如何使用boost :: mutex作为std :: map中的映射类型？(How to use a boost::mutex as the mapped type in std::map?)

如何使用boost :: mutex作为std :: map中的映射类型？(How to use a boost::mutex as the mapped type in std::map?)

我想要锁定另一张地图中的键/索引，如下所示：

std::map<int, boost::mutex> pointCloudsMutexes_; pointCloudsMutexes_[index].lock();

但是，我收到以下错误：

/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) { } ^

它似乎与std::vector一起工作，但与std::map不兼容。 我究竟做错了什么？

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?

最满意答案

在C ++ 11之前的C ++中，调用operator[]时， std::map的映射类型必须既可以是default-constructible也可以是copy-constructible 。 但是， boost::mutex被明确设计为不可复制，因为通常不清楚复制互斥量的语义应该是什么。 由于boost::mutex不可复制，因此使用pointCloudsMutexes_[index]插入此类值无法编译。

最好的解决方法是使用一些共享指针来boost::mutex作为映射类型，例如：

#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删除了映射类型的要求，以便可复制。

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.