c++ - is_lock_free 未在 gcc 4.7.2 的 std::atomic 中定义？

Question

我遇到这个编译器错误

function std::atomic::is_lock_free() const: error: undefined reference to '__atomic_is_lock_free' 

when compiling code like below using gcc 4.7.2 on linux.

struct S {
  int a;
  int b;
};


  std::atomic<S> s;
  cout << s.is_lock_free() << endl;

Answer 1

Atomic API isn't complete in GCC 4.7:

• When lock free instructions are not available (either through hardware or OS support) atomic operations are left as function calls to be resolved by a library. Due to time constraints and an API which is not finalized, there is no libatomic supplied with GCC 4.7. This is easily determined by encountering unsatisfied external symbols beginning with __atomic_*.

由于 GCC 4.7 没有附带 libatomic，您需要使用另一个编译器，它实际上支持您想要的功能或提供缺少的功能 (sample implementation)。