December 2002 - Boost-users

shared_ptr does not call destructor
by Ani Taggu 15 Dec '02

15 Dec '02

Hi: I am using windows 2000 with VC 6.0 and boost 1.28. In my project, I have an array of pointers to objects: class foo { public: ~foo() {} private: std::vector<boost::shared_ptr<MyType> > myArr_; }; I found that the destructor for MyType is never called. Printing the shared_ptr::use_count = 6 at ~foo() above. Any suggestions on what could be happening and how to approach the debugging? Thanks, -Ani

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Test Library: Program Execution Monitor output
by klapshin <klapshin＠yahoo.com> 13 Dec '02

13 Dec '02

Hello, I just plugged program execution monitor in my code and there are certain things I don't really like. First of all is not it odd to see a contradictory messages like: --------------------------- no errors detected **** error return code 1 ********** errors detected; see standard output for details *********** --------------------------- I don't really need this "no errors detected" message. Looking into code I found a way to turn it off -- I have to define an environment variable. I have a way to control this behavior. This is good. Bad news though that the way to control is quite an awkward one. I would like to have some internal control, probably overwritable via environment variable. Another concern is that I have no control on return codes in case of exceptions and runtime errors. For instance in my company all programs have to return 1 in case of failure (and 0 on success). Other return codes are no-no. I am sure there are zillions of different environments with different, often contradictory requirements for error handling. The point I am trying to make is that it is not that difficult to make Monitor more flexible, and it will increase its value tremendously. The ultimate solution would be giving user an opportunity to supply error-handling function which will print out whatever it want to, and return desired return code. Best regards, Kirill Lapshin

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weak_ptr and threads
by Duane Murphy 12 Dec '02

12 Dec '02

The application I am working on uses a number of threads to do work. In some cases pointers from one thread (usually the "main" thread) are passed to a worker thread. The worker thread will use this pointer to handle processing of the results (in various ways). The problem that I am concerned about is lifetime control. Objects in the main thread could be deleted before the worker thread has a chance to use them. This of course would be a "bad thing." I am considering investigating the use of weak_ptr as a potential solution to this problem. The basic idea would be to pass weak_ptr's to the worker thread. The worker thread can then check the validity of the weak_ptr before accessing it. Can weak_ptr be used without using shared_ptr? It seems like they are closely tied. I was hoping to use weak_ptr without forcing the use of shared_ptr. Are there other solutions to this problem, besides the obvious "Dont let it happen." :-) [ Note that we are not yet using boost::threads so this is a more general question about managing inter-thread object lifetimes. ] Thanks for your tips and suggestions, ...Duane

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weak_ptr and threads
by Duane Murphy 12 Dec '02

12 Dec '02

The application I am working on uses a number of threads to do work. In some cases pointers from one thread (usually the "main" thread) are passed to a worker thread. The worker thread will use this pointer to handle processing of the results (in various ways). The problem that I am concerned about is lifetime control. Objects in the main thread could be deleted before the worker thread has a chance to use them. This of course would be a "bad thing." I am considering investigating the use of weak_ptr as a potential solution to this problem. The basic idea would be to pass weak_ptr's to the worker thread. The worker thread can then check the validity of the weak_ptr before accessing it. Can weak_ptr be used without using shared_ptr? It seems like they are closely tied. I was hoping to use weak_ptr without forcing the use of shared_ptr. Are there other solutions to this problem, besides the obvious "Dont let it happen." :-) [ Note that we are not yet using boost::threads so this is a more general question about managing inter-thread object lifetimes. ] Thanks for your tips and suggestions, ...Duane

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uBLAS and fast matrix multiplication
by klapshin <klapshin＠yahoo.com> 12 Dec '02

12 Dec '02

Hello, I am considering switching from in-house matrix implementation to uBLAS. Overall impression from uBLAS is quite good, but it seems that uBLAS does not take advantage of fast matrix multiplication algorithms such as Strassen or Vinograd. Is that correct? If yes, are there plans to implement such algorithms? Best regards, Kirill Lapshin.

