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

Re: [Boost-users] How to retrieve a value from a thread
by Nat Goodspeed 09 Mar '06

09 Mar '06

________________________________________ From: boost-users-bounces(a)lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Sliwa, Przemyslaw (London) Sent: Thursday, March 09, 2006 9:47 AM To: boost-users(a)lists.boost.org Subject: [Boost-users] How to retrieve a value from a thread I would like to know if it is possible to retrieve a value returned from a function which is called by a thread. [Nat] Is this thread running continuously, doing other things? Or did you start it for the purpose of calling that function, so that when the function is done the thread terminates? In Java, I've always kind of liked Doug Lea's FutureResult idiom: http://gee.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/Future Result.html I don't know of anything similar in the existing library.

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Help needed with random exponential_distribution
by dahaverk＠rockwellcollins.com 09 Mar '06

09 Mar '06

Hello, I am trying to convert from boost_1_29_0 to boost_1_33_1 with the random functions. I am using GCC 2.95.3 on Solaris 8. with the Older version of boost_1_29_0 We used the following: exp_(rnd_, 1.0/lambda_), // Initialization list Class constructor. And then used it as follows... lastArrival_ += exp_() * 1000.0; // rnd_.seed already initialized For boost_1_33_1 We changed this to be: exp_(1.0/lambda_), Then used it as follows: lastArrival_ += exp_(rnd_) * 1000.0; Declarations used: // exponential distribution to determine // arrival time double lambda_; boost::exponential_distribution<> exp_; boost::poisson_distribution<> poisson_; However, with the older 1_29 version of boost we were getting numbers such as 3.xxxxxx, 0.xxxxxxx and so on when I printed "exp_()" out. With the new boost_1_33_1 all I see printed out is "Infinite" for the value ot the "exp_(rnd_)" I'm new to boost so any help would be appreciated. This was someone else's code, and I am supposed to plug in the poisson_distribution, but I'd like it to work with the exponential_distribution as it did previously. I assume that I'm either not doing the Initialization correctly or didn't understand what the "Engine" was supposed to be to convert from the previous version. Any tips on using the boost poisson_distribution would be appreciated also. I am assuming Poisson will be initialized with "poisson_(lambda_)" and used as "lastArrival_ += poisson_(exp_) * 1000.0; " Thanks for any help. David Haverkamp

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How to retrieve a value from a thread
by Sliwa, Przemyslaw (London) 09 Mar '06

09 Mar '06

All, I would like to know if it is possible to retrieve a value returned from a function which is called by a thread. Using boost::bind one can pass a list of arguments to a function which is called when the boost::thread starts. But I would like to know what will happen if the function returns a certain value, e.g. failure flag. Is there a way to retrieve it? The usual way would be to pass a reference to the function and then wait for the thread to join. Is there another way? Thanks a lot for help, Pshemek Przemyslaw Sliwa Global Foreign Exchange FX Risk Engine Development Merrill Lynch ( +44 (0)20 7995 4182 ) +44 (0)79 6325 2319 * Email: przemyslaw_sliwa(a)ml.com -------------------------------------------------------- If you are not an intended recipient of this e-mail, please notify the sender, delete it and do not read, act upon, print, disclose, copy, retain or redistribute it. Click here for important additional terms relating to this e-mail. http://www.ml.com/email_terms/ --------------------------------------------------------

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[BGL] Why there is no special handler for "discover_source_vertex" event in BFS visitor?
by Dmitry 09 Mar '06

09 Mar '06

Hi there! Current implementation calls vis.discover_vertex(s, g); at this point, the same function being called for all others discovered vertices. I have one small problem wich could be nicely solved with such special handler and I believe that there are others when such handler could be usefull. Any suggestings why things is going exacly in this way? Best regards, --dima

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TR1
by Thomas Gulbrandsen 09 Mar '06

09 Mar '06

Hello! I wan't to get started with tr1 and the unordered_set etc., but I can't find it. Can anyone tell me where I can download tr1 for VC8? -Thomas

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Re: [Boost-users] Boost.Preprocessor with __LINE__ in MSVC71
by Wu Yinghui, Freddie 09 Mar '06

