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status of circular buffer
by Vincent Torri 14 Apr '05

14 Apr '05

Hello, I would like to know what is the status of circular buffer, in particular if there is a chance that it will be included in the next version of boost. Thank you Vincent Torri

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Re: Network library: What we have until now
by Don G 14 Apr '05

14 Apr '05

Hi Boris, > I updated > http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl?BoostNet > to document why what decisions were made. > We have until now: > * The network library should support four I/O models > which are known to many programmers as blocking, > non-blocking, multiplexing and asynchronous. Personally, I don't think the multiplexing interface is appropriate or necessary. Essentially the same style can be achieved with multi-threaded async and a boos::function queueing solution. In other words, it is not a group of network objects that is being manipulated. It is a portable dispatcher that gets boost::function<>'s queued to it. It therefore suffers none of the portability issues that a direct wrapper to select would have. I also believe that non-blocking is an I/O only thing; it is not needed for connect or accept. > * It should be possible to switch between I/O models at > runtime (which means you have one socket class supporting > all I/O models instead of different socket classes each > of them supporting only one I/O model). Perhaps "switch" isn't the best term. On a per-operation basis, the user should chose between styles. > * There should be an asynchronous I/O library as other > libraries might want to do asynchronous I/O, too. I don't see this as practical. There is no such thing as async I/O that can be portably described. This means that each kind of async object has to provide the right implementation. Perhaps the scope of portability needs to be stated and agreed upon. When I implemented async pipe I/O on Windows NT/9x, I could not use the same code for I/O as I did with sockets or as I would for files (subtle differences). I think a common pattern for async behavior should be agreed upon and if some implementation details turn out to be reusable, that's a good happenstance. My prediction is that on Unix platforms, there will be more to reuse between sockets, pipes, files, etc.. On Windows, there will be little. > * There should be an asynchronous design pattern which > should be used by all Boost libraries which support > asynchronous operations. I agree completely on this one :) > * On a low level the network library should be close to > what is known as Berkeley sockets to many programmers. I think sockets should be hidden. They are not universally used, for example Mac OS9 doesn't and I just assume others exist. They don't have any magical powers; they are just a C abstraction. A C++ abstraction should replace them. > * On a high level there should be I/O streams support. I agree again ;) > As far as I can see from all the discussions that's > what we agree on. There have been some ideas like > event handlers and dispatchers but I am not sure > where to put them - have a look at > http://www.highscore.de/boost/net/packages.png > please (which is also in the Wiki page). This is the > overall architecture of the network library. If you > want me to change or add something please tell me. We have a couple straw men started (Michel's and mine). Perhaps it is just as good to start just throwing darts at them? I could probably have a full implementation of the interfaces I propose in a small number of weeks (2-3). Having done it once before really helps<g>, but I wanted to get to some common ground on the philosophy before going to that step. The philosophy I have on this may be out of sync with some (pun intended), but IMHO, we need to hash over the philosophy as much as anything. We have a lot of folks that are very comfortable with the sockets interface, but I don't believe that exposing its idiosyncrasies is the right approach. Everyone that writes sockets code runs into the same problems, and solves them in varying degrees of sophistication and completeness. A robust solution is not as difficult as some might think. It's certainly easier than getting agreement on philosophical matters. ;) Best regards, Don __________________________________ Do you Yahoo!? Yahoo! Small Business - Try our new resources site! http://smallbusiness.yahoo.com/resources/

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Re: async socket i/o [long]
by Don G 14 Apr '05

