Re: [Boost-Users] Mutex scoped_lock compile errors

From: William E. Kempf (wekempf_at_[hidden])
Date: 2003-06-10 13:18:20

Darren Vincent Hart said:
> Esteemed Boost Gurus,
>
> I am trying to compile a method with a scoped_lock call.  If I use a
> mutex object declared in the class implementation file (logger.cpp) it
> builds, if I use a mutex of the same type declared as a private member
> of the logger class (in logger.h), I get the following compiler error:
>
> logger.cpp: In member function `void pel::logger::info(const
> std::string&,
>    const std::string&, int, const std::string&) const':
> logger.cpp:36: error: no matching function for call to `
>    boost::detail::thread::scoped_lock<boost::mutex>::scoped_lock(const
> boost::mutex&)'
> /usr/include/boost/thread/detail/lock.hpp:62: error: candidates are:
>    boost::detail::thread::scoped_lock<boost::mutex>::scoped_lock(const
> boost::detail::thread::scoped_lock<boost::mutex>&)
> /usr/include/boost/thread/detail/lock.hpp:67: error:
>    boost::detail::thread::scoped_lock<Mutex>::scoped_lock(Mutex&, bool =
> true)
>    [with Mutex = boost::mutex]
> make: *** [logger.o] Error 1
>
>
> The relevant method from the implementation file is as follows:
>
> void logger::info(const std::string& msg, const std::string& file, int
> line, const std::string& function) const
> {
>   // io_mutex is declared above in the pel namespace
>   boost::mutex::scoped_lock scoped_lock(io_mutex);  // no problem
>   // mutex is a private member of the logger class
>   boost::mutex::scoped_lock scoped_lock2(mutex);    // line 36, fails
> std::cout << "...blah..." << std::endl;
> }
>
> Can someone explain why these are treated differently by the compiler ?

It's a cv problem.  The lock must take a non-const reference, and you're
in a const method so the reference is const.  Declare your mutex to be
mutable.  This is in the FAQ.

-- 
William E. Kempf