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Re: [Boost-Users] testing if shared_ptr has been assigned
by dick.bridges＠tais.com 12 Dec '02

12 Dec '02

I should point out that I went 'back' to get() because I got tired of explaining the 'correct' way [ie, if( b ) ] Darin Adler provided in his answer. |---------+----------------------------------------------------> | | Dick | | | Bridges/CSE/IRV/CONTRACTOR/TOSHIBA-TAIS@T| | | OSHIBA-TAIS | | | | | | 12/12/2002 08:07 AM | | | Please respond to Boost-Users | | | | |---------+----------------------------------------------------> >----------------------------------------------------------------------------------------------| | | | To: Boost-Users(a)yahoogroups.com | | cc: | | Subject: Re: [Boost-Users] testing if shared_ptr has been assigned | >----------------------------------------------------------------------------------------------| >From the docs: <snippet> get T * get() const; // never throws Returns: the stored pointer. Throws: nothing. </snippet> Therefore you can use if( b.get() ) or if( b.get() == NULL ) "TEA Hartmann, Steven" To: boost-users(a)yahoogroups.com <SHartmann(a)aus.t cc: elusa.com> Subject: [Boost-Users] testing if shared_ptr has been assigned 12/11/2002 11:01 AM Please respond to Boost-Users I need some help in testing for the condition of whether a shared_ptr has been assigned. In the following example, the "if( b != NULL ) does not work. How would I do this test? typedef boost::shared_ptr<int> IPtr; int i( 0 ); IPtr a( i ); IPtr b; if( some condition ) b = a; if( b != NULL ) { // How should this really be coded? } Best Regards, Steve [Non-text portions of this message have been removed] Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

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RE: [Boost-Users] Test Library: Program Execution Monitor output
by Tom Matelich 12 Dec '02

12 Dec '02

> I don't really need this "no errors detected" message. Looking into > code I found a way to turn it off -- I have to define an environment > variable. > I have a way to control this behavior. This is good. Bad news though > that the way to control is quite an awkward one. I would like to > have some internal control, probably overwritable via environment > variable. In case you hadn't though of this workaround: if(getenv("VAR") == 0) putenv("VAR=defaultvalue"); Not to say a programmatic method is not worthwhile. ----------------------------------------------------------------------- DISCLAIMER: Information contained in this message and/or attachment(s) may contain confidential information of Zetec, Inc. If you have received this transmission in error, please notify the sender by return email. -----------------------------------------------------------------------

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RE: [Boost-Users] testing if shared_ptr has been assigned
by TEA Hartmann, Steven 12 Dec '02

12 Dec '02

Thanks all. That works beautifully. -----Original Message----- From: Tom Matelich [mailto:tmatelich@zetec.com] Sent: Thursday, December 12, 2002 12:25 AM To: 'Boost-Users(a)yahoogroups.com' Subject: RE: [Boost-Users] testing if shared_ptr has been assigned if(b) should do it. shared_ptr has an implicit conversion to bool (sort of). > -----Original Message----- > From: TEA Hartmann, Steven [mailto:SHartmann@aus.telusa.com] > Sent: Wednesday, December 11, 2002 11:02 AM > To: boost-users(a)yahoogroups.com > Subject: [Boost-Users] testing if shared_ptr has been assigned > > > I need some help in testing for the condition of whether a > shared_ptr has > been assigned. In the following example, the "if( b != NULL > ) does not > work. How would I do this test? > > typedef boost::shared_ptr<int> IPtr; > > int i( 0 ); > IPtr a( i ); > IPtr b; > > if( some condition ) > b = a; > > if( b != NULL ) { // How should this really be coded? > } > > > Best Regards, > > Steve > > > [Non-text portions of this message have been removed] > > > ------------------------ Yahoo! Groups Sponsor > ---------------------~--> > Get 128 Bit SSL Encryption! > http://us.click.yahoo.com/CBxunD/vN2EAA/xGHJAA/EbFolB/TM > -------------------------------------------------------------- > -------~-> > > Info: <http://www.boost.org> > Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> > Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> > > > Your use of Yahoo! Groups is subject to > http://docs.yahoo.com/info/terms/ > > ----------------------------------------------------------------------- DISCLAIMER: Information contained in this message and/or attachment(s) may contain confidential information of Zetec, Inc. If you have received this transmission in error, please notify the sender by return email. ----------------------------------------------------------------------- Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ [Non-text portions of this message have been removed]

