Re: [Boost-users] Using Boost Mutex

Subject: Re: [Boost-users] Using Boost Mutex
From: Neil Groves (neil_at_[hidden])
Date: 2009-09-18 14:16:54

On Fri, Sep 18, 2009 at 6:21 PM, Wesley Bland <wesbland_at_[hidden]> wrote:

> This is firmly in n00b territory.
> I'm trying to use a boost::mutex to lock a STL queue.  The mutex is stored
> in a class in a map.  When I pass the mutex to the boost::mutex::scoped_lock
> constructor, I get this error:
>
> /usr/local/include/boost/noncopyable.hpp: In copy constructor
> ‘boost::mutex::mutex(const boost::mutex&)’:
> /usr/local/include/boost/thread/pthread/mutex.hpp:31:   instantiated from
> ‘_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with
> _Key = int, _Tp = boost::mutex, _Compare = std::less<int>, _Alloc =
> std::allocator<std::pair<const int, boost::mutex> >]’
> SwitchBox.cpp:15:   instantiated from here
> /usr/local/include/boost/noncopyable.hpp:27: error:
> ‘boost::noncopyable_::noncopyable::noncopyable(const
> boost::noncopyable_::noncopyable&)’ is private
> /usr/local/include/boost/thread/pthread/mutex.hpp:31: error: within this
> context
> /usr/include/c++/4.2.1/bits/stl_map.h: In member function ‘_Tp&
> std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key =
> int, _Tp = boost::mutex, _Compare = std::less<int>, _Alloc =
> std::allocator<std::pair<const int, boost::mutex> >]’:
> /usr/include/c++/4.2.1/bits/stl_map.h:350: note: synthesized method
> ‘boost::mutex::mutex(const boost::mutex&)’ first required here
>
> This appears to be complaining about me passing the mutex into the
> scoped_lock.  Can anyone give me some help here?  I've included a much
> shortened version of the code that otherwise compiles.
>
>
It's complaining about the mutex being in a map. The map requires the
elements within it to be copy constructable which boost::mutex isn't by
design. You might want to consider using a shared_ptr<mutex>.

> Thanks for your help,
> Wesley
>
>  <snip code />

Regards,
Neil Groves