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Asynchronous, composable return value for vector/stream data in Java 9


Asynchronous, composable return value for vector/stream data in Java 9

By : Lee Sear
Date : November 20 2020, 03:01 PM
To fix the issue you can do Your use case falls very naturally into the world that RxJava is addressing. If we have an observable:
code :
Observable<Widget> getMatchingWidgets(wc);
getMatchingWidgets(wc)
  .subscribeOn( backgroundScheduler )
  .subscribe( w -> processWidget(w),
              error -> handleError(error) );
getMatchingWidgets(wc)
  .subscribeOn( backgroundScheduler )
  .observeOn( uiScheduler )
  .subscribe( w -> processWidget(w),
              error -> handleError(error) );


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Writing composable asynchronous monads from ffi

Writing composable asynchronous monads from ffi


By : Nainil Chheda
Date : March 29 2020, 07:55 AM
wish helps you You might want to consider using the continuation monad transformer ContT from the purescript-transformers package.
The definition of ContT in that package is given as
code :
newtype ContT r m a = ContT ((a -> m r) -> m r)
(a -> Eff eff Unit) -> Eff eff Unit
asyncGetNumberCont :: ContT Unit (Eff SomeEffects) Number
asyncGetNumberCont = ContT $ \callback -> 
  asyncGetNumber "/numberLocation" callback
asyncGetNumberCont = ContT $ asyncGetNumber "/numberLocation"
do n <- asyncGetNumberCont
   m <- asyncGetNumberCont
   return (n + m)
-- Ignore effects to keep things simple
-- The runtime representation of 'Async a' is a function which takes a callback,
-- performs some side effects an returns.
foreign import data Async :: * -> *

-- Make an async computation from a function taking a callback
foreign import makeAsync 
  "function makeAsync(f) {\
  \  return function(k) {\
  \    f(function(a) {\
  \      return function() {\
  \        k(a)();\
  \      };\
  \    })();\
  \  };\
  \}" :: forall a eff. ((a -> Eff eff Unit) -> Eff eff Unit) -> Async a

-- Now we need to define instances for Async, which we can do using FFI
-- calls, for example:
foreign import fmapAsync
  "function fmapAsync(f) {\
  \  return function (comp) {\
  \    return function (k) {\
  \      comp(function(a) {\
  \        k(f(a));\
  \      });
  \    };\
  \  };\
  \}" :: forall a b. (a -> b) -> Async a -> Async b

instance functorAsync :: Functor Async where
  (<$>) = fmapAsync
java.io.EOFException: no more data available - expected end tag </stream:stream> to close start tag <stream:str

java.io.EOFException: no more data available - expected end tag </stream:stream> to close start tag <stream:str


By : Deepak
Date : March 29 2020, 07:55 AM
around this issue What is the reason for the above error?
Then connection went down unexpectedly. For example because the server closed it in an unclean way.
Rxjs filter a composable stream based on another stream

Rxjs filter a composable stream based on another stream


By : Rahul Sangareddy
Date : March 29 2020, 07:55 AM
Any of those help I have an array of cars that have properties: , I think you are looking for either combineLatest or withLatestFrom
code :
var carsOfACertainMake = new BehaviorSubject('mazda');
carsObservable.withLatestFrom(carsOfACertainMake, (cars, make) =>
  _.filter(cars, car => car.make === make)
).cache();
How to process a vector as an asynchronous stream?

How to process a vector as an asynchronous stream?


By : user3478196
Date : March 29 2020, 07:55 AM
this will help
How to execute that stream? I was thinking about using task::spawn but it doesn't seems to work
code :
//# tokio = { version = "0.2.4", features = ["full"] }
//# futures = "0.3.1"
use tokio::time::delay_for;
use futures::stream::StreamExt;
use futures::stream::futures_unordered::FuturesUnordered;
use std::error::Error;
use std::time::{Duration, Instant};

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
    let start = Instant::now();
    let feeds = (0..10).collect::<Vec<_>>();
    let res = read_feeds(feeds).await;
    dbg!(res);
    dbg!(start.elapsed());

    Ok(())
}

async fn read_feeds(feeds: Vec<u32>) -> Vec<u32> {
    feeds.iter()
        .map(read_feed)
        .collect::<FuturesUnordered<_>>()
        .collect::<Vec<_>>()
        .await
}

async fn read_feed(feed: &u32) -> u32 {
    delay_for(Duration::from_millis(500)).await;

    feed * 2
}
How do I efficiently build a vector and an index of that vector while processing a data stream?

How do I efficiently build a vector and an index of that vector while processing a data stream?


By : Khudeja Akbar
Date : March 29 2020, 07:55 AM
around this issue In general, what you are trying to accomplish is unsafe and Rust is correctly preventing you from doing something you shouldn't. For a simple example why, consider a Vec. If the vector has one item and a capacity of one, adding another value to the vector will cause a re-allocation and copying of all the values in the vector, invalidating any references into the vector. This would cause all of your keys in your index to point to arbitrary memory addresses, thus leading to unsafe behavior. The compiler prevents that.
In this case, there's two extra pieces of information that the compiler is unaware of but the programmer isn't:
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