Question

我在使用NCrunch在 parallel 中运行我的测试时使用OWIN自我主机Web API，我在BeforeEach中启动它并在AfterEach方法中停止。

在每次测试之前我都试图获得可用的端口，但是85中的5-10个测试通常会失败，但有以下异常：

System.Net.HttpListenerException : Failed to listen on prefix  
'http://localhost:3369/' because it conflicts with an existing registration on the machine.

所以看来，有时候我没有可用的端口。我尝试使用Interlocked类来共享多个线程之间的最后使用的端口，但它没有帮助。

这是我的测试基类：

public class BaseSteps
{
    private const int PortRangeStart = 3368;
    private const int PortRangeEnd = 8968;
    private static long _portNumber = PortRangeStart;
    private IDisposable _webServer;

    //.....

    [BeforeScenario]
    public void Before()
    {
        Url = GetFullUrl();
        _webServer = WebApp.Start<TestStartup>(Url);
    }

    [AfterScenario]
    public void After()
    {
        _webServer.Dispose();
    }

    private static string GetFullUrl()
    {
        var ipAddress = IPAddress.Loopback;

        var portAvailable = GetAvailablePort(PortRangeStart, PortRangeEnd, ipAddress);

        return String.Format("http://{0}:{1}/", "localhost", portAvailable);
    }

    private static int GetAvailablePort(int rangeStart, int rangeEnd, IPAddress ip, bool includeIdlePorts = false)
    {
        IPGlobalProperties ipProps = IPGlobalProperties.GetIPGlobalProperties();

        // if the ip we want a port on is an 'any' or loopback port we need to exclude all ports that are active on any IP
        Func<IPAddress, bool> isIpAnyOrLoopBack = i => IPAddress.Any.Equals(i) ||
                                                       IPAddress.IPv6Any.Equals(i) ||
                                                       IPAddress.Loopback.Equals(i) ||
                                                       IPAddress.IPv6Loopback.
                                                           Equals(i);
        // get all active ports on specified IP.
        List<ushort> excludedPorts = new List<ushort>();

        // if a port is open on an 'any' or 'loopback' interface then include it in the excludedPorts
        excludedPorts.AddRange(from n in ipProps.GetActiveTcpConnections()
                               where
                                   n.LocalEndPoint.Port >= rangeStart &&
                                   n.LocalEndPoint.Port <= rangeEnd && (
                                   isIpAnyOrLoopBack(ip) || n.LocalEndPoint.Address.Equals(ip) ||
                                    isIpAnyOrLoopBack(n.LocalEndPoint.Address)) &&
                                    (!includeIdlePorts || n.State != TcpState.TimeWait)
                               select (ushort)n.LocalEndPoint.Port);

        excludedPorts.AddRange(from n in ipProps.GetActiveTcpListeners()
                               where n.Port >= rangeStart && n.Port <= rangeEnd && (
                               isIpAnyOrLoopBack(ip) || n.Address.Equals(ip) || isIpAnyOrLoopBack(n.Address))
                               select (ushort)n.Port);

        excludedPorts.AddRange(from n in ipProps.GetActiveUdpListeners()
                               where n.Port >= rangeStart && n.Port <= rangeEnd && (
                               isIpAnyOrLoopBack(ip) || n.Address.Equals(ip) || isIpAnyOrLoopBack(n.Address))
                               select (ushort)n.Port);

        excludedPorts.Sort();

        for (int port = rangeStart; port <= rangeEnd; port++)
        {
            if (!excludedPorts.Contains((ushort)port) && Interlocked.Read(ref _portNumber) < port)
            {
                Interlocked.Increment(ref _portNumber);

                return port;
            }
        }

        return 0;
    }
}

有谁知道如何确保我始终获得可用端口？

Answer 1

您的代码中存在问题：

if (!excludedPorts.Contains((ushort)port) && Interlocked.Read(ref _portNumber) < port)
{
    Interlocked.Increment(ref _portNumber);
    return port;
}

首先，您可以在每个测试开始时计算excludedPorts一次，并将它们存储在某个静态字段中。

其次，问题是由错误的逻辑定义端口是否可用：Interlocked.Read和Interlocked.Increment之间的其他线程可以执行相同的检查并返回相同的端口！ EG：

主题A：检查3369：它不在excludedPorts，_portNumber等于3368，因此检查通过。但是停下来，我会想一会儿......
主题B：检查3369：它不在excludedPorts，_portNumber等于3368，所以检查也通过了！哇，我很兴奋，让它Increment，然后返回3369。
主题A：好的，我们在哪里？哦，是的，Increment，并返回3369！

典型的比赛条件。您可以通过两种方式解决它：

使用CAS-operation CompareExchange from Interlocked class（您可以删除port变量，如下所示（请自行测试此代码）：

var portNumber = _portNumber;
if (excludedPorts.Contains((ushort)portNumber))
{
    // if port already taken
    continue;
}
if (Interlocked.CompareExchange(ref _portNumber, portNumber + 1, portNumber) != portNumber))
{
    // if exchange operation failed, other thread passed through
    continue;
}
// only one thread can succeed
return portNumber;

使用静态ConcurrentDictionary端口，并为它们添加新端口，如下所示（您可以选择其他集合）：

// static field in your class
// value item isn't useful
static ConcurrentDictionary<int, bool>() ports = new ConcurrentDictionary<int, bool>();

foreach (var p in excludedPorts)
    // you may check here is the adding the port succeed
    ports.TryAdd(p, true);
var portNumber = _portNumber;
if (!ports.TryAdd(portNumber, true))
{
    continue;
}
return portNumber;

在并行运行测试时获取WebApi OWIN自托管的自由端口

1 个答案: