May 2008 - Boost-users - lists.preview.boost.org

[boost-users] boost::function object alignment question
by Neil Fang 31 May '08

31 May '08

Hi I have a win32 static library with a class like this : typedef boost::function<void (int)> TimerCallbackType; class TimerManager { public: int addTimer(int interval, TimerCallbackType callback); }; I use this lib in a Win32 exe, but it crashed on calling TimerManager::addTimer(), the error is: "Run-time check failure #0 - The value of ESP was not properly saved across a function call ... ". Both the exe and lib are compiled with "Struct Alignment" set to "4 Bytes". Finally, I find out a way make it work -- include the boost like this : #pragma pack(push,8) #include <boost/xxxx> #pragma pop() But, I don't know why? Could anybody here help to clear this question? I'm using MS Viusal C++ 2005. Thanks! -- Neil.Fang.CN

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async_XXX() functions
by Longyu Mei 31 May '08

31 May '08

I noticed that there are couple of async_XXX methods, such as async_wait, async_connect, async_write and async_fill. Just wondering why we need those async_XXX methods? without the "async", those methods will block the execution and next statements will be deferred. with the "async", those methods will return immediately and the work will be deferred a little time but will still be executed in the same thread. I feel it confuses people. If we need next statements being executed immediately, we can use another thread to do the wait, connect, write or fill. It is more clear and clean. And the user/programmer has fully control on this. Maybe I have missed something here. please give me your comments. thanks, James

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Re: [Boost-users] shared memory overhead
by Jason Sachs 30 May '08

30 May '08

> > Modern systems use on demand allocation. I.e. you can allocate a (f.ex.) > 32 MB > SHM chunk, but the actual resource usage (RAM) will correspond to what you > actually use. For example: > > 0 1M 32M > [****|..................] > | | > | +- unused part > | > +- used part of the SHM segment > As long as your program does not touch (neither reads nor writes) the > unused part, > the actual physical memory usage will be 1M + small amount for page tables > (worst > case: 4kB of page tables for 4MB of virtual address space). This is at > least how > SYSV SHM works on Solaris 10 (look up DISM - dynamic intimate shared > memory); I > would expect it to work in the same way on new linux kernels too. I'm not > sufficiently acquainted with NT kernel to be able to comment on it. Interesting. I hadn't thought about that. I tried a test program (running on Windows XP), and had a number of separate processes each allocate a new managed_windows_shared_memory object (with a different name for each process) with size 2^29 bytes (=512MB). I'm not exactly sure what resources it allocates; using TaskInfo to view resource usage, each process's "virtual KB" usage goes up by 512MB, but its "working set KB" usage doesn't increase until I actually allocate memory within the shared memory segment. Sounds good, but the 6th one of these failed and I got a warning saying my system was low on virtual memory. So it sounds like there is a 4GB total system limit for WinXP even for just reserving virtual address space -- which seems silly since each process should have its own address space and therefore as long as I don't actually allocate the memory, and each process's reserved address space doesn't exceed 2^32 (or 2^31 or whatever the per-process limit is), I should be able to reserve an unlimited amount of total address space. No can do. :( So strategy #1 of being profligate in choosing shared memory segment size fails on WinXP; there's a significant resource cost even if you don't actually allocate any memory. Drat.

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[multi_array] how to use iterators ?
by r0d 30 May '08

30 May '08

Hello everybody, i'm trying to use boost::multi_array objects with functions of the <algorithm> stl lib. That's why i need to use the iterators of the multi_arrays. But i don't understand the doc about them, and i can't find any example of source code that use them. Could anyone here show me an example of use, or explain me a little bit how they work? Thank you. -- View this message in context: http://www.nabble.com/-multi_array--how-to-use-iterators---tp17556775p17556… Sent from the Boost - Users mailing list archive at Nabble.com.

