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scala logoscala-async

An asynchronous programming facility for Scala

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Quick Overview

The scala/scala-async project is a library that provides support for asynchronous programming in Scala. It allows developers to write asynchronous code using a synchronous-looking syntax, making it easier to reason about and manage concurrent operations.

Pros

  • Improved Readability: The async/await syntax provided by the library makes asynchronous code more readable and easier to understand, compared to traditional callback-based approaches.
  • Seamless Integration: The library integrates well with the Scala language and ecosystem, allowing developers to use it alongside other Scala features and libraries.
  • Flexibility: The library supports a variety of asynchronous primitives, including Futures, Promises, and Actors, making it versatile for different use cases.
  • Reduced Complexity: The library helps to reduce the complexity of asynchronous code, making it easier to write, maintain, and reason about.

Cons

  • Dependency on Scala: The library is tightly coupled with the Scala language and may not be as useful for developers working in other JVM-based languages.
  • Limited Adoption: While the library is well-designed and useful, it has not seen as widespread adoption as some other asynchronous programming libraries in the Scala ecosystem.
  • Potential Performance Overhead: The library's use of macros and code transformation may introduce some performance overhead, which may be a concern for certain high-performance applications.
  • Compatibility Challenges: The library has undergone several major version changes, which may introduce compatibility issues for existing projects.

Code Examples

Here are a few examples of how to use the scala/scala-async library:

Asynchronous Function

import scala.async.Async.{async, await}
import scala.concurrent.Future

def fetchData(): Future[String] = async {
  val result = await(Future.successful("Hello, Async!"))
  result
}

This example demonstrates how to define an asynchronous function using the async and await constructs provided by the library.

Parallel Execution

import scala.async.Async.{async, await}
import scala.concurrent.Future

def fetchData1(): Future[String] = async {
  await(Future.successful("Data 1"))
}

def fetchData2(): Future[String] = async {
  await(Future.successful("Data 2"))
}

def fetchAllData(): Future[(String, String)] = async {
  val (data1, data2) = await(fetchData1(), fetchData2())
  (data1, data2)
}

This example shows how to execute multiple asynchronous operations in parallel using the await construct.

Error Handling

import scala.async.Async.{async, await}
import scala.concurrent.Future
import scala.util.{Failure, Success}

def fetchData(): Future[String] = async {
  try {
    await(Future.successful("Hello, Async!"))
  } catch {
    case e: Exception =>
      println(s"Error: $e")
      throw e
  }
}

This example demonstrates how to handle errors in asynchronous code using the try-catch construct within the async block.

Getting Started

To use the scala/scala-async library in your Scala project, you can add the following dependency to your build.sbt file:

libraryDependencies += "org.scala-lang.modules" %% "scala-async" % "0.9.7"

Once you have the library added, you can start using the async and await constructs in your code, as shown in the examples above.

For more detailed information on using the library, you can refer to the project's README and the official documentation.

Competitor Comparisons

13,047

Build highly concurrent, distributed, and resilient message-driven applications on the JVM

Pros of Akka

  • Comprehensive actor-based concurrency model for distributed systems
  • Supports various patterns like clustering, persistence, and streams
  • Large ecosystem with extensive documentation and community support

Cons of Akka

  • Steeper learning curve due to its extensive feature set
  • Heavier runtime overhead compared to lightweight async operations
  • More complex setup and configuration for smaller projects

Code Comparison

Scala-async:

async {
  val f1 = async { ... }
  val f2 = async { ... }
  await(f1) + await(f2)
}

Akka:

class MyActor extends Actor {
  def receive = {
    case "message" => sender() ! "response"
  }
}
val system = ActorSystem("MySystem")
val actor = system.actorOf(Props[MyActor], "myactor")

Key Differences

  • Scala-async focuses on simplifying asynchronous programming within a single JVM
  • Akka provides a full-fledged toolkit for building distributed, resilient systems
  • Scala-async uses macro-based transformations, while Akka relies on the actor model
  • Akka offers more advanced features like clustering and persistence
  • Scala-async is more suitable for simpler async scenarios, while Akka excels in complex distributed environments

Both libraries have their merits, and the choice depends on the specific requirements of your project, its scale, and the complexity of concurrency needs.

1,926

Asynchronous, Reactive Programming for Scala and Scala.js.

