March 2010 - Boost-users - lists.preview.boost.org

vc++ assertion error upon runtime
by hitesh dhiman 19 Mar '10

19 Mar '10

Hi all, I'm trying to gain access to functions that use pointers as arguments. I have written the wrapper file that converts the arguments into pointers. The compilation works successfully, but when i try to run the code from python, it gives an assertion error: Debug Assertion Failed! Expression: Vector subscript out of range Surprisingly, this error only occurs when a particular function is called, Until that point, the code works perfectly. Could someone guide me what to do?? -- Regards, Hitesh Dhiman Electrical Engineering National University of Singapore

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scoped_lock lock&unlock
by weii 19 Mar '10

19 Mar '10

Dear all, I got a compiler(gcc 3.4.5) error while using boost.thread: ----------------------------------------------------------------------------- g++ -IC:\Program Files\boost\boost_1_40 -O0 -g3 -Wall -c -fmessage-length=0 -omain.o ..\main.cpp C:/Program Files/boost/boost_1_40/boost/thread/win32/basic_timed_mutex.hpp: In member function `bool boost::detail::basic_timed_mutex::timed_lock(const Duration&) [with Duration = bool]': C:/Program Files/boost/boost_1_40/boost/thread/locks.hpp:353: instantiated from `bool boost::unique_lock<Mutex>::timed_lock(const TimeDuration&) [with TimeDuration = bool, Mutex = boost::mutex]' C:/Program Files/boost/boost_1_40/boost/thread/locks.hpp:241: instantiated from `boost::unique_lock<Mutex>::unique_lock(Mutex&, const TimeDuration&) [with TimeDuration = bool, Mutex = boost::mutex]' ..\main.cpp:17: instantiated from here C:/Program Files/boost/boost_1_40/boost/thread/win32/basic_timed_mutex.hpp:118: error: no match for 'operator+' in 'boost::get_system_time() + timeout' C:/Program Files/boost/boost_1_40/boost/date_time/time.hpp:140: note: candidates are: T boost::date_time::base_time<T, time_system>::operator+(const typename time_system::date_duration_type&) const [with T = boost::posix_time::ptime, time_system = boost::posix_time::posix_time_system] C:/Program Files/boost/boost_1_40/boost/date_time/time.hpp:160: note: T boost::date_time::base_time<T, time_system>::operator+(const typename time_system::time_duration_type&) const [with T = boost::posix_time::ptime, time_system = boost::posix_time::posix_time_system] C:/Program Files/boost/boost_1_40/boost/operators.hpp:255: note: boost::date_time::date_duration<boost::gregorian::date_duration_rep> boost::operator+(const boost::date_time::date_duration<boost::gregorian::date_duration_rep>&, const boost::date_time::date_duration<boost::gregorian::date_duration_rep>&) C:/Program Files/boost/boost_1_40/boost/date_time/posix_time/date_duration_operators.hpp:76: note: boost::posix_time::ptime boost::posix_time::operator+(const boost::posix_time::ptime&, const boost::gregorian::years&) C:/Program Files/boost/boost_1_40/boost/date_time/posix_time/date_duration_operators.hpp:32: note: boost::posix_time::ptime boost::posix_time::operator+(const boost::posix_time::ptime&, const boost::gregorian::months&) C:/Program Files/boost/boost_1_40/boost/date_time/date_duration_types.hpp:245: note: boost::gregorian::date boost::date_time::operator+(const boost::gregorian::date&, const boost::date_time::years_duration<boost::gregorian::greg_durations_config>&) C:/Program Files/boost/boost_1_40/boost/date_time/date_duration_types.hpp:133: note: boost::gregorian::date boost::date_time::operator+(const boost::gregorian::date&, const boost::date_time::months_duration<boost::gregorian::greg_durations_config>&) Build error occurred, build is stopped ----------------------------------------------------------------------------------------------------------------------------- The following is my code: ----------------------------------------------------------------------------------------------------------------------------- #include <boost/thread/thread.hpp> #include <boost/thread/mutex.hpp> #include <boost/bind.hpp> #include <iostream> boost::mutex io_mutex; void count(int id) { boost::mutex::scoped_lock lock(io_mutex,false); for (int i = 0; i < 10; ++i) { lock.lock(); std::cout << id << ": " << i << std::endl; lock.unlock(); } } int main(int argc, char* argv[]) { boost::thread thrd1(count, 1); boost::thread thrd2(count, 2); thrd1.join(); thrd2.join(); return 0; } ----------------------------------------------------------------------------- I know I can just abandon the lock() and unlock() function since the constructor and destructor will do them for me. But I can't understand how this error occurs and why the compiler has something to do with basic_timed_mutex. Anyone can give me some clues? Thanks in advance.

