Merge branch 'master' into wip-2162-membership-change-listener-spec-jboner

Signed-off-by: Jonas Bonér <jonas@jonasboner.com>

akka-actor-tests/src/test/scala/akka/pattern/CircuitBreakerMTSpec.scala

@@ -0,0 +1,121 @@
+/**
+ * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.pattern
+
+import akka.testkit._
+import akka.util.duration._
+import org.scalatest.BeforeAndAfter
+import akka.dispatch.{ Promise, Await, Future }
+
+class CircuitBreakerMTSpec extends AkkaSpec with BeforeAndAfter {
+
+  @volatile
+  var breakers: BreakerState = null
+
+  class BreakerState {
+
+    val halfOpenLatch = new TestLatch(1)
+
+    val breaker = new CircuitBreaker(system.scheduler, 5, 100.millis.dilated, 500.millis.dilated)
+      .onHalfOpen(halfOpenLatch.countDown())
+
+  }
+
+  before {
+    breakers = new BreakerState()
+  }
+
+  def unreliableCall(param: String) = {
+    param match {
+      case "fail" ⇒ throw new RuntimeException("FAIL")
+      case _      ⇒ param
+    }
+  }
+
+  def openBreaker: Unit = {
+    for (i ← 1 to 5)
+      Await.result(breakers.breaker.withCircuitBreaker(Future(unreliableCall("fail"))) recoverWith {
+        case _ ⇒ Promise.successful("OK")
+      }, 1.second.dilated)
+  }
+
+  "A circuit breaker being called by many threads" must {
+    "allow many calls while in closed state with no errors" in {
+
+      val futures = for (i ← 1 to 100) yield breakers.breaker.withCircuitBreaker(Future { Thread.sleep(10); unreliableCall("succeed") })
+
+      val futureList = Future.sequence(futures)
+
+      val result = Await.result(futureList, 1.second.dilated)
+
+      result.size must be(100)
+      result.distinct.size must be(1)
+      result.distinct must contain("succeed")
+
+    }
+
+    "transition to open state upon reaching failure limit and fail-fast" in {
+
+      openBreaker
+
+      val futures = for (i ← 1 to 100) yield breakers.breaker.withCircuitBreaker(Future {
+        Thread.sleep(10); unreliableCall("success")
+      }) recoverWith {
+        case _: CircuitBreakerOpenException ⇒ Promise.successful("CBO")
+      }
+
+      val futureList = Future.sequence(futures)
+
+      val result = Await.result(futureList, 1.second.dilated)
+
+      result.size must be(100)
+      result.distinct.size must be(1)
+      result.distinct must contain("CBO")
+    }
+
+    "allow a single call through in half-open state" in {
+      openBreaker
+
+      Await.ready(breakers.halfOpenLatch, 2.seconds.dilated)
+
+      val futures = for (i ← 1 to 100) yield breakers.breaker.withCircuitBreaker(Future {
+        Thread.sleep(10); unreliableCall("succeed")
+      }) recoverWith {
+        case _: CircuitBreakerOpenException ⇒ Promise.successful("CBO")
+      }
+
+      val futureList = Future.sequence(futures)
+
+      val result = Await.result(futureList, 1.second.dilated)
+
+      result.size must be(100)
+      result.distinct.size must be(2)
+      result.distinct must contain("succeed")
+      result.distinct must contain("CBO")
+    }
+
+    "recover and reset the breaker after the reset timeout" in {
+      openBreaker
+
+      Await.ready(breakers.halfOpenLatch, 2.seconds.dilated)
+
+      Await.ready(breakers.breaker.withCircuitBreaker(Future(unreliableCall("succeed"))), 1.second.dilated)
+
+      val futures = for (i ← 1 to 100) yield breakers.breaker.withCircuitBreaker(Future {
+        Thread.sleep(10); unreliableCall("succeed")
+      }) recoverWith {
+        case _: CircuitBreakerOpenException ⇒ Promise.successful("CBO")
+      }
+
+      val futureList = Future.sequence(futures)
+
+      val result = Await.result(futureList, 1.second.dilated)
+
+      result.size must be(100)
+      result.distinct.size must be(1)
+      result.distinct must contain("succeed")
+    }
+  }
+
+}

akka-actor-tests/src/test/scala/akka/pattern/CircuitBreakerSpec.scala

@@ -0,0 +1,243 @@
+
+/**
+ * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+
+package akka.pattern
+
+import akka.util.duration._
+import akka.testkit._
+import org.scalatest.BeforeAndAfter
+import akka.dispatch.Future
+import akka.dispatch.Await
+
+object CircuitBreakerSpec {
+
+  class TestException extends RuntimeException
+
+}
+
+@org.junit.runner.RunWith(classOf[org.scalatest.junit.JUnitRunner])
+class CircuitBreakerSpec extends AkkaSpec with BeforeAndAfter {
+
+  import CircuitBreakerSpec.TestException
+
+  val awaitTimeout = 2.seconds.dilated
+
+  @volatile
+  var breakers: TestCircuitBreakers = null
+
+  class TestCircuitBreakers {
+    val halfOpenLatch = new TestLatch(1)
+    val openLatch = new TestLatch(1)
+    val closedLatch = new TestLatch(1)
+
+    val shortCallTimeoutCb = new CircuitBreaker(system.scheduler, 1, 50.millis.dilated, 500.millis.dilated)
+      .onClose(closedLatch.countDown())
+      .onHalfOpen(halfOpenLatch.countDown())
+      .onOpen(openLatch.countDown())
+
+    val shortResetTimeoutCb = new CircuitBreaker(system.scheduler, 1, 1000.millis.dilated, 50.millis.dilated)
+      .onClose(closedLatch.countDown())
+      .onHalfOpen(halfOpenLatch.countDown())
+      .onOpen(openLatch.countDown())
+
+    val longCallTimeoutCb = new CircuitBreaker(system.scheduler, 1, 5 seconds, 500.millis.dilated)
+      .onClose(closedLatch.countDown())
+      .onHalfOpen(halfOpenLatch.countDown())
+      .onOpen(openLatch.countDown())
+
+    val longResetTimeoutCb = new CircuitBreaker(system.scheduler, 1, 100.millis.dilated, 5 seconds)
+      .onClose(closedLatch.countDown())
+      .onHalfOpen(halfOpenLatch.countDown())
+      .onOpen(openLatch.countDown())
+
+    val multiFailureCb = new CircuitBreaker(system.scheduler, 5, 200.millis.dilated, 500.millis.dilated)
+      .onClose(closedLatch.countDown())
+      .onHalfOpen(halfOpenLatch.countDown())
+      .onOpen(openLatch.countDown())
+  }
+
+  before {
+    breakers = new TestCircuitBreakers
+  }
+
+  def checkLatch(latch: TestLatch) {
+    Await.ready(latch, awaitTimeout)
+  }
+
+  def throwException = throw new TestException
+
+  def sayHi = "hi"
+
+  "A synchronous circuit breaker that is open" must {
+    "throw exceptions when called before reset timeout" in {
+
+      intercept[TestException] {
+        breakers.longResetTimeoutCb.withSyncCircuitBreaker(throwException)
+      }
+      checkLatch(breakers.openLatch)
+
+      intercept[CircuitBreakerOpenException] {
+        breakers.longResetTimeoutCb.withSyncCircuitBreaker(sayHi)
+      }
+    }
+
+    "transition to half-open on reset timeout" in {
+      intercept[TestException] {
+        breakers.shortResetTimeoutCb.withSyncCircuitBreaker(throwException)
+      }
+      checkLatch(breakers.halfOpenLatch)
+    }
+  }
+
+  "A synchronous circuit breaker that is half-open" must {
+    "pass through next call and close on success" in {
+      intercept[TestException] {
+        breakers.shortResetTimeoutCb.withSyncCircuitBreaker(throwException)
+      }
+      checkLatch(breakers.halfOpenLatch)
+      assert("hi" == breakers.shortResetTimeoutCb.withSyncCircuitBreaker(sayHi))
+      checkLatch(breakers.closedLatch)
+    }
+
+    "open on exception in call" in {
+      intercept[TestException] {
+        breakers.shortResetTimeoutCb.withSyncCircuitBreaker(throwException)
+      }
+      checkLatch(breakers.halfOpenLatch)
+      intercept[TestException] {
+        breakers.shortResetTimeoutCb.withSyncCircuitBreaker(throwException)
+      }
+      checkLatch(breakers.openLatch)
+    }
+  }
+
+  "A synchronous circuit breaker that is closed" must {
+    "allow calls through" in {
+      breakers.longCallTimeoutCb.withSyncCircuitBreaker(sayHi) must be("hi")
+    }
+
+    "increment failure count on failure" in {
+      intercept[TestException] {
+        breakers.longCallTimeoutCb.withSyncCircuitBreaker(throwException)
+      }
+      checkLatch(breakers.openLatch)
+      breakers.longCallTimeoutCb.currentFailureCount must be(1)
+    }
+
+    "reset failure count after success" in {
+      intercept[TestException] {
+        breakers.multiFailureCb.withSyncCircuitBreaker(throwException)
+      }
+
+      breakers.multiFailureCb.currentFailureCount must be(1)
+      breakers.multiFailureCb.withSyncCircuitBreaker(sayHi)
+      breakers.multiFailureCb.currentFailureCount must be(0)
+    }
+
+    "increment failure count on callTimeout" in {
+      breakers.shortCallTimeoutCb.withSyncCircuitBreaker({
+        100.millis.dilated.sleep()
+      })
+      breakers.shortCallTimeoutCb.currentFailureCount must be(1)
+    }
+  }
+
+  "An asynchronous circuit breaker that is open" must {
+    "throw exceptions when called before reset timeout" in {
+      breakers.longResetTimeoutCb.withCircuitBreaker(Future(throwException))
+
+      checkLatch(breakers.openLatch)
+
+      intercept[CircuitBreakerOpenException] {
+        Await.result(
+          breakers.longResetTimeoutCb.withCircuitBreaker(Future(sayHi)),
+          awaitTimeout)
+      }
+    }
+
+    "transition to half-open on reset timeout" in {
+      breakers.shortResetTimeoutCb.withCircuitBreaker(Future(throwException))
+      checkLatch(breakers.halfOpenLatch)
+    }
+  }
+
+  "An asynchronous circuit breaker that is half-open" must {
+    "pass through next call and close on success" in {
+      breakers.shortResetTimeoutCb.withCircuitBreaker(Future(throwException))
+      checkLatch(breakers.halfOpenLatch)
+
+      Await.result(
+        breakers.shortResetTimeoutCb.withCircuitBreaker(Future(sayHi)),
+        awaitTimeout) must be("hi")
+      checkLatch(breakers.closedLatch)
+    }
+
+    "re-open on exception in call" in {
+      breakers.shortResetTimeoutCb.withCircuitBreaker(Future(throwException))
+      checkLatch(breakers.halfOpenLatch)
+
+      intercept[TestException] {
+        Await.result(
+          breakers.shortResetTimeoutCb.withCircuitBreaker(Future(throwException)),
+          awaitTimeout)
+      }
+      checkLatch(breakers.openLatch)
+    }
+
+    "re-open on async failure" in {
+      breakers.shortResetTimeoutCb.withCircuitBreaker(Future(throwException))
+      checkLatch(breakers.halfOpenLatch)
+
+      breakers.shortResetTimeoutCb.withCircuitBreaker(Future(throwException))
+      checkLatch(breakers.openLatch)
+    }
+  }
+
+  "An asynchronous circuit breaker that is closed" must {
+    "allow calls through" in {
+      Await.result(
+        breakers.longCallTimeoutCb.withCircuitBreaker(Future(sayHi)),
+        awaitTimeout) must be("hi")
+    }
+
+    "increment failure count on exception" in {
+      intercept[TestException] {
+        Await.result(
+          breakers.longCallTimeoutCb.withCircuitBreaker(Future(throwException)),
+          awaitTimeout)
+      }
+      checkLatch(breakers.openLatch)
+      breakers.longCallTimeoutCb.currentFailureCount must be(1)
+    }
+
+    "increment failure count on async failure" in {
+      breakers.longCallTimeoutCb.withCircuitBreaker(Future(throwException))
+      checkLatch(breakers.openLatch)
+      breakers.longCallTimeoutCb.currentFailureCount must be(1)
+    }
+
+    "reset failure count after success" in {
+      breakers.multiFailureCb.withCircuitBreaker(Future(sayHi))
+      val latch = TestLatch(4)
+      for (n ← 1 to 4) breakers.multiFailureCb.withCircuitBreaker(Future(throwException))
+      awaitCond(breakers.multiFailureCb.currentFailureCount == 4, awaitTimeout)
+      breakers.multiFailureCb.withCircuitBreaker(Future(sayHi))
+      awaitCond(breakers.multiFailureCb.currentFailureCount == 0, awaitTimeout)
+    }
+
+    "increment failure count on callTimeout" in {
+      breakers.shortCallTimeoutCb.withCircuitBreaker {
+        Future {
+          100.millis.dilated.sleep()
+          sayHi
+        }
+      }
+
+      checkLatch(breakers.openLatch)
+      breakers.shortCallTimeoutCb.currentFailureCount must be(1)
+    }
+  }
+
+}

