scala.actors.Actor.scala Maven / Gradle / Ivy
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2005-2010, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.actors
import scala.util.control.ControlThrowable
import java.util.{Timer, TimerTask}
/**
* The Actor object provides functions for the definition of
* actors, as well as actor operations, such as
* receive, react, reply,
* etc.
*
* @author Philipp Haller
*/
object Actor extends Combinators {
/** An actor state. An actor can be in one of the following states:
*
* - New
* An actor that has not yet started is in this state.
* - Runnable
* An actor executing is in this state.
* - Suspended
* An actor that is suspended waiting in a react is in this state.
* - TimedSuspended
* An actor that is suspended waiting in a reactWithin is in this state.
* - Blocked
* An actor that is blocked waiting in a receive is in this state.
* - TimedBlocked
* An actor that is blocked waiting in a receiveWithin is in this state.
* - Terminated
* An actor that has terminated is in this state.
*
*/
object State extends Enumeration {
val New,
Runnable,
Suspended,
TimedSuspended,
Blocked,
TimedBlocked,
Terminated = Value
}
private[actors] val tl = new ThreadLocal[ReplyReactor]
// timer thread runs as daemon
private[actors] val timer = new Timer(true)
private[actors] val suspendException = new SuspendActorControl
/**
* Returns the currently executing actor. Should be used instead
* of this in all blocks of code executed by
* actors.
*
* @return returns the currently executing actor.
*/
def self: Actor = self(Scheduler)
private[actors] def self(sched: IScheduler): Actor =
rawSelf(sched).asInstanceOf[Actor]
private[actors] def rawSelf: ReplyReactor =
rawSelf(Scheduler)
private[actors] def rawSelf(sched: IScheduler): ReplyReactor = {
val s = tl.get
if (s eq null) {
val r = new ActorProxy(currentThread, sched)
tl.set(r)
r
} else
s
}
private def parentScheduler: IScheduler = {
val s = tl.get
if (s eq null) Scheduler else s.scheduler
}
/**
* Resets an actor proxy associated with the current thread.
* It replaces the implicit ActorProxy instance
* of the current thread (if any) with a new instance.
*
* This permits to re-use the current thread as an actor
* even if its ActorProxy has died for some reason.
*/
def resetProxy {
val a = tl.get
if ((null ne a) && a.isInstanceOf[ActorProxy])
tl.set(new ActorProxy(currentThread, parentScheduler))
}
/**
* Removes any reference to an Actor instance
* currently stored in thread-local storage.
*
* This allows to release references from threads that are
* potentially long-running or being re-used (e.g. inside
* a thread pool). Permanent references in thread-local storage
* are a potential memory leak.
*/
def clearSelf {
tl.