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  1. #include <iostream>
  2.  
  3. static volatile int *entered;
  4.  
  5. void once(void) {
  6.   int result;
  7.   result = __sync_val_compare_and_swap(entered, 0, 1);  // cmpxchg になる
  8.  
  9.   if (result == 1) {
  10.     return;
  11.   }
  12.   std::cout << "once" << std::endl;
  13. }
  14.  
  15. int main() {
  16.   entered = new int;
  17.   *entered = 0;
  18.  
  19.   once();
  20.   once();
  21.   return 0;
  22.  
  23.   delete entered;
  24. }
  25. /* end */
  26.  
Success #stdin #stdout 0s 4500KB
comments (?)
stdin 
Standard input is empty
stdout 
once
https://ideone.com/tpefmL
language:
C++ (gcc 8.3)
created:
5 years ago
visibility:
public

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