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Re: [Boost-Users] testing if shared_ptr has been assigned
by dick.bridges＠tais.com 12 Dec '02

12 Dec '02

>From the docs: <snippet> get T * get() const; // never throws Returns: the stored pointer. Throws: nothing. </snippet> Therefore you can use if( b.get() ) or if( b.get() == NULL ) "TEA Hartmann, Steven" To: boost-users(a)yahoogroups.com <SHartmann(a)aus.t cc: elusa.com> Subject: [Boost-Users] testing if shared_ptr has been assigned 12/11/2002 11:01 AM Please respond to Boost-Users I need some help in testing for the condition of whether a shared_ptr has been assigned. In the following example, the "if( b != NULL ) does not work. How would I do this test? typedef boost::shared_ptr<int> IPtr; int i( 0 ); IPtr a( i ); IPtr b; if( some condition ) b = a; if( b != NULL ) { // How should this really be coded? } Best Regards, Steve [Non-text portions of this message have been removed] Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

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RE: [Boost-Users] testing if shared_ptr has been assigned
by Tom Matelich 12 Dec '02

12 Dec '02

if(b) should do it. shared_ptr has an implicit conversion to bool (sort of). > -----Original Message----- > From: TEA Hartmann, Steven [mailto:SHartmann@aus.telusa.com] > Sent: Wednesday, December 11, 2002 11:02 AM > To: boost-users(a)yahoogroups.com > Subject: [Boost-Users] testing if shared_ptr has been assigned > > > I need some help in testing for the condition of whether a > shared_ptr has > been assigned. In the following example, the "if( b != NULL > ) does not > work. How would I do this test? > > typedef boost::shared_ptr<int> IPtr; > > int i( 0 ); > IPtr a( i ); > IPtr b; > > if( some condition ) > b = a; > > if( b != NULL ) { // How should this really be coded? > } > > > Best Regards, > > Steve > > > [Non-text portions of this message have been removed] > > > ------------------------ Yahoo! Groups Sponsor > ---------------------~--> > Get 128 Bit SSL Encryption! > http://us.click.yahoo.com/CBxunD/vN2EAA/xGHJAA/EbFolB/TM > -------------------------------------------------------------- > -------~-> > > Info: <http://www.boost.org> > Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> > Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> > > > Your use of Yahoo! Groups is subject to > http://docs.yahoo.com/info/terms/ > > ----------------------------------------------------------------------- DISCLAIMER: Information contained in this message and/or attachment(s) may contain confidential information of Zetec, Inc. If you have received this transmission in error, please notify the sender by return email. -----------------------------------------------------------------------

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Re: Please post Boost.Python questions to Python's c++-sig
by William Trenker <wtrenker＠hotmail.com> 11 Dec '02

11 Dec '02

David, Thanks for this clarification. I was checking out the c++-sig group yesterday and was wondering what that list's relationship was to the official boost list. Now I know why some of my Pythonic questions here were getting blank stares. Cheers, Bill > William, please post Boost.Python questions here: > http://mail.python.org/mailman/listinfo/c++-sig > > Thanks, > -- > David Abrahams

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Python: Wrapping #define's and enum's
by William Trenker <wtrenker＠hotmail.com> 11 Dec '02

