HPC Pack 2016 Job and Task Events in SignalR

Article
06/08/2020

You can receive HPC Pack Job and Task events in a SingalR client. There're various clients for different programming languages. Here we take C# for an example of how to receive Job and Task events.

Install the C# client Microsoft.AspNet.SignalR.Client.
using Microsoft.AspNet.SignalR.Client and Microsoft.AspNet.SignalR.Client.Transports in your code.

Then you create an instance of HubConnection like:

var hubConnection = new HubConnection(url)

Here the url is "https://{your-cluster-name-or-ip}/hpc".

You can optionally trace errors of the connection by

var hubConnection = new HubConnection(url) { TraceLevel = TraceLevels.All, TraceWriter = Console.Error };

And you can also add an error handler like:

hubConnection.Error += ex => Console.Error.WriteLine($"HubConnection Exception:\n{ex}");

You must provide credential for accessing the events. HTTP Basic Auth is used here:

hubConnection.Headers.Add("Authorization", BasicAuthHeader(username, password));

Then you create hub proxy objects from the hub connection and listen for events from them.

For Job events, you create a JobEventHub and listen to the JobStateChange event:

var jobEventHubProxy = hubConnection.CreateHubProxy("JobEventHub");
jobEventHubProxy.On("JobStateChange", (int id, string state, string previousState) =>
{
  Console.WriteLine($"Job: {id}, State: {state}, Previous State: {previousState}");
});

For Task events, you create a TaskEventHub and listen to the TaskStateChange event:

var taskEventHubProxy = hubConnection.CreateHubProxy("TaskEventHub");
taskEventHubProxy.On("TaskStateChange", (int id, int taskId, int instanceId, string state, string previousState) => 
{
  Console.WriteLine($"Job: {id}, Task: {taskId}, Instance: {instanceId}, State: {state}, Previous State: {previousState}");
});

Then you connect to the server by
```
await hubConnection.Start(new WebSocketTransport())
```
Here we explicitly specify the WebSocketTransport. SignalR supports various ways of transport. But we choose WebSocket. You may not get any events or fail to connect at all if you use transport other than WebSocket.
At last, you call BeginListen method on the hub proxy object to start listening. You must specify the job id which you want to listen to its job/task events.
```
try
{
  await jobEventHubProxy.Invoke("BeginListen", jobId);
  await taskEventHubProxy.Invoke("BeginListen", jobId);
}
catch (Exception ex)
{
  Console.Error.WriteLine($"Exception on invoking server method:\n{ex}");
  return null;
}
```
The catch block will catch errors on server when invoking the BeginListen method. For other errors on hub connection, you may need to use an error handler like the one in previous step.

The whole code snippet is:

using Microsoft.AspNet.SignalR.Client;
using Microsoft.AspNet.SignalR.Client.Transports;

//...

string BasicAuthHeader(string username, string password)
{
    string credentials = $"{username}:{password}";
    byte[] bytes = Encoding.ASCII.GetBytes(credentials);
    string base64 = Convert.ToBase64String(bytes);
    return $"Basic {base64}";
}

async Task<HubConnection> ListenToJobAndTasks(string url, int jobId, string username, string password)
{
    var hubConnection = new HubConnection(url) { TraceLevel = TraceLevels.All, TraceWriter = Console.Error };
    hubConnection.Headers.Add("Authorization", BasicAuthHeader(username, password));
    hubConnection.Error += ex => Console.Error.WriteLine($"HubConnection Exception:\n{ex}");

    var jobEventHubProxy = hubConnection.CreateHubProxy("JobEventHub");
    jobEventHubProxy.On("JobStateChange", (int id, string state, string previousState) =>
    {
        Console.WriteLine($"Job: {id}, State: {state}, Previous State: {previousState}");
    });

    var taskEventHubProxy = hubConnection.CreateHubProxy("TaskEventHub");
    taskEventHubProxy.On("TaskStateChange", (int id, int taskId, int instanceId, string state, string previousState) =>
    {
        Console.WriteLine($"Job: {id}, Task: {taskId}, Instance: {instanceId}, State: {state}, Previous State: {previousState}");
    });

    Console.WriteLine($"Connecting to {url} ...");
    try
    {
        await hubConnection.Start(new WebSocketTransport());
    }
    catch (Exception ex)
    {
        Console.Error.WriteLine($"Exception on starting:\n{ex}");
        return null;
    }

    Console.WriteLine($"Begin to listen...");
    try
    {
        await jobEventHubProxy.Invoke("BeginListen", jobId);
        await taskEventHubProxy.Invoke("BeginListen", jobId);
    }
    catch (Exception ex)
    {
        Console.Error.WriteLine($"Exception on invoking server method:\n{ex}");
        return null;
    }

    return hubConnection;
}

HPC Pack 2016 Job and Task Events in SignalR

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