akka-actor/src/main/java/akka/pattern/AbstractCircuitBreaker.java

@@ -0,0 +1,18 @@
+/**
+ * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.pattern;
+
+import akka.util.Unsafe;
+
+class AbstractCircuitBreaker {
+    protected final static long stateOffset;
+
+    static {
+        try {
+            stateOffset = Unsafe.instance.objectFieldOffset(CircuitBreaker.class.getDeclaredField("_currentStateDoNotCallMeDirectly"));
+        } catch(Throwable t){
+            throw new ExceptionInInitializerError(t);
+        }
+    }
+}

akka-actor/src/main/scala/akka/pattern/CircuitBreaker.scala

@@ -0,0 +1,560 @@
+/**
+ * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.pattern
+
+import java.util.concurrent.atomic.{ AtomicInteger, AtomicLong, AtomicBoolean }
+import akka.AkkaException
+import akka.actor.Scheduler
+import akka.dispatch.{ Future, ExecutionContext, Await, Promise }
+import akka.util.{ Deadline, Duration, NonFatal, Unsafe }
+import akka.util.duration._
+import util.control.NoStackTrace
+import java.util.concurrent.{ Callable, CopyOnWriteArrayList }
+
+/**
+ * Companion object providing factory methods for Circuit Breaker which runs callbacks in caller's thread
+ */
+object CircuitBreaker {
+
+  /**
+   * Synchronous execution context to run in caller's thread - used by companion object factory methods
+   */
+  private[CircuitBreaker] val syncExecutionContext = new ExecutionContext {
+    def execute(runnable: Runnable): Unit = runnable.run()
+
+    def reportFailure(t: Throwable): Unit = ()
+  }
+
+  /**
+   * Callbacks run in caller's thread when using withSyncCircuitBreaker, and in same ExecutionContext as the passed
+   * in Future when using withCircuitBreaker. To use another ExecutionContext for the callbacks you can specify the
+   * executor in the constructor.
+   *
+   * @param scheduler Reference to Akka scheduler
+   * @param maxFailures Maximum number of failures before opening the circuit
+   * @param callTimeout [[akka.util.Duration]] of time after which to consider a call a failure
+   * @param resetTimeout [[akka.util.Duration]] of time after which to attempt to close the circuit
+   */
+  def apply(scheduler: Scheduler, maxFailures: Int, callTimeout: Duration, resetTimeout: Duration): CircuitBreaker =
+    new CircuitBreaker(scheduler: Scheduler, maxFailures: Int, callTimeout: Duration, resetTimeout: Duration)(syncExecutionContext)
+
+  /**
+   * Java API alias for apply
+   *
+   * @param scheduler Reference to Akka scheduler
+   * @param maxFailures Maximum number of failures before opening the circuit
+   * @param callTimeout [[akka.util.Duration]] of time after which to consider a call a failure
+   * @param resetTimeout [[akka.util.Duration]] of time after which to attempt to close the circuit
+   */
+  def create(scheduler: Scheduler, maxFailures: Int, callTimeout: Duration, resetTimeout: Duration): CircuitBreaker =
+    apply(scheduler: Scheduler, maxFailures: Int, callTimeout: Duration, resetTimeout: Duration)
+}
+
+/**
+ * Provides circuit breaker functionality to provide stability when working with "dangerous" operations, e.g. calls to
+ * remote systems
+ *
+ * Transitions through three states:
+ * - In *Closed* state, calls pass through until the `maxFailures` count is reached.  This causes the circuit breaker
+ * to open.  Both exceptions and calls exceeding `callTimeout` are considered failures.
+ * - In *Open* state, calls fail-fast with an exception.  After `resetTimeout`, circuit breaker transitions to
+ * half-open state.
+ * - In *Half-Open* state, the first call will be allowed through, if it succeeds the circuit breaker will reset to
+ * closed state.  If it fails, the circuit breaker will re-open to open state.  All calls beyond the first that
+ * execute while the first is running will fail-fast with an exception.
+ *
+ *
+ * @param scheduler Reference to Akka scheduler
+ * @param maxFailures Maximum number of failures before opening the circuit
+ * @param callTimeout [[akka.util.Duration]] of time after which to consider a call a failure
+ * @param resetTimeout [[akka.util.Duration]] of time after which to attempt to close the circuit
+ * @param executor [[akka.dispatch.ExecutionContext]] used for execution of state transition listeners
+ */
+class CircuitBreaker(scheduler: Scheduler, maxFailures: Int, callTimeout: Duration, resetTimeout: Duration)(implicit executor: ExecutionContext) extends AbstractCircuitBreaker {
+
+  def this(executor: ExecutionContext, scheduler: Scheduler, maxFailures: Int, callTimeout: Duration, resetTimeout: Duration) = {
+    this(scheduler, maxFailures, callTimeout, resetTimeout)(executor)
+  }
+
+  /**
+   * Holds reference to current state of CircuitBreaker - *access only via helper methods*
+   */
+  @volatile
+  private[this] var _currentStateDoNotCallMeDirectly: State = Closed
+
+  /**
+   * Helper method for access to underlying state via Unsafe
+   *
+   * @param oldState Previous state on transition
+   * @param newState Next state on transition
+   * @return Whether the previous state matched correctly
+   */
+  @inline
+  private[this] def swapState(oldState: State, newState: State): Boolean =
+    Unsafe.instance.compareAndSwapObject(this, AbstractCircuitBreaker.stateOffset, oldState, newState)
+
+  /**
+   * Helper method for accessing underlying state via Unsafe
+   *
+   * @return Reference to current state
+   */
+  @inline
+  private[this] def currentState: State =
+    Unsafe.instance.getObjectVolatile(this, AbstractCircuitBreaker.stateOffset).asInstanceOf[State]
+
+  /**
+   * Wraps invocations of asynchronous calls that need to be protected
+   *
+   * @param body Call needing protected
+   * @tparam T return type from call
+   * @return [[akka.dispatch.Future]] containing the call result
+   */
+  def withCircuitBreaker[T](body: ⇒ Future[T]): Future[T] = {
+    currentState.invoke(body)
+  }
+
+  /**
+   * Java API for withCircuitBreaker
+   *
+   * @param body Call needing protected
+   * @tparam T return type from call
+   * @return [[akka.dispatch.Future]] containing the call result
+   */
+  def callWithCircuitBreaker[T](body: Callable[Future[T]]): Future[T] = {
+    withCircuitBreaker(body.call)
+  }
+
+  /**
+   * Wraps invocations of synchronous calls that need to be protected
+   *
+   * Calls are run in caller's thread
+   *
+   * @param body Call needing protected
+   * @tparam T return type from call
+   * @return The result of the call
+   */
+  def withSyncCircuitBreaker[T](body: ⇒ T): T = {
+    Await.result(withCircuitBreaker(
+      {
+        try
+          Promise.successful(body)(CircuitBreaker.syncExecutionContext)
+        catch {
+          case NonFatal(t) ⇒ Promise.failed(t)(CircuitBreaker.syncExecutionContext)
+        }
+      }), callTimeout)
+  }
+
+  /**
+   * Java API for withSyncCircuitBreaker
+   *
+   * @param body Call needing protected
+   * @tparam T return type from call
+   * @return The result of the call
+   */
+
+  def callWithSyncCircuitBreaker[T](body: Callable[T]): T = {
+    withSyncCircuitBreaker(body.call)
+  }
+
+  /**
+   * Adds a callback to execute when circuit breaker opens
+   *
+   * The callback is run in the [[akka.dispatch.ExecutionContext]] supplied in the constructor.
+   *
+   * @param callback Handler to be invoked on state change
+   * @tparam T Type supplied to assist with type inference, otherwise ignored by implementation
+   * @return CircuitBreaker for fluent usage
+   */
+  def onOpen[T](callback: ⇒ T): CircuitBreaker = {
+    Open.addListener(() ⇒ callback)
+    this
+  }
+
+  /**
+   * Java API for onOpen
+   *
+   * @param callback Handler to be invoked on state change
+   * @tparam T Type supplied to assist with type inference, otherwise ignored by implementation
+   * @return CircuitBreaker for fluent usage
+   */
+  def onOpen[T](callback: Callable[T]): CircuitBreaker = {
+    onOpen(callback.call)
+  }
+
+  /**
+   * Adds a callback to execute when circuit breaker transitions to half-open
+   *
+   * The callback is run in the [[akka.dispatch.ExecutionContext]] supplied in the constructor.
+   *
+   * @param callback Handler to be invoked on state change
+   * @tparam T Type supplied to assist with type inference, otherwise ignored by implementation
+   * @return CircuitBreaker for fluent usage
+   */
+  def onHalfOpen[T](callback: ⇒ T): CircuitBreaker = {
+    HalfOpen.addListener(() ⇒ callback)
+    this
+  }
+
+  /**
+   * JavaAPI for onHalfOpen
+   *
+   * @param callback Handler to be invoked on state change
+   * @tparam T Type supplied to assist with type inference, otherwise ignored by implementation
+   * @return CircuitBreaker for fluent usage
+   */
+  def onHalfOpen[T](callback: Callable[T]): CircuitBreaker = {
+    onHalfOpen(callback.call)
+  }
+
+  /**
+   * Adds a callback to execute when circuit breaker state closes
+   *
+   * The callback is run in the [[akka.dispatch.ExecutionContext]] supplied in the constructor.
+   *
+   * @param callback Handler to be invoked on state change
+   * @tparam T Type supplied to assist with type inference, otherwise ignored by implementation
+   * @return CircuitBreaker for fluent usage
+   */
+  def onClose[T](callback: ⇒ T): CircuitBreaker = {
+    Closed.addListener(() ⇒ callback)
+    this
+  }
+
+  /**
+   * JavaAPI for onClose
+   *
+   * @param callback Handler to be invoked on state change