11 Dec '02

Many C/C++ libraries contain one or more .h/.hpp files that define various constants used by that library's API. What is the prescribed method for wrapping #defines that are used to represent constants? Also, how do I wrap anonymous enums? For example, I have a project with an Enumerations.h file containing: #define MSG_A 23 #define MSG_B 25 enum {Red, White, Blue = 40 }; What would the boost wrapper code for the above look like? Thanks, Bill

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RE: [Boost-Users] .cvsignore - I'm stuck
by Tom Matelich 11 Dec '02

11 Dec '02

This won't help with an initial checkout, but you could write a small script like: #this is to be run in the base directory #update just the files in boost, don't recurse cvs up -l #now update the subdirectories you care about cvs up boost cvs up libs Obviously, you'll need to put your own options in there. If you need help making a real script or batch file, let me know. > -----Original Message----- > From: William Trenker <wtrenker(a)hotmail.com> > [mailto:wtrenker@hotmail.com] > Sent: Tuesday, December 10, 2002 1:56 PM > To: Boost-Users(a)yahoogroups.com > Subject: [Boost-Users] .cvsignore - I'm stuck > > > (This isn't really a boost question but I've spent half a day reading > the cvs documentation and am hoping for a bit of help on what I think > is probably a very simple question.) > > I have a blazing 33.6K modem connection to the Internet. So when I > do a cvs update of my copy of the boost tree, the mug shots (.jpg > files) in the people subdirectory take quite a long time to be > checked for differences. I don't really need to update those files > so I am trying to get a .cvsignore file to work in the "people" > subdirectory. (I realize these files may not change very often; > still, I would appreciate knowing how to do a .cvsignore for boost > libraries that I'm not using.) But I can't get cvs to recognize the > .cvsignore file. > > I created a .cvsignore file, with the line "*.jpg", in the people > sub-directory. But when I run "cvs update" in the people > sub-directory (after "cvs login") cvs gives me a "? .cvsignore" > response and continues updating anyway. I thought maybe I have to > "cvs add" the .cvsignore file, but that doesn't work. > > How do I get cvs to "see" my .cvsignore file? > > Thanks, > Bill > > > > ------------------------ Yahoo! Groups Sponsor > ---------------------~--> > Get 128 Bit SSL Encryption! > http://us.click.yahoo.com/CBxunD/vN2EAA/xGHJAA/EbFolB/TM > -------------------------------------------------------------- > -------~-> > > Info: <http://www.boost.org> > Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> > Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> > > > Your use of Yahoo! Groups is subject to > http://docs.yahoo.com/info/terms/ > > ----------------------------------------------------------------------- DISCLAIMER: Information contained in this message and/or attachment(s) may contain confidential information of Zetec, Inc. If you have received this transmission in error, please notify the sender by return email. -----------------------------------------------------------------------

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.cvsignore - I'm stuck
by William Trenker <wtrenker＠hotmail.com> 11 Dec '02

11 Dec '02

(This isn't really a boost question but I've spent half a day reading the cvs documentation and am hoping for a bit of help on what I think is probably a very simple question.) I have a blazing 33.6K modem connection to the Internet. So when I do a cvs update of my copy of the boost tree, the mug shots (.jpg files) in the people subdirectory take quite a long time to be checked for differences. I don't really need to update those files so I am trying to get a .cvsignore file to work in the "people" subdirectory. (I realize these files may not change very often; still, I would appreciate knowing how to do a .cvsignore for boost libraries that I'm not using.) But I can't get cvs to recognize the .cvsignore file. I created a .cvsignore file, with the line "*.jpg", in the people sub-directory. But when I run "cvs update" in the people sub-directory (after "cvs login") cvs gives me a "? .cvsignore" response and continues updating anyway. I thought maybe I have to "cvs add" the .cvsignore file, but that doesn't work. How do I get cvs to "see" my .cvsignore file? Thanks, Bill

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Boost Preprocessor - Nested repeat?
by midnight2silverlake 11 Dec '02

