I would like to know what is the best method to get data in iPhone as soon as a user entered or modified data in server. I can send a request for a small time interval to server to check any modifications done in server(Like Polling). I know it is very awkward. Pleas suggest a best one !!!
EDIT
I am not talking about push notifications. I need some Data something like while having a cricket match, when each time score updates in server I need to get that data (via XML,JSON, or any other medium) in my iPhone.
You're talking about push notifications: http://developer.apple.com/library/mac/#documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/ApplePushService/ApplePushService.html
These let you send specific messages from your server, to devices that opt in to receiving push notifications from your app.
What you are looking for is known as "Push Technology" (there are several variations of the same idea). In your case, what I think is best suited is "long polling". In short:
you poll specifying a very long timeout;
the server will not reply until it has some new data, so your request will be kept open as long as timeouts allow;
as soon as the server has got new data, it will reply, and you get the changes immediately;
when the timeout expires, you send a new request.
The fact of having a long poll will reduce the overhead you are worried about with "short" polling. Indeed, with short polls the idea is sending frequent requests, with a very short round-around time. This will make you send constantly requests to check for new data. With long polling you send a request only when you have got new data, or when a timeout fires (which can be several minutes).
In this S.O. post, you will find a way to implement it.
Related
I'm making a simple mmorpg server with IOCP.
I implemented a simple movement function so I tested with dummy clients(also IOCP).
Everything works fine only when few clients are connected. After around 500~1000 clients are connected, some dummy clients occasionally read weird data. I checked that server sends data as I expected but when it comes to dummy clients reading them, they read random data.
My guess is that it could be related to operation system's recv buffer being overflowed but I'm only guessing right now... I have no idea how to check them.
Any suggestion would be very thankful!
The problem with too many WSASends doesn't usually manifest as corrupted data; that's more likely to be a bug in your code. Perhaps your problem is caused by you failing to manage the lifetime of the buffer that is being used to send data correctly? It needs to stay stable until you get the completion for the WSASend call. If you were reusing it sooner than that then you would corrupt the data being sent.
The reason this may show up when you have lots of WSASends outstanding to lots of clients is that the send operations may be taking longer to complete and so make it more likely that your bug will be hit...
It doesn't matter how many WSASends you issue as long as your clients are able to receive the data as fast as you can send it. As soon as you are sending faster than they can receive then there will be problems. I address these problems in this answer.
I'm working with an API which only permits a maximum of 5 requests per second. If this limit is exceeded the API returns a 429 server error.
My intuition says that to handle this, I should put all requests into some form of serial queue, and enforce a delay of 0.21s between requests, but I'm not quite sure how to accomplish this. I'm also not sure if using a serial queue is a good idea, as then I'll lose the ability to have multiple requests running at the same time.
I am using adapter and retrier objects to handle refreshing my OAuth session token, so I guess this may be a good place to put my logic.
Has anyone done something like this before, or have any ideas?
Actually I'd probably go a different direction, rather than trying to throttle all requests, I'd look at the response from each request and if it's a 429, I'd re-queue the request via an async closure with a 1 second time delay.
This means that as long as requests are coming in slowly they are executed immediately. But when you try the 6th request, it's shifted into the next second.
The only problem you're going to have to consider (regardless of solution) is what happens if requests keep coming in faster than the API will allow. ie. what happens if you get 6, or 7 or 100 requests per second, for every second? How are you going to deal with the extra requests that will never get executed.
At some point your code is going to have to start failing requests. Alternatively you need to push the server people to run up more servers or give you more bandwidth.
In my conversation dialogflow, I would like to add some progress messages like hang in with me, I'm looking up for that data or similar in the conversation. Is there any guidance or best practice to do this?
Unfortunately, there is no good way to do this at this time. If your webhook takes longer than about 5 seconds, Dialogflow will return one of the default responses it is set with. If you're not using Dialogflow, the Action SDK will say your webhook isn't responding and will close the conversation.
There is currently no way to send a reply, and then send another reply without the user saying something first.