09 Mar '06

>>> -----Original Message----- >>> That's what I feel. The error message indicate that the >>> compiler somehow considers "id" and __LINE__ two identifier >>> when the error occurs. I tried using the /P parameter to dump >>> the preprocessed source, and that looked fine, though. So I >>> guess it is the problem with MSVC compiler mixing >>> preprocessing and parsing phases together... > > Yes. There is nothing that the pp-lib can do about it. I agree. But I pointed this out after much effort trying to debug the mysterious bug. Maybe it'd be better to document this in pp-lib's manual as "known issues?" That'd make future victims' lives easier. :) >>> > What do you mean by "certain scope"? Or, more precisely, >>> given a > finite scope such as that defined by a function, >>> why do you need > unique identifiers? Most of the time when >>> people want unique > identifiers, they want an identifier >>> that is unique across an entire > program or, at minimum, >>> inside a translation unit. >>> >>> Well... The scope can be the whole program, or in a >>> namespace, or in a translation unit. The unique ID is used in >>> a macro in the library for some tidious code that can be >>> automatically generated using preprocessor. > >For the record, doing this sort of thing is almost guaranteed to produce ODR >violations. With that said... Well... I think I know what I'm doing now. The use of __LINE__ (or __COUNTER__ on MSVC) is working for me after combining with some salt as keyword. Thanks for your concern, but the current solution seems suffice for me purpose. >>> Anyway, thanks for Stewart Tootill's suggestion. I had to >>> resort to using __COUNTER__ at the meantime, which seemed >>> working so far. (But one thing that worries me is that >>> __COUNTER__ is only unique within a translation unit. So what >>> if I need a unique identifier throughout the >>> program?) > >The pp-lib contains a similar construct, but it must be manually >updated. E.g. >#include BOOST_PP_UPDATE_COUNTER() >BOOST_PP_COUNTER() // 1 >#include BOOST_PP_UPDATE_COUNTER() >BOOST_PP_COUNTER() // 2 >BOOST_PP_COUNTER() // 2 >#include BOOST_PP_UPDATE_COUNTER() >BOOST_PP_COUNTER() // 3 But this is not documented. :( I didn't know its existence until you told me and then I did a grep.) >I could provide the means to seed this value for a translation unit, but I'm not >sure if this is really a good idea. Thoughts? I don't think there is a general solution for "all cases" here. (At least I don't have one with me right now.) But given some restricted usage, this solution actually works out quite well. BTW, I think I'm still sticking to __LINE__/__COUNTER__ solution for now, since it is not possible for me to encode the "#include ..." line into my macro. >Regards, >Paul Mensonides Thanks a lot for your efforts and insight! Cheers, Freddie

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[Serialization] Status of bug in 1.33?
by Andrew Lin 09 Mar '06

09 Mar '06

Hi everyone, Some time back I wrote asking about a problem I was having with the 1.33 serialization library which turned out to be a bug: http://lists.boost.org/boost-users/2005/12/15969.php In short, custom archives had some kind of compilation failure which I never really understood, but which didn't fail in 1.32. Does anyone know what ever came of this? Is there a bug tracker where I can follow its status? (I didn't see it in the 1.33.1 release notes, so I'm assuming it's still broken.) I thought I'd be able to use 1.32 until 1.34 came out, but something has come up in the project which would be perfect for the multi_index library with hashing, new in 1.33. Thanks, Andrew ============================================================================================= Email transmissions can not be guaranteed to be secure or error-free, as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message which arise as a result of email transmission. In addition, the information contained in this email message is intended only for use of the individual or entity named above. If the reader of this message is not the intended recipient, or the employee or agent responsible to deliver it to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication, disclosure of the parties to it, or any action taken or omitted to be taken in reliance on it, is strictly prohibited, and may be unlawful. If you are not the intended recipient please delete this email message. ==============================================================================================

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[Lambda] Help with if_then_else
by Scott Meyers 09 Mar '06

09 Mar '06

Consider this (working) code using Boost.FileSystem: fs::directory_iterator di(dir); fs::directory_iterator end; while (di != end) { if (is_directory(*di)) cout << "D\n"; else cout << "~D\n"; ++di; } This looks like it should be lambda-able. Here's my attempt: for_each(fs::directory_iterator(dir), fs::directory_iterator(), if_then_else(bind(&fs::is_directory, _1), cout << "D\n", cout << "~D\n")); VC7.1 doesn't like this -- the diagnostics are below. Any idea how I can make this work? Thanks, Scott fs.cpp(39) : error C2784: 'const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::ifthenelse_action,boost::tuples: :tuple<boost::lambda::lambda_functor<Arg1>,boost::lambda::lambda_functor<Arg2>,boost::lambda::lambda_functor<Arg3>>>> boost::lambda::if_then_else (const boost::lambda::lambda_functor<Arg1> &,const boost::lambda::lambda_functor<Arg2> &,const boost::lambda::lambda_functor<Arg3> &)' : could no t deduce template argument for 'const boost::lambda::lambda_functor<T2> &' from 'std::basic_ostream<_Elem,_Traits>' with [ _Elem=char, _Traits=std::char_traits<char> ] D:\C++\Boost\Current\boost\lambda\if.hpp(100) : see declaration of 'boost::lambda::if_then_else' fs.cpp(39) : error C2784: 'const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::ifthenelse_action,boost::tuples: :tuple<boost::lambda::lambda_functor<Arg1>,boost::lambda::lambda_functor<Arg2>,boost::lambda::lambda_functor<Arg3>>>> boost::lambda::if_then_else (const boost::lambda::lambda_functor<Arg1> &,const boost::lambda::lambda_functor<Arg2> &,const boost::lambda::lambda_functor<Arg3> &)' : could no t deduce template argument for 'const boost::lambda::lambda_functor<T2> &' from 'std::basic_ostream<_Elem,_Traits>' with [ _Elem=char, _Traits=std::char_traits<char> ] D:\C++\Boost\Current\boost\lambda\if.hpp(100) : see declaration of 'boost::lambda::if_then_else' fs.cpp(39) : error C2784: 'const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::ifthenelse_action,boost::tuples: :tuple<boost::lambda::lambda_functor<Arg1>,boost::lambda::lambda_functor<Arg2>,boost::lambda::lambda_functor<Arg3>>>> boost::lambda::if_then_else (const boost::lambda::lambda_functor<Arg1> &,const boost::lambda::lambda_functor<Arg2> &,const boost::lambda::lambda_functor<Arg3> &)' : could no t deduce template argument for 'const boost::lambda::lambda_functor<T2> &' from 'std::basic_ostream<_Elem,_Traits>' with [ _Elem=char, _Traits=std::char_traits<char> ] D:\C++\Boost\Current\boost\lambda\if.hpp(100) : see declaration of 'boost::lambda::if_then_else' fs.cpp(39) : error C2784: 'const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::ifthenelse_action,boost::tuples: :tuple<boost::lambda::lambda_functor<Arg1>,boost::lambda::lambda_functor<Arg2>,boost::lambda::lambda_functor<Arg3>>>> boost::lambda::if_then_else (const boost::lambda::lambda_functor<Arg1> &,const boost::lambda::lambda_functor<Arg2> &,const boost::lambda::lambda_functor<Arg3> &)' : could no t deduce template argument for 'const boost::lambda::lambda_functor<T2> &' from 'std::basic_ostream<_Elem,_Traits>' with [ _Elem=char, _Traits=std::char_traits<char> ] D:\C++\Boost\Current\boost\lambda\if.hpp(100) : see declaration of 'boost::lambda::if_then_else'

