Is it possible to get the last added value or previous values from a StreamController.broadcast / Stream.
Basically I have some subscriptions to streams like on('data') and on('ready') and I want for example that if someone listens to on('ready') after the event was triggered they can get the last value from the broadcast stream, eg. 'I\'m ready'.
Something like:
StreamController x = StreamController.broadcast();
first = x.first.then(doSomething);
x.add('oneOffEvent');
// first ~ 'oneOffEvent'
x.close()
other = x.last.then(doSomethingElse);
// other ~ 'oneOffEvent'
Is this even possible without caching the value somewhere else?
Broadcast Streams, by design, do not wait for subscriptions to fire events.
You can, however, do both a first and last subscription before adding events.
Add many subscriptions. That's the upside of broadcast subscriptions.
Related
I have a rule chain in ThingsBoard that does a Create Alarm when temperature is outside threshold and does a Clear Alarm otherwise. I receive a message using a Telegram bot when these events occur. That all works fine.
However when the temperature is hovering around the threshold, I can get many notifications as it goes in and out of the threshold temperature. That is somewhat annoying.
I would like to have the Clear Alarm activity only trigger if it is more than 5 minutes (say) since the last Create Alarm event was triggered.
Any tips on how to achieve this?
I finally worked out how to do this.
I added some server attributes to my device that define the temperatures that trigger alarms. I have a rule chain for controlling these alarms with the following nodes:
Enrichment - originator attributes to add the relevant attributes into the metadata associated with this message
Filter - script to detect if the temperature is outside the expected range
Filter - script to detect if the delay period has expired since the last time the alarm was triggered
Action - create alarm when script detects that temp is out of range
Action - clear alarm when script detects that delay period has expired
Transformation - script to update last alarm time attribute
Action - save attributes to persist updated alarm time attribute
Transformation - script to create a message about alarm set or cleared
Rule chain to handle sending the message to a Telegram bot
As an example, here is the script for checking if the delay period has expired before clearing the alarm:
var alarmTime = Number(metadata.ss_lastWaterTempAlarmTime);
var alarmDelay = Number(metadata.ss_clearAlarmTimeDelay);
return metadata.ts >= alarmDelay + alarmTime;
ss is the prefix added for server side attributes that have been added to metadata.
You can see the complete rule chain json in my Aquamon repo.
After logon, i would like to send a chat message to the Guild channel.
I'm currently listening for events:
PLAYER_ENTERING_WORLD
GUILD_ROSTER_UPDATE
Once those have fired (in order), i'd like to send a chat message. However, it never sends.
Code:
print("Should_send")
SendChatMessage(msgToSend, "GUILD");
It's also worth noting that if i then trigger this manually, it works.
I do see the "Should_send" print statement appearing in the default chat window each time - as expected. I've also checked that "msgToSend" contains content - and is less than 255 characters.
So, when can i call SendChatMessage?
Ok, in order to be able to send a chat message to guild, you need to wait for the event "CLUB_STREAM_SUBSCRIBED" to fire.
This is due to the Guild channel becoming a "community" channel of sorts - previously, it seems this wasn't required.
So, adding an event listener:
frame:RegisterEvent("CLUB_STREAM_SUBSCRIBED");
Resolves the issue.
You will likely need to set a flag for the event, then print later on another event.
You can send chat messages any time after you see the welcome message or after the welcome message was posted. Which is pretty soon after you able to receive events from your frames.
Here is what I would do to complete a similar mission:
Just put your send code in a macro to test it first. Don't worry about timing the message until you see it work in a macro.
You can make your own print to send generic messages to the chat window which should always work similar to:
function MyPrint( msg, r, g, b, frame, id)
(frame or DEFAULT_CHAT_FRAME):AddMessage(msg, r or 1, g or 1, b or 0, id or 0)
end
-- put these in your event handlers
MyPrint("event PLAYER_ENTERING_WORLD")
MyPrint("event GUILD_ROSTER_UPDATE")
And use that for debugging instead.
You need to divide and conquer the problem, because there are so many things that could be wrong causing your issue, no one here can really have a definitive answer.
I know for sure that if you try to write to chat before the welcome message with print it at least used to not work. I remember spooling messages in the past until a certain event had fired then printing them.
Flux<Integer> shared = Flux.just(1, 2).share();
shared.subscribe(System.out::println);
shared.subscribe(System.out::println);
Since share() turns the flux into a hot one, I expect the first subscriber to get all values and the second one to get none, since the stream has completed at the time of subscription. But the output is the same as without share: 1 2 1 2, but it should be just 1 2.
When I replace share() with publish.autoconnect() it works as expected. Why is that?
The answer is simple, but it took me a while to figure it out.
share() is a shortcut for publish().refCount(). refCount() is like autoConnect() except for one additional feature: It disconnects when all subscribers have cancelled or - and that's the situation here - the stream has completed.
The first shared.subscribe creates a subscription (via share) to the original flux. All values are emitted immediately, the stream completes, the subscription is cancelled.
Since there is no subscription now, the second shared.subscribe again creates a subscription and the stream starts again, from the beginning.
autoConnect, however, does not cancel the subscription. If you use it instead of refCount the subscription to the original flux remains, but because the stream has completed, any additional subscriber won't receive any values.