14 Apr '05

Hi Michel, >Don G wrote: >> I have also been putting together some ideas which are >> similar to those you outlined, though perhaps at a >> higher level of abstraction. I will try to wrap up what >> I have and post it in the next day or two. I will also >> try to look more closely at your code. > > It's not that much code more interfaces ;), but > implementability on at least linux, solaris, windows is > a minimum. I have implemented these interfaces (for my work) on Linx, Solaris, Windows (all versions) and Mac OS/X (and even OS 9, though we have removed that support at this point). The interfaces I am proposing don't mention socket or sockaddr or select et.al.. As a matter of fact, not all OS's even use sockets (MacOS < X doesn't if that matters). I have even implemented these interfaces as a pseudo-network over HTTP tunnels and reflection servers. About the only portability requirements that I can think of are: threads and a network access API of some kind. Not just any network API will do, but just about any system with threads should have the necessary power. There are implementations that would fit only certain platforms that may be better (epoll vs. kqueue vs. select), but a select() based version would be extremely portable for a first version. Subsequent versions could add an epoll implementation and others. I suppose that if multiple choices exist for a given platform, different concrete classes could provide the user with a choice, but see my comments below. I really do believe that the best choice for a given platform should be made (via profiler as necessary) and that should be that. >> From a quick read, it looks similar to the implementation >> path I had used at my work, but probably more flexible in >> how event_dispatcher relates to event_handler. I think >> there is a good likelihood that the two are complementary. > > Ok could you expand a bit? What do you mean by complementary? The code I wrote for work had an implementation-side abstraction with an abstract base like event_handler, though I called it Selectable. It had a signal mask that mapped to your event_handler::event_type_t enum. The thread pool internal to the network object managed calls to select (or whatever) based on the signal mask. At least for Windows, one cannot mix sockets with other types of objects (files or whatnot). And, while I have not tried it, the docs seem to suggest that sockets for IPv4 and IPv6 may not be able to go to a single select call. All this makes matching event_handler instances to an appropriate event_dispatcher tricky and not portable. In other words, something that should be hidden from the user. The real complexity, though, comes when the number of objects gets large, in particular larger than a single call to select() can handle. This necessitated some load balancing logic to shuffle Selectable objects between threads, create new threads, cleanup extra threads, etc.. All of this is stuff that should only be written once! :) As a user of the library (again, at my work), I never have to worry about that mundane stuff. That is the job of the network library. And it scales pretty well. Though I haven't tested N*1000 simultaneous connections using drones across the network to simulate heavy CPU load, I have stress tested the library upto the limit of Windows XP Pro (not Server) and on Linux with N*1000 where N < 3, using lots of threads to generate the load. While all thread pooling and connection aggregation is managed behind the scenes, some of this could be exposed in an abstract manner to allow user code to influence the load balancing algorithm. This, I think, would be for only the very advanced user and not something to tackle initially. >> 1. Should the network library provide different choices >> of implementation to the user? For the most part, the >> platform will dictate the available solutions, so >> having the user decide would make their code >> non-portable. [my thought so far is no] >> >> 2. Would it be better perhaps to only provide behavior >> choices (sync, async, non-blocking) as part of the >> interface? [my thought is yes] > > I think two but not providing choices just support them > all automatically and efficiently. And give the user a > possibilty to plugin own implementations of the concepts. This is where our goals diverge I guess ;). I don't see any point in the user deciding these details, especially implementing their own concrete classes. And I do see it creating confusion amongst those that don't have the "Network API Guru" honor badge<g>. Because of the _long_ history of having to work directly at the socket/select/epoll layer, some of us aren't bothered by it (and some of us may even like it<g>). But this stuff is just unapproachable for anyone less than an advanced developer, is error prone at best and just plain tedious. Hard to tell how much I like select, eh? :) The interfaces I proposed provide a very clean and complete interface, IMHO<g>, and the implementation can be quite scalable (for those that need it to be) and I know it is extremely portable, even to non-socket based systems. Best regards, Don __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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Re: async socket i/o [long]
by Don G 14 Apr '05

