Units

Time

import com.twitter.conversions.time._

val duration1 = 1.second
val duration2 = 2.minutes
duration1.inMillis // => 1000L

Space

import com.twitter.conversions.storage._
val amount = 8.megabytes
amount.inBytes // => 8192L
amount.inGigabytes // => 0.0078125

Futures

A Non-actor re-implementation of Scala Futures.

import com.twitter.util.{Future, Promise}

val f = new Promise[Int]
val g = f map { result => result + 1 }
f.setValue(1
g.get(1.second) // => This blocks for the futures result (and eventually returns 2)

// Another option:
g respond { result =>
  println(result) // => prints "2"
}

// Using for expressions:
val xFuture = Future(1)
val yFuture = Future(2)

for (
  x <- xFuture
  y <- yFuture
) {
  println(x + y) // => prints "3"
}

Collections

LruMap

The LruMap is an LRU with a maximum size passed in. If the map is full it expires items in FIFO order. Reading a value will move an item to the top of the stack.

import com.twitter.util.LruMap

val f = new LruMap[Key, Value](15) // this is of type mutable.Map[Key, Value]

Google MapMaker

import com.twitter.util.MapMaker

val map = MapMaker[Key, Value] { config =>
  config.weakKeys()
  config.weakValues()
} // this is of type mutable.Map[Key, Value]

Object Pool

The pool order is FIFO

A pool of constants

  val queue = new mutable.Queue[Int] ++ List(1, 2, 3)
  val pool = new SimplePool(queue)
  // Note that the pool returns Futures, it doesn't block on exhaustion.
  pool.reserve()() mustEqual 1
  pool.reserve { item =>
    println(item) // prints "2"
  }

A pool of dynamically created objects

Here is a pool of even-number generators. It stores 4 numbers at a time:

val pool = new FactoryPool[Int](4) {
  var count = 0
  def makeItem() = { count += 1; Future(count) }
  def isHealthy(i: Int) = i % 2 == 0
}

It checks the health when you successfully reserve an object (i.e., when the Future yields).

Eval

Dynamically evaluates Scala strings and files.

This is motivated by the desire to have a type-safe alternative to textual configuration formats such as YAML, JSON, or .properties files. Its advantages over these text formats are

Strong typing and compiler checking. If it doesn't compile and doesn't conform to the type you expect, you get an exception
The full power of Scala in your config. You don't have to use it. But you can.

in config/Development.scala

import com.xxx.MyConfig

new MyConfig {
  val myValue = 1
  val myTime = 2.seconds
  val myStorage = 14.kilobytes
}

in Main.scala

import com.xxx.MyConfig

val config = Eval[MyConfig](new File("config/Development.scala"))

dth/util