Question

on linux, gcc 4.3, compiling a class with boost::thread implementation and mutexes / condition variables I get the following strange error, apparently due to type conflicts with the posix thread library:

*Compiling: filter.cpp /usr/include/boost/thread/condition.hpp: In member function »void boost::condition::wait(L&) [with L = boost::mutex]«: /host/.../filter.cpp:68:   instantiated from here /usr/include/boost/thread/condition.hpp:90: Error: no match für »operator!« in »!lock«* */usr/include/boost/thread/condition.hpp:90: Notice: candidates are: operator!(bool) <built in>* */usr/include/boost/thread/mutex.hpp:66: Error: »pthread_mutex_t boost::mutex::m_mutex« is private /usr/include/boost/thread/condition.hpp:93: Error: in this context* 

The code is:

void CFilter::process( CData **s ) {     boost::mutex::scoped_lock bufferLock(m_mutex);     while (!m_bStop)         m_change.wait(bufferLock);                      //<- line 68      // ... further processing } 

with the class declaration

#include <boost/shared_ptr.hpp> #include <boost/bind.hpp> #include <boost/thread/condition.hpp> #include <boost/thread/thread.hpp> #include <boost/thread/mutex.hpp>  class CFilter {     // ...     boost::shared_ptr<boost::thread> m_thread;     boost::mutex m_mutex;     boost::condition m_change;     // ...      process( CData **s ); } 

The operator error takes place in boost’s condition.hpp, in

if (!lock)     throw lock_error(); 

I’m using Boost 1.38.0, on Windows I don’t find any problems. Any help is appreciated!

Answer 1

You must wait on the bufferLock, not m_mutex:

while (!m_bStop)     m_change.wait(bufferLock); 

Condition<>::wait() takes a ScopedLock as parameter, not a Mutex.