11 Dec '02

I have what looks like a perfect application for Boost/Preprocessor. I have 192 entries in a Factory Map a portion of which are show below. I'd like to generate the permutations of the three macro inputs, but can't figure out where to start. Any help would be appreciated. #define MAP_ENTRY_MCR( aLang, aType, aAcc ) \ \ mMap[ CKey( aLang, aType, aAcc ) ] \ = CVarX< aLang, aType, aAcc >::Make; MAP_ENTRY_MCR( DCTlanguageC, DCT_DOUBLE , DCT_NONE ); MAP_ENTRY_MCR( DCTlanguageC, DCT_DOUBLE , DCT_INIT ); MAP_ENTRY_MCR( DCTlanguageC, DCT_DOUBLE , DCT_ANYTIME ); MAP_ENTRY_MCR( DCTlanguageC, DCT_FLOAT , DCT_NONE ); ... Thanks, Jeff Flinn

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Errors running thread samples on W2K
by Mahendra Chheda <mchheda＠yahoo.com> 10 Dec '02

10 Dec '02

Hi, I downloaded boost recently and compiled it on my win2000 server using VC++ ver 7.0 (VS.Net) I then compiled some samples from an article by Bill Kempf (http://www.cuj.com/articles/2002/0205/0205a/0205a.htm? topic=articles). I have defined the debug version of boost libs (boost_threadmon.lib & libboost_thread.lib) in my link process. My code samples do compile and link without any errors. However, I seem to be hitting a common error across most of the samples. The error msg is: Assertion failed: !this->empty(), file D:\MMC\Code\boost_1_29_0 \boost/function/f unction_template.hpp, line 324 Assertion failed: !this->empty(), file D:\MMC\Code\boost_1_29_0 \boost/function/f unction_template.hpp, line 324 I get an abort screen to stop my code. Has anyone seen this before. Can someone pls guide me on how to fix this. Thanx. Mahendra

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Which doorway
by Malcolm Smith 10 Dec '02

10 Dec '02

I'm no expert on these type of libraries but I have come to the point where I must find time to study *this* library more. I have a current project that requires some re-writes in specific areas and I'm hoping Boost will be able to make this job easier. Is there something in boost that will ease the implementation of a state-machine type functor. As an example, I am using a 3rd party C++Builder component that makes socket connections to hardware devices. I need to modify the connection code so 'what needs to be done after a connection success/failure' is handled in the appropriate events. The thing is, this connection event can be called due to connections in other areas of the application under different conditions. If I can implement a state based connection handler then I could re-direct the calls to the appropriate (alternate) event. As an example (I'm only just starting to read up on the STL), I know I could use a std::map to hold state values as the key and call the appropriate handler via a pointer to a function in .second - what I'm hoping is there is a library that allows for unrestricted function signatures (different parameter lists) to be associated with state values. To make this clearer // I know this is not valid code but it explains what I'm after typedef std::map<int, *pf(...)> StateFunctions; void Method1(void); int Method2(TCustomClass &MyClass); StateFunctions[1] = Method1; StateFunctions[2] = Method2; Does this make sense to anyone ? I've probably got all the terminology wrong so feel free to correct me where ever applicable. Thanks in advance. -- Malcolm Smith MJ Freelancing- http://www.mjfreelancing.com Software Protection for C++Builder Borland Technology Partner

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Regex++ for CE? Also, trimming code size.
by Brady Reed 10 Dec '02

10 Dec '02

I am very interested in the Unicode version of this library for some Pocket PC apps. Is anyone aware of any ports of regex++ to Windows CE? The dll version of the parser seems to be rather large, about œ meg for the release version, and 600K for the debug version. This seems to be very large (the gnu rx parser is well below 100K), and I would expect there to be a greater difference in the code size between debug and release versions. Is there a way to cut this code sized down? Or do I need to do something different to build it? Thanks, Brady Reed _________________________________________________________________ MSN 8 with e-mail virus protection service: 2 months FREE* http://join.msn.com/?page=features/virus