14 Apr '05

Hi Michel, > IOCP provides the most scalable way to do I/O on > Windows NT and later and it will blow the sock off > just about anything it minimizes context switching > by activaiting threads in FIFO order keeping a > single thread hot, and blocks dequeing completions > if there are more runnable threads on the port than > cpus in the machine. Any serious server application > should consider using it. But having a solid > portable select based mechanism to fall back on > could be used on any platform (supporting BSD > sockets at least). Sounds like it should, but it would be "easy" to measure down the line and verify. > Anyways maybe we should settle for the requirements, > before we decide the details, Agreed. The requirements are the hard part and important to agree upon. > but preferably I think the interface shouldn't rule > out an IOCP based implementation. There is nothing in the interface I proposed that would prevent an ICOP implementation. > And there seems to be a lot of different opinions on > what kind of servers and scalability requirements > the interface should provide. From simple blocking > to full blown asynch with best implentation on any > given plattform. Quite a diversity :) Best, Don __________________________________ Do you Yahoo!? Make Yahoo! your home page http://www.yahoo.com/r/hs

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Re: Network library: What we have until now
by Don G 14 Apr '05

14 Apr '05

Hi Edward, --- Edward Diener wrote: > While a non-blocking connect is a must-have I think a > non-blocking accept is essential also. A server needs > to be just as responsive to other things happening as > a client. > One might need to pause or stop the server completely, > depending on the meaning given to each, and a server > might be accepting connections on more than one > endpoint. Without a non-blocking accept, both these > general possibilities become impossible and one ends > up with a single end-point server which must be killed > to end the process, which I do not think scales well > in today's world of network programming. But an async interface provides this capability. You say something like async_accept(call_here_for_a_connection) and proceed with life. If the callback must occur on a given thread, that is a different concern. I have been suggesting that this situation be handled by a purely async library that handles a queue of boost::function<> objects, so instead of blocking on select, you block on the queue. For scaling, one really needs to consider threads in order to take advantage of multiple processors. To gain this benefit in a single-threaded server, one would have to have multiple processes. It can be done, but I think the multi-threaded single process would scale better. Not to say that I have gathered any hard statistics to prove my assertion. :) This is the approach I have taken for scalability in the proposal I posted. Best, Don __________________________________ Do you Yahoo!? Yahoo! Small Business - Try our new resources site! http://smallbusiness.yahoo.com/resources/

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Re: Network library: What we have until now
by Don G 14 Apr '05

14 Apr '05

I think this presupposes a mostly manual association of selectable_object with select_set? The select_set is then used to wait? If not, please explain the importance of "when can non-blocking operations proceed" vs. "async operations are done". If the "operation is done" callback occurs by calling dequeuing a boost::function<> then the app is still "single threaded" to the user. Seeking understanding, Don --- Iain Hanson <Iain.Hanson(a)videonetworks.com> wrote: > On Wed, 2005-04-13 at 11:09 -0400, Caleb Epstein wrote: > > On 4/13/05, Don G <dongryphon(a)yahoo.com> wrote: > > > I also believe that non-blocking is an I/O only thing; it is > not > > > needed for connect or accept. > > > > Not sure about the need for a non-blocking accept, but a > non-blocking > > connect is a must-have. > > > Non blocking accept is also a must have for single threaded > reactive > servers. > > /ikh > > _______________________________________________ > Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost __________________________________ Do you Yahoo!? Yahoo! Small Business - Try our new resources site! http://smallbusiness.yahoo.com/resources/

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[shared_ptr] ia64 implementation by Ben Hutchings
by Peter Dimov 13 Apr '05

13 Apr '05

The attached patch is a tested implementation for IA64 by Ben Hutchings. What should we do with it? a) add it to 1.33 b) add it to 1.33 but disable it by default c) ship 1.33 without it Opinions? Ben Hutchings wrote: > Here's a patch against current CVS that actually produces compliable > code and passes the tests. It adds -D_REENTRANT to the command-line > options in a gcc/ia64 multithreaded build because this is not implied > by -pthread (see <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10865>).

