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. Thanks for your help, Wesley SwitchBox.hpp ----- #include <map> #include <queue> #include <boost/thread/mutex.hpp> #include <boost/asio.hpp> using boost::asio::ip::tcp; using namespace std; namespace Network { typedef struct Message { int type; unsigned long sender; unsigned long destination; int size; void *body; char *PackHeader(); void UnpackHeader(char *); } Message; class SwitchBox { protected: unsigned long myID; int headerSize; map< int, queue< Message > > sendQueues; map< int, boost::mutex > sendMutexes; bool Initialize(); void SendThread(unsigned long id, tcp::socket sock); }; } SwitchBox.cpp ------ #include "Switchbox.hpp" using namespace Network; bool SwitchBox::Initialize() { myID = 0; headerSize = sizeof(int) + sizeof(unsigned long) * 2 + sizeof(int); return true; } void SwitchBox::SendThread(unsigned long id, tcp::socket sock) { // Set up the lock so it can be locked and unlocked as we need boost::mutex::scoped_lock sendLock(sendMutexes[id], boost::defer_lock); while (true) { // First get the message off of the message queue // Lock the message queue so nothing is moved unexpectedly sendLock.lock(); Message m = sendQueues[id].front(); sendQueues[id].pop(); // Unlock the message queue so everyone else can get to it now sendLock.unlock(); // Next send the message through the socket boost::asio::write(sock, boost::asio::buffer(m.PackHeader(), headerSize)); boost::asio::write(sock, boost::asio::buffer((char *) m.body, m.size)); } }