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[interprocess] Sharing data in a peer-to-peer fashion
by Brett Gmoser 19 Mar '10

19 Mar '10

Hello, I'm working on what seems to be a fairly interesting problem, and I'm looking for any interprocess experts to lend any advice. After reading all of the documentation for Interprocess, it seems that all of the examples work with a "one parent, many children" type model. The problem that I am having is that I am working with a "many children, no parent" model. My processes are spawned by the web server (and FastCGI), so there is no easy way to modify that code to manage the interprocess data. At least one instance of my program is meant to stay alive forever, so I'm not very concerned about deleting the interprocess data at any time. My problem however is the mutexes, and the stale locks that result if one of the processes crashes or exits abnormally. It seems that once an instance of my application crashes, no other instance may ever get a lock on the shared mutex, because the original process still holds a lock. I've thought of a few different ideas to solve this problem: * Using an interprocess shared_ptr for the mutex and data, with a custom deleter to remove all instances once the last application is exiting and the use count is zero. However this suffers from the same problem - it seems the use count is never decremented when the application exits abnormally (for example, kill -9, crash, or CTRL+C). * Using a "heart beat" type system to keep track of processes. My idea was to do something like this: Keep an interprocess associative array of process ID's mapped to last heartbeat time, with each process updating it's own heartbeat. At the same time, every other process (since there is no one parent process) must keep track of the heartbeats, and remove processes from the array which have not responded with a heartbeat in awhile. The problem is this - what about the mutex for the associative array? And the locks that another application might have on them? I wind up back at the point that I started at. The stale locks are destroyed if the mutex is deleted (via boost::interprocess::named_mutex::delete), and I can detect the stale lock pretty reliably with a timed try lock (wait 30 seconds or so to aquire the lock, if it can never be acquired then there is obviously a problem). But what of thread safety, since I now have to delete the lock and re-create it, where other processes might wind up doing the same thing? And what if those other processes are also trying to obtain a lock on the mutex at the same time I'm deleting and recreating it? Those are pretty much the only ideas I've had. Does anybody have anything better? Maybe some of you have tackled a similar problem? Thanks!

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passing pointers from python
by hitesh dhiman 19 Mar '10

19 Mar '10

Hi all, i'm trying to wrap c++ functions that have pointer variables. The test example i'm using is shown below: int World::addition(int* a, int* b) { int z = *a + *b; return z; } Now, i defined it in my wrapper as : .def("addition", &World::addition) My code compiles, but when I try to execute it from python, i get this error: Python Argument types in World.Addition(World, int, int) did not match C++ signature: addition(class World {lvalue}, int* , int*) The problem is, how to get hold of a pointer in python? Or is there a workaround to define the function differently in the wrapper file? -- Regards, Hitesh Dhiman Electrical Engineering National University of Singapore

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Initialising boost::interprocess::basic_string using std::string
by med ennemri 19 Mar '10

19 Mar '10

Hi all How to initialising boost::interprocess::basic_string using std::string; -- One God is Allah, all prophets are humans.

