Benching fastest way to keep logLevel publised safely - spoiler: volatile wins

varaccessbench.scala

/**
 * Copyright (C) 2014 Typesafe Inc. <http://www.typesafe.com>
 */
package akka.event

import java.util.concurrent.TimeUnit

import akka.actor._
import akka.testkit._
import akka.event.Logging.LogLevel
import org.openjdk.jmh.annotations._

@Fork(3)
@State(Scope.Benchmark)
@BenchmarkMode(Array(Mode.Throughput))
@Warmup(iterations = 10)
@Measurement(iterations = 20, timeUnit = TimeUnit.MILLISECONDS)
class LoggingBusBench {

  /*

  GUARD `ReentrantGuard`, 1 thread reading, 2 threads writing
    a.e.LoggingBusBench.g:readWithGuard          thrpt        10     1811.514      277.492   ops/ms
    a.e.LoggingBusBench.g:writeDebugWithGuard    thrpt        10     1174.610       62.096   ops/ms
    a.e.LoggingBusBench.g:writeErrorWithGuard    thrpt        10     1168.009       36.615   ops/ms
  GUARD `ReentrantGuard`, 10 threads reading, 2 threads writing
    a.e.LoggingBusBench.g:readWithGuard          thrpt        10    12386.594      913.637   ops/ms
    a.e.LoggingBusBench.g:writeDebugWithGuard    thrpt        10      906.733       43.803   ops/ms
    a.e.LoggingBusBench.g:writeErrorWithGuard    thrpt        10      909.726       53.118   ops/ms
  GUARD `ReentrantGuard`, 20 threads reading, 2 threads writing
    a.e.LoggingBusBench.g                        thrpt        60    18567.983      537.772   ops/ms
    a.e.LoggingBusBench.g:readWithGuard          thrpt        60    17446.248      566.094   ops/ms
    a.e.LoggingBusBench.g:writeDebugWithGuard    thrpt        60      563.237       25.699   ops/ms
    a.e.LoggingBusBench.g:writeErrorWithGuard    thrpt        60      558.498       26.414   ops/ms


  VOLATILE - `@volatile var _logLevel`, 1 thread reading, 2 threads writing
    a.e.LoggingBusBench.g:readWithGuard          thrpt        10   228537.352    12446.850   ops/ms
    a.e.LoggingBusBench.g:writeDebugWithGuard    thrpt        10     2359.561      106.098   ops/ms
    a.e.LoggingBusBench.g:writeErrorWithGuard    thrpt        10     1180.412       52.141   ops/ms
  VOLATILE - `@volatile var _logLevel`, 10 threads reading, 2 threads writing
    a.e.LoggingBusBench.g:readWithGuard          thrpt        10  1398386.010    78949.306   ops/ms
    a.e.LoggingBusBench.g:writeDebugWithGuard    thrpt        10     2578.375      144.119   ops/ms
    a.e.LoggingBusBench.g:writeErrorWithGuard    thrpt        10     1891.309      194.537   ops/ms
  VOLATILE - `@volatile var _logLevel`, 20 threads reading, 2 threads writing
    a.e.LoggingBusBench.g:readWithGuard          thrpt        60  1175143.477    36065.242   ops/ms
    a.e.LoggingBusBench.g:writeDebugWithGuard    thrpt        60      951.258       43.214   ops/ms
    a.e.LoggingBusBench.g:writeErrorWithGuard    thrpt        60      882.009       40.019   ops/ms


  READ WRITE GUARD - `ReentrantReadWriteGuard`, 0 threads writing
    a.e.LoggingBusBench.g                        thrpt        10    36055.192      999.268   ops/ms
  READ WRITE GUARD - `ReentrantReadWriteGuard`, 1 threads writing
    a.e.LoggingBusBench.g:readWithGuard          thrpt        10      274.800      314.774   ops/ms
    a.e.LoggingBusBench.g:writeErrorWithGuard    thrpt        10     2835.826      670.500   ops/ms
  READ WRITE GUARD - `ReentrantReadWriteGuard`, 2 threads writing
    a.e.LoggingBusBench.g:readWithGuard          thrpt        10       12.956        1.998   ops/ms
    a.e.LoggingBusBench.g:writeDebugWithGuard    thrpt        10     1420.432       75.205   ops/ms
    a.e.LoggingBusBench.g:writeErrorWithGuard    thrpt        10     1429.204       78.902   ops/ms
  READ WRITE GUARD - `ReentrantReadWriteGuard`, 10 threads reading, 2 threads writing
    a.e.LoggingBusBench.g:readWithGuard          thrpt        10  1632481.289   109734.216   ops/ms
    a.e.LoggingBusBench.g:writeDebugWithGuard    thrpt        10     1974.814      158.129   ops/ms
    a.e.LoggingBusBench.g:writeErrorWithGuard    thrpt        10     1890.501      269.516   ops/ms
  READ WRITE GUARD - `ReentrantReadWriteGuard`, 20 threads reading, 2 threads writing, V1
    a.e.LoggingBusBench.g:readWithGuard          thrpt        60     4890.522       92.922   ops/ms
    a.e.LoggingBusBench.g:writeDebugWithGuard    thrpt        60        0.221        0.289   ops/ms
    a.e.LoggingBusBench.g:writeErrorWithGuard    thrpt        60        0.139        0.055   ops/ms

   */

  implicit var system: ActorSystem = _

  var probe: TestProbe = _

  var log: BusLogging = _

  @Setup
  def setup() {
    system = ActorSystem("log-touching")
    probe = TestProbe()

    log = akka.event.Logging(system, probe.ref).asInstanceOf[BusLogging]
  }

  @TearDown
  def shutdown() {
    system.shutdown()
    system.awaitTermination()
  }

  @Benchmark
  @GroupThreads(20)
  @Group("g")
  def readWithGuard(): LogLevel =
    log.bus.logLevel

  @Benchmark
  @Group("g")
  def writeErrorWithGuard(): Unit =
    log.bus.setLogLevel(Logging.ErrorLevel)

  @Benchmark
  @Group("g")
  def writeDebugWithGuard(): Unit =
    log.bus.setLogLevel(Logging.DebugLevel)

}

Wins with quite nice margin ;)