Scala Async alternatives and similar packages
Based on the "Extensions" category.
Alternatively, view Scala Async alternatives based on common mentions on social networks and blogs.
-
Twitter Util
General-purpose Scala libraries, including a future implementation and other concurrency tools. -
better-files
Simple, safe and intuitive Scala I/O. better-files is a dependency-free pragmatic thin Scala wrapper around Java NIO. -
Cassovary
A Scala library that is designed from the ground up for space efficiency, handling graphs with billions of nodes and edges. -
Enumeratum
A macro to replace Scala enumerations with a sealed family of case objects. This allows additional checks for the compiler, e.g. for missing cases in a match statement. Has additinal support for Json libraries and the Play framework. -
Scala Graph
A Scala library with basic graph functionality that seamlessly fits into the Scala standard collections library. -
Eff
Extensible effects are an alternative to monad transformers for computing with effects in a functional way. -
Hamsters
A mini Scala utility library. Compatible with functional programming beginners. Featuring validation, monad transformers, HLists, Union types. -
scribe
Practical logging framework that doesn't depend on any other logging framework and can be completely configured programmatically. -
Scala Blitz
A library to speed up Scala collection operations by removing runtime overheads during compilation, and a custom data-parallel operation runtime. -
Play monadic actions
A simple scala DSL to allow clean and monadic style for Play! Actions -
Resolvable
A library to optimize fetching immutable data structures from several endpoints in several formats. -
Freedsl
A library to implement composable side effects, weaving typeclasses on a wrapping type and the free monad.
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README
scala-async
A DSL to enable a direct style of programming with when composing values wrapped in Scala Future
s.
Quick start
To include scala-async in an existing project use the library published on Maven Central. For sbt projects add the following to your build definition - build.sbt or project/Build.scala:
Use a modern Scala compiler
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" % "0.10.0"
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>1.0.0</version>
</dependency>
<dependency>
<groupId>org.scala-lang</groupId>
<artifactId>scala-reflect</artifactId>
<version>2.13.3</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
:
- The code more directly reflects the programmer's intent,
and does not require us to name the results
r1
andr2
. This advantage is even more pronounced when we mix control structures inasync
blocks. 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.