/// <summary>
/// 删除并返回顶部元素
/// </summary>
/// <returns></returns>
public T Poll()
{
while (true)
{
Element element = GetFirstElement();
if (element == null)
{
return(default(T));
}
try
{
bool flag = _zkClient.Delete(element.name);
if (flag)
{
return(element.data);
}
else
{
//如果删除失败，证明已被其他线程获取
//重新获取最新的元素，直到获取成功为止。
}
}
catch (ZKNoNodeException e)
{
}
catch (Exception e)
{
throw ExceptionUtil.ConvertToException(e);
}
}
}
/// <summary>
/// 获取队列顶部元素
/// </summary>
/// <returns></returns>
private Element GetFirstElement()
{
try
{
while (true)
{
List <string> list = _zkClient.GetChildren(_root);
if (list.Count == 0)
{
return(null);
}
string elementName = GetSmallestElement(list);
try
{
return(new Element(_root + "/" + elementName, _zkClient.ReadData <T>(_root + "/" + elementName)));
}
catch (ZKNoNodeException e)
{
// somebody else picked up the element first, so we have to
// retry with the new first element
}
}
}
catch (Exception e)
{
throw ExceptionUtil.ConvertToException(e);
}
}
/// <summary>
/// 添加一个元素
/// </summary>
/// <param name="element"></param>
/// <returns></returns>
public bool Offer(T element)
{
try
{
_zkClient.CreatePersistentSequential(_root + "/" + ELEMENT_NAME + "-", element);
}
catch (Exception e)
{
throw ExceptionUtil.ConvertToException(e);
}
return(true);
}
public T RetryUntilConnected <T>(Func <T> callable)
{
if (_zookeeperEventThread != null && Thread.CurrentThread == _zookeeperEventThread)
{
throw new Exception("Must not be done in the zookeeper event thread.");
}
long operationStartTime = DateTime.Now.ToUnixTime();
while (true)
{
if (_closed)
{
throw new Exception("ZKClient already closed!");
}
try
{
return(callable());
}
catch (ConnectionLossException e)
{
// we give the event thread some time to update the status to 'Disconnected'
Thread.Yield();
WaitForRetry();
}
catch (SessionExpiredException e)
{
// we give the event thread some time to update the status to 'Expired'
Thread.Yield();
WaitForRetry();
}
catch (KeeperException e)
{
throw ZKException.Create(e);
}
catch (ThreadInterruptedException e)
{
throw new ZKInterruptedException(e);
}
catch (Exception e)
{
throw ExceptionUtil.ConvertToException(e);
}
// before attempting a retry, check whether retry timeout has elapsed
if (_operationRetryTimeoutInMillis > -1 &&
(DateTime.Now.ToUnixTime() - operationStartTime) >= _operationRetryTimeoutInMillis)
{
throw new ZKTimeoutException("Operation cannot be retried because of retry timeout (" + _operationRetryTimeoutInMillis + " milli seconds)");
}
}
}
