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[boost][interprocess] upgradable_mutex is semi-recursive...
by Lars Hagström 23 Jan '09

23 Jan '09

The subject is misleading, but hopefully eye-catching :-) I do understand that this is not an interprocess bug, but more of a result of how upgradeable locks work. But the behavior can be dangerous, as will be seen. What I've got happening is that one process locks the mutex recursively (sharable, of course). And this works (most of the time), since it is okay to lock the mutex shareably any number of times (even if it is within the same thread). But the problem occurs when a writer (in another thread) manages to get inbetween these lockings, when we get this sequence thread A locks mutex shareably thread B waits for exclusive lock thread A waits for sharable lock Since the upgradable mutex is written so that if there is an exclusive locker waiting it doesnt let any more sharable lockers in this will deadlock. Something that explains this could be useful in the interprocess documentation. Or, maybe the problem could be solved. I see two ways: 1. Detect recursive sharable locking, so that my thread A would always get an exception when trying to lock a lock that I've already got (it is a recipe for disaster) 2. Allow recursive sharable locks. If you've got the lock it's okay to take it again. Since I'm not really a fan of recursive locking (the above locking is a mistake, really) I think I would prefer solution 1 of these two. (I'm fixing my code to not be recursive now, but I thought this might be of interest to either Ion or anyone using boost interprocess.) Cheers Lars

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[boost program options] missing value validation
by Andy F 23 Jan '09

23 Jan '09

If I have a parameter which needs a value, but the value is not specified in the command line, I get an unknown exception in VisualStudio 2005. Meaning, if I declare a --compression=something, but then call the program with just --compression, the exception is thrown at the po::store() method. How do I intercept this and validate? I am just using the code from the example program: po::options_description desc("Allowed options"); desc.add_options() ("help", "produce help message") ("compression", po::value<std::string>(), "set compression level") ; po::variables_map vm; po::store(po::parse_command_line(ac, av, desc), vm); po::notify(vm); if (vm.count("help")) { std::cout << desc << "\n"; return 1; } if (vm.count("compression")) { std::cout << "Compression level was set to " << vm["compression"].as<std::string>() << ".\n"; } else { std::cout << "Compression level was not set.\n"; }

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[BGL] Remove vertices/edges from a subgraph
by Grzegorz Slodkowicz 23 Jan '09

23 Jan '09

What is the reason for vertex/edge removal functions in subgraphs being unimplemented? Is it simple oversight / lack of demand or would that pose some problems? Regards, Greg

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Help with a boost::lambda problem and boost::array?
by jesseperla＠gmail.com 23 Jan '09

23 Jan '09

> Is there a solution? It appeared to me that the likely winner was: http://www.boost.org/doc/libs/1_37_0/doc/html/lambda/extending.html Then it seems we would use the boost array's typedef value_type to get the return type. However, I do not see operator[] overloading in the list of supporting operators here. But the following code compiles: //Testing lambda and vectors/arrays. using lambda::_1; std::vector<Real> vec(1); vec[1] = 0; boost::function<Real (std::vector<Real>)> vec_f = _1[0]; //Returns the 0'th element. Hence, it seems that this type of action is supported. Any idea where the sourcecode for the std::vector lambda operators are? might be useful to just copy/paste. Also, I wonder if there is any way to do this generically for all vector/array types supporting the Container concept? (I use a lot of ublas::vectors). And if operator() is also supported, I use a lot of ublas::matrix as well, so this would be nice to have in lambda. Jesse

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Help with a boost::lambda problem and boost::array?
by jesseperla＠gmail.com 23 Jan '09

23 Jan '09

Does anyone have an idea why the following doesn't compile: using lambda::_1; using lambda::_2; boost::function<double (const boost::array<double, 2>&)> f = lambda::ret<double>(_1[0] * _1[1]); But the following does as a double-check: using lambda::_1; using lambda::_2; boost::function<double (const double&, const double&)> f2 = lambda::ret<double>(_1 * _2); Thanks, Jesse

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WinCE family
by Marat Abrarov 22 Jan '09

22 Jan '09

Does anybody can describe what happens with the development process of support of WM 5-6x and WinCE 5-6? What is the current state of affairs? It would make boost more popular if boost supports (either particular, but official) such modern and famous mobile platforms like Symbian (S60), WM (5 and above), WinCE (5 and especially 6), Android. I understand that it's rather difficult to support such a different case of platforms, but boost (for me) ~ Standard C++ Library, and if Qt supports S60 3rd edition, WM 5-6, WinCE 5-6, Linux Embedded - why boost can't? Best regards, Marat Abrarov.