+   * @tparam T Type supplied to assist with type inference, otherwise ignored by implementation
+   * @return CircuitBreaker for fluent usage
+   */
+  def onClose[T](callback: Callable[T]): CircuitBreaker = {
+    onClose(callback.call)
+  }
+
+  /**
+   * Retrieves current failure count.
+   *
+   * @return count
+   */
+  private[akka] def currentFailureCount: Int = Closed.get
+
+  /**
+   * Implements consistent transition between states
+   *
+   * @param fromState State being transitioning from
+   * @param toState State being transitioning from
+   * @throws IllegalStateException if an invalid transition is attempted
+   */
+  private def transition(fromState: State, toState: State): Unit = {
+    if (swapState(fromState, toState))
+      toState.enter()
+    else
+      throw new IllegalStateException("Illegal transition attempted from: " + fromState + " to " + toState)
+  }
+
+  /**
+   * Trips breaker to an open state.  This is valid from Closed or Half-Open states.
+   *
+   * @param fromState State we're coming from (Closed or Half-Open)
+   */
+  private def tripBreaker(fromState: State): Unit = {
+    transition(fromState, Open)
+  }
+
+  /**
+   * Resets breaker to a closed state.  This is valid from an Half-Open state only.
+   *
+   */
+  private def resetBreaker(): Unit = {
+    transition(HalfOpen, Closed)
+  }
+
+  /**
+   * Attempts to reset breaker by transitioning to a half-open state.  This is valid from an Open state only.
+   *
+   */
+  private def attemptReset(): Unit = {
+    transition(Open, HalfOpen)
+  }
+
+  /**
+   * Internal state abstraction
+   */
+  private sealed trait State {
+    private val listeners = new CopyOnWriteArrayList[() ⇒ _]
+
+    /**
+     * Add a listener function which is invoked on state entry
+     *
+     * @param listener listener implementation
+     * @tparam T return type of listener, not used - but supplied for type inference purposes
+     */
+    def addListener[T](listener: () ⇒ T) {
+      listeners add listener
+    }
+
+    /**
+     * Test for whether listeners exist
+     *
+     * @return whether listeners exist
+     */
+    private def hasListeners: Boolean = !listeners.isEmpty
+
+    /**
+     * Notifies the listeners of the transition event via a Future executed in implicit parameter ExecutionContext
+     *
+     * @return Promise which executes listener in supplied [[akka.dispatch.ExecutionContext]]
+     */
+    protected def notifyTransitionListeners() {
+      if (hasListeners) {
+        val iterator = listeners.iterator
+        while (iterator.hasNext) {
+          val listener = iterator.next
+          //FIXME per @viktorklang: it's a bit wasteful to create Futures for one-offs, just use EC.execute instead
+          Future(listener())
+        }
+      }
+    }
+
+    /**
+     * Shared implementation of call across all states.  Thrown exception or execution of the call beyond the allowed
+     * call timeout is counted as a failed call, otherwise a successful call
+     *
+     * @param body Implementation of the call
+     * @tparam T Return type of the call's implementation
+     * @return Future containing the result of the call
+     */
+    def callThrough[T](body: ⇒ Future[T]): Future[T] = {
+      val deadline = callTimeout.fromNow
+      val bodyFuture = try body catch {
+        case NonFatal(t) ⇒ Promise.failed(t)
+      }
+      bodyFuture onFailure {
+        case _ ⇒ callFails()
+      } onSuccess {
+        case _ ⇒
+          if (deadline.isOverdue()) callFails()
+          else callSucceeds()
+      }
+    }
+
+    /**
+     * Abstract entry point for all states
+     *
+     * @param body Implementation of the call that needs protected
+     * @tparam T Return type of protected call
+     * @return Future containing result of protected call
+     */
+    def invoke[T](body: ⇒ Future[T]): Future[T]
+
+    /**
+     * Invoked when call succeeds
+     *
+     */
+    def callSucceeds(): Unit
+
+    /**
+     * Invoked when call fails
+     *
+     */
+    def callFails(): Unit
+
+    /**
+     * Invoked on the transitioned-to state during transition.  Notifies listeners after invoking subclass template
+     * method _enter
+     *
+     */
+    final def enter(): Unit = {
+      _enter()
+      notifyTransitionListeners()
+    }
+
+    /**
+     * Template method for concrete traits
+     *
+     */
+    def _enter(): Unit
+  }
+
+  /**
+   * Concrete implementation of Closed state
+   */
+  private object Closed extends AtomicInteger with State {
+
+    /**
+     * Implementation of invoke, which simply attempts the call
+     *
+     * @param body Implementation of the call that needs protected
+     * @tparam T Return type of protected call
+     * @return Future containing result of protected call
+     */
+    override def invoke[T](body: ⇒ Future[T]): Future[T] = {
+      callThrough(body)
+    }
+
+    /**
+     * On successful call, the failure count is reset to 0
+     *
+     * @return
+     */
+    override def callSucceeds(): Unit = { set(0) }
+
+    /**
+     * On failed call, the failure count is incremented.  The count is checked against the configured maxFailures, and
+     * the breaker is tripped if we have reached maxFailures.
+     *
+     * @return
+     */
+    override def callFails(): Unit = {
+      if (incrementAndGet() == maxFailures) tripBreaker(Closed)
+    }
+
+    /**
+     * On entry of this state, failure count is reset.
+     *
+     * @return
+     */
+    override def _enter(): Unit = {
+      set(0)
+    }
+
+    /**
+     * Override for more descriptive toString
+     *
+     * @return
+     */
+    override def toString: String = {
+      "Closed with failure count = " + get()
+    }
+  }
+
+  /**
+   * Concrete implementation of half-open state
+   */
+  private object HalfOpen extends AtomicBoolean(true) with State {
+
+    /**
+     * Allows a single call through, during which all other callers fail-fast.  If the call fails, the breaker reopens.
+     * If the call succeeds the breaker closes.
+     *
+     * @param body Implementation of the call that needs protected
+     * @tparam T Return type of protected call
+     * @return Future containing result of protected call
+     */
+    override def invoke[T](body: ⇒ Future[T]): Future[T] = {
+      if (compareAndSet(true, false))
+        callThrough(body)
+      else
+        Promise.failed[T](new CircuitBreakerOpenException(Duration.Zero))
+    }
+
+    /**
+     * Reset breaker on successful call.
+     *
+     * @return
+     */
+    override def callSucceeds(): Unit = { resetBreaker() }
+
+    /**
+     * Reopen breaker on failed call.
+     *
+     * @return
+     */
+    override def callFails(): Unit = { tripBreaker(HalfOpen) }
+
+    /**
+     * On entry, guard should be reset for that first call to get in
+     *
+     * @return
+     */
+    override def _enter(): Unit = {
+      set(true)
+    }
+
+    /**
+     * Override for more descriptive toString
+     *
+     * @return
+     */
+    override def toString: String = {
+      "Half-Open currently testing call for success = " + get()
+    }
+  }
+
+  /**
+   * Concrete implementation of Open state
+   */
+  private object Open extends AtomicLong with State {
+
+    /**
+     * Fail-fast on any invocation
+     *
+     * @param body Implementation of the call that needs protected
+     * @tparam T Return type of protected call
+     * @return Future containing result of protected call
+     */
+    override def invoke[T](body: ⇒ Future[T]): Future[T] = {
+      Promise.failed[T](new CircuitBreakerOpenException(remainingTimeout().timeLeft))
+    }
+
+    /**
+     * Calculate remaining timeout to inform the caller in case a backoff algorithm is useful
+     *
+     * @return [[akka.util.Deadline]] to when the breaker will attempt a reset by transitioning to half-open
+     */
+    private def remainingTimeout(): Deadline = get match {
+      case 0L ⇒ Deadline.now
+      case t  ⇒ (t.millis + resetTimeout).fromNow
+    }
+
+    /**
+     * No-op for open, calls are never executed so cannot succeed or fail
+     *
+     * @return
+     */
+    override def callSucceeds(): Unit = {}
+
+    /**
+     * No-op for open, calls are never executed so cannot succeed or fail
+     *
+     * @return
+     */
+    override def callFails(): Unit = {}
+
+    /**
+     * On entering this state, schedule an attempted reset via [[akka.actor.Scheduler]] and store the entry time to
+     * calculate remaining time before attempted reset.
+     *
+     * @return
+     */
+    override def _enter(): Unit = {
+      set(System.currentTimeMillis)
+      scheduler.scheduleOnce(resetTimeout) {
+        attemptReset()
+      }
+    }
+
+    /**
+     * Override for more descriptive toString
+     *
+     * @return
+     */
+    override def toString: String = {
+      "Open"
+    }
+  }
+
+}
+
+/**
+ * Exception thrown when Circuit Breaker is open.
+ *
+ * @param remainingDuration Stores remaining time before attempting a reset.  Zero duration means the breaker is
+ *                          currently in half-open state.
+ * @param message Defaults to "Circuit Breaker is open; calls are failing fast"
+ */
+class CircuitBreakerOpenException(
+  val remainingDuration: Duration,
+  message: String = "Circuit Breaker is open; calls are failing fast")
+  extends AkkaException(message) with NoStackTrace

