这是我的情况:
private CancellationTokenSource cancellationTokenSource;
private CancellationToken cancellationToken;
public IoTHub()
{
cancellationTokenSource = new CancellationTokenSource();
cancellationToken = cancellationTokenSource.Token;
receive();
}
private void receive()
{
eventHubClient = EventHubClient.CreateFromConnectionString(connectionString, iotHubD2cEndpoint);
var d2cPartitions = eventHubClient.GetRuntimeInformation().PartitionIds;
foreach (string partition in d2cPartitions)
{
ReceiveMessagesFromDeviceAsync(partition, cancellationToken);
}
}
private async Task ReceiveMessagesFromDeviceAsync(CancellationToken ct)
{
var eventHubReceiver = eventHubClient.GetDefaultConsumerGroup().CreateReceiver(partition, DateTime.UtcNow);
while (true)
{
if(ct.IsCancellationRequested)
{
break;
}
EventData eventData = await eventHubReceiver.ReceiveAsync();
if (eventData == null) continue;
string data = Encoding.UTF8.GetString(eventData.GetBytes());
// Javascript function with Websocket
Clients.All.setMessage(data);
}
}
public void cancelToken()
{
cancellationTokenSource.Cancel();
}
当调用 cancelToken 方法时,任务不会被取消。怎么会?
我已阅读Microsoft guide ,关于任务取消的其他 Stackoverflow 问题。
但仍然难以正确使用它们。
最佳答案
您可以将 CancellationToken
视为一个标志,指示是否收到取消信号。因此:
while (true)
{
//you check the "flag" here, to see if the operation is cancelled, correct usage
if(ct.IsCancellationRequested)
{
break;
}
//your instance of CancellationToken (ct) can't stop this task from running
await LongRunningTask();
}
如果你想取消LongRunningTask
,你应该在任务体内使用CancellationToken
,并在必要时检查它,像这样:
async Task LongRunningTask()
{
await DoPrepareWorkAsync();
if (ct.IsCancellationRequested)
{
//it's cancelled!
return;
}
//let's do it
await DoItAsync();
if (ct.IsCancellationRequested)
{
//oh, it's cancelled after we already did something!
//fortunately we have rollback function
await RollbackAsync();
}
}
关于c# - 正确使用 CancellationToken,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/36173674/