I've heard a LOT in the past about how programming with Threads and Tasks is very dangerous to the naive. Well, I'm naive, but I've got to learn sometime. I am making a program (really, it's a Generic Handler for ASP.Net) that needs to call to a 3rd party and wait for a response. While waiting, I'd like to have the handler continue doing some other things, so I am trying to figure out how to do the 3rd party web request asynchronously. Based on some answers to some other questions I've received, here is what I've come up with, but I want to make sure I won't get into big problems when my handler is called multiple time concurrently.
To test this I've built a console project.
class Program
{
static void Main(string[] args)
{
RunRequestAsynch test = new RunRequestAsynch();
test.TestingThreadSafety = Guid.NewGuid().ToString();
Console.WriteLine("Started:" + test.TestingThreadSafety);
Task tTest = new Task(test.RunWebRequest);
tTest.Start();
while (test.Done== false)
{
Console.WriteLine("Still waiting...");
Thread.Sleep(100);
}
Console.WriteLine("Done. " + test.sResponse);
Console.ReadKey();
}
}
I instantiate a separate object (RunRequestAsynch) set some values on it, and then start it. While that is processing I'm just outputting a string to the console window.
public class RunRequestAsynch
{
public bool Done = false;
public string sResponse = "";
public string sXMLToSend = "";
public string TestingThreadSafety = "";
public RunRequestAsynch() { }
public void RunWebRequest()
{
Thread.Sleep(500);
// HttpWebRequest stuff goes here
sResponse = TestingThreadSafety;
Done = true;
Thread.Sleep(500);
}
}
So...if I run 1000 of these simultaneously, I can count on the fact that each instance has its own memory and properties, right? And that the line "Done = true;" won't fire and then every one of the instances of the Generic Handler die, right?
I wrote a .bat file to run several instances, and the guid I set on each specific object seems to stay the same for each instance, which is what I want...but I want to make sure I'm not doing something really stupid that will bite me in the butt under full load.
I don't see any glaring problems, however you should consider using the Factory.StartNew instead of Start. Each task will only be executed once, so there isn't any problem with multiple tasks running simultaneously.
If you want to simplify your code a little and take advantage of the Factory.StartNew, in your handler you could do something like this (from what I remember of your last question):
Task<byte[]> task = Task.Factory.StartNew<byte[]>(() => // Begin task
{
//Replace with your web request, I guessed that it's downloading data
//change this to whatever makes sense
using (var wc = new System.Net.WebClient())
return wc.DownloadData("Some Address");
});
//call method to parse xml, will run in parallel
byte[] result = task.Result; // Wait for task to finish and fetch result.
Related
I am working on making a scheduler, just like Windows Scheduler using Quartz.Net.
In Windows Scheduler, there is an option to stop a task from running if it takes more than the specified time. I have to implement the same in my scheduler.
But I am not able to find any extension method/setting to configure Trigger or Job accordingly.
I request some inputs or suggestions for it.
You can write small code to set a custom timout running on another thread. Implement IInterruptableJob interface and make a call to its Interrupt() method from that thread when the job should be interrupted. You can modify the following sample code as per your need. Please make necessary checks/config inputs wherever required.
public class MyCustomJob : IInterruptableJob
{
private Thread runner;
public void Execute(IJobExecutionContext context)
{
int timeOutInMinutes = 20; //Read this from some config or db.
TimeSpan timeout = TimeSpan.FromMinutes(timeOutInMinutes);
//Run your job here.
//As your job needs to be interrupted, let us create a new task for that.
var task = new Task(() =>
{
Thread.Sleep(timeout);
Interrupt();
});
task.Start();
runner = new Thread(PerformScheduledWork);
runner.Start();
}
private void PerformScheduledWork()
{
//Do what you wish to do in the schedled task.
}
public void Interrupt()
{
try
{
runner.Abort();
}
catch (Exception)
{
//log it!
}
finally
{
//do what you wish to do as a clean up task.
}
}
}
When calling WebMethod on a Webpage using jQuery. We define this as static.
However static methods always have one instance. What happens when multiple web requests are made.
Does it really happen asynchronously or
all the requests are pipelined waiting for the WebMethod to accept the requests?
I created a sample console program to simulate the scenario on static method work & found them to execute in sequential order.
class Program
{
static int count = 10;
static void Main(string[] args)
{
new Program().foobar();
Console.ReadLine();
}
public void foobar()
{
Parallel.Invoke(() => work("one"), () => work("two"), () => work("three"), ()=> work("four"));
}
static void work(string str)
{
Thread.Sleep(3000);
count++;
Console.WriteLine(str + " " + count);
}
}
Can you please put some light on this concept?
They will not execute sequentially. If you created multiple apps in a client server scenario it would be a better example since your console app inherently runs everything sequentially.
That said, with the static methods you just need to be aware of shared resources, data, etc. Local data is fine.
I want to use Rollback() or commit() functions after multiple process.
There is no error, but it does not commit() to update DB.