akka-cluster/src/multi-jvm/scala/akka/cluster/LeaderDowningNodeThatIsUnreachableSpec.scala

@@ -17,7 +17,7 @@ object LeaderDowningNodeThatIsUnreachableMultiJvmSpec extends MultiNodeConfig {
   val third = role("third")
   val fourth = role("fourth")
 
-  commonConfig(debugConfig(on = false).
+  commonConfig(debugConfig(on = true).
     withFallback(ConfigFactory.parseString("""
       akka.cluster {
         auto-down = on

akka-cluster/src/multi-jvm/scala/akka/cluster/LeaderElectionSpec.scala

@@ -49,6 +49,7 @@ abstract class LeaderElectionSpec extends MultiNodeSpec(LeaderElectionMultiJvmSp
         cluster.join(firstAddress)
         awaitUpConvergence(numberOfMembers = roles.size)
         cluster.isLeader must be(myself == roles.head)
+        assertLeaderIn(roles)
       }
       testConductor.enter("after")
     }
@@ -58,6 +59,7 @@ abstract class LeaderElectionSpec extends MultiNodeSpec(LeaderElectionMultiJvmSp
       currentRoles.size must be >= (2)
       val leader = currentRoles.head
       val aUser = currentRoles.last
+      val remainingRoles = currentRoles.tail
 
       myself match {
 
@@ -78,13 +80,14 @@ abstract class LeaderElectionSpec extends MultiNodeSpec(LeaderElectionMultiJvmSp
           cluster.down(leaderAddress)
           testConductor.enter("after-down", "completed")
 
-        case _ if currentRoles.tail.contains(myself) ⇒
+        case _ if remainingRoles.contains(myself) ⇒
           // remaining cluster nodes, not shutdown
           testConductor.enter("before-shutdown", "after-shutdown", "after-down")
 
           awaitUpConvergence(currentRoles.size - 1)
-          val nextExpectedLeader = currentRoles.tail.head
+          val nextExpectedLeader = remainingRoles.head
           cluster.isLeader must be(myself == nextExpectedLeader)
+          assertLeaderIn(remainingRoles)
 
           testConductor.enter("completed")
 

akka-cluster/src/multi-jvm/scala/akka/cluster/MultiNodeClusterSpec.scala

@@ -42,15 +42,20 @@ trait MultiNodeClusterSpec { self: MultiNodeSpec ⇒
     expectedAddresses.sorted.zipWithIndex.foreach { case (a, i) ⇒ members(i).address must be(a) }
   }
 
+  def assertLeader(nodesInCluster: RoleName*): Unit = if (nodesInCluster.contains(myself)) {
+    assertLeaderIn(nodesInCluster)
+  }
+
   /**
    * Assert that the cluster has elected the correct leader
    * out of all nodes in the cluster. First
    * member in the cluster ring is expected leader.
    */
-  def assertLeader(nodesInCluster: RoleName*): Unit = if (nodesInCluster.contains(myself)) {
+  def assertLeaderIn(nodesInCluster: Seq[RoleName]): Unit = if (nodesInCluster.contains(myself)) {
     nodesInCluster.length must not be (0)
     val expectedLeader = roleOfLeader(nodesInCluster)
     cluster.isLeader must be(ifNode(expectedLeader)(true)(false))
+    cluster.status must (be(MemberStatus.Up) or be(MemberStatus.Leaving))
   }
 