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Re: async socket i/o [long]
by Don G 13 Apr '05

13 Apr '05

Hi Michel, Please see below. --- Michel Andr� <michel.andre(a)swipnet.se> wrote: > Caleb Epstein wrote: >> I disagree. On some platforms, there are multiple choices >> for the underlying event dispatching implementation. For >> example, on Linux you can use select, poll, or on newer >> kernels, epoll and kqueue. >> Even on Windows, there is more than one implementation >> that can be used (e.g. WaitForMultipleObjects, select >> (which I assume just wraps WFMO), and IO Completion >> Ports). >> >> Some of these are semi-portable (e.g. select, poll) but >> the others are very specific to the platform. As a user >> I want the ability to choose the one that is most >> suitable to the task at hand. > > But reasonable and efficient defaults should be used so > you would not have to choose. Eg iocp on windows and > kqueue on linux. There should be some measurement made to show IOCP as better than select (it might be, but by how much?). The reasons to prefer select to IOCP are significant: select is much more portable (meaning no extra work for Windows); IOCP is NT only (no 9x/Me). So, if IOCP just blows the doors off select, it might be one of these places where a user needs to chose an implementation for a single platform. An important note: the _only_ reason is to trade backwards compatibility with old an OS family for performance. There should be _no_ difference in the interface and behavior. I don't see any reason this would need to be a run-time choice, though it could be in the approach I am proposing. It would just be a different concrete network object. >>>2. Would it be better perhaps to only provide behavior >>> choices (sync, async, non-blocking) as part of the >>> interface? [my thought is yes] >> >> Not sure what you mean here. Connections may be either >> synchronous or asynchronous? This seems too limiting IMHO. > > Aggreed you should be able to do eg synch/blocking write as > a response to a asynch read, or do the handshaking/login > synch and then go asynch. I agree as well. This was just a misunderstanding of my question. > But I think most of the time the user will choos asynch or > synch. Indeed. Best, Don __________________________________ Do you Yahoo!? Yahoo! Small Business - Try our new resources site! http://smallbusiness.yahoo.com/resources/

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Proposal: is_swapable, is_nothrow_swapable, nothrow_swap, swap
by Pavel Chikulaev 13 Apr '05

13 Apr '05

Hi boosters, We often need to swap contents of two objects, but even more often we need to swap contents with no-throw exception guarantee. But currently we have no general way to swap two objects with no-throw exception guarantee. What we do have now is std::swap, and member functions which can be named swap, Swap, and so on. But now we can't swap arbitary types with no-throw exception guarantee in a general way. Yes, we can overload std::swap to support other than std:: types, but we can't guarantee that invocation of std::swap won't throw. So, I propose the following: New traits classes: boost::is_swappable<T>::value, boost::is_nothrow_swappable<T>::value. and specialize them for known types, but by default both should return false. Introduce new function boost::nothrow_swap(T &, T &); which will swap two objects if boost::is_nothrow_swappable<T>::value == true, else compile-time error will occur. Introduce new function boost::swap(T &, T &); which will swap two objects if boost::is_swappable<T>::value == true, else compile-time error will occur. Introduce template<typename T> struct do_nothrow_swap { static void nothow_swap (T &, T&); } and specialize it for types that can be swapped with no-throw guarantee such as std::vector, invoking default implementation will lead to compile-time error. Introduce template<typename T> struct do_swap { static void swap(T &, T &); }; and specialize it for types that can be swapped(but without guarantees) such as boost::array, invoking do_nothow_swap<T>::nothow_swap if no specialization found. Using this technique, we can support even such classes that doesn't have swap member-function, but have Swap or any other. I guess it would be helpful at least in boost::ptr_container library. This gives new standard way to do the swapping work, and in contrast to std::swap now we can be expilictly specify no-throw guarantee if needed. As always any comments are appreciated. P.S. Sorry if it was already proposed, didn't found it. -- Pavel Chikulaev

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Re: [boost] Re: Network library: What we have until now
by Iain Hanson 13 Apr '05

13 Apr '05

On Wed, 2005-04-13 at 11:09 -0400, Caleb Epstein wrote: > On 4/13/05, Don G <dongryphon(a)yahoo.com> wrote: > > I also believe that non-blocking is an I/O only thing; it is not > > needed for connect or accept. > > Not sure about the need for a non-blocking accept, but a non-blocking > connect is a must-have. > Non blocking accept is also a must have for single threaded reactive servers. /ikh

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