Twitter Util

A bunch of idiomatic, small, general purpose tools.

See the Scaladoc here.

Status

This project is used in production at Twitter (and many other organizations), and is being actively developed and maintained.

Releases

Releases are done on an approximately monthly schedule. While semver is not followed, the changelogs are detailed and include sections on public API breaks and changes in runtime behavior.

Contributing

The master branch of this repository contains the latest stable release of Util, and weekly snapshots are published to the develop branch. In general pull requests should be submitted against develop. See CONTRIBUTING.md for more details about how to contribute.

Using in your project

An example SBT dependency string for the util-collection tools would look like this:

val collUtils = "com.twitter" %% "util-collection" % "19.9.0"

Units

Time

import com.twitter.conversions.DurationOps._

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

Space

import com.twitter.conversions.StorageUnitOps._
val amount = 8.megabytes
amount.inBytes // => 8388608L
amount.inKilobytes // => 8192L

Futures

A Non-actor re-implementation of Scala Futures.

import com.twitter.conversions.DurationOps._
import com.twitter.util.{Await, Future, Promise}

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

// Another option:
g.onSuccess { 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"
}

Future interrupts

Method raise on Future (def raise(cause: Throwable)) raises the interrupt described by cause to the producer of this Future. Interrupt handlers are installed on a Promise using setInterruptHandler, which takes a partial function:

val p = new Promise[T]
p.setInterruptHandler {
  case exc: MyException =>
    // deal with interrupt..
}

Interrupts differ in semantics from cancellation in important ways: there can only be one interrupt handler per promise, and interrupts are only delivered if the promise is not yet complete.

Object Pool

The pool order is FIFO.

A pool of constants

import scala.collection.mutable
import com.twitter.util.{Await, SimplePool}

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.
assert(Await.result(pool.reserve()) == 1)
pool.reserve().onSuccess { 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:

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

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).

Hashing

util-hashing is a collection of hash functions and hashing distributors (eg. ketama).

To use one of the available hash functions:

import com.twitter.hashing.KeyHasher

KeyHasher.FNV1_32.hashKey("string".getBytes)

Available hash functions are:

FNV1_32
FNV1A_32
FNV1_64
FNV1A_64
KETAMA
CRC32_ITU
HSIEH

To use KetamaDistributor:

import com.twitter.hashing.{KetamaDistributor, KetamaNode, KeyHasher}

val nodes = List(KetamaNode("host:port", 1 /* weight */, "foo" /* handle */))
val distributor = new KetamaDistributor(nodes, 1 /* num reps */)
distributor.nodeForHash("abc".##) // => client

Time and Duration

Like arithmetic on doubles, Time and Duration arithmetic is now free of overflows. Instead, they overflow to Top and Bottom values, which are analogous to positive and negative infinity.

Since the resolution of Time.now has been reduced (and is also more expensive due to its use of system time), a new Stopwatch API has been introduced in order to calculate durations of time.

It's used simply:

import com.twitter.util.{Duration, Stopwatch}
val elapsed: () => Duration = Stopwatch.start()

which is read by applying elapsed:

val duration: Duration = elapsed()