   /**

akka-cluster/src/multi-jvm/scala/akka/cluster/NodeLeavingAndExitingSpec.scala

@@ -20,8 +20,8 @@ object NodeLeavingAndExitingMultiJvmSpec extends MultiNodeConfig {
     debugConfig(on = false)
     .withFallback(ConfigFactory.parseString("""
         akka.cluster {
-          leader-actions-frequency           = 5000 ms  # increase the leader action task frequency
-          unreachable-nodes-reaper-frequency = 30000 ms # turn "off" reaping to unreachable node set
+          leader-actions-frequency           = 5 s  # increase the leader action task frequency to make sure we get a chance to test the LEAVING state
+          unreachable-nodes-reaper-frequency = 30 s # turn "off" reaping to unreachable node set
         }
       """)
     .withFallback(MultiNodeClusterSpec.clusterConfig)))
@@ -64,6 +64,8 @@ abstract class NodeLeavingAndExitingSpec extends MultiNodeSpec(NodeLeavingAndExi
       runOn(first, third) {
 
         // 1. Verify that 'second' node is set to LEAVING
+        //   We have set the 'leader-actions-frequency' to 5 seconds to make sure that we get a
+        //   chance to test the LEAVING state before the leader moves the node to EXITING
         awaitCond(cluster.latestGossip.members.exists(_.status == MemberStatus.Leaving)) // wait on LEAVING
         val hasLeft = cluster.latestGossip.members.find(_.status == MemberStatus.Leaving) // verify node that left
         hasLeft must be('defined)

akka-cluster/src/multi-jvm/scala/akka/cluster/NodeLeavingSpec.scala

@@ -18,8 +18,8 @@ object NodeLeavingMultiJvmSpec extends MultiNodeConfig {
   commonConfig(
     debugConfig(on = false)
     .withFallback(ConfigFactory.parseString("""
-        akka.cluster.leader-actions-frequency           = 5000 ms
-        akka.cluster.unreachable-nodes-reaper-frequency = 30000 ms # turn "off" reaping to unreachable node set
+        akka.cluster.leader-actions-frequency           = 5 s
+        akka.cluster.unreachable-nodes-reaper-frequency = 30 s # turn "off" reaping to unreachable node set
       """))
     .withFallback(MultiNodeClusterSpec.clusterConfig))
 }

akka-cluster/src/multi-jvm/scala/akka/cluster/NodeShutdownSpec.scala

@@ -51,16 +51,17 @@ abstract class NodeShutdownSpec extends MultiNodeSpec(NodeShutdownMultiJvmSpec)
       }
       awaitUpConvergence(numberOfMembers = 2)
       cluster.isSingletonCluster must be(false)
+      assertLeader(first, second)
     }
 
-    "become singleton cluster when one node is shutdown" in {
+    "become singleton cluster when one node is shutdown" taggedAs LongRunningTest in {
       runOn(first) {
         val secondAddress = node(second).address
-        testConductor.shutdown(first, 0)
-        testConductor.removeNode(first)
+        testConductor.shutdown(second, 0)
+        testConductor.removeNode(second)
         awaitUpConvergence(numberOfMembers = 1, canNotBePartOfMemberRing = Seq(secondAddress), 30.seconds)
         cluster.isSingletonCluster must be(true)
-        cluster.isLeader must be(true)
+        assertLeader(first)
       }
 
     }

akka-docs/common/circuitbreaker.rst

@@ -0,0 +1,130 @@
+.. _circuit-breaker:
+
+###############
+Circuit Breaker
+###############
+
+==================
+Why are they used?
+==================
+A circuit breaker is used to provide stability and prevent cascading failures in distributed
+systems.  These should be used in conjunction with judicious timeouts at the interfaces between
+remote systems to prevent the failure of a single component from bringing down all components.
+
+As an example, we have a web application interacting with a remote third party web service.  
+Let's say the third party has oversold their capacity and their database melts down under load.  
+Assume that the database fails in such a way that it takes a very long time to hand back an
+error to the third party web service.  This in turn makes calls fail after a long period of 
+time.  Back to our web application, the users have noticed that their form submissions take
+much longer seeming to hang.  Well the users do what they know to do which is use the refresh
+button, adding more requests to their already running requests.  This eventually causes the 
+failure of the web application due to resource exhaustion.  This will affect all users, even
+those who are not using functionality dependent on this third party web service.
+
+Introducing circuit breakers on the web service call would cause the requests to begin to 
+fail-fast, letting the user know that something is wrong and that they need not refresh 
+their request.  This also confines the failure behavior to only those users that are using
+functionality dependent on the third party, other users are no longer affected as there is no
+resource exhaustion.  Circuit breakers can also allow savvy developers to mark portions of
+the site that use the functionality unavailable, or perhaps show some cached content as 
+appropriate while the breaker is open.
+
+The Akka library provides an implementation of a circuit breaker called 
+:class:`akka.pattern.CircuitBreaker` which has the behavior described below.
+
+=================
+What do they do?
+=================
+* During normal operation, a circuit breaker is in the `Closed` state:
+	* Exceptions or calls exceeding the configured `callTimeout` increment a failure counter
+	* Successes reset the failure count to zero 
+	* When the failure counter reaches a `maxFailures` count, the breaker is tripped into `Open` state
+* While in `Open` state:
+	* All calls fail-fast with a :class:`CircuitBreakerOpenException`
+	* After the configured `resetTimeout`, the circuit breaker enters a `Half-Open` state
+* In `Half-Open` state:
+	* The first call attempted is allowed through without failing fast
+	* All other calls fail-fast with an exception just as in `Open` state
+	* If the first call succeeds, the breaker is reset back to `Closed` state
+	* If the first call fails, the breaker is tripped again into the `Open` state for another full `resetTimeout`
+* State transition listeners: 
+	* Callbacks can be provided for every state entry via `onOpen`, `onClose`, and `onHalfOpen`
+	* These are executed in the :class:`ExecutionContext` provided. 
+
+.. graphviz::
+
+	digraph circuit_breaker {
+		rankdir = "LR";
+		size = "6,5";
+		graph [ bgcolor = "transparent" ]
+		node [ fontname = "Helvetica",
+					 fontsize = 14,
+					 shape = circle, 
+					 color = white, 
+					 style = filled ];
+	  edge [ fontname = "Helvetica", fontsize = 12 ]
+		Closed [ fillcolor = green2 ];
+		"Half-Open" [fillcolor = yellow2 ];
+		Open [ fillcolor = red2 ];
+		Closed -> Closed [ label = "Success" ];
+		"Half-Open" -> Open [ label = "Trip Breaker" ];
+		"Half-Open" -> Closed [ label = "Reset Breaker" ];
+		Closed -> Open [ label = "Trip Breaker" ];
+		Open -> Open [ label = "Calls failing fast" ];
+		Open -> "Half-Open" [ label = "Attempt Reset" ];
+	}
+
+========
+Examples
+========
+
+--------------
+Initialization
+--------------
+
+Here's how a :class:`CircuitBreaker` would be configured for:
+  * 5 maximum failures
+  * a call timeout of 10 seconds 
+  * a reset timeout of 1 minute
+
+^^^^^^^
+Scala
+^^^^^^^
+
+.. includecode:: code/docs/circuitbreaker/CircuitBreakerDocSpec.scala
+   :include: imports1,circuit-breaker-initialization
+
+^^^^^^^
+Java
+^^^^^^^
+
+.. includecode:: code/docs/circuitbreaker/DangerousJavaActor.java
+   :include: imports1,circuit-breaker-initialization
+
+---------------
+Call Protection
+---------------
+
+Here's how the :class:`CircuitBreaker` would be used to protect an asynchronous
+call as well as a synchronous one:
+
+^^^^^^^
+Scala
+^^^^^^^
+
+.. includecode:: code/docs/circuitbreaker/CircuitBreakerDocSpec.scala
+   :include: circuit-breaker-usage
+
+^^^^^^
+Java
+^^^^^^
+
+.. includecode:: code/docs/circuitbreaker/DangerousJavaActor.java
+   :include: circuit-breaker-usage
+
+.. note::
+
+	Using the :class:`CircuitBreaker` companion object's `apply` or `create` methods
+	will return a :class:`CircuitBreaker` where callbacks are executed in the caller's thread.
+	This can be useful if the asynchronous :class:`Future` behavior is unnecessary, for
+	example invoking a synchronous-only API.

