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Confused about shared_mutex usage.
by Jason Cipriani 02 Jul '09

02 Jul '09

Hi all, I'm looking at the shared_mutex documentation here: http://www.boost.org/doc/libs/1_35_0/doc/html/thread/synchronization.html#t… But the documentation seems to be a little bit sparse and I'm having trouble figuring out how to use shared_mutex as a read/write lock. Just to make sure, lock_shared/unlock_shared is for the "readers", and lock/unlock is for the "writers"? If not, how do I lock/unlock it for reading, and how do I lock/unlock it for writing (exclusive lock)? Also I'm having trouble understanding what a "lock" is as opposed to a mutex. What is boost::shared_lock? Thanks! Jason

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Using mpl to instantiate template function
by Richard Hazlewood 02 Jul '09

02 Jul '09

Is there a type-only based way (e.g. with fold) of getting mpl to stamp out template functions for a collection of types? For example, this appears to work using mpl::for_each template <typename T> void Foo(); typedef mpl::vector<t1, t2, t3> Types; struct StampOut { template <typename T void operator()(const T *) const { Foo<T>(); } }; void dummy_() { mpl::for_each<Types>(Types, add_pointer<mpl::_1> >(StampOut()); } However, it requires the "dummy_" function to force instantiation. Is there an alternative trick?

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[interprocess] named_upgradable_mutex
by Moritz 02 Jul '09

02 Jul '09

Hi everybody, I have a question concerning the interprocess::updgradable::mutex. My scenario: I have a writer, which is manipulating an object in a interprocess::managed_shared_memory. And I have 'n' readers which are reading the object in the shared mem. If the writer is ready to write, it should get the possibility as fast as possible. So this is a variety of the classical readers/writers problem and I already found a good solution that fits my requirements. But this solution uses 3 mutexes and 1 counter so I am looking for a more efficient solution. The idea is that the writer locks the upgradable_mutex normally (calling lock()) and the readers lock it sharable (calling lock_sharable()). If the mutex is locked sharable and the writer tries to lock it normally, another attempt to lock it sharable has to wait until the writer succeeded in locking and unlocking the mutex. Is this correct proceeding? Thank you Moritz

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python context scope question
by Christopher Harvey 02 Jul '09

02 Jul '09

I'm running a bunch of python scripts from a directory, one after the other. I want to make sure that those scripts don't interfere with each other. My code looks like this: for(directory_iterator itr(filterDir);itr!=directory_iterator();++itr) { if(itr->path().extension()==".py") { try { object global = import("__main__").attr("__dict__"); object sys = import("sys"); sys.attr("path").attr("append")(str(filterDir)); exec_file(str(itr->path().string()), global, global); } catch(error_already_set const &) { cout<<"Python syntax/runtime error."<<endl; PyErr_Print(); } catch(...) { cout<<"Uknown error from script file: "<<itr->path()<<endl; } } } Basically what I want to know is this: For every iteration of the exterior for loop will any of the scripts that are executed be able to impact in any way another script that is executed? For example, I was thinking a script could remove that path that I want to add from the import search paths and break the next script that is run, since it wouldn't have that path. thanks.

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[Interprocess] [AIX 6.0] Abort and Segfault when calling destroy
by Thomas d'Erceville 01 Jul '09

01 Jul '09

Hello, Is there any support for boost on AIX 6.0? Because I got some trouble using boost::interprocess in this system. Actually, the rbtree_best_fit aborts (or Segfaults) when I try to destroy an object previsouly created by a construct. Here below a sample that aborts on AIX 6.0, compiled with boost 1.37: * managed_mapped_file mapfile(bi::create_only, address, size); Message * message = (mapfile.construct<Message>(bi::anonymous_instance))(); mapfile.destroy_ptr<Message>(message);* This abort message is : *Assertion failed :priv_is_allocated_block(block), file /..../boost/interprocess/mem_algo/rbtree_best_fit.hpp, line 1280* The full example is given by the linked file to this mail. I tried to replace the *rbtree_best_fit* by a *simple_seq_fit* but it doesn't change anything (except the abort message). Currently I can't use boost 1.38 or 1.39 because it can't compile it with xlc_r on AIX 6.0. So if someone has any option to solve this problem I take it! Best regards. Thomas d'Erceville

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[Proto] Recreating an expression
by christophe henry 01 Jul '09

01 Jul '09

Hi to all proto experts, I have a grammar whose only goal is to build a type: template <class Expr> struct ActionBuilder with an operator() which simply calls: proto::eval(Expr(),my_context); Unfortunately, I have an expression like: boost::proto::exprns_::expr<boost::proto::tag::plus,boost::proto::argsns_::list2<const A&,const B&> > And the compiler is unhappy about finding no appropriate default constructor (I suppose because of the references). deep_copy is probably not usable inside a grammar definition, so is there an easy way of getting rid of the references (if they are really the problem) or do I have to go and get my MPL canon? I am really just interested in having the recreated expression use a new instance of A and B, not the original ones. Thanks, Christophe _________________________________________________________________ Drag n’ drop—Get easy photo sharing with Windows Live™ Photos. http://www.microsoft.com/windows/windowslive/products/photos.aspx

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interprocess::message_queue thread safety
by Moritz 01 Jul '09

01 Jul '09

Hi everybody, I have a question concerning the interprocess::message_queue. Is the send(..) function thread safe? I have one message_queue and only one thread which is reading messages from the queue. But I have 'n' threads that are writing to the queue. Is there any synchronization mechanism needed to avoid unexpected behavior? Thank You Moritz

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[Locks/Mutex] choices between types
by Axel 01 Jul '09

01 Jul '09

Hello This post may not be well suited to this mailing list. I have some questions about the lockable concept provided in boost. There are many "lock" types, and many "mutex" types. My main question is then : when should I chose a given lock type rather a given mutex type ? Given the fact that some of lock types are not thread-safe, if only one thread needs locks, why should I use one of these lock types and why shouldnt I use some mutex type ? Finally, what were the goals of providing so much different ways to lock/unlock resources ? (I may not be aware of all the concepts related to secure resource access) Since the "lock" et "mutex" types provide ways to lock/unlock access to resources, why are not these types defined under the same name ? Are the concepts they implements much more different than I think ? Thanks Axel

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[tuple][hash] Hashing a tuple question
by Chris Hite 01 Jul '09

01 Jul '09

The code using fusion::fold is elegant, but you still have to define a functor before using it. Couldn't boost just define a default hasher for tuple like the default comparison <boost/tuple/tuple_comparison.hpp>? I've got a tuple with 3 ints in it. I can compare them for free. Why can't I just hash them for free? All we'd have to do is define a hash_value function for tuple that calls fold.

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Getting started with boost: Linker error on boost::system::get_system_category
by Alex Black 01 Jul '09

01 Jul '09

I'm just getting started with boost: - I'm using boost::asio - I'm on Vista x64, using Visual Studio 2008 SP1 - I built the x64 libs using bjam --address-mode=64 .... - I've got my code compiling (but not linking) - I got it pointed to the libs, so it finds the datetime, regex lib etc I get these errors: Error 84 error LNK2001: unresolved external symbol "class boost::system::error_category const & __cdecl boost::system::get_system_category(void)" (?get_system_category@system@boost@@YAAEBVerror_category@12@XZ) Error 85 error LNK2001: unresolved external symbol "class boost::system::error_category const & __cdecl boost::system::get_generic_category(void)" (?get_generic_category@system@boost@@YAAEBVerror_category@12@XZ) any tips? thx - Alex

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