问题
I would like to lock the keys/index in another map like this:
std::map<int, boost::mutex> pointCloudsMutexes_;
pointCloudsMutexes_[index].lock();
However, I am getting the following error:
/usr/include/c++/4.8/bits/stl_pair.h:113: error: no matching function for call to 'boost::mutex::mutex(const boost::mutex&)'
: first(__a), second(__b) { }
^
It seems to work with std::vector
, but not with std::map
. What am I doing wrong?
回答1:
In C++ before C++11, the mapped type of a std::map
must be both default-constructible and copy-constructible, when calling operator[]
. However, boost::mutex
is explicitly designed not to be copy-constructible, because it is generally unclear what the semantics of copying a mutex should be. Due to boost::mutex
not being copyable, insertion of such value using pointCloudsMutexes_[index]
fails to compile.
The best workaround is to use some shared pointer to boost::mutex
as the mapped type, e.g:
#include <boost/smart_ptr/shared_ptr.hpp>
#include <boost/thread/mutex.hpp>
#include <map>
struct MyMutexWrapper {
MyMutexWrapper() : ptr(new boost::mutex()) {}
void lock() { ptr->lock(); }
void unlock() { ptr->unlock(); }
boost::shared_ptr<boost::mutex> ptr;
};
int main() {
int const index = 42;
std::map<int, MyMutexWrapper> pm;
pm[index].lock();
}
PS: C++11 removed the requirement for the mapped type to be copy-constructible.
回答2:
Map require a copy constructor,but unfortunately boost::mutex
has no public copy constructor. Mutex declared as below:
class mutex
{
private:
pthread_mutex_t m;
public:
BOOST_THREAD_NO_COPYABLE(mutex)
I don't think vector works either, it should have same problem. Can you push_back
an boost::mutex
into vector?
来源:https://stackoverflow.com/questions/36468270/how-to-use-a-boostmutex-as-the-mapped-type-in-stdmap