akka-docs/common/code/docs/circuitbreaker/CircuitBreakerDocSpec.scala

@@ -0,0 +1,43 @@
+/**
+ * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+
+package docs.circuitbreaker
+
+//#imports1
+import akka.util.duration._ // small d is important here
+import akka.pattern.CircuitBreaker
+import akka.actor.Actor
+import akka.dispatch.Future
+import akka.event.Logging
+
+//#imports1
+
+class CircuitBreakerDocSpec {}
+
+//#circuit-breaker-initialization
+class DangerousActor extends Actor {
+
+  val log = Logging(context.system, this)
+  implicit val executionContext = context.dispatcher
+  val breaker =
+    new CircuitBreaker(context.system.scheduler, 5, 10.seconds, 1.minute)
+      .onOpen(notifyMeOnOpen)
+
+  def notifyMeOnOpen =
+    log.warning("My CircuitBreaker is now open, and will not close for one minute")
+  //#circuit-breaker-initialization
+
+  //#circuit-breaker-usage
+  def dangerousCall: String = "This really isn't that dangerous of a call after all"
+
+  def receive = {
+    case "is my middle name" ⇒
+      sender ! breaker.withCircuitBreaker(Future(dangerousCall))
+    case "block for me" ⇒
+      sender ! breaker.withSyncCircuitBreaker(dangerousCall)
+  }
+  //#circuit-breaker-usage
+
+}
+

akka-docs/common/code/docs/circuitbreaker/DangerousJavaActor.java

@@ -0,0 +1,83 @@
+/**
+ * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+package docs.circuitbreaker;
+
+//#imports1
+
+import akka.actor.UntypedActor;
+import akka.dispatch.Future;
+import akka.event.LoggingAdapter;
+import akka.util.Duration;
+import akka.pattern.CircuitBreaker;
+import akka.event.Logging;
+
+import static akka.dispatch.Futures.future;
+
+import java.util.concurrent.Callable;
+
+//#imports1
+
+//#circuit-breaker-initialization
+public class DangerousJavaActor extends UntypedActor {
+
+    private final CircuitBreaker breaker;
+    private final LoggingAdapter log = Logging.getLogger(getContext().system(), this);
+
+    public DangerousJavaActor() {
+        this.breaker = new CircuitBreaker(
+                getContext().dispatcher(), getContext().system().scheduler(),
+                5, Duration.parse("10s"), Duration.parse("1m"))
+                .onOpen(new Callable<Object>() {
+                    public Object call() throws Exception {
+                        notifyMeOnOpen();
+                        return null;
+                    }
+                });
+    }
+
+    public void notifyMeOnOpen() {
+        log.warning("My CircuitBreaker is now open, and will not close for one minute");
+    }
+//#circuit-breaker-initialization
+
+    //#circuit-breaker-usage
+    public String dangerousCall() {
+        return "This really isn't that dangerous of a call after all";
+    }
+
+    @Override
+    public void onReceive(Object message) {
+        if (message instanceof String) {
+            String m = (String) message;
+            if ("is my middle name".equals(m)) {
+                final Future<String> f = future(
+                        new Callable<String>() {
+                            public String call() {
+                                return dangerousCall();
+                            }
+                        }, getContext().dispatcher());
+
+                getSender().tell(breaker
+                        .callWithCircuitBreaker(
+                                new Callable<Future<String>>() {
+                                    public Future<String> call() throws Exception {
+                                        return f;
+                                    }
+                                }));
+            }
+            if ("block for me".equals(m)) {
+                getSender().tell(breaker
+                        .callWithSyncCircuitBreaker(
+                                new Callable<String>() {
+                                    @Override
+                                    public String call() throws Exception {
+                                        return dangerousCall();
+                                    }
+                                }));
+            }
+        }
+    }
+//#circuit-breaker-usage
+
+}

akka-docs/common/index.rst

@@ -5,3 +5,4 @@ Common utilities
    :maxdepth: 2
 
    duration
+   circuitbreaker

akka-docs/conf.py

@@ -8,7 +8,7 @@ import sys, os
 # -- General configuration -----------------------------------------------------
 
 sys.path.append(os.path.abspath('_sphinx/exts'))
-extensions = ['sphinx.ext.todo', 'includecode']
+extensions = ['sphinx.ext.todo', 'includecode', 'sphinx.ext.graphviz']
 
 templates_path = ['_templates']
 source_suffix = '.rst'

akka-docs/modules/code/docs/actor/mailbox/DurableMailboxDocSpec.scala

@@ -50,6 +50,8 @@ import akka.dispatch.MailboxType
 import akka.dispatch.MessageQueue
 import akka.actor.mailbox.DurableMessageQueue
 import akka.actor.mailbox.DurableMessageSerialization
+import akka.pattern.CircuitBreaker
+import akka.util.duration._
 
 class MyMailboxType(systemSettings: ActorSystem.Settings, config: Config)
   extends MailboxType {
@@ -65,20 +67,23 @@ class MyMessageQueue(_owner: ActorContext)
   extends DurableMessageQueue(_owner) with DurableMessageSerialization {
 
   val storage = new QueueStorage
+  // A real-world implmentation would use configuration to set the last 
+  // three parameters below
+  val breaker = CircuitBreaker(_owner.system.scheduler, 5, 30.seconds, 1.minute)
 
-  def enqueue(receiver: ActorRef, envelope: Envelope) {
+  def enqueue(receiver: ActorRef, envelope: Envelope): Unit = breaker.withSyncCircuitBreaker {
     val data: Array[Byte] = serialize(envelope)
     storage.push(data)
   }
 
-  def dequeue(): Envelope = {
+  def dequeue(): Envelope = breaker.withSyncCircuitBreaker {
     val data: Option[Array[Byte]] = storage.pull()
     data.map(deserialize).orNull
   }
 
-  def hasMessages: Boolean = !storage.isEmpty
+  def hasMessages: Boolean = breaker.withSyncCircuitBreaker { !storage.isEmpty }
 
-  def numberOfMessages: Int = storage.size
+  def numberOfMessages: Int = breaker.withSyncCircuitBreaker { storage.size }
 
   /**
    * Called when the mailbox is disposed.

akka-docs/modules/durable-mailbox.rst

@@ -80,7 +80,9 @@ a configurator (MailboxType) and a queue implementation (DurableMessageQueue).
 The envelope contains the message sent to the actor, and information about sender. It is the
 envelope that needs to be stored. As a help utility you can mixin DurableMessageSerialization
 to serialize and deserialize the envelope using the ordinary :ref:`serialization-scala`
-mechanism. This optional and you may store the envelope data in any way you like.
+mechanism. This optional and you may store the envelope data in any way you like. Durable
+mailboxes are an excellent fit for usage of circuit breakers.  These are described in the 
+:ref:`circuit-breaker` documentation.
 
 .. includecode:: code/docs/actor/mailbox/DurableMailboxDocSpec.scala
    :include: custom-mailbox

akka-durable-mailboxes/akka-file-mailbox/src/main/resources/reference.conf

@@ -46,6 +46,18 @@ akka {
         
         # whether to sync the journal after each transaction
         sync-journal = off
+
+        # circuit breaker configuration
+        circuit-breaker {
+            # maximum number of failures before opening breaker
+            max-failures = 3
+
+            # duration of time beyond which a call is assumed to be timed out and considered a failure
+            call-timeout = 3 seconds
+
+            # duration of time to wait until attempting to reset the breaker during which all calls fail-fast
+            reset-timeout = 30 seconds
+        }
       }
     }
   }

akka-durable-mailboxes/akka-file-mailbox/src/main/scala/akka/actor/mailbox/FileBasedMailbox.scala

@@ -5,14 +5,14 @@
 package akka.actor.mailbox
 
 import akka.actor.ActorContext
-import akka.dispatch.{ Envelope, MessageQueue }
 import akka.event.Logging
 import akka.actor.ActorRef
-import akka.dispatch.MailboxType
 import com.typesafe.config.Config
-import akka.util.NonFatal
 import akka.ConfigurationException
 import akka.actor.ActorSystem
+import akka.dispatch._
+import akka.util.{ Duration, NonFatal }
+import akka.pattern.{ CircuitBreakerOpenException, CircuitBreaker }
 
 class FileBasedMailboxType(systemSettings: ActorSystem.Settings, config: Config) extends MailboxType {
   private val settings = new FileBasedMailboxSettings(systemSettings, config)
@@ -26,6 +26,8 @@ class FileBasedMessageQueue(_owner: ActorContext, val settings: FileBasedMailbox
   // TODO Is it reasonable for all FileBasedMailboxes to have their own logger?
   private val log = Logging(system, "FileBasedMessageQueue")
 
