多线程BLE地址获取函数cv.notify_all()触发访问违规错误排查

错误根因分析 #

• 核心问题：函数栈变量生命周期和回调生命周期不匹配
  你代码中用到的std::mutex m、std::condition_variable cv、addr、stopCalled、advWatcher都是GetFirstAdvertisingBLEAddr函数的栈上局部变量。两个事件回调（Received、Stopped）都是按引用捕获这些栈变量，而WinRT的BLE事件回调是异步执行的：当cv.wait条件满足返回后，函数会立刻开始销毁栈上的局部变量，此时如果回调还在执行（甚至还没开始调度执行），访问已经被销毁的cv、mutex等对象就会触发"访问违规"错误，你报错的cv.notify_all()行就是刚好访问到了已析构的cv对象。
• 其他多线程问题
  1. 共享变量存在数据竞争：Received回调中写addr时没有加锁，和wait谓词中读addr的操作构成数据竞争，属于C++未定义行为。
  2. 回调移除时机过晚：你在wait返回后才移除事件回调，此时已经有处于调度中、未执行的回调无法被拦截，依然会访问已销毁的栈变量。

修复方案 #

1. 把所有跨线程共享的状态封装到堆上，用std::shared_ptr持有，让回调的生命周期和共享状态的生命周期绑定，避免提前销毁：

#include <memory>
#include <mutex>
#include <condition_variable>

using namespace winrt::Windows::Devices::Bluetooth;
using namespace winrt::Windows::Devices::Bluetooth::Advertisement;

struct BleWatchState
{
    std::mutex mtx;
    std::condition_variable cv;
    uint64_t foundAddr = 0;
    bool isStopped = false;
};

uint64_t GetFirstAdvertisingBLEAddr()
{
    auto state = std::make_shared<BleWatchState>();
    BluetoothLEAdvertisementWatcher advWatcher;

    auto recvToken = advWatcher.Received([state, advWatcher](BluetoothLEAdvertisementWatcher const&, BluetoothLEAdvertisementReceivedEventArgs const& eventArgs) {
        ShowAdvertisement(eventArgs);
        // 加锁访问共享变量，避免重复处理
        {
            std::unique_lock l(state->mtx);
            if (state->foundAddr != 0) return;
            state->foundAddr = eventArgs.BluetoothAddress();
        }
        advWatcher.Stop();
        std::unique_lock l(state->mtx);
        state->cv.notify_all();
    });

    auto stoppedToken = advWatcher.Stopped([state](BluetoothLEAdvertisementWatcher const&, BluetoothLEAdvertisementWatcherStoppedEventArgs const&) {
        std::unique_lock l(state->mtx);
        state->isStopped = true;
        state->cv.notify_all();
    });

    uint64_t result = 0;
    {
        std::unique_lock l(state->mtx);
        advWatcher.Start();
        state->cv.wait(l, [&] { 
            return state->foundAddr != 0 && state->isStopped 
                && (advWatcher.Status() == BluetoothLEAdvertisementWatcherStatus::Aborted 
                    || advWatcher.Status() == BluetoothLEAdvertisementWatcherStatus::Stopped); 
        });
        result = state->foundAddr;
    }

    // 先停止再移除回调
    if (advWatcher.Status() == BluetoothLEAdvertisementWatcherStatus::Started)
    {
        advWatcher.Stop();
    }
    advWatcher.Received(recvToken);
    advWatcher.Stopped(stoppedToken);

    return result;
}

2. 额外优化点：如果需要处理超时场景，可以把cv.wait换成cv.wait_for，避免设备未扫描到时函数永久阻塞。

内容的提问来源于stack exchange，提问作者xikov