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boost::condition question
by svanechel 26 Feb '02

26 Feb '02

Hi, I'm trying to create a mechanism that synchronizes access to shared data on a per-operation basis. The idea is that some operations (E.g. read operations) can proceed concurrently, while others (write operations) must block all other threads. I thought boost::condition would do the trick. Since I do not have that much experience in multithreaded programming it is entirely possible that I do not fully understand boost::condition or its allowable usage. I tried to put operations in an "Operation Group". All operations belonging to the same group are allowed to execute concurrently, while all others are blocked (E.g. all read operations are in the same group). It is also possible that an operation doesn't specify an Operation Group, in which case a temporary group is assigned to the operation for each thread that calls it. Write operations are constructed this way. Below is an example of what I mean (OperationLevelLockable is defined below): class SomeClass : private OperationLevelLockable { public: int ReadData() { Lock lock( this, READ_OP_GROUP ); return ( mData ); } void WriteData( int data ) { Lock lock( this ); // assign temp group to operation, // so each write // operation blocks all other accesses mData = data; } private: int mData; }; I'm developing on Windows 2000 on a multiprocessor machine. This is the code I use to test my idea: const int32 OPERATION_GROUP_1 = 1; const int32 OPERATION_GROUP_2 = 2; const int NUM_THREADS = 4; class TestOperationLevelLockable : public MTTestCase { public: TestOperationLevelLockable() : mShared( this ), mCurrentGroup( 0 ), mThreadCount( 0 ) { // Create two sets of threads, each performing a // different operation // When the TestOperationLevelLockable object is // constructed all // registered threads are created an start running RegisterThread( this, &TestOperationLevelLockable::Operation1Thread, NUM_THREADS ); RegisterThread( this, &TestOperationLevelLockable::Operation2Thread, NUM_THREADS ); } void CallFromGroup( int32 opGroup ) { boost::mutex::scoped_lock lock( mMutex ); if ( 0 == mCurrentGroup ) { mCurrentGroup = opGroup; } if ( ( mCurrentGroup != opGroup ) && ( mThreadCount < NUM_THREADS ) ) { ReportFailure( "OperationLevelLockable failed to lock out operations of different group", __FILE__, __LINE__ ); } ++mThreadCount; } protected: class MTObject : public OperationLevelLockable { public: MTObject( TestOperationLevelLockable* target ) : mTarget( target ) {} void CallFromGroup( int32 opGroup ) { mTarget->CallFromGroup( opGroup ); } private: TestOperationLevelLockable* mTarget; }; MTObject mShared; int32 mCurrentGroup; int mThreadCount; boost::mutex mMutex; void DoMTTest() { } void Operation1Thread() { MTObject::Lock lock( mShared, OPERATION_GROUP_1 ); mShared.CallFromGroup( OPERATION_GROUP_1 ); SleepThread( 30 ); // seconds, to keep the thread busy } void Operation2Thread() { MTObject::Lock lock( mShared, OPERATION_GROUP_2 ); mShared.CallFromGroup( OPERATION_GROUP_2 ); SleepThread( 30 ); // seconds, to keep the thread busy } }; And here is OperationLevelLockable: class OperationLevelLockable { class AccessCounter; public: OperationLevelLockable(){} typedef Internal::DefaultTMIntType IntType; template<typename T> struct MakeSharedType { typedef T volatile Type; }; class Lock; friend class Lock; class Lock { public: Lock( OperationLevelLockable& obj ) : mCounter( obj.mOpAccessCounter ) { mCounter.EnterOperation( Lock::TempOpGroup() ); } Lock( OperationLevelLockable& obj, int32 opGroup ) : mCounter( obj.mOpAccessCounter ) { mCounter.EnterOperation( opGroup ); } ~Lock() { mCounter.LeaveOperation(); } private: Lock( Lock const& ); Lock& operator=( Lock const& ); static IntType TempOpGroup() { static volatile IntType opGroup = Internal::kFIRST_AUTO_GROUP; IntType newGroup = OperationLevelLockable::AtomicIncrement( opGroup ); if ( newGroup >= Internal::kLAST_AUTO_GROUP ) { OperationLevelLockable::AtomicAssign( opGroup, Internal::kFIRST_AUTO_GROUP ); } return ( newGroup ); } AccessCounter& mCounter; }; static inline IntType AtomicIncrement( volatile IntType& lval ); static inline IntType AtomicDecrement( volatile IntType& lval ); static inline void AtomicAssign( IntType& lval, IntType rVal ); static inline void AtomicAssign( volatile IntType& lval, IntType rVal ); private: class AccessCounter : private boost::base_from_member<boost::recursive_mutex> { public: AccessCounter() : mLock( member ), mRefCnt( 0 ), mOpGroup( Internal::kANY_GROUP ) {} bool IsOpGroupActive( IntType opGroup ) const { return ( ( Internal::kANY_GROUP == mOpGroup ) || ( opGroup == mOpGroup ) ); } void LeaveOperation() { if ( 0 == OperationLevelLockable::AtomicDecrement( mRefCnt ) ) { SetOpGroup( Internal::kANY_GROUP ); mCanOpProceed.notify_all(); } } void EnterOperation( IntType opGroup ) { mCanOpProceed.wait( mLock, CanOpProceed( *this, opGroup ) ); SetOpGroup( opGroup ); OperationLevelLockable::AtomicIncrement( mRefCnt ); } private: AccessCounter( AccessCounter const& ); AccessCounter& operator=( AccessCounter const& ); struct CanOpProceed { CanOpProceed( AccessCounter const& counter, IntType opGroup ) : mOpGroup( opGroup ), mCounter( counter ) {} bool operator()() const { return ( mCounter.IsOpGroupActive( mOpGroup ) ); } private: CanOpProceed& operator=( CanOpProceed const& ); int32 mOpGroup; AccessCounter const& mCounter; }; void SetOpGroup( IntType opGroup ) { OperationLevelLockable::AtomicAssign( mOpGroup, opGroup ); } boost::recursive_mutex::scoped_lock mLock; boost::condition mCanOpProceed; volatile IntType mRefCnt; volatile IntType mOpGroup; }; OperationLevelLockable( OperationLevelLockable const& ); OperationLevelLockable& operator=( OperationLevelLockable const& ); AccessCounter mOpAccessCounter; }; The idea is that the first operation that is executed acquires the lock and blocks out all threads not belonging to the same Operation Group. The original blocking works fine. Only threads executing in the same Operation Group are allowed to continue. When the last thread of the group leaves the operation in OperationLevelLockable::AccessCounter::LeaveOperation it releases all waiting threads and a thread from the other group is allowed to run. However when this thread finishes no new threads are allowed to run anymore and the application hangs. Am I using boost::condition incorrectly. Should I use something else? It the test code wrong? Are there any other errors in the code that prevent it from behaving as expected. Should I use another technique to achieve the same? I hope there is someone out there who has the hart to read through the entire posting and help me. I hope I have given enough information. Thx. Sven Van Echelpoel.