One workaround might be to have the default response be something like "I'm looking that information up. Ask me again in a few seconds." When your lookup finally completes, cache the information so when/if the user asks the question again, you can return it more quickly.
Depending how long it takes, you may also wish to register a dynamic reprompt. This will send an event to your webhook if the user doesn't say anything. In a situation like this, they may say nothing for a few seconds, but that may be long enough for you to have computed the reply. So after a few seconds of silence you can suddenly announce "I've figured it out, the answer you were looking for is..." or something similar. This has some limitations - you can only reprompt twice like this before Google sends you a final reprompt and closes the conversation.
Although the platform does support notifications, these are still in developer preview and don't work with all devices. They also don't quite continue the conversation (it doesn't just start talking) - they just send a notification to a phone that there is a message and that they can restart the conversation. Depending on your use case, this may be useful combined with the above.
Update
The Media Response includes a feature that we can take advantage of to handle this. Similar to the dynamic reprompt method above, you'll get a call automatically when the media you're playing ends. So you can play a short "hold music" and your webhook will be called when it is finished. You can then either give the result or say you're still working on it and play more hold music.
I am working on a chat client. To get new messages (or post new one) I have to perform GET (or POST) request. All new messages are stored via core data. At the moment I don't know how to implement it in most optimal way.
My thoughts:
On view controller init stage create background thread which will periodically checks for new messages (if conversation is active - with short period, if not - with period about 60 secs). If there are new messages, we store them in DB and signal delegate that there are new messages to display.
Friend suggested to use performSelector afterDelay, but I don't understand how to use it in my app.
Something else?
Thanks in advance.
Don't use performSelector afterDelay. Using NSTimer is much better (as the trigger for starting the next download). Also, use NSOperationQueue to manage your background tasks. Create yourself a custom NSOperation that you can instantiate and it will complete your request process. When you create a new operation to check for new messages, check if one is already in progress (there is no point having multiple requests in progress at the same time).
Other notes:
Make sure you consider the threading with regards to the Core Data store (having the operation call back to the main thread with the results will probably be easiest as the result data will always be relatively small).
If you have lots of messages being sent and you want to show constant status (like Skype does, showing you when someone is typing) you would need to use sockets to keep the connection alive the whole time (the cost of new connections each time would be prohibitive).
I just got asked to reduce the traffic made by my GWT app. There is one method that checks for status.
This method is an asynchronous call wrapped in a Timer. I know web apps are stateless and all that, but I do wonder if there is some other way to do this, or if everyone has a Timer wrapped around a call when they need this kind of behaviour.
You can check out gwteventservice. It claims to have a way to push server events and notify the client.
I have a feeling they might be implemented as long running (hanging) client to server RPC calls which time out after an interval (say 20sec), and then are re-made. The server returns the callback if an event happens in the meanwhile.
I haven't used it personally but know of people using it to push events to the client. Have a look at the docs . If my assumption is correct, the idea is to send an RPC call to the server which does not return (hangs). If an event happens on the server, the server responds and that RPC call returns with the event. If there is no event, the call will time out in 20 seconds. Then a new call is made to the server which hangs in the same way until there is an event.
What this achieves is that it reduces the number of calls to the server to either one for each event (if there is one), or a call once every 20 seconds (if there isn't one). It looks like the 20 sec interval can be configured.
I imagine that if there is no event the amount of data sent back will be minimal - it might be possible to cancel the callback entirely, or have it fail without data transfer, but I don't really know.
Here is another resource on ServerPush - which is likely what's implemented by gwteventservice.
Running on Google app engine you could use they Channel technology
http://code.google.com/intl/en-US/appengine/docs/java/channel/overview.html
If you need the client to get the status from the server, then you pretty much have to make a call to the server to get it's status.
You could look at reducing the size of some of your messages
You could wind back the timer so the status call goes out less often
You could "optimise" so that the timer gets reset when some other client/server IO happens (i.e. if the server replies you know it is ok, so you don't need to send the next status request).