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boost::interprocess shared memory performance
by Andy Wiese 22 Jan '09

22 Jan '09

This is my first experience with using shared memory for anything more than trivial IPC. Thanks again to Ion Gaztañaga for getting the library working on FreeBSD. I'm developing initially on OS-X 10.5.6 with boost_trunk, but the eventual target platform is FreeBSD--I'm just an old mac programmer used to cushy development tools. I originally used managed_mapped_file, and got everything working, but I was disappointed by performance. Profiling with shark, I found that the application was spending a lot of time in msync, which according to man(2) is used to synchronize mapped memory with the filesystem. It makes sense to me that the interprocess containers I was creating could have a lot of file I/O overhead, and managed_mapped_file was probably not a good choice. So I rewrote the code to use managed_shared_memory instead of managed_mapped_file, thinking that it would eliminate the file I/O and therefore be faster. However, I am surprised that it is not much faster, and when I profile with Shark on os-x I see that it is still spending a lot of time in msync, specifically whenever a managed_shared_memory object is destroyed. (in boost::interprocess::mapped_region::flush(unsigned long, unsigned long), which is called within basic_managed_shared_memory's destructor) Does managed_shared_memory really need to call msync? I see that I should optimize my code to cache the managed_shared_memory objects so that fewer create/deletes are necessary, but this is still going to happen fairly frequently and I wonder if this expensive msync call is necessary. In the tradition of coder forums everywhere, someone will probably ask what I'm trying to accomplish and whether there may be a better way. Suggestions welcome. I'm writing a little cgi driven database utility that queries data stored in a filesystem directory using a simple query language. I would like to keep indexes of the data to speed query resolution. The utility is old-school cgi, so all its resources (such as indexes) have to be instantiated into memory each time the cgi process is started. I could write indexes to files, but then I incur a de/serialization overhead that is expensive. My intention was to keep the indexes as ready-to-use interprocess::maps in shared memory, to be used by all invocations of the cgi. It works, but the performance of the shared memory is poor enough that I'm not getting much increase over just doing a brute force search through the datafiles. All suggestions appreciated! Andy

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[MPL] meta-function returning the arity of lambda expression
by Joel Falcou 22 Jan '09

22 Jan '09

Is there any meta-function that returns the arity of a MPL meta-function as an integral constant ? -- ___________________________________________ Joel Falcou - Assistant Professor PARALL Team - LRI - Universite Paris Sud XI Tel : (+33)1 69 15 66 35

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Transferring files across a network.
by Andrew Maclean 22 Jan '09

22 Jan '09

We have a situation where there are several computers that have a folder where files are periodically deposited. Currently, in each computer, this folder is scanned periodically and the files are parsed by a program that then sends the SQL data to a central machine where there is postgresql server running. The files are generally small because they are compressed. But the uncompressing and subsequent parsing into SQL strings dramatically inflates the amount of data that is sent across the network. What I am thinking of doing is sending the all the files to a directory on the central machine then parsing them there for subsequent inclusion into the database. So I need a program to periodically scan the folder on the computer and send these files to the central machine. On the central machine I need a similar program to listen for incoming files and put them into a directory for subsequent processing. The listner on the central machine will need to process files arriving simultaneously from several machine. There is no issue with file name conflicts as the names are unique. Can anyone give me any pointers? I think I should use boost asio but I don't know where to start with it. The tutorial and examples, while good haven't provided me with an insight yet! The main requirement I have is that it should be cross-platform. I looked at cURL/cURLpp but there are immense difficulties building this in a windows environment. I would like to stick with boost if possible. Thanks Andrew -- ___________________________________________ Andrew J. P. Maclean Centre for Autonomous Systems The Rose Street Building J04 The University of Sydney 2006 NSW AUSTRALIA Ph: +61 2 9351 3283 Fax: +61 2 9351 7474 URL: http://www.acfr.usyd.edu.au/ ___________________________________________

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[Program Options] Streaming of actual option values.
by Rodolfo Federico Gamarra 22 Jan '09

22 Jan '09

Hi all!! I'm using <boost/program_options.hpp> to allow options in my program to be configured using 3 flavors: - Command line values - Config-file values ( parse_config_file). - Default values ( value<double>(&myDouble)->default_value(3.3) ) prioritized in the given order and put all together in the same variables_map. Upon finalization I'd like to generate a config-file (as required by the 2nd flavor) with the actual values used in the run. So far I've come with a solution that involves iterating over the map, and performing the outstreaming by myself. Something in the line of for(variables_map::const_iterator i = vm.begin(); i != vm.end();++i) { std::cout << i->first << " " << i->second.as<std::string>() << std::endl; } What is cumbersome of this approach is that, actually, not all my args are "std::string", so in reality the call to as<>() ends with bad_any_cast in some cases: it seems that there's no operator << defined for i->second or its underlying "boost::any". So I'd have to switch-case over all the types I'm using for the values. Second, I have to format the output in accordance to parse_config_file by myself. Is there any better solution to this? Thanks a lot in advance. -- Rodolfo Federico Gamarra

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