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Re: [Boost-users] shared memory overhead
by Jason Sachs 30 May '08

30 May '08

>Another thing that just occurred to me: allocate huge SHM segment but >don't commit it immediately; let the os allocate the swap on-demand. >Now, when you run out of swap, the OS should signal the condition >somehow (structured exception handling? something else?). You can >catch the condition and take appropriate action, whatever that might be. See ticket #1975: http://svn.boost.org/trac/boost/ticket/1975

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Boost interprocess map in shared memory
by Jan Suchý 30 May '08

30 May '08

Hallo, I have problem when using interprocess package from boost lib. I would like to have map object in memory. I created example files for creating and reading this object from shared memory. http://www.boost.org/doc/libs/1_35_0/doc/html/interprocess/quick_guide.html… It is working ok. Now, I want to have library, where i want to find previously created shared segment and read it more-times. But I do not want to open it on every runQ function call. I need to open this segment only once and use it more-times when runQ in lib is called. I tried this: #include .... managed_shared_memory segment; int init() { managed_shared_memory localsegment(open_only, "MySharedMemory"); segment = localsegment; } int runQ() { mymap = segment.find<MyMap>("MyMap").first; work with mymap.... } But the declaration of "managed_shared_memory segment" raise error when compiling: /usr/local/include/boost-1_35/boost/interprocess/managed_shared_memory.hpp:61: error: ‘boost::interprocess::basic_managed_shared_memory<CharType, MemoryAlgorithm, IndexType>::basic_managed_shared_memory() [with CharType = char, AllocationAlgorithm = boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family, boost::interprocess::offset_ptr<void>, 0u>, IndexType = boost::interprocess::iset_index]’ is private xqtrans.cpp:261: error: within this context How can use and assign segment globaly in my lib?? Thank you very much for any idea :-) Jan Suchy

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Re: [Boost-users] Should we usually, if not always, create and use weak pointers weak_ptrs with shared pointers shared_ptrs?
by Zhiyang Ong 30 May '08

30 May '08

Greetings All, Should we usually, if not always, create and use weak pointers weak_ptrs with shared pointers shared_ptrs? Is setting all weak_ptrs to null the only reason for using weak_ptrs? Cheers mates. /zhiyang

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[Boost.Asio] Udp::Socket->send_to
by Ryan McConnehey 30 May '08

30 May '08

Hi, In using the Boost.Asio library, the Udp::Socket->send_to() function throws an error if the endpoint is unreachable. I thought in udp datagrams its a send and forget mentality. The send_to function would send the message even if the endpoint was unreachable. Is there a setting I need to use for this to work? Ryan

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Re: [Boost-users] shared memory overhead
by Jason Sachs 30 May '08

30 May '08

>> of these going on at once (though usually just one or two). On my own >> computer I have increased my max swap file size from 3GB to 7GB (so >> the hard limit is somewhat adjustable), though it didn't take effect >> until I restarted my PC. I'm going to be using my programs on several >> computers + it seems silly to have to go to this extent. > >Ok, and you'll run your job on a machine with e.g. 1GB of swap[*], and this >particular instance will need 4GB of swap. What will happen when the >allocation fails? Note that growing the SHM segment in small chunks will >not help you with insufficient virtual memory, so you might as well allocate >M*N at once and exit immediately if the memory is not available. I wouldn't allocate M*N at once. Each process could start/stop at random times (this is triggered by users other than me who would start multiple logs as necessary) so N changes as a function of time. What I will probably do is just use one memory segment of size M[i] memory per process #i, where M[i] has a default value M0, say 64MB, that I can preset to a larger value if I know I'm going to have a long duration log. It's not a huge deal to increase the swap file (even in an old computer, which most of our lab pc's are, I could add a 2nd hard drive if I needed), & is almost certainly the most expedient solution for the time being. >(I'm sorry, I'm very pragmatic, and I don't seem to have enough info to really >understand why you're making such a fuss over the swap size issue. I'm afraid >I can't offer you any further suggestions, since I consider this a non-problem >unless you have further constraints.) Not a fuss, just trying to be aware of all the problems. This discussion has been helpful. I have a career where my resources are spread thinly among a wide range of things, & it's much more expensive for me to design quickly for 90% success + then refactor 1-2yrs later when absolutely necessary, than it is to spend the extra effort up front to design for 99% success, understand where the 1% failure lies, and move on to other things knowing I'm far less likely to have to revisit. Especially when 90% success rates have a tendency to be overestimated as there are customers who forget to mention certain design requirements ;)

