Error with copy constructor/assignment operator for a class which has std::atomic member variable

c++ multithreading c++11 atomic
polapts picture polapts · Aug 17, 2012 · Viewed 15.5k times · Source

I have a class like below. 

#include <atomic>

static const long  myValue = 0;

class Sequence
{

public:

    Sequence(long initial_value = myValue) : value_(initial_value) {}


private:

     std::atomic<long> value_;
};

int main()
{
         Sequence firstSequence;
         Sequence secondSequence = firstSequence;
         return 0;
}

I am getting compilation error like this,

test.cpp:21:36: error: use of deleted function ‘Sequence::Sequence(const Sequence&)’
test.cpp:5:7: error: ‘Sequence::Sequence(const Sequence&)’ is implicitly deleted because the default definition would be ill-formed:
test.cpp:5:7: error: use of deleted function ‘std::atomic<long int>::atomic(const std::atomic<long int>&)’

Is that the default copy constructor and assignment opertaor do not work in such case?

PS: I am using gcc version 4.6.3

Answer

Kerrek SB picture Kerrek SB · Aug 17, 2012

You can't copy atomics with a standard copy constructor, since all loads and stores must happen explicitly. You'll have to write your own copy constructor for Sequence which does some initialization of the form value_(rhs.value_.load()) (possibly with more relaxed memory ordering).

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