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Building regex with msvc6sp5 and stlport
by John Maddock 25 Feb '02

25 Feb '02

>I have succesfully built the regex library >under msvc6sp5, using the vc6-sltport.mak file. > >But I notice that the compiler gives me warnings >relating to the microsoft stl include directories: > >example: vc98\include\iterator: blah blah blah Then you aren't compiling / linking to STLport >Should it not be linking to the stlport include files? Yes. Did you either * update your INCLUDE and LIB environment variables to point to STLport. or * invoke the makefile using something like: nmake CXXFLAGS="-Ic:\STLport-4.5.1\stlport" -fvc6-stlport.mak - John Maddock http://ourworld.compuserve.com/homepages/john_maddock/

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Thread support?
by John Maddock 24 Feb '02

24 Feb '02

>If I'm using Boost in a single threaded app, do I need to define >BOOST_DISABLE_THREADS to avoid Boost using locks, etc. internally? You don't need to, but it may remove some redundent code, if your app is single threaded *and* links to a multithreaded runtime. - John Maddock http://ourworld.compuserve.com/homepages/john_maddock/

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Problem linking with regex on Win32
by John Maddock 23 Feb '02

23 Feb '02

>Run-time Library: Multithreaded DLL/Debug Multithreaded DLL > >I've got a couple of problems trying to get my app to link against regex. > >I've tried linking to the debug and release versions of both the DLL and >non-DLL versions of the regex library and in each case I get errors about >unresolved external symbols for w32_regex_traits. > >w32_regex_traits.obj has been produced by Jam. > >In addition the static version winges about lots of locally defined symbols. > >I've specified BOOST_REGEX_NO_LIB as the generated filenames are not what >Jam produces. There could be a number of problems: Where the libs compiled with STLport (even a small error in the STLport include path could have messed this up)? The debug STLport libs are probably compiled by jam with __STL_DEBUG defined, your source will need to set this also. If you want to check your jam compiled libs, get a dump of the symbols they contain - if they're using the Dinkumware std lib then you'll see them referencing std::basic_string, release STLport will reference _STL::basic_string, and debug STLport will reference _STLD::basic_string. Failing that just create a static lib project in your IDE and add the regex sources to that with the build setting you want (this is probably the quickest solution IMO). Finally define BOOST_REGEX_STATIC_LINK to suppress the import/export warnings - John Maddock http://ourworld.compuserve.com/homepages/john_maddock/

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Building regex with msvc6sp5 and stlport
by boxerab 22 Feb '02

22 Feb '02

Hello, I have succesfully built the regex library under msvc6sp5, using the vc6-sltport.mak file. But I notice that the compiler gives me warnings relating to the microsoft stl include directories: example: vc98\include\iterator: blah blah blah Should it not be linking to the stlport include files? I have added the stlport directory location into the mak file, and I have it added to the list of include directories via the compiler gui. Thanks. Aaron Boxer boxerab(a)NOSPAMyahoo.com

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Iterators
by Colin Fox 21 Feb '02