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[xpressive] first try: error handling, nested refs
by Christoph Duelli 30 May '08

30 May '08

[I am using Boost 1.35, on Linux, running gcc 4.1.2] I want to parse a string like the following --- ResA { opt1=>val1, opt2 => val2}, ResB ResC {opt3=> valllll } ResD --- I thought that maybe it is easier to to this using xpressive rather than Spirit (which I have used for more complicated stuff so far). I am happy to say, that with the very helpful docs I was able to create a sregex that parses the above. Also, I found it the solution is quite short, so I am basically happy with xpressive. As this was my first try, there is certainly (lots of) room for improvement: I have attached my program, and would welcome comments (and suggestions for enhancements.) #include <boost/xpressive/xpressive.hpp> #include <boost/xpressive/regex_actions.hpp> using namespace boost::xpressive; using namespace std; #include <boost/foreach.hpp> #include <iostream> #include <map> int main(int, char **) { string input = "ResA { opt1=>val1, opt2 => val2}, ResB\n" " ResC {opt3=> valllll }\n\n\n" "ResD"; typedef map<string, string> options_t; typedef map<string, options_t> resources_t; resources_t result; // The name of the resource we are parsing now. string res_name; // Pointer to options (map) of the resource we are parsing now. options_t *optsref; // Match an option(name) and its value. Both strings, // separated by =>, and then stuff the result into the // options-map of the resource we are parsing now. sregex rx_opt = ( (s1= +_w) >> *_s >> "=>" >> *_s >> (s2= +_w) ) [ (*ref(optsref)) [s1] = s2 ]; // A resource has a name and, enclosed in {}, option=>name // pairs. We store the name of the resource and the address // of its options map. sregex rx_res = *_s >> (s1= +_w)[ref(res_name)=s1, ref(optsref)=&(ref(result)[s1])] >> *_s >> optional( '{' >> *_s >> rx_opt >> *(*_s >> ',' >> *_s >> rx_opt) >> *_s >> '}' >> *_s); // A line may contains comma separated resource definitions. sregex rx_line = rx_res >> * (*_s >> ',' >> *_s >> rx_res); // A file consists of multiple lines. sregex rx_file = rx_line >> *(*_n >> rx_line) >> *_n; if(regex_match(input, rx_file)) { // output the parsed structure. cerr << "resname="<<res_name<<endl; BOOST_FOREACH(const resources_t::value_type &p, result) { cerr << p.first << " : " << endl; BOOST_FOREACH(const options_t::value_type &o, p.second) cerr << " " << o.first << " => " << o.second << endl; } } else cerr << "NO MATCH!" << endl; return 0; } In particular, I'd like to know: 1) Is it possible to avoid my (ugly) use of "*optsref"? I would have liked to write something like sregex rx_opt = ( (s1= +_w) >> *_s >> "=>" >> *_s >> (s2= +_w) ) [ (ref(result[ref(res_name)])) [s1] = s2 ]; ie nest the maps directly. The way I tried, it would not compile. 2) Can I tell xpressive to allow arbitrary whitespace around ">>"? I'd rather avoid cluttering the regexes with all that ">> *_s". 3) If the string does *not* match the sregex, can I find out where the failure occured (ie what is the length of the prefix that could have been completed to a succesful match.)? Thank you and best regards, keep up the good work, Christoph

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