TAS & Clear

TAS performs test_and_set operation on a bit.

• x86 platform

  static inline bool
  pg_atomic_test_set_flag_impl(volatile pg_atomic_flag *ptr)
  {
          register char _res = 1;
          __asm__ __volatile__(
                  "       lock                    \n"
                  "       xchgb   %0,%1   \n"
  :               "+q"(_res), "+m"(ptr->value)
  :
  :               "memory");
          return _res == 0;
  }
  static inline void
  pg_atomic_clear_flag_impl(volatile pg_atomic_flag *ptr)
  {
          /*
           * On a TSO architecture like x86 it's sufficient to use a compiler
           * barrier to achieve release semantics.
           */
          __asm__ __volatile__("" ::: "memory");
          ptr->value = 0;
  }

• AArch64 platform

  static inline bool
  pg_atomic_test_set_flag_impl(volatile pg_atomic_flag *ptr)
  {
          return __sync_lock_test_and_set(&ptr->value, 1) == 0;
  }
  static inline void
  pg_atomic_clear_flag_impl(volatile pg_atomic_flag *ptr)
  {
          __sync_lock_release(&ptr->value);
  }