I have a reminder functionality using signal R in asp.net mvc
I have userinterface to set the reminder time, If the current time matches the reminder time , it invokes a popup.
I successfully implemented this functionality with Signal R by checking the database once in every 30 seconds by using javascript timer. If current time does not match, it gives '0'.If it matches, it return '1' and the popup is shown across all browsers. But can this checking the db for every 30 seconds can be replaced by signal R ? is there any way to bring this whole thing to signal R?
You can use System.Threading.Timer to create a periodical method call to both client and server side. According to Sample project created for stocks
_timer = new Timer(UpdateStockPrices, null, _updateInterval, _updateInterval);
It creates and Event-Delegate and calls UpdateStockPrices event timely with period of __updateInterval.
In This event(code given below) you can broadcast the remainder message from server to all clients or clients who are associated with that remainder.
You can write code as :-
Clients.All.updateStockPrice(stock);
You can refer to Timer from link:-
http://msdn.microsoft.com/en-us/library/system.threading.timer.aspx
Yes, you can use Timer in the appdomain scope, application scope or at the hub level. Just get the sample from nuget, called "Microsoft.AspNet.SignalR.Sample". It implements stock timer that periodically broadcasts changes to all clients.
I'm not sure why, but for some reason when using the observable that is created via concat I will always get all values that are pushed from my list (works as intended). Where as with the normal subscribe it seems that some values never make it to those who have subscribed to the observable (only in certain conditions).
These are the two cases that I am using. Could anyone attempt to explain why in certain cases when subscribing to the second version not all values are received? Are they not equivalent? The intent here is to rewind the stream. What are some reasons that could explain why Case 2 fails while Case 1 does not.
Replay here is just a list of the ongoing stream.
Case 1.
let observable =
Observable.Create(fun (o:IObserver<'a>) ->
let next b =
for v in replay do
o.OnNext(v.Head)
o.OnNext(b)
o.OnCompleted()
someOtherObs.Subscribe(next, o.OnError, o.OnCompleted))
let toReturn = observable.Concat(someOtherObs).Publish().RefCount()
Case 2.
let toReturn =
Observable.Create(fun (o:IObserver<'a>) ->
for v in replay do
o.OnNext(v.Head)
someOtherObs.Subscribe(o)
).Publish().RefCount()
Caveat! I don't use F# regularly enough to be 100% comfortable with the syntax, but I think I see what's going on.
That said, both of these cases look odd to me and it greatly depends on how someOtherObs is implemented, and where (in terms of threads) things are running.
Case 1 Analysis
You apply concat to a source stream which appears to work like this:
It subscribes to someOtherObs, and in response to the first event (a) it pushes the elements of replay to the observer.
Then it sends event (a) to the observer.
Then it completes. At this point the stream is finished and no further events are sent.
In the event that someOtherObs is empty or just has a single error, this will be propagated to the observer instead.
Now, when this stream completes, someOtherObs is concatenated on to it. What happens now is a little unpreditcable - if someOtherObs is cold, then the first event would be sent a second time, if someOtherObs is hot, then the first event is not resent, but there's a potential race condition around which event of the remainder will go next which depends on how someOtherObs is implemented. You could easily miss events if it's hot.
Case 2 Analysis
You replay all the replay events, and then send all the events of someOtherObs - but again there's a race condition if someOtherObs is hot because you only subscribe after pushing replay, and so might miss some events.
Comments
In either case, it seems messy to me.
This looks like an attempt to do a merge of a state of the world (sotw) and a live stream. In this case, you need to subscribe to the live stream first, and cache any events while you then acquire and push the sotw events. Once sotw is pushed, you push the cached events - being careful to de-dupe events that may been read in the sotw - until you are caught up with live at which point you can just pass live events though.
You can often get away with naive implementations that flush the live cache in an OnNext handler of the live stream subscription, effectively blocking the source while you flush - but you run the risk of applying too much back pressure to the live source if you have a large history and/or a fast moving live stream.
Some considerations for you to think on that will hopefully set you on the right path.
For reference, here is an extremely naïve and simplistic C# implementation I knocked up that compiles in LINQPad with rx-main nuget package. Production ready implementations I have done in the past can get quite complex:
void Main()
{
// asynchronously produce a list from 1 to 10
Func<Task<List<int>>> sotw =
() => Task<List<int>>.Run(() => Enumerable.Range(1, 10).ToList());
// a stream of 5 to 15
var live = Observable.Range(5, 10);
// outputs 1 to 15
live.MergeSotwWithLive(sotw).Subscribe(Console.WriteLine);
}
// Define other methods and classes here
public static class ObservableExtensions
{
public static IObservable<TSource> MergeSotwWithLive<TSource>(
this IObservable<TSource> live,
Func<Task<List<TSource>>> sotwFactory)
{
return Observable.Create<TSource>(async o =>
{
// Naïve indefinite caching, no error checking anywhere
var liveReplay = new ReplaySubject<TSource>();
live.Subscribe(liveReplay);
// No error checking, no timeout, no cancellation support
var sotw = await sotwFactory();
foreach(var evt in sotw)
{
o.OnNext(evt);
}
// note naive disposal
// and extremely naive de-duping (it really needs to compare
// on some unique id)
// we are only supporting disposal once the sotw is sent
return liveReplay.Where(evt => !sotw.Any(s => s.Equals(evt)))
.Subscribe(o);
});
}
}