问题描述
请检查此代码是否存在多线程错误。有时我在第 cv.notify_all();
行(代码中标记)收到错误“访问冲突读取位置”。
uint64_t GetFirstAdvertisingBLEAddr()
{
std::mutex m;
std::condition_variable cv;
bluetoothleadvertisementwatcher advWatcher;
uint64_t addr = 0;
bool stopCalled = false;
auto recvToken = advWatcher.Received([&addr,&m,&cv](bluetoothleadvertisementwatcher watcher,BluetoothLEAdvertisementReceivedEventArgs eventArgs) {
ShowAdvertisement(eventArgs);
addr = eventArgs.BluetoothAddress();
watcher.Stop();
std::unique_lock l(m);
cv.notify_all(); // <----- HERE ------------------------------------
});
auto stoppedToken = advWatcher.Stopped([&stopCalled,bluetoothleadvertisementwatcherStoppedEventArgs eventArgs) {
std::unique_lock l(m);
stopCalled = true;
cv.notify_all();
});
{
std::unique_lock l(m);
advWatcher.Start();
cv.wait(l,[&addr,&stopCalled,&advWatcher] { return addr != 0 && stopCalled && (advWatcher.Status() == bluetoothleadvertisementwatcherStatus::Aborted || advWatcher.Status() == bluetoothleadvertisementwatcherStatus::Stopped); });
}
// remove event handlers
advWatcher.Received(recvToken);
advWatcher.Stopped(stoppedToken);
return addr;
}
如果您需要更多代码:
int main()
{
winrt::init_apartment();
std::wcout << "Main thread: " << std::this_thread::get_id() << std::endl;
uint64_t addr = GetFirstAdvertisingBLEAddr();
if (addr == 0) {
std::wcout << L"Failed to find advertising BLE device." << std::endl;
return 1;
}
std::wcout << "Found BLE device: " << GetDeviceName(addr) << std::endl;
BluetoothLEDevice dev = BluetoothLEDevice::FromBluetoothAddressAsync(addr).get();
GattDeviceServicesResult result = dev.GetGattServicesAsync(BluetoothCacheMode::Uncached).get();
.......
解决方法
当函数 GetFirstAdvertisingBLEAddr
返回时,互斥量和条件变量都超出范围。 lambda 表达式中捕获的变量然后悬空,读取这些变量会使您的程序具有未定义的行为。
一种可能的解决方法是让它们static
:
static std::mutex m;
static std::condition_variable cv;