Function __libcpp_contention_wait

system/lib/libcxx/src/atomic.cpp:151–161

  return __cxx_atomic_load(__platform_state, memory_order_acquire);
}
static void __libcpp_contention_wait(__cxx_atomic_contention_t volatile* __contention_state,
                                     __cxx_atomic_contention_t const volatile* __platform_state,
                                     __cxx_contention_t __old_value) {
  __cxx_atomic_fetch_add(__contention_state, __cxx_contention_t(1), memory_order_relaxed);
  // https://github.com/llvm/llvm-project/issues/109290
  // There are no platform guarantees of a memory barrier in the platform wait implementation
  __cxx_atomic_thread_fence(memory_order_seq_cst);
  // We sleep as long as the monitored value hasn't changed.
  __libcpp_platform_wait_on_address(__platform_state, __old_value);
  __cxx_atomic_fetch_sub(__contention_state, __cxx_contention_t(1), memory_order_release);
}

/* When the incoming atomic is the wrong size for the platform wait size, need to
   launder the value sequence through an atomic from our table. */