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parent_iterator
by matt 09 Dec '02

09 Dec '02

I am a newbie to the graph library. I have a directed graph, and given a vertex_descriptor, I would like to access its parents. It is sort of an adjacency_iterator in reverse I believe. Is there such a thing, or do i have to derive it from and existing iterator...? Thanks, Matt

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Python: C++ parse tree tools?
by William Trenker <wtrenker＠hotmail.com> 09 Dec '02

09 Dec '02

Does anyone know if there is a GCC option to save the C++ parse tree to a file? Or has anyone come across a C++ parser utility that does this? I'm building a Python extension for a library that has many .hpp files and I would like to try and automate the generation of the Boost.Python headers for this library. Thanks, Bill

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Regex Match() Abortion
by eydelber 07 Dec '02

07 Dec '02

This probably is annoying me to no end. I have a string that I am matching against a pattern called 'sql'. My program tests 'sql' against 14 possible patterns. The patterns are in an array of strings. EVERYTHING works except for the last pattern. And even then, only when the 2nd sub-expression is longer than a certain length. For example, this works: insert into test (one,two,three) values () Through a lot of testing, I have seen that after the comma delimitted list in the second sub-expression surpasses a certain length, then my program gets aborted at the line if(sqlRegex.Match (sql)) { I am running the latest version of boost regex++, and I am running g++ 2.96 on Linux. I ran gdb, and I seemed to have narrowed down the problem to c_str(), but this is not logical. Here is the part of my program: string checks[] = { /* 0 */ "create table (_ID_) (\\(((\\s*,?\\s*(_ID_) (_TYPES_)( not null)?( unique)?( default ((\\d+(\\.\\d+)?)|(\"[^\"] *\")))?( unique)?\\s*)+)\\))", /* 1 */ "show tables", /* 2 */ "drop table (_ID_)", /* 3 */ "show tdb\\.xml", /* 4 */ "desc( table)? (_ID_)", /* 5 */ "alter table (_ID_) add( column)? ((_ID_) (_TYPES_) ( not null)?( unique)?( default ((\\d+(\\.\\d+)?)|(\"[^\"]*\")))?( unique)?( first| after (_ID_))?)", /* 6 */ "alter table (_ID_) drop( column)? (_ID_)", /* 7 */ "alter table (_ID_) add( column)? \\(((\\s*,?\\s* (_ID_) (_TYPES_)( not null)?( unique)?( default ((\\d+(\\.\\d+)?)| (\"[^\"]*\")))?( unique)?( first| after (_ID_))?\\s*)+)\\)", /* 8 */ "rename table (_ID_) (to|as) (_ID_)", /* 9 */ "alter table (_ID_) alter( column)? (_ID_) (set default ((\\d+(\\.\\d+)?)|(\"[^\"]*\"))|drop default)", /* 10 */ "alter table (_ID_) modify( column)? ((_ID_) (_TYPES_)( not null)?( unique)?( default ((\\d+(\\.\\d+)?)|(\"[^\"] *\")))?( unique)?( first| after (_ID_))?)", /* 11 */ "alter table (_ID_) change( column)? (_ID_) ((_ID_) (_TYPES_)( not null)?( unique)?( default ((\\d+(\\.\\d+)?)|(\"[^\"] *\")))?( unique)?( first| after (_ID_))?)", /* 12 */ "alter table (_ID_) rename( to| as) (_ID_)", /* 13 */ "insert( into)? (_ID_)( \\(((\\s*,?\\s*(_ID_)\\s*)+) \\))? values \\(\\)" }; int checksLength = sizeof checks / sizeof *checks; int i; RegEx sqlRegex; for(i=0;i<checksLength;i++) { sqlRegex.SetExpression(checks[i],true); if(sqlRegex.Match(sql)) { break; } } The interesting thing is that the first string, checks[0] is similar to the insert syntax, and when I use a very long string for the create table syntax, it works perfectly fine. Also, I tried just adding another element to checks, just trying, but that didn't work. Also, I had no such problem for the other 12 cases, it only happens with this last insert case. Any help will be greatly appreciated, I have been stuck on this for days!! Thanks, Kevin

