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  1. #include <iostream>
  2. #include <atomic>
  3. #include <mutex>
  4. using namespace std;
  5.  
  6. class Foo {
  7. public:
  8. 	static Foo* Instance();
  9. private:
  10. 	Foo() {init();}
  11. 	void init() { cout << "init done." << endl;} // your init cache function.
  12. 	static atomic<Foo*> pinstance;
  13. 	static mutex m_;
  14. };
  15.  
  16. atomic<Foo*> Foo::pinstance { nullptr };
  17. std::mutex Foo::m_;
  18.  
  19. Foo* Foo::Instance() {
  20.   if(pinstance == nullptr) {
  21.   	lock_guard<mutex> lock(m_);
  22.   	if(pinstance == nullptr) {
  23.   		pinstance = new Foo();
  24.   	}
  25.   }
  26.   return pinstance;
  27. }
  28.  
  29.  
  30.  
  31. int main() {
  32. 	Foo* foo1 = Foo::Instance();
  33. 	Foo* foo2 = Foo::Instance();
  34. 	return 0;
  35. }
Success #stdin #stdout 0s 3272KB
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Standard input is empty
stdout
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init done.
https://ideone.com/olvK13
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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