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[boost-users][[proto] : Seeking advice on a DSL
by Manjunath Kudlur 19 Mar '10

19 Mar '10

Hello, I want to create a DSL where users are allowed to create "free" variables and then use them are parameters and local variables in their mini-program. For example, I want to have something like int_ a,b,c; Program(&a,b) [c = b*2, a = c] The parameter with the '&' prefix represents output, the ones without represent input. So, Program(&a, b)[...] should behave as a function object with prototype void foo(int&, const int), and I should be able to do the following : int ra; BOOST_AUTO(pr, Program(&a,b) [c = b*2, a = c]); pr(ra, 4); I am seeking some advice on implementing the "evaluator" for this language. In particular, where do I store the values corresponding to these free variables? To draw parallels with Boost.Phoenix, in phoenix, arg1, arg2.. etc are uniquely typed, and the evaluator just creates a fusion::vector<...> with the values passed in, and argN evaluation just returns fusion::at_c<N>(env.args()). In my case, I could create a unique ID for each free variable, and create a std::map from ID to value, and use that as the environment. Evaluator of the free variables can then look up that map to find values. But I consider this too heavy weight. In contrast, the fusion::vector<...> would incur very little overhead during run time. I will be grateful for any suggestions on other ways to implement the evaluator. Thanks in advance, Manjunath

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custom allocators, pool_alloc release_memory() seems to be broken
by B Hart 18 Mar '10

18 Mar '10

I tried contacting Stephen the pool_allocator author, but his e-mail is invalid (shouldn't the docs be updated?) Here is what I wrote in case someone else here can offer some help: I'm trying unsuccessfully to use your Boost::pool_alloc. In the documentation at the boost website: http://www.boost.org/doc/libs/1_42_0/libs/pool/doc/interfaces.html it says: // Exiting the function does NOT free the system memory allocated by the pool allocator // You must call // boost::singleton_pool<boost::pool_allocator_tag, sizeof(int)>::release_memory() // in order to force that release_memory() does not seem to work. Not sure why. I called a function in my code to verify my processes memory usage, and see that indeed memory was not being released. I also google searched and found that others experienced the same: http://groups.google.ms/group/boost-list/browse_thread/thread/7d350f4c30d76… http://article.gmane.org/gmane.comp.lib.boost.devel/179196 http://lists.boost.org/Archives/boost/2008/08/141468.php http://archives.free.net.ph/message/20080827.184624.21654313.en.html Your help on this is requested. Thanks.

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shared_ptr with custom allocator but default deleter?
by Rhys Ulerich 18 Mar '10

18 Mar '10

I'm missing something w.r.t. shared_ptr and custom allocators... I'd like to use the following shared_ptr constructor template<class Y, class D, class A> shared_ptr(Y * p, D d, A a); with a custom allocator but "the usual deleter behavior". I'm confused about what to supply for 'd'. Restating my confusion, first pretend the signature was this template<class Y, class A> shared_ptr(Y * p, A a); and ignore the normal shared_ptr two argument constructor for the moment. Now pretend I could implement this hypothetical two argument version by delegating to the three argument version. What would I supply as the 'd' parameter? - Rhys

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[SoC] Summer of Code
by Andrew Sutton 18 Mar '10

18 Mar '10

All, Boost is once again participating in the Google Summer of Code program. If you are a student who is interested in contributing to Boost, now would be a good time to discuss your plans on the *developer's* mailing list ( http://lists.boost.org/mailman/listinfo.cgi/boost). Student applications will be accepted here starting March 29, and can be submitted here: http://socghop.appspot.com/. If you have any questions, please feel free to ask me directly or respond to this message. Cheers, Andrew Sutton andrew.n.sutton(a)gmail.com

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[asio] Problem Assignin a File Descriptor to posix:basic_stream_descriptor
by Nader Salehi 18 Mar '10

18 Mar '10

Hi All, I want to use Boost ASIO as an event manager in a server which, among other things, asynchronously writes into a file. I use open() to create my file and then try to assign it to a posix::stream_descriptor object. However, the following simple code throws an "Operation not permitted" exception. int main () { boost::asio::io_service ioService; int fd = open("./asio_sample.txt", O_WRONLY | O_CREAT | O_ASYNC | O_NONBLOCK, S_IRUSR | S_IWUSR | S_IRGRP); assert(fd != -1); boost::asio::posix::stream_descriptor descriptor(ioService); descriptor.assign(fd); return 0; } I traced down the epoll_reactor::register_descriptor() where the function fails to add the descriptor to the poll list. Any idea what I am doing wrong? I would appreciate any comment. Cheers, Nader

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