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Missing bjam executable
by Jacek Generowicz 06 Dec '02

06 Dec '02

I'm trying to install Boost on Linux, but the bjam executable http://boost.sourceforge.net/jam-executables/bin.linuxx86/bjam.gz seems to be missing. Is this a known problem, or am I missing something obvious ?

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RE: [Boost-Users] object_pool use ordered_malloc ordered_free. wh y?
by scleary＠jerviswebb.com 06 Dec '02

06 Dec '02

> if construct only, and freeall in ~object_pool. i think it is good. Yes. The destuctor of object_pool will call the destructor of each allocated or constructed object that has not yet been deallocated or destroyed. > can i use object_pool to replace 'new delete'? object_pool provides object-based allocation and deallocation, very similar to new and delete. > the destroy is slow. Destroying single objects that were created from an object_pool uses ordered_free, as you discovered. An object_pool will keep its free list ordered, so that it can run through the "list of allocated objects" in O(N) time instead of O(N**2) time in ~object_pool. It's a performance tradeoff with object_pool::destroy; object_pool was designed more for a "allocate a bunch of objects and then destroy all of them" type of scenario. -Steve

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RE: [Boost-Users] Boost.Threads question
by James Zappia 05 Dec '02

05 Dec '02

> Thanks for all you help. I have a few new questions now, though. ;) > Again, I'm a newbie to C++ so this may seem stupid... > > I created a boost::thread object and even though it goes out of scope, > the thread continues to run. > >As it should, and as it's well documented. The boost::thread object is >analogous to a std::fstream, where the file doesn't get deleted when the >object goes out of scope. In other words, it's just a handle to the >actual running thread. Understood. > Also, when passing a class with the > operator() defined to boost::thread, it constructs and destructs the > object several times which seems odd. > >Also well documented, and essential. If this didn't occur, you'd have to >insure the lifetime of the object passed was longer than the lifetime of >the thread of execution (not the boost::thread object, the actual thread >of execution). Understood. > What I'm basically trying to do > is run a thread, have that thread lock a timed_mutex, then do its job. > Then, in main, I try to lock the same timed_mutex and if I can't get a > lock before the time expires, I need to terminate the thread. Below is > the source code and the output generated. My questions are below, after > the output. > > SOURCE: > #include <iostream> > #include <boost/thread/xtime.hpp> > #include <boost/thread/thread.hpp> > #include <boost/thread/exceptions.hpp> > > using namespace std; > > boost::timed_mutex mutex; > > class thread_class > { > public: > explicit thread_class(int sleep): _sleep(sleep) {}; > > void operator()() > { > boost::xtime xt; > > cout << "thread: locking mutex\n"; > boost::timed_mutex::scoped_timed_lock lock(mutex,true); > >Why do you continue to use this syntax? This performs an explicit lock, >not a timed lock. This overload is for two use cases: > >1) Creating an unlocked lock object: > >scoped_time_lock lock(mutex, false); > >2) Creating a locked lock object which later will be unlocked and then >locked again through a timed lock: > >scoped_time_lock lock(mutex, true); >// .. some code >lock.unlock(); >// .. some code >if (lock.timed_lock()) { > // .. some code >} > >Obviously the second use case will be extremely rare. In your case you're >doing neither of these, and you'd be better served just using a simple >scoped_lock. > > boost::xtime_get(&xt,boost::TIME_UTC); > > cout << "thread: sleeping for " << _sleep << " seconds\n"; > > xt.sec += _sleep; > boost::thread::sleep(xt); > > cout << "thread: freeing lock -- goodbye\n"; > } > > ~thread_class() { cout << "thread_class destructed\n"; } > > private: > int _sleep; > }; > > int main( void ) > { > { > cout << "main: creating thread\n"; > > thread_class test(10); > boost::thread thrd(test); > > cout << "main: sleeping for 2 seconds\n"; > sleep(2); > > cout << "main: trying to lock mutex -- waiting 5 > seconds...