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While asynchronous APIs can bring advantages, they certainly complicate programming by forcing developers to manually string together sequential operations using callbacks, causing a phenomenon called "Callback Hell".
The increasing popularity of asynchronous APIs, partially due to the rise of JavaScript and Node.js, means that many developers are now faced with a prolonged stay in Callback Hell. As is usual, developers with enough of an itch will find a way to scratch it. In the case of Callback Hell, there's a rich supply of hacks, workarounds, and solutions.
InfoQ wants to know: how do you handle asynchronous APIs? How do you stay out of Callback Hell or how do you manage it?
Language features and related
These are solutions that are either straight up language features or are supported by language features (eg. macros, etc).
- C# Async/Await
- Scala Async/Await
- Clojure's core.async
- F# Async Workflows
- Stratified JS
- Ocaml lightweight threading (Lwt, Async and others)
- Haskell lightweight threads
- Ruby Fibers
- Other language with lightweight threads
Extensions of the language runtime or bytecode
- Node.js fibers
- Java lightweight thread solutions like Kilim or Quasar.
Libraries
- Reactive Extensions (Rx)
An increasingly popular approach that started on .NET and has been ported to other platforms including Java and JavaScript. As an example, Netflix is behind the Java port RxJava; see Netflix' Ben Christensen interview on RxJava. - Promises or Futures
Promises (and their namesakes) have been adopted by many (standard) libraries and make it easier to chain operations. - Embedded DSL-style libraries
Libraries that allow one to chain statements, often using Promises underneath, are particularly popular in JavaScript.
Misc
- State machines
Using libraries like ignite.js, Ragel, etc. - Just write callbacks!
Is "Callback Hell" just bad developers complaining about their tools? Do you just grit your teeth and nest your callbacks rather spend weeks researching alternative solutions? - Synchronous APIs
Do you avoid asynchronous APIs at all costs?
Note: if we missed your favorite language, library or solution, please tell us about it in the comments.
Community comments
What other language with lightweight threads?
by Yichao Zhang,
Protothreads
by John Carter,
Law of Demeter
by John Carter,
Re: Law of Demeter
by Ted Slusser,
We use kontraktor :-)
by Rüdiger Möller,
bad poll
by Rüdiger Möller,
Continuations?
by Cameron Purdy,
Re: Continuations?
by Mark Sasler,
Async API in Java
by Zhong Yu,
What other language with lightweight threads?
by Yichao Zhang,
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If that other language is Erlang, then I think it's quite mature and widely adopted.
Protothreads
by John Carter,
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At the intersection of light weight threads, C, evil abuses of language standards and state machines there exists Protothreads.
dunkels.com/adam/pt/
Law of Demeter
by John Carter,
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Actually, call back hell is a code smell.
It's a stench of a Law of Demeter Violation in progress.
The solution is to Tell, don't Ask.
We use kontraktor :-)
by Rüdiger Möller,
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github.com/RuedigerMoeller/kontraktor
Re: Law of Demeter
by Ted Slusser,
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I'll Ask you to Tell me more about it :)
bad poll
by Rüdiger Möller,
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You should abstract out general patterns (e.g. actors, csp, traditional multithreading, lightweight mt). It mixes up implementations, language and methodology. There are many terminologies for identical models.
check out this
java-is-the-new-c.blogspot.de/2014/01/comparisi...
java-is-the-new-c.blogspot.de/2014/06/java-conc...
Continuations?
by Cameron Purdy,
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Surprised that "continuations" was not one of the options.
Async API in Java
by Zhong Yu,
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Please also check out bayou Async API - bayou.io/release/0.9/docs/async/Async_Programmi...
Re: Continuations?
by Mark Sasler,
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Take a look at www.dragome.com, this tool is capable of avoiding callback hell using continuations.
Its CallbackEvictor module works creating a proxy over invoked service, it pauses the application flow while is waiting the async reply and continue the execution when internal callback is executed with the expected result.
It allows the use of continuations and dynamic proxies in javascript thanks to an automatic Java to Javascript conversion. Since this conversion is based in generated bytecode and not the source code, libraries such as Javaflow are used to achieved this.