Here is my example code,
public void startTransaction(){
using(Ads_A_Connection = new AdsConnection(Ads_A_connection_string))
using(Ads_B_Connection = new AdsConnection(Ads_B_connection_string))
{
Ads_A_Connection.Open();
Ads_B_Connection.Open();
AdsTransaction aTxn = Ads_A_Connection.BeginTransaction();
AdsTransaction bTxn = Ads_B_Connection.BeginTransaction();
try{
string aResult = this.process1(Ads_A_Connection);
this.process2(Ads_B_Connection, aResult);
this.process3(Ads_A_Connection. Ads_B_Connection);
aTxn.Commit();
bTxn.Commit();
// there is no error, but it couldn't commit.
}catch(Exception e){
aTxn.Rollback();
bTxn.Rollback();
}
}
}
public string process1(conn){
// Insert data
return result;
}
public void process2(conn. aResult){
// update
}
public void process3(aConn, bConn){
// delete
// update
}
I guess, its because out of using scope. because I tried to put all the code into
startTransaction() method, then it works. but it look too dirty.
How can I use rollback() or commit() after multiple (METHOD) process?
anybody know, please advice me.
Thanks!
[EDIT]
I just add TransactionScope before connection,
using (TransactionScope scope = new TransactionScope())
{
using(Ads_A_Connection = new AdsConnection(Ads_A_connection_string))
using(Ads_B_Connection = new AdsConnection(Ads_B_connection_string))
{
.
.
but it makes an error, it say "Error 5047: The transaction command was not in valid sequence."
I need a little more hint please :)
To extend what Etch mentioned, their are several issues with manually managing transactions on your connections:
You need to pass the SQL connection around your methods
Need to manually remember to commit or rollback when you are finished
If you have more than one connection to manage under a transaction, you should really use DTC or XA to enroll the transactions into a Distributed / 2 phase transaction.
TransactionScopes are supported with the Advantage Database Server, although you will need to enable the MSDTC service and possibly also enable XA compliance.
Note that I'm assuming that the advantage .NET client has some sort of connection pooling mechanism - this makes the cost of obtaining connections very lightweight.
Ultimately, this means that your code can be refactored to something like the following, which is easier to maintain:
private void Method1()
{
using(Ads_A_Connection = new AdsConnection(Ads_A_connection_string))
{
Ads_A_Connection.Open();
string aResult = this.process1(Ads_A_Connection);
} // Can logically 'close' the connection here, although it is actually now held by the transaction manager
}
private void Method2()
{
using(Ads_B_Connection = new AdsConnection(Ads_B_connection_string))
{
Ads_B_Connection.Open();
this.process2(Ads_B_Connection, aResult);
} // Can logically 'close' the connection here, although it is actually now held by the transaction manager
}
public void MyServiceWhichNeedToBeTransactional(){
using(TransactionScope ts = new TransactionScope()) { // NB : Watch isolation here. Recommend change to READ_COMMITTED
try{
Method1();
Method2();
ts.Complete();
}
catch(Exception e){
// Do Logging etc. No need to rollback, as this is done by default if Complete() not called
}
}
}
TransactionScope is your friend!
TransactionScope
I want to make a service that notify the user in case there are some new messages sent to him. Thus I want to use some Comet framework that provide the server push ability. So I have looked into PokeIn.
Just wondering a thing. I have checked on the samples that they have on the website. None of them look into the database to retrieve new entries if there are some. But it is just a matter of modification to it I guess.
One of the sample implement this long polling by using a sleep on the server side. So if I use the same approach I can check the database, if there are any new entries, every 5 seconds. However this approach doesn't seem to be much different from when using polling on the client side with javascript.
This part is from a sample. As can be seen they put a sleep there for to update current time for everybody.
static void UpdateClients()
{
while (true)
{
//.. code to check database
if (CometWorker.ActiveClientCount > 0)
{
CometWorker.SendToAll(JSON.Method("UpdateTime", DateTime.Now));
}
Thread.Sleep(500);
}
}
So I wonder is this how I should implement the message notifier? It seems that the above approach is still going to push a huge load demand on the server side. The message notifier is intend to work same way as the one found Facebook.
You shouldn't implement this way, that sample is only implemented like that because the keep PokeIn related part is clear. You should implement SQL part as mentioned http://www.codeproject.com/Articles/12335/Using-SqlDependency-for-data-change-events
in order to track changes on database.
So, when you have something to send, call one of the PokeIn methods for the client side delivery. I don't know, how much your application is time critical because in addition to reverse ajax, PokeIn's internal websocket feature is very easy to activate and delivers messages to client quite fast.
You can do this with database as #Zuuum said, but I implemented it in a different way.
I'm using ASP.NET MVC with PokeIn and EF in a Windows Azure environment:
I have domain events similar to this approach: Strengthening your domain: Domain Events
When someone invokes an action, that's a Unit of Work
If that UOW succeeds then I raise a domain event (e.g. ChatMessageSent)
I have subscribers for these domain events so they can receive the event and forward the message to the PokeIn listeners
I use this pattern for all my real-time needs on my game site (making moves, actions etc in a game), I don't want to advertise it here, you can find it through me if you want.