+  val breaker = CircuitBreaker(_owner.system.scheduler, settings.CircuitBreakerMaxFailures, settings.CircuitBreakerCallTimeout, settings.CircuitBreakerResetTimeout)
+
   private val queue = try {
     (new java.io.File(settings.QueuePath)) match {
       case dir if dir.exists && !dir.isDirectory ⇒ throw new IllegalStateException("Path already occupied by non-directory " + dir)
@@ -42,18 +44,28 @@ class FileBasedMessageQueue(_owner: ActorContext, val settings: FileBasedMailbox
       throw e
   }
 
-  def enqueue(receiver: ActorRef, envelope: Envelope): Unit = queue.add(serialize(envelope))
+  def enqueue(receiver: ActorRef, envelope: Envelope) {
+    breaker.withSyncCircuitBreaker(queue.add(serialize(envelope)))
+  }
 
-  def dequeue(): Envelope = try {
+  def dequeue(): Envelope = {
+    breaker.withSyncCircuitBreaker(
+      try {
         queue.remove.map(item ⇒ { queue.confirmRemove(item.xid); deserialize(item.data) }).orNull
       } catch {
         case _: java.util.NoSuchElementException ⇒ null
-    case NonFatal(e) ⇒
-      log.error(e, "Couldn't dequeue from file-based mailbox")
+        case e: CircuitBreakerOpenException ⇒
+          log.debug(e.getMessage())
           throw e
+        case NonFatal(e) ⇒
+          log.error(e, "Couldn't dequeue from file-based mailbox, due to [{}]", e.getMessage())
+          throw e
+      })
   }
 
-  def numberOfMessages: Int = queue.length.toInt
+  def numberOfMessages: Int = {
+    breaker.withSyncCircuitBreaker(queue.length.toInt)
+  }
 
   def hasMessages: Boolean = numberOfMessages > 0
 

akka-durable-mailboxes/akka-file-mailbox/src/main/scala/akka/actor/mailbox/FileBasedMailboxSettings.scala

@@ -29,4 +29,7 @@ class FileBasedMailboxSettings(val systemSettings: ActorSystem.Settings, val use
   val KeepJournal: Boolean = getBoolean("keep-journal")
   val SyncJournal: Boolean = getBoolean("sync-journal")
 
+  val CircuitBreakerMaxFailures = getInt("circuit-breaker.max-failures")
+  val CircuitBreakerCallTimeout = Duration.fromNanos(getNanoseconds("circuit-breaker.call-timeout"))
+  val CircuitBreakerResetTimeout = Duration.fromNanos(getNanoseconds("circuit-breaker.reset-timeout"))
 }

akka-durable-mailboxes/akka-file-mailbox/src/test/scala/akka/actor/mailbox/FileBasedMailboxSpec.scala

@@ -1,7 +1,6 @@
 package akka.actor.mailbox
 
 import org.apache.commons.io.FileUtils
-import com.typesafe.config.ConfigFactory
 import akka.dispatch.Mailbox
 
 object FileBasedMailboxSpec {
@@ -10,6 +9,8 @@ object FileBasedMailboxSpec {
       mailbox-type = akka.actor.mailbox.FileBasedMailboxType
       throughput = 1
       file-based.directory-path = "file-based"
+      file-based.circuit-breaker.max-failures = 5
+      file-based.circuit-breaker.call-timeout = 5 seconds
     }
                """
 }
@@ -17,16 +18,23 @@ object FileBasedMailboxSpec {
 @org.junit.runner.RunWith(classOf[org.scalatest.junit.JUnitRunner])
 class FileBasedMailboxSpec extends DurableMailboxSpec("File", FileBasedMailboxSpec.config) {
 
-  val queuePath = new FileBasedMailboxSettings(system.settings, system.settings.config.getConfig("File-dispatcher")).QueuePath
+  val settings = new FileBasedMailboxSettings(system.settings, system.settings.config.getConfig("File-dispatcher"))
 
   "FileBasedMailboxSettings" must {
     "read the file-based section" in {
-      queuePath must be("file-based")
+      settings.QueuePath must be("file-based")
+      settings.CircuitBreakerMaxFailures must be(5)
+
+      import akka.util.duration._
+
+      settings.CircuitBreakerCallTimeout must be(5 seconds)
     }
   }
 
+  def isDurableMailbox(m: Mailbox): Boolean = m.messageQueue.isInstanceOf[FileBasedMessageQueue]
+
   def clean() {
-    FileUtils.deleteDirectory(new java.io.File(queuePath))
+    FileUtils.deleteDirectory(new java.io.File(settings.QueuePath))
   }
 
   override def atStartup() {

akka-remote/src/main/resources/reference.conf

@@ -133,6 +133,18 @@ akka {
       # (I) Maximum total size of all channels, 0 for off
       max-total-memory-size = 0b
 
+      # (I&O) Sets the high water mark for the in and outbound sockets, set to 0b for platform default
+      write-buffer-high-water-mark = 0b
+
+      # (I&O) Sets the low water mark for the in and outbound sockets, set to 0b for platform default
+      write-buffer-low-water-mark = 0b
+
+      # (I&O) Sets the send buffer size of the Sockets, set to 0b for platform default
+      send-buffer-size = 0b
+
+      # (I&O) Sets the receive buffer size of the Sockets, set to 0b for platform default
+      receive-buffer-size = 0b
+
       # (O) Time between reconnect attempts for active clients
       reconnect-delay = 5s
 

akka-remote/src/main/scala/akka/remote/netty/Client.scala

@@ -147,6 +147,10 @@ private[akka] class ActiveRemoteClient private[akka] (
       b.setOption("tcpNoDelay", true)
       b.setOption("keepAlive", true)
       b.setOption("connectTimeoutMillis", settings.ConnectionTimeout.toMillis)
+      settings.ReceiveBufferSize.foreach(sz ⇒ b.setOption("receiveBufferSize", sz))
+      settings.SendBufferSize.foreach(sz ⇒ b.setOption("sendBufferSize", sz))
+      settings.WriteBufferHighWaterMark.foreach(sz ⇒ b.setOption("writeBufferHighWaterMark", sz))
+      settings.WriteBufferLowWaterMark.foreach(sz ⇒ b.setOption("writeBufferLowWaterMark", sz))
       settings.OutboundLocalAddress.foreach(s ⇒ b.setOption("localAddress", new InetSocketAddress(s, 0)))
       bootstrap = b
 

akka-remote/src/main/scala/akka/remote/netty/Server.scala

@@ -45,6 +45,10 @@ private[akka] class NettyRemoteServer(val netty: NettyRemoteTransport) {
     b.setOption("tcpNoDelay", true)
     b.setOption("child.keepAlive", true)
     b.setOption("reuseAddress", true)
+    settings.ReceiveBufferSize.foreach(sz ⇒ b.setOption("receiveBufferSize", sz))
+    settings.SendBufferSize.foreach(sz ⇒ b.setOption("sendBufferSize", sz))
+    settings.WriteBufferHighWaterMark.foreach(sz ⇒ b.setOption("writeBufferHighWaterMark", sz))
+    settings.WriteBufferLowWaterMark.foreach(sz ⇒ b.setOption("writeBufferLowWaterMark", sz))
     b
   }
 

akka-remote/src/main/scala/akka/remote/netty/Settings.scala

@@ -37,8 +37,21 @@ private[akka] class NettySettings(config: Config, val systemName: String) {
   val WriteTimeout: Duration = Duration(getMilliseconds("write-timeout"), MILLISECONDS)
   val AllTimeout: Duration = Duration(getMilliseconds("all-timeout"), MILLISECONDS)
   val ReconnectDelay: Duration = Duration(getMilliseconds("reconnect-delay"), MILLISECONDS)
+
   val MessageFrameSize: Int = getBytes("message-frame-size").toInt
 
+  private[this] def optionSize(s: String): Option[Int] = getBytes(s).toInt match {
+    case 0 ⇒ None
+    case x if x < 0 ⇒
+      throw new ConfigurationException("Setting '%s' must be 0 or positive (and fit in an Int)" format s)
+    case other ⇒ Some(other)
+  }
+
+  val WriteBufferHighWaterMark: Option[Int] = optionSize("write-buffer-high-water-mark")
+  val WriteBufferLowWaterMark: Option[Int] = optionSize("write-buffer-low-water-mark")
+  val SendBufferSize: Option[Int] = optionSize("send-buffer-size")
+  val ReceiveBufferSize: Option[Int] = optionSize("receive-buffer-size")
+
   val Hostname: String = getString("hostname") match {
     case ""    ⇒ InetAddress.getLocalHost.getHostAddress
     case value ⇒ value

akka-remote/src/test/scala/akka/remote/RemoteConfigSpec.scala

@@ -56,6 +56,10 @@ class RemoteConfigSpec extends AkkaSpec(
       WriteTimeout must be(10 seconds)
       AllTimeout must be(0 millis)
       ReconnectionTimeWindow must be(10 minutes)
+      WriteBufferHighWaterMark must be(None)
+      WriteBufferLowWaterMark must be(None)
+      SendBufferSize must be(None)
+      ReceiveBufferSize must be(None)
     }
 
