How can the web server invoke a method on the client synchronously using SignalR? The key part here is that the server should wait for client to send data back to the server before continuing on?
Basically I'm looking to treat a client method invoke like a WCF service request. Invoke the client and wait for the data to be returned.
SignalR does not provide a way to synchronously invoke client-side methods.
To achieve the same functionality as a synchronous call, you could pass some sort of invocation ID as an argument to your client-side method. The client could then invoke a server-side method like ClientMethodCompleted with its invocation ID when the client-side method is done. Basically you will be implementing your own ACK.
If you go this route, you will have to track the client invocations along with their respective ID's on the server. You can then execute whatever logic you would have done after a synchronous call in the ClientMethodCompleted method on the server.
This should be fairly simple if you are invoking the method on only one client. If you are invoking the method on multiple clients you will have to keep track of which clients you are invoking your method on so you can ensure all the clients have acknowledged the invocation before running your followup code.
I would also make sure that you periodically clean up the data structure storing unacknowledged client invocations if you are at all worried about a DOS attack, since this would be an obvious attack vector that could allow a malicious client blowup memory consumption.
Related
Are Meteor.methods they only way to call server-side functions from the client?
http://docs.meteor.com/#/full/meteor_methods
the docs don't make it clear that they are they only way, but the fact that they exist seems to imply they are the only way. What is their purpose?
There are several ways to communicate back and forth between the server and client in Meteor :
Using Meteor.methods to perform Remote Method Invokation on the server, these calls are initiated by the client, ask for a computation to be performed on the server and receive a result.
Using the Pub/Sub mechanism, the server publishes a set of data and the client is subscribing to a subset of this data, being notified in real-time of data-updates taking place in the server and thus receiving modifications.
Using plain old HTTP requests with the HTTP module.
So Meteor.methods are not the only way to execute some code on the server upon a client request.
Their purpose is usually to update the database by providing new values for server-side collections, as a matter of fact, client-side collection inserts and updates are implemented as Meteor.methods.
The Pub/Sub mechanism is used to propagate DB updates to every connected client and to make sure they receive only the minimal subset they need.
The HTTP communication is used by the server to send the initial source code (HTML/JS/CSS) of the app on load time as well as performing standard operations such as requesting and downloading a file.
In my Camel Route I need to send message to a JMS when an Exception hits my onException handlers. To speed up the main route, I try to send the messages asynchronously via a Wiretap
I try to use something like this:
onException().handled(true).logHandled(true)
.wiretap("seda:another_queue").end();
...
from("seda:another_queue?concurrentConsumers=5")
.to("jms:queue_for_my_exception_messages");
Is it necessary to use the Wiretap, or could I go with just the SEDA queues like this:
onException().handled(true).logHandled(true)
.to("seda:another_queue").end();
...
from("seda:another_queue?concurrentConsumers=5")
.to("jms:queue_for_my_exception_messages");
You do not need to use wiretap. Only seda-queues shall work.
Wiretap pattern should be used where you want to intercept messages between components for analysis or debugging purpose.
An important difference between Wiretap and SEDA is that when consuming from polling consumers (e.g. file or ftp) only wiretap is fire-and-forget.
When a thread consuming from a polling consumer reaches a .to(seda:xx) it will hand off the exchange and continue the route as expected or consume new exchanges from the endpoint. The exchange delivered to the seda endpoint will be commited to the originating Consumer by the seda thread and not the original consumer thread. That means that if you for instance have delete=true in your polling consumer endpoint definition, the file will not be deleted before the seda thread has finished.
I need to send a asynchronous message to client from my CXF (JAX WS) webservice layer...
How client would be capable of receiving it?What steps need to be taken care to achieve this?Is there a sample tutorial available?
You have two options to achieve asynchronous calls from client with CXF.
You can poll the service for response
You can define a callback which will be executed when the server's job is done
Each solution has pros and cons, so choose according to your needs.
The polling gives you a Response object and you can test if the call is complete on it by response.isDone(). (if not, wait some time, then send another request)
The callback gives you a Future object which wraps the call, you can define an AsyncHandler for instance when you call the service to define what will be run when the process is finished.
From the server side, you should take a look at WS-Addressing (to define a replyTo endpoint for callback if needed) and WS-POLICY: http://cxf.apache.org/docs/ws-addressing.html
Note that if you need to use callbacks (it seems so), you will have to define a CXF client on the client side to enable WS-addressing (on the cxf bus).