21 Feb '02

This isn't a boost specific message per se, I guess, but I thought someone here may know the answer. I have a list<> of smart_ptrs. Some of the elements in the list are ready for processing under various circumstances. What I'd like would be a custom iterator that when I say "++i" it checks the element to see if it's ready, and if not, advance to the next, and so on until it finds a ready element. If it doesn't find one, then i == list.end(). This would simulate having a list that contained only ready elements, without having to have multiple lists. I have a number of books on C++, but I can't figure out from them how to create a custom iterator. Can anyone help? -- Colin Fox CF Consulting Inc. cfox(a)crystalcherry.com

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[BGL] BGL Book Erratum
by Eric Eide 21 Feb '02

21 Feb '02

Page 12, Figure 1.2: the edge (a,d) should be black, and (b,d) should be gray. ...unless `breadth_first_search' is using the `delay_map' in some way that is not obvious to me. Eric. -- ------------------------------------------------------------------------------- Eric Eide <eeide(a)cs.utah.edu> . University of Utah School of Computing http://www.cs.utah.edu/~eeide/ . +1 (801) 585-5512 voice, +1 (801) 581-5843 FAX

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const smart pointers
by nckgl 21 Feb '02

21 Feb '02

how do I define const smart pointer? for example for "int" type 1. scoped_ptr<const int> 2. const scoped_ptr<int> If the latter then it may be better to re-define get() as follows T* get(){ return px; } // never throws const T* get()const { return px; } // never throws Now scoped_ptr::get() is defined as follows T* get() const { return px; } // never throws The same apply to other accessors (operator-> and so on)

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Problem linking with regex on Win32
by Dale Peakall 21 Feb '02

21 Feb '02

I'll try and add some content before sending a message this time ;) Platform: 2K Compiler: VC6 SP5 Library: stlport-4.0 Boost: 1.27.0 Build Tool for Boost: Jam Run-time Library: Multithreaded DLL/Debug Multithreaded DLL I've got a couple of problems trying to get my app to link against regex. I've tried linking to the debug and release versions of both the DLL and non-DLL versions of the regex library and in each case I get errors about unresolved external symbols for w32_regex_traits. w32_regex_traits.obj has been produced by Jam. In addition the static version winges about lots of locally defined symbols. I've specified BOOST_REGEX_NO_LIB as the generated filenames are not what Jam produces. Here's the full details: --------------------Configuration: request_line_test - Win32 Debug-------------------- Linking... http_request_line.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: static void __cdecl boost::w32_regex_traits<char>::transform_primary(class _STL::basic_string<char,struct std::char_traits<char>,class _STL::allocator<c har> > &,class _STL::basic_string<char,struct std::char_traits<char>,class _STL::allocator<char> > const &)" (__imp_?transform_primary@?$w32_regex_traits@D@boost@@SAXAAV?$basic_string@D U?$char_traits@D@std@@V?$allocator@D@_STL@@@_STL@@ABV34@@Z) http_request_line.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: static bool __cdecl boost::w32_regex_traits<char>::lookup_collatename(class _STL::basic_string<char,struct std::char_traits<char>,class _STL::allocator< char> > &,char const *,char const *)" (__imp_?lookup_collatename@?$w32_regex_traits@D@boost@@SA_NAAV?$basic_string @DU?$char_traits@D@std@@V?$allocator@D@_STL@@@_STL@@PBD1@Z) http_request_line.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: __thiscall boost::bad_expression::bad_expression(class _STL::basic_string<char,struct std::char_traits<char>,class _STL::allocator<char> > const &)" (__ imp_??0bad_expression@boost@@QAE@ABV?$basic_string@DU?$char_traits@D@std@@V? $allocator@D@_STL@@@_STL@@@Z) http_request_line.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: static class _STL::basic_string<char,struct std::char_traits<char>,class _STL::allocator<char> > __cdecl boost::re_detail::w32_traits_base::error_strin g(unsigned int)" (__imp_?error_string@w32_traits_base@re_detail@boost@@SA?AV?$basic_string@DU ?$char_traits@D@std@@V?$allocator@D@_STL@@@_STL@@I@Z) http_request_line.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: static void __cdecl boost::w32_regex_traits<char>::transform(class _STL::basic_string<char,struct std::char_traits<char>,class _STL::allocator<char> > & ,class _STL::basic_string<char,struct std::char_traits<char>,class _STL::allocator<char> > const &)" (__imp_?transform@?$w32_regex_traits@D@boost@@SAXAAV?$basic_string@DU?$char_ traits@D@std@@V?$allocator@D@_STL@@@_STL@@ABV34@@Z) Debug/request_line_test.exe : fatal error LNK1120: 5 unresolved externals Error executing link.exe. request_line_test.exe - 6 error(s), 0 warning(s) Thanks, - Dale.

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scoped_try_lock
by schalk_cronje＠nai.com 20 Feb '02

20 Feb '02

I was wondering about this line in boost::detail::thread::scoped_try_lock: if(m_locked) throw lock_error(); Since it is known that the lock attempt might fail and we do not want to block until the lock becomes available, is it not better to simply return false in the above case instead of throwing lock_error? ----------------------------------[ .signature ]--- Schalk W. Cronjé, Codernaut, Webshield Engineering, Network Associates. ++C or C++ ?

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