   }

project/AkkaBuild.scala

@@ -11,6 +11,8 @@ import com.typesafe.sbtmultijvm.MultiJvmPlugin.{ MultiJvm, extraOptions, jvmOpti
 import com.typesafe.sbtscalariform.ScalariformPlugin
 import com.typesafe.sbtscalariform.ScalariformPlugin.ScalariformKeys
 import com.typesafe.sbtosgi.OsgiPlugin.{ OsgiKeys, osgiSettings }
+import com.typesafe.tools.mima.plugin.MimaPlugin.mimaDefaultSettings
+import com.typesafe.tools.mima.plugin.MimaKeys.previousArtifact
 import java.lang.Boolean.getBoolean
 import sbt.Tests
 import Sphinx.{ sphinxDocs, sphinxHtml, sphinxLatex, sphinxPdf, sphinxPygments, sphinxTags }
@@ -27,7 +29,8 @@ object AkkaBuild extends Build {
   lazy val akka = Project(
     id = "akka",
     base = file("."),
-    settings = parentSettings ++ Release.settings ++ Unidoc.settings ++ Sphinx.settings ++ Publish.versionSettings ++ Dist.settings ++ Seq(
+    settings = parentSettings ++ Release.settings ++ Unidoc.settings ++ Sphinx.settings ++ Publish.versionSettings ++
+      Dist.settings ++ mimaSettings ++ Seq(
       testMailbox in GlobalScope := System.getProperty("akka.testMailbox", "false").toBoolean,
       parallelExecution in GlobalScope := System.getProperty("akka.parallelExecution", "false").toBoolean,
       Publish.defaultPublishTo in ThisBuild <<= crossTarget / "repository",
@@ -54,7 +57,8 @@ object AkkaBuild extends Build {
       artifact in (Compile, packageBin) ~= (_.copy(`type` = "bundle")),
       // to fix scaladoc generation
       fullClasspath in doc in Compile <<= fullClasspath in Compile,
-      libraryDependencies ++= Dependencies.actor
+      libraryDependencies ++= Dependencies.actor,
+      previousArtifact := akkaPreviousArtifact("akka-actor")
     )
   )
 
@@ -63,7 +67,8 @@ object AkkaBuild extends Build {
     base = file("akka-testkit"),
     dependencies = Seq(actor),
     settings = defaultSettings ++ Seq(
-      libraryDependencies ++= Dependencies.testkit
+      libraryDependencies ++= Dependencies.testkit,
+      previousArtifact := akkaPreviousArtifact("akka-testkit")
     )
   )
 
@@ -101,7 +106,8 @@ object AkkaBuild extends Build {
         (name: String) => (src ** (name + ".conf")).get.headOption.map("-Dakka.config=" + _.absolutePath).toSeq
       },
       scalatestOptions in MultiJvm := defaultMultiJvmScalatestOptions,
-      jvmOptions in MultiJvm := defaultMultiJvmOptions
+      jvmOptions in MultiJvm := defaultMultiJvmOptions,
+      previousArtifact := akkaPreviousArtifact("akka-remote")
     )
   ) configs (MultiJvm)
 
@@ -117,7 +123,8 @@ object AkkaBuild extends Build {
         (name: String) => (src ** (name + ".conf")).get.headOption.map("-Dakka.config=" + _.absolutePath).toSeq
       },
       scalatestOptions in MultiJvm := defaultMultiJvmScalatestOptions,
-      jvmOptions in MultiJvm := defaultMultiJvmOptions
+      jvmOptions in MultiJvm := defaultMultiJvmOptions,
+      previousArtifact := akkaPreviousArtifact("akka-remote")
     )
   ) configs (MultiJvm)
 
@@ -135,7 +142,8 @@ object AkkaBuild extends Build {
     base = file("akka-agent"),
     dependencies = Seq(actor, testkit % "test->test"),
     settings = defaultSettings ++ OSGi.agent ++ Seq(
-      libraryDependencies ++= Dependencies.agent
+      libraryDependencies ++= Dependencies.agent,
+      previousArtifact := akkaPreviousArtifact("akka-agent")
     )
   )
 
@@ -144,7 +152,8 @@ object AkkaBuild extends Build {
     base = file("akka-transactor"),
     dependencies = Seq(actor, testkit % "test->test"),
     settings = defaultSettings ++ OSGi.transactor ++ Seq(
-      libraryDependencies ++= Dependencies.transactor
+      libraryDependencies ++= Dependencies.transactor,
+      previousArtifact := akkaPreviousArtifact("akka-transactor")
     )
   )
 
@@ -163,6 +172,7 @@ object AkkaBuild extends Build {
     dependencies = Seq(remote, testkit % "compile;test->test"),
     settings = defaultSettings ++ OSGi.mailboxesCommon ++ Seq(
       libraryDependencies ++= Dependencies.mailboxes,
+      previousArtifact := akkaPreviousArtifact("akka-mailboxes-common"),
         // DurableMailboxSpec published in akka-mailboxes-common-test
       publishArtifact in Test := true
     )
@@ -173,7 +183,8 @@ object AkkaBuild extends Build {
     base = file("akka-durable-mailboxes/akka-file-mailbox"),
     dependencies = Seq(mailboxesCommon % "compile;test->test", testkit % "test"),
     settings = defaultSettings ++ OSGi.fileMailbox ++ Seq(
-      libraryDependencies ++= Dependencies.fileMailbox
+      libraryDependencies ++= Dependencies.fileMailbox,
+      previousArtifact := akkaPreviousArtifact("akka-file-mailbox")
     )
   )
 
@@ -182,7 +193,8 @@ object AkkaBuild extends Build {
     base = file("akka-zeromq"),
     dependencies = Seq(actor, testkit % "test;test->test"),
     settings = defaultSettings ++ OSGi.zeroMQ ++ Seq(
-      libraryDependencies ++= Dependencies.zeroMQ
+      libraryDependencies ++= Dependencies.zeroMQ,
+      previousArtifact := akkaPreviousArtifact("akka-zeromq")
     )
   )
 
@@ -191,7 +203,8 @@ object AkkaBuild extends Build {
     base = file("akka-kernel"),
     dependencies = Seq(actor, testkit % "test->test"),
     settings = defaultSettings ++ Seq(
-      libraryDependencies ++= Dependencies.kernel
+      libraryDependencies ++= Dependencies.kernel,
+      previousArtifact := akkaPreviousArtifact("akka-kernel")
     )
   )
 
@@ -339,7 +352,7 @@ object AkkaBuild extends Build {
     (if (useOnlyTestTags.isEmpty) Seq.empty else Seq("-n", if (multiNodeEnabled) useOnlyTestTags.mkString("\"", " ", "\"") else useOnlyTestTags.mkString(" ")))
   }
 
-  lazy val defaultSettings = baseSettings ++ formatSettings ++ Seq(
+  lazy val defaultSettings = baseSettings ++ formatSettings ++ mimaSettings ++ Seq(
     resolvers += "Typesafe Repo" at "http://repo.typesafe.com/typesafe/releases/",
 
     // compile options
@@ -403,6 +416,16 @@ object AkkaBuild extends Build {
           (Tests.overall(r.values), r)
       }
   )
+
+  lazy val mimaSettings = mimaDefaultSettings ++ Seq(
+    // MiMa
+    previousArtifact := None
+  )
+
+  def akkaPreviousArtifact(id: String, organization: String = "com.typesafe.akka", version: String = "2.0"): Option[sbt.ModuleID] = {
+    // the artifact to compare binary compatibility with
+    Some(organization % id % version)
+  }
 }
 
 // Dependencies

project/plugins.sbt

@@ -7,6 +7,8 @@ addSbtPlugin("com.typesafe.sbtscalariform" % "sbtscalariform" % "0.4.0")
 
 addSbtPlugin("com.typesafe.sbtosgi" % "sbtosgi" % "0.2.0")
 
+addSbtPlugin("com.typesafe" % "sbt-mima-plugin" % "0.1.3")
+
 resolvers ++= Seq(
   // needed for sbt-assembly, which comes with sbt-multi-jvm
   Resolver.url("sbtonline", url("http://scalasbt.artifactoryonline.com/scalasbt/sbt-plugin-releases"))(Resolver.ivyStylePatterns),

project/scripts/release

@@ -219,6 +219,13 @@ echolog "Creating gzipped tar download..."
 try tar -cz -C ${unzipped_dir} -f ${release_dir}/downloads/akka-${version}.tgz akka-${version}
 echolog "Successfully created local release"
 
+# check binary compatibility for dry run
+if [ $dry_run ]; then
+  echodry "Running migration manager report..."
+  sbt mima-report-binary-issues
+  echodry "Finished migration manager report"
+fi
+
 # commit and tag this release
 echolog "Committing and tagging..."
 try git add .