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[Smart_Ptr] Error in intrusive_ptr ctors' exception specification?
by Scott Meyers 08 Mar '06

08 Mar '06

Consider this constructor from the intrusive_ptr doc (http://boost.org/libs/smart_ptr/intrusive_ptr.html) intrusive_ptr(T * p, bool add_ref = true); Effects: if(p != 0 && add_ref) intrusive_ptr_add_ref(p);. Note in particular that nothing is said about exceptions being thrown. Presumably intrusive_ptr_add_ref may throw, as I can't find any restriction to the contrary. Now consider these constructors from the same document: intrusive_ptr(intrusive_ptr const & r); // never throws template<class Y> intrusive_ptr(intrusive_ptr<Y> const & r); // never throws Effects: if(r.get() != 0) intrusive_ptr_add_ref(r.get());. They are documented not to throw, yet both call intrusive_ptr_add_ref. How can it be that the top constructor above may throw, but these constructors may not? FWIW, it seems to me that all three should be allowed to throw, unless some constraint is imposed on the implementation of intrusive_ptr_add_ref. For example, perhaps intrusive_ptr_add_ref wants to throw if its reference count will overflow -- maybe because it's using only an 8-bit counter. Isn't that possible? Scott

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Re: [Boost-users] Boost.Preprocessor with __LINE__ in MSVC71
by Wu Yinghui, Freddie 08 Mar '06

08 Mar '06

> What is going wrong? I tried it on VC7, VC7.1, and VC8, and it appeared to work correctly on all three versions of the compiler. >> Does anyone on the list has more insight on this issue? > I've seen strange problems related to __LINE__ on VC before, but I > can't remember off the top of my head what the issue was. > (Thinking...) It has something to do with the generation of debug > information. Okay, yes, I see the error that you are getting now. It > only happens in during a debug build. You are right. It occurs only in debug builds. (Sorry for forgetting to mention this.) > This is just one of the *many* ways in which VC's preprocessor is > wacky. It suffices to say it isn't even in the ballpark of > implementing the phases of translation correctly. That's what I feel. The error message indicate that the compiler somehow considers "id" and __LINE__ two identifier when the error occurs. I tried using the /P parameter to dump the preprocessed source, and that looked fine, though. So I guess it is the problem with MSVC compiler mixing preprocessing and parsing phases together... >> Or, what're the common ways to generate an unique identifier >> automatically within certain scope? > What do you mean by "certain scope"? Or, more precisely, given a > finite scope such as that defined by a function, why do you need > unique identifiers? Most of the time when people want unique > identifiers, they want an identifier that is unique across an entire > program or, at minimum, inside a translation unit. Well... The scope can be the whole program, or in a namespace, or in a translation unit. The unique ID is used in a macro in the library for some tidious code that can be automatically generated using preprocessor. Anyway, thanks for Stewart Tootill's suggestion. I had to resort to using __COUNTER__ at the meantime, which seemed working so far. (But one thing that worries me is that __COUNTER__ is only unique within a translation unit. So what if I need a unique identifier throughout the program?) > Regards, > Paul Mensonides Thanks for your comments. Cheers, Freddie

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