Do I need to do anything to make all requests asynchronous or are they automatically handled that way?
I ran some tests and it appears that each request comes in on its own thread, but I figure better to ask as I might have tested wrong.
Update: (I have a bad habit of not explaining fully - sorry) Here's my concern. A client browser makes a REST request to my server of http://data.domain/com/employee_database/?query=state:Colorado. That comes in to the appropriate method in the controller. That method queries the database and returns an object which is then turned into a JSON structure and returned to the calling app.
Now let's say 10,000 clients all make a similar query to the same server. So I have 10,000 requests coming in at once. Will my controller method be called simultaneously in 10,000 distinct threads? Or must the first request return before the second request is called?
I'm not asking about the code in my handler method having asynchronous components. For my case the request becomes a single SQL query so the code has nothing that can be handled asynchronously. And until I get the requested data, I can't return from the method.
No REST is not async by default. the request are handled synchronously. However, your web server (IIS) has a number of max threads setting which can work at the same time, and it maintains a queue of the request received. So, the request goes in the queue and if a thread is available it gets executed else, the request waits in the IIS queue till a thread is available
I think you should be using async IO/operations such as database calls in your case. Yes in Web Api, every request has its own thread, but threads can run out if there are many consecutive requests. Also threads use memory so if your api gets hit by too many request it may put pressure on your system.
The benefit of using async over sync is that you use your system resources wisely. Instead of blocking the thread while it is waiting for the database call to complete in sync implementation, the async will free the thread to handle more requests or assign it what ever process needs a thread. Once IO (database) call completes, another thread will take it from there and continue with the implementation. Async will also make your api run faster if your IO operations take longer to complete.
To be honest, your question is not very clear. If you are making an HTTP GET using HttpClient, say the GetAsync method, request is fired and you can do whatever you want in your thread until the time you get the response back. So, this request is asynchronous. If you are asking about the server side, which handles this request (assuming it is ASP.NET Web API), then asynchronous or not is up to how you implemented your web API. If your action method, does three things, say 1, 2, and 3 one after the other synchronously in blocking mode, the same thread is going to the service the request. On the other hand, say #2 above is a call to a web service and it is an HTTP call. Now, if you use HttpClient and you make an asynchronous call, you can get into a situation where one request is serviced by more than one thread. For that to happen, you should have made the HTTP call from your action method asynchronously and used async keyword. In that case, when you call await inside the action method, your action method execution returns and the thread servicing your request is free to service some other request and ultimately when the response is available, the same or some other thread will continue from where it was left off previously. Long boring answer, perhaps but difficult to explain just through words by typing, I guess. Hope you get some clarity.
UPDATE:
Your action method will execute in parallel in 10,000 threads (ideally). Why I'm saying ideally is because a CLR thread pool having 10,000 threads is not typical and probably impractical as well. There are physical limits as well as limits imposed by the framework as well but I guess the answer to your question is that the requests will be serviced in parallel. The correct term here will be 'parallel' but not 'async'.
Whether it is sync or async is your choice. You choose by the way to write your action. If you return a Task, and also use async IO under the hood, it is async. In other cases it is synchronous.
Don't feel tempted to slap async on your action and use Task.Run. That is async-over-sync (a known anti-pattern). It must be truly async all the way down to the OS kernel.
No framework can make sync IO automatically async, so it cannot happen under the hood. Async IO is callback-based which is a severe change in programming model.
This does not answer what you should do of course. That would be a new question.
Is it possible to call (Post to) a Method in a ASPX (Code behind) page via HTTP endpoint in Sql server 2008/2005.
HTTP endpoints are first of all, deprecated. No new development should rely on them. Second, they have been, even for their brief lifetime, exclusively for incomming HTTP requests. HTTP endpoints can only serve a SOAP response, can never make an outbound call (GET or POST, mathers not). And last, all the points #gbn already made: never block a transaction on an outbound call. Do the business validation from a process call, before insert into the DB.
At worst, if no validation is possible before the insert, queue up a request for validation and place the data in a 'pending' state in the trigger, then commit. Then an external process can scan that queue and service the validation requests. You can Use Tables as Queues.
And no, CLR Web calls from triggers are no a solution (I'm sure some will mention them)...