\n"; > > boost::timed_mutex::scoped_timed_lock lock(mutex,false); > > boost::xtime xt; > boost::xtime_get(&xt,boost::TIME_UTC); > xt.sec += 5; > > if ( lock.timed_lock(xt) ) > { > cout << "obtain lock -- joining thread\n"; > thrd.join(); > } > else > { > cout << "failed to obtain lock\n"; > } > } > >I'd code this as: > >boost::xtime xt; >boost::xtime_get(&xt, boost::TIME_UTC); >xt.sec += 5; >boost::timed_mutex::scoped_time_lock lock(mutex); >if (lock) // or if (lock.locked()) >{ >// etc I assume you mean boost::timed_mutex::scoped_timed_lock lock(mutex,xt) because I don't see a constructor that takes only a timed_mutex. That said, I agree that your way of doing it is better. Above you asked why I continue to use the syntax I do for locking the mutex in the thread. I want to immediately lock it, then in the main thread try to lock it for a finite amount of time. I can't do that with scoped_lock. Perhaps my strategy is wrong. I want to run a thread for only a specified amount of time. I can't afford to block on a join() to wait for that thread to finish. > cout << "main: making sure thread is gone\n"; > >That's what join is for. I realize this is a toy example, but I can't see >a valid reason for coding it this way. All you've done is introduce race >conditions, even if they are conditions you can feel fairly confident will >do what you want. > > sleep(10); > > return 0; > } > > OUTPUT: > main: creating thread > thread_class destructed > thread_class destructed > thread_class destructed > thread_class destructed > main: sleeping for 2 seconds > thread: locking mutex > thread: sleeping for 10 seconds > main: trying to lock mutex -- waiting 5 seconds... > failed to obtain lock > thread_class destructed > main: making sure thread is gone > thread: freeing lock -- goodbye > thread_class destructed > > 1) Why are so many thread_class objects constructed/destructed when > calling boost::thread? > >The number surprises me a little. I'd have expected two copies, knowing >what I do about the implementation and with out carefully evaluating the >code here. But the documentation is clear that the object will be copied >AT LEAST once, and is free to copy the object any number of times. You >need to account for this in your implementation if it matters. Understood. Apologies for not thoroughly reading the doc first. > 2) After the thread object (test) goes out of scope, why does the thread > continue to run? Is it copied when calling boost::thread and run > detached from the main thread? > >I don't know what you mean by "run detached from the main thread", but >yes, test IS copied (but then, you know that based on what you asked in >1). But then, maybe you meant something else. The "thread object" is >actually "thrd" in your code above, not "test". > > 3) Is there a way I can cancel a thread if going out of scope doesn't > stop it? > >Not yet, but there will be. However, I'm not sure that what you want to >do is really to cancel the thread. It's hard to tell from this toy >example. What the application does is run a job (thread) that has a finite amount of time to finish. If it doesn't finish in that time it needs to send an alert and explicitly terminate the thread (because it can't be blocked with a join() unless it knows the thread is done). As stated above, perhaps my strategy of using the mutex to see if a thread ran in a given amount of time is wrong. Hopefully I'm making some sense, if not, I apologies. James >William E. Kempf Info: <http://www.boost.org> Wiki: <http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

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ublas::matrix debugging values
by Nick Toze 05 Dec '02

05 Dec '02

Hello, I'm using ublas in MSVC6. How do I find out the values of elements of a matrix when debugging? If I try putting for example mat[0][0] in the 'watch' window then it says 'CXX0058: Error: overloaded operator not found'. Thanks in advance, Nick

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