[Boost-users] Why is boost::thread::mutex noncopyable?

From: Phil Endecott (spam_from_boost_users_at_[hidden])
Date: 2005-12-31 18:01:15

Dear All,

Can someone help me to understand why boost::thread::mutex is 
noncopyable?  I expect that there is a good reason, but I can't see it 
at the moment.

In my multithreaded application I have a struct with some uninteresting 
data in it, but I want updates to the struct as a whole to be atomic so 
I have a mutex.  For example:

struct person {
   string firstname;
   string surname;
   mutex m;
};

I want to be able to put these structs in a container.  Say a map:

map<int,person> people;

person p;
people.insert(make_pair(1,p));

But I can't do this because the mutex is noncopyable and inserting 
copies it.

Yes, I could have a map<int,person*>.  But I don't understand why I'm 
forced to do that.

Of course, copying a struct person while the mutex is locked would be a 
bad thing to do.  And copying the struct is not thread safe.  But 
higher-level constraints can prevent this sort of thing from happening; 
for example, I might create my map while only one thread exists.

Can anyone offer any insight?

Thanks,

--Phil.