[Boost-bugs] [Boost C++ Libraries] #2704: range lock algorithm fails with iterators

Subject: [Boost-bugs] [Boost C++ Libraries] #2704: range lock algorithm fails with iterators
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-01-31 16:14:54

#2704: range lock algorithm fails with iterators
--------------------------------------+-------------------------------------
 Reporter:  jwakely.boost_at_[hidden]  |       Owner:  anthonyw
     Type:  Bugs                      |      Status:  new     
Milestone:  Boost 1.38.0              |   Component:  thread  
  Version:  Boost 1.37.0              |    Severity:  Problem 
 Keywords:                            |  
--------------------------------------+-------------------------------------
 #include <boost/thread.hpp>

 #include <vector>

 int main()
 {
     std::vector<boost::mutex> v;

     // boost::lock(&v.front(), &v.front()+v.size());
     boost::lock(v.begin(), v.end());

     return 0;
 }

 With GCC 4.3.2 and 4.4 this fails to compile, complaining that
 std::vector<mutex>::iterator does not have members lock, unlock and
 try_lock e.g.
 /home/redi/src/boost/boost/thread/locks.hpp: In static member function
 ‘static char boost::detail::has_member_try_lock<T>::has_member(U*, bool
 (U::*)()) [with U = __gnu_cxx::__normal_iterator<boost::mutex*,
 std::vector<boost::mutex, std::allocator<boost::mutex> > >, T =
 __gnu_cxx::__normal_iterator<boost::mutex*, std::vector<boost::mutex,
 std::allocator<boost::mutex> > >]’:
 /home/redi/src/boost/boost/thread/locks.hpp:75:   instantiated from ‘const
 bool
 boost::detail::has_member_try_lock<__gnu_cxx::__normal_iterator<boost::mutex*,
 std::vector<boost::mutex, std::allocator<boost::mutex> > > >::value’
 /home/redi/src/boost/boost/thread/locks.hpp:84:   instantiated from ‘const
 bool boost::is_mutex_type<__gnu_cxx::__normal_iterator<boost::mutex*,
 std::vector<boost::mutex, std::allocator<boost::mutex> > > >::value’
 /home/redi/src/boost/boost/thread/locks.hpp:1133:   instantiated from
 ‘void boost::lock(const MutexType1&, const MutexType2&) [with MutexType1 =
 __gnu_cxx::__normal_iterator<boost::mutex*, std::vector<boost::mutex,
 std::allocator<boost::mutex> > >, MutexType2 =
 __gnu_cxx::__normal_iterator<boost::mutex*, std::vector<boost::mutex,
 std::allocator<boost::mutex> > >]’
 lock_range.cc:10:   instantiated from here

 The commented-out line above compiles fine, using mutex* as the Iterator
 type rather than std::vector<mutex>::iterator.

 I don't think SFINAE applies in has_member_try_lock<T>::has_member<U>,
 because bool(U::*)() is a valid type for iterators classes, so
 substitution succeeds, but &U::try_lock is not a valid expression.

 In the pointer case where U is a pointer, bool(U::*)() is not a valid
 type, so substitution fails, but is not an error.

 The attached patch (against trunk) adds another default argument to
 has_member_{lock,try_lock,unlock}::has_member with a type that depends on
 the presence of a member with the right name.  I think this would still
 fail to compile if used with an iterator type that had a member
 lock/try_lock/unlock with a different signature to that expected by the
 Lockable concept.

 Jonathan

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/2704>
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