I always use this pattern as a duplex communication solution so everybody gets their update via PokeIn, even the user who invoked the action so every client will behave the same. So when someone calls an action it won't return anything except the success signal.
The next examples are won't work because they are only snippets to demonstrate the flow
Here is an action snippet from my code:
[HttpPost]
[UnitOfWork]
[RestrictToAjax]
[ValidateAntiForgeryToken]
public JsonResult Post(SendMessageViewModel msg)
{
if (ModelState.IsValid)
{
var chatMessage = new ChatMessage
{
ContainerType = msg.ContainerType,
ContainerID = msg.ContainerID,
Message = _xssEncoder.Encode(msg.Message),
User = _profileService.CurrentUser
};
_chatRepository.AddMessage(chatMessage);
OnSuccessfulUoW = () => EventBroker.Current.Send(this, new ChatMessageSentPayload(chatMessage));
}
return Json(Constants.AjaxOk);
}
And the (simplified) EventBroker implementation:
public class UnityEventBroker : EventBroker
{
private readonly IUnityContainer _container;
public UnityEventBroker(IUnityContainer container)
{
_container = container;
}
public override void Send<TPayload>(object sender, TPayload payload)
{
var subscribers = _container.ResolveAll<IEventSubscriber<TPayload>>();
if (subscribers == null) return;
foreach (var subscriber in subscribers)
{
subscriber.Receive(sender, payload);
}
}
}
And the even more simplified subscriber:
public class ChatMessageSentSubscriber : IEventSubscriber<ChatMessageSentPayload>
{
public void Receive(object sender, ChatMessageSentPayload payload)
{
var message = payload.Message;
var content = SiteContent.Global;
var clients = Client.GetClients(c => c.ContentID == message.ContainerID && c.Content == content)
.Select(c => c.ClientID)
.ToArray();
var dto = ObjectMapper.Current.Map<ChatMessage, ChatMessageSentDto>(message);
var json = PokeIn.JSON.Method("pokein", dto);
CometWorker.SendToClients(clients, json);
}
}
I am learning WF4 and got stuck at the following place. Please help.Thanks.
1) I have created a static method, MyMethod in a static class called Worker. Within this method I call Thread.Sleep(3000) and then print "MyMethod" called.
2) I then created an activity, DoWork (DoWork.xaml) which consists of a InvokeMethod (The target type is the Worker class in step 1 and MethodName = MyMethod).
3) In the main method, I call 2 methods called OutputSequence() and OutputParallel() which are as follows
private static void OutputSequence()
{
Sequence s = new Sequence() { Activities = new DoWork(), new DoWork() } };
WorkflowInvoker.Invoke(s);
}
private static void OutputParallel()
{
Parallel p = new Parallel() { Branches = new DoWork(), new DoWork() } };
WorkflowInvoker.Invoke(p);
}
The OutputSequence() is OK as it calls the target method twice (in sequence) but the parallel one seems to execute sequentially as well. I expected it to execute in parallel.
What am I missing.
The Parallel activity is not what you think it is - it allows you to wait for things in parallel not to execute CPU based code in parallel. The WF4 threading mode is that there is exactly one thread at a time active in the workflow.
If you put two delays in the parallel then both of those waits would occur in parallel as opposed to sequentially as they would in a sequence
The idea is you want to wait for a number of actions when you don;t know the order in which they will occur. Then the parallel activity is complete when all of its child branches have completed
Actually Parallel activity really executes all branches one-by-one and has nothing related to concurrent code execution, like two thread do.
But there is MS sample, that shows "true" concurrent execution for blocks inside of parallel activity. There is the AsyncCodeActivity in the .net 4 that allows to get concurrent execution of activities. Please check http://msdn.microsoft.com/en-us/library/ee358731(VS.100).aspx
Below you can find copy-pasted sample from link above:
public sealed class GenerateRandom : AsyncCodeActivity<int>
{
static Random r = new Random();
protected override IAsyncResult BeginExecute(AsyncCodeActivityContext context, AsyncCallback callback, object state)
{
// Create a delegate that references the method that implements
// the asynchronous work. Assign the delegate to the UserState,
// invoke the delegate, and return the resulting IAsyncResult.
Func<int> GetRandomDelegate = new Func<int>(GetRandom);
context.UserState = GetRandomDelegate;
return GetRandomDelegate.BeginInvoke(callback, state);
}
protected override int EndExecute(AsyncCodeActivityContext context, IAsyncResult result)
{
// Get the delegate from the UserState and call EndInvoke
Func<int> GetRandomDelegate = (Func<int>)context.UserState;
return (int)GetRandomDelegate.EndInvoke(result);
}
int GetRandom()
{
// This activity simulates taking a few moments
// to generate the random number. This code runs
// asynchronously with respect to the workflow thread.
Thread.Sleep(5000);
return r.Next(1, 101);
}
}
hope this will help for someone else