uart_rx_config_gate.hpp

#pragma once
 
#include <atomic>
#include <cstdint>
 
#include "libxr_assert.hpp"
 
namespace LibXR
{
 
class UartRxConfigGate
{
 public:
  void RequestConfig() { state_.fetch_or(CONFIG_PENDING, std::memory_order_release); }
 
  [[nodiscard]] bool TryEnterRx()
  {
    uint32_t expected = 0U;
    return state_.compare_exchange_strong(expected, RX_ACTIVE, std::memory_order_acquire,
                                          std::memory_order_relaxed);
  }
 
  [[nodiscard]] bool LeaveRx()
  {
    uint32_t observed = state_.load(std::memory_order_relaxed);
    while (true)
    {
      ASSERT((observed & RX_ACTIVE) != 0U);
      const uint32_t desired = observed & ~RX_ACTIVE;
      if (state_.compare_exchange_weak(observed, desired, std::memory_order_release,
                                       std::memory_order_relaxed))
      {
        return (observed & CONFIG_PENDING) != 0U;
      }
    }
  }
 
  [[nodiscard]] bool TryEnterConfig()
  {
    uint32_t expected = CONFIG_PENDING;
    return state_.compare_exchange_strong(
        expected, CONFIG_ACTIVE, std::memory_order_acquire, std::memory_order_relaxed);
  }
 
  void LeaveConfig()
  {
    uint32_t observed = state_.load(std::memory_order_relaxed);
    while (true)
    {
      ASSERT((observed & CONFIG_ACTIVE) != 0U);
      const uint32_t desired = observed & ~CONFIG_ACTIVE;
      if (state_.compare_exchange_weak(observed, desired, std::memory_order_release,
                                       std::memory_order_relaxed))
      {
        return;
      }
    }
  }
 
  [[nodiscard]] bool ConfigRequested() const
  {
    return (state_.load(std::memory_order_acquire) & (CONFIG_PENDING | CONFIG_ACTIVE)) !=
           0U;
  }
 
  UartRxConfigGate() = default;
  UartRxConfigGate(const UartRxConfigGate&) = delete;
  UartRxConfigGate& operator=(const UartRxConfigGate&) = delete;
 
 private:
  static constexpr uint32_t RX_ACTIVE = 1U << 0U;
  static constexpr uint32_t CONFIG_PENDING = 1U << 1U;
  static constexpr uint32_t CONFIG_ACTIVE = 1U << 2U;
 
  std::atomic<uint32_t> state_{0U};
};
 
}  // namespace LibXR