持久双工

本主题适用于 Windows Workflow Foundation 4。

当工作流服务要求向初始调用方发送回调时，持久双工相关性（也称为回调相关性）非常有用。与 WCF 双工不同的是，该回调可以在将来的任何时间发生，并且不会绑定到同一通道或通道生存期；唯一要求是，调用方应具有一个用于侦听回调消息的活动终结点。这样，这两个工作流服务便可在长期运行的对话中进行通信。本主题概述了持久双工相关性。

使用持久双工相关性

若要使用持久双工相关性，这两个服务必须使用启用了上下文且支持双向操作的绑定，如 NetTcpContextBinding 或 WSHttpContextBinding。调用服务使用所需绑定向其客户端 Endpoint 注册 ClientCallbackAddress。接收服务将接收初始调用中的上述数据，然后在回调调用服务的 Send 活动中对自己的 Endpoint 使用此数据。在本示例中，这两个服务互相通信。第一个服务对第二个服务调用某个方法，然后等待答复。第二个服务知晓回调方法的名称，但在设计时，实现该方法的服务的终结点是未知的。在下面的示例中，使用 WSHttpContextBinding 承载工作流服务，该服务将创建回调 Endpoint。

// Host WF Service 1.
string baseAddress1 = "https://localhost:8080/Service1";
WorkflowServiceHost host1 = new WorkflowServiceHost(GetWF1(), new Uri(baseAddress1));

// Add the callback endpoint.
WSHttpContextBinding Binding1 = new WSHttpContextBinding();
host1.AddServiceEndpoint("ICallbackItemsReady", Binding1, "ItemsReady");

// Add the service endpoint.
host1.AddServiceEndpoint("IService1", Binding1, baseAddress1);

// Open the first workflow service.
host1.Open();
Console.WriteLine("Service1 waiting at: {0}", baseAddress1);

实现此工作流服务的工作流通过其 Send 活动初始化回调相关性，并从与 Send 相关的 Receive 活动引用此回调终结点。下面的示例表示通过 GetWF1 方法返回的工作流。

Variable<CorrelationHandle> CallbackHandle = new Variable<CorrelationHandle>();

Receive StartOrder = new Receive
{
    CanCreateInstance = true,
    ServiceContractName = "IService1",
    OperationName = "StartOrder"
};

Send GetItems = new Send
{
    CorrelationInitializers = 
    {
        new CallbackCorrelationInitializer
        {
            CorrelationHandle = CallbackHandle
        }
    },
    ServiceContractName = "IService2",
    OperationName = "StartItems",
    Endpoint = new Endpoint
    {
        AddressUri = new Uri("https://localhost:8081/Service2"),
        Binding = new WSHttpContextBinding
        {
            ClientCallbackAddress = new Uri("https://localhost:8080/Service1/ItemsReady")                        
        }
    }
};

Receive ItemsReady = new Receive
{
    ServiceContractName = "ICallbackItemsReady",
    OperationName = "ItemsReady",
    CorrelatesWith = CallbackHandle,
};

Activity wf = new Sequence
{
    Variables =
    {
        CallbackHandle
    },
    Activities =
    {
        StartOrder,
        new WriteLine
        {
            Text = "WF1 - Started"
        },
        GetItems,
        new WriteLine
        {
            Text = "WF1 - Request Submitted"
        },
        ItemsReady,
        new WriteLine
        {
            Text = "WF1 - Items Received"
        }
     }
};

使用系统提供的基于上下文的绑定来承载第二个工作流服务。

// Host WF Service 2.
string baseAddress2 = "https://localhost:8081/Service2";
WorkflowServiceHost host2 = new WorkflowServiceHost(GetWF2(), new Uri(baseAddress2));

// Add the service endpoint.
WSHttpContextBinding Binding2 = new WSHttpContextBinding();
host2.AddServiceEndpoint("IService2", Binding2, baseAddress2);

// Open the second workflow service.
host2.Open();
Console.WriteLine("Service2 waiting at: {0}", baseAddress2);

实现此工作流服务的工作流以 Receive 活动开头。此 Receive 活动初始化此服务的回调相关性，延迟一段时间以模拟长时间运行的工作，然后使用第一次调用第一个服务时传递的回调上下文回调来该服务。下面的示例表示通过调用 GetWF2 返回的工作流。请注意，Send 活动包含占位符地址 https://www.contoso.com；在运行时使用的实际地址即为提供的回调地址。

Variable<CorrelationHandle> ItemsCallbackHandle = new Variable<CorrelationHandle>();

Receive StartItems = new Receive
{
    CorrelationInitializers = 
    {
        new CallbackCorrelationInitializer
        {
            CorrelationHandle = ItemsCallbackHandle
        }
    },
    CanCreateInstance = true,
    ServiceContractName = "IService2",
    OperationName = "StartItems"
};

Send ItemsReady = new Send
{
    CorrelatesWith = ItemsCallbackHandle,
    Endpoint = new Endpoint
    {
        // The callback address on the binding is used
        // instead of this placeholder address.
        AddressUri = new Uri("https://www.contoso.com"),

        Binding = new WSHttpContextBinding()
    },
    OperationName = "ItemsReady",
    ServiceContractName = "ICallbackItemsReady"
};

Activity wf = new Sequence
{
    Variables =
    {
        ItemsCallbackHandle
    },
    Activities =
    {
        StartItems,
        new WriteLine
        {
            Text = "WF2 - Request Received"
        },
        new Delay
        {
            Duration = TimeSpan.FromMinutes(90)
        },
        new WriteLine
        {
            Text = "WF2 - Sending items"
        },
        ItemsReady,
        new WriteLine
        {
            Text = "WF2 - Items sent"
        }
     }
};

当对第一个工作流调用 StartOrder 方法时，将显示以下输出，该输出显示经过两个工作流的执行流。

Service1 waiting at: https://localhost:8080/Service1Service2 waiting at: https://localhost:8081/Service2Press enter to exit.WF1 - StartedWF2 - Request ReceivedWF1 - Request SubmittedWF2 - Sending itemsWF2 - Items sentWF1 - Items Received

在本示例中，两个工作流均使用 CallbackCorrelationInitializer 显式管理相关性。由于上述示例工作流中仅存在一个相关性，因此默认的 CorrelationHandle 管理足以满足需求。