Pros of Monix

  • More comprehensive and feature-rich, offering a wide range of reactive programming tools
  • Better performance and scalability for complex asynchronous operations
  • Active development and maintenance with frequent updates

Cons of Monix

  • Steeper learning curve due to its extensive API and concepts
  • Potentially overkill for simple asynchronous tasks
  • Larger dependency footprint in projects

Code Comparison

Scala-async:

async {
  val f1 = async { ... }
  val f2 = async { ... }
  await(f1) + await(f2)
}

Monix:

Task.parMap2(
  Task { ... },
  Task { ... }
)(_ + _)

Summary

Scala-async provides a simpler, more straightforward approach to handling asynchronous operations in Scala, focusing primarily on async/await syntax. It's easier to learn and use for basic asynchronous tasks.

Monix, on the other hand, offers a more comprehensive toolkit for reactive and asynchronous programming. It provides better performance and scalability for complex scenarios but comes with a steeper learning curve.

Choose Scala-async for simpler projects or when getting started with asynchronous programming in Scala. Opt for Monix when building more complex, reactive systems that require advanced features and optimized performance.

The pure asynchronous runtime for Scala

Pros of cats-effect

  • Provides a more comprehensive and flexible approach to functional concurrency
  • Offers a rich ecosystem of libraries and integrations
  • Supports a wider range of effect types and abstractions

Cons of cats-effect

  • Steeper learning curve due to its more complex and abstract nature
  • May introduce additional overhead for simpler use cases
  • Requires more boilerplate code for basic operations

Code Comparison

scala-async:

async {
  val f1 = async { ... }
  val f2 = async { ... }
  await(f1) + await(f2)
}

cats-effect:

for {
  fiber1 <- IO.async_ { ... }.start
  fiber2 <- IO.async_ { ... }.start
  result1 <- fiber1.join
  result2 <- fiber2.join
} yield result1 + result2

Summary

scala-async provides a simpler, more straightforward approach to handling asynchronous operations, making it easier to use for developers familiar with traditional synchronous code. It's particularly useful for basic async scenarios.

cats-effect, on the other hand, offers a more powerful and flexible toolkit for managing concurrency and effects in functional programming. It provides a wider range of features and abstractions, making it suitable for more complex applications and advanced use cases.

The choice between the two depends on the specific requirements of the project, the team's familiarity with functional programming concepts, and the desired level of control over concurrency and effects.

4,064

ZIO — A type-safe, composable library for async and concurrent programming in Scala

Pros of ZIO

  • More comprehensive and feature-rich ecosystem for functional effects
  • Better performance and resource management
  • Stronger type safety and error handling capabilities

Cons of ZIO

  • Steeper learning curve due to its more complex API
  • Potentially overkill for simpler asynchronous tasks
  • Requires more boilerplate code for basic operations

Code Comparison

scala-async:

async {
  val f1 = async { ... }
  val f2 = async { ... }
  await(f1) + await(f2)
}

ZIO:

for {
  f1 <- ZIO.async { ... }
  f2 <- ZIO.async { ... }
  result <- ZIO.succeed(f1 + f2)
} yield result

Summary

scala-async provides a simpler, more lightweight approach to handling asynchronous operations in Scala, focusing primarily on async/await syntax. It's easier to learn and use for basic tasks but lacks advanced features.

ZIO offers a more comprehensive solution for functional effect management, with better performance and stronger type safety. However, it comes with a steeper learning curve and may be excessive for simpler use cases.

The choice between the two depends on project requirements, team expertise, and the complexity of asynchronous operations needed in the application.

2,685

Wonderful reusable code from Twitter

Pros of util

  • Broader utility library with a wide range of features beyond async operations
  • More actively maintained with frequent updates and contributions
  • Extensive documentation and examples for various use cases

Cons of util

  • Larger dependency footprint due to its comprehensive nature
  • Steeper learning curve for developers new to the Twitter ecosystem
  • May include unnecessary features for projects only needing async functionality

Code Comparison

scala-async:

async {
  val f1 = async { ... }
  val f2 = async { ... }
  await(f1)
  await(f2)
}

util:

import com.twitter.util.Future

val f1 = Future { ... }
val f2 = Future { ... }
Future.join(f1, f2)

Summary

scala-async focuses specifically on asynchronous programming in Scala, providing a more lightweight and targeted solution. It offers a simpler API for handling async operations using async and await constructs.

util, on the other hand, is a comprehensive utility library that includes async functionality along with many other features. It provides a broader set of tools and abstractions for building scalable applications, particularly within the Twitter ecosystem.

The choice between the two depends on project requirements, existing dependencies, and the need for additional utilities beyond async programming.

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README

scala-async

A Scala DSL to enable a direct style of coding when composing Futures.

Usage

As of scala-async 1.0, Scala 2.12.12+ or 2.13.3+ are required.

Add dependency

SBT Example

libraryDependencies += "org.scala-lang.modules" %% "scala-async" % "1.0.1"
libraryDependencies += "org.scala-lang" % "scala-reflect" % scalaVersion.value % Provided

For Maven projects add the following to your (make sure to use the correct Scala version suffix to match your project’s Scala binary version):

Maven Example

<dependency>
  <groupId>org.scala-lang.modules</groupId>
  <artifactId>scala-async_2.13</artifactId>
  <version>1.0.1</version>
</dependency>
<dependency>
  <groupId>org.scala-lang</groupId>
  <artifactId>scala-reflect</artifactId>
  <version>2.13.8</version>
  <scope>provided</scope>
</dependency>

Enable compiler support for async

Add the -Xasync to the Scala compiler options.

SBT Example

scalacOptions += "-Xasync"

Maven Example

<project>
  ...
  <plugin>
    <groupId>net.alchim31.maven</groupId>
    <artifactId>scala-maven-plugin</artifactId>
    <version>4.4.0</version>
    <configuration>
      <args>
        <arg>-Xasync</arg>
      </args>
    </configuration>
  </plugin>
  ...
</project>

Start coding

import scala.concurrent.ExecutionContext.Implicits.global
import scala.async.Async.{async, await}

val future = async {
  val f1: Future[Boolean] = async { ...; true }
  val f2 = async { ...; 42 }
  if (await(f1)) await(f2) else 0
}

What is async?

async marks a block of asynchronous code. Such a block usually contains one or more await calls, which marks a point at which the computation will be suspended until the awaited Future is complete.

By default, async blocks operate on scala.concurrent.{Future, Promise}. The system can be adapted to alternative implementations of the Future pattern.

Consider the following example:

def slowCalcFuture: Future[Int] = ...             // 01
def combined: Future[Int] = async {               // 02
  await(slowCalcFuture) + await(slowCalcFuture)   // 03
}
val x: Int = Await.result(combined, 10.seconds)   // 05

Line 1 defines an asynchronous method: it returns a Future.

Line 2 begins an async block. During compilation, the contents of this block will be analyzed to identify the await calls, and transformed into non-blocking code.

Control flow will immediately pass to line 5, as the computation in the async block is not executed on the caller's thread.

Line 3 begins by triggering slowCalcFuture, and then suspending until it has been calculated. Only after it has finished, we trigger it again, and suspend again. Finally, we add the results and complete combined, which in turn will release line 5 (unless it had already timed out).

It is important to note that while lines 1-4 are non-blocking, they are not parallel. If we wanted to parallelize the two computations, we could rearrange the code as follows:

def combined: Future[Int] = async {
  val future1 = slowCalcFuture
  val future2 = slowCalcFuture
  await(future1) + await(future2)
}

Limitations

await must be directly in the control flow of the async expression

The await cannot be nested under a local method, object, class or lambda:

async {
  List(1).foreach { x => await(f(x) } // invalid
}

await must be not be nested within try / catch / finally.

This implementation restriction may be lifted in future versions.

Comparison with direct use of Future API

This computation could also be expressed by directly using the higher-order functions of Futures:

def slowCalcFuture: Future[Int] = ...
val future1 = slowCalcFuture
val future2 = slowCalcFuture
def combined: Future[Int] = for {
  r1 <- future1
  r2 <- future2
} yield r1 + r2

The async approach has two advantages over the use of map and flatMap:

  1. The code more directly reflects the programmer's intent, and does not require us to name the results r1 and r2. This advantage is even more pronounced when we mix control structures in async blocks.
  2. async blocks are compiled to a single anonymous class, as opposed to a separate anonymous class for each closure required at each generator (<-) in the for-comprehension. This reduces the size of generated code, and can avoid boxing of intermediate results.