this signal, and the main thread might free the resources before the callback ended and the axis framework used them. Yes, this is a pretty serious limitation. I have been trying to find out if Axis2/C provides a way to either know the thread id of the communication threads created internally or to be notified exactly when the threads exit. As you suggest, this is treated as an implementation detail and we are expected to code without a precise notification of when these threads finishes their tasks. It sounds like you would like to free resources on a per-call basis. Is that right? I'm quite new to the Axis2/C architecture so perhaps a more experienced person could suggest a mechanism that would fit into the existing methodology and provide this extra feature. My impression is that the design philosophy so far is to free resources after all calls are completed. With the fd_set in winsock and the select() function, you can wait at a maximum of 64 (current implementation) sockets at once. With I/O Completion Ports you can use one thread for an infinite number of ports... But I think they don't fit well in the modular (transportation) design of axis That's very interesting. I'm curious as to more of the details of how this functions... If you have one thread waiting on 12 sockets and want to make a new call, can this thread begin the next call, or does a second thread open the socket and pass the job of waiting on it to the first thread? I think we would all agree that your use case would benefit from adding this capability to Axis2/C. You mention a potential conflict with the modular design of Axis; there is also the idea that making such a powerful feature accessible to the average programmer using Axis could be a challenge. Maybe the solution would be to add a new communication mode instead of changing all asynchronous communication to one-thread-multi-socket. I wish I understood the Axis2/C architecture more fully because this would be an interesting area to contribute. The pleasure is all mine in this conversation. So far I am learning more about winsock :) _ Ce message est confidentiel, a l'usage exclusif du destinataire ci-dessus et son contenu ne represente en aucun cas un engagement de la part de AXA, sauf en cas de stipulation expresse et par ecrit de la part de AXA. Toute publication, utilisation ou diffusion, meme partielle, doit etre autorisee prealablement. Si vous n'etes pas destinataire de ce message, merci d'en avertir immediatement l'expediteur. This e-mail message is confidential, for the exclusive use of the addressee and its contents shall not constitute a commitment by AXA, except as otherwise specifically provided in writing by AXA. Any unauthorized disclosure, use or dissemination, either whole or partial, is prohibited. If you are not the intended recipient of the message, please notify the sender immediately.
Re: RE : Multi-threading
Hello Carl, What Axis does well is freeing resources (once we figure out how to set everything up right!) so I am a little confused as to where exactly the limitations are. You say the callback system provided is not good in terms of freeing resources, but have you tried freeing your resources from another function which itself waits for the callback to occur? (either error callback or success callback) I think this is the way Axis was designed with as implied by Dimuthu: wait in a loop in your main thread while the callbacks are outstanding, do no cleanup in the callback itself, let that thread exit completely and after it is done, then from your main thread detect that the callback ocurred and do the cleanup there. Correct. But I think the design is missing one thing. If I allocate the stub and env and then do an async call, I'm not allowed to free those two resources in the callback, because they're used by the axis framework. But if I signal the main thread from the callback, to free the resources, the callback might be switched out directly after this signal, and the main thread might free the resources before the callback ended and the axis framework used them. As you indicate, the only safe way is to wait until the thread is finished. But the axis framework does not provide an api to find out which thread is processing you request. And it shouldn't, because the thread mechanism is an implementation detail of the axis framework. Future versions might re-use the thread or even use no threading at all for asynchronous calls. So the only safe way to free resources is for the axis framework to signal the caller that the resources are no longer needed. A (second?) callback is the most used (elegant) way to do this. Right now, the framework does not provide a safe way of freeing resources in async calls. My reason for responding though is really to comment on this phrase: Threads are a rather expensive resource to use for just waiting on an IO completion. It may be my lack of understanding, but I am pretty sure that -- at least in the win32 tcp/ip stack -- once your thread goes into asynchronous communication on a socket, you do not see it again until there is some result. This means if there is a timeout your thread is inactive for a long time. Correct. So if I've got a couple of hundred outstanding calls, they all consume precious memory. In our case, this is a lot of memory, since we have a heavy server applications with a greedy memory allocation strategy per thread (for performance) and a rather large default stacks. Of course, both can be optimized for the 'just waiting on io-completion'-threads... CPU-wise, it's no problem. How can one thread wait on more than one asychronous communication? I admit this would be a far better solution, however from my understanding of winsock2 it is not possible. With the fd_set in winsock and the select() function, you can wait at a maximum of 64 (current implementation) sockets at once. With I/O Completion Ports you can use one thread for an infinite number of ports (though a pool of threads might be a good idea if the number of sockets grows large). This is also used by the well known boost (C++) library. Mechanisms like these would be a much better implementation. But I think they don't fit well in the modular (transportation) design of axis, since they require knowledge about the lower level transportation on a higher level. Seen this way, one thread per socket communication is maybe expensive in resources, but it is the only way to ensure your main thread continues to operate in a timely fashion. But prone to explode with a log of async calls. As a 'workaround' I've now my own static-sized thread pool that perform synchronous calls. If there are more async calls then threads in the pool, they're queued. Thank you for your input. -- Patrick van Beem Sr. Software engineer Quintiq T +31 (0) 73 691 07 39 F +31 (0) 73 691 07 54 M +31 (0) 06 15 01 65 83 E patrick.van.b...@quintiq.com I www.quintiq.com This message contains information that may be privileged or confidential and is the property of Quintiq. It is only intended for the person to whom it is addressed. If you are not the intended recipient, you are not authorized to read, print, retain, copy, disseminate, distribute or use this message or any part thereof. If you have received this message in error, please notify the sender immediately and delete all copies of this message. Please note that e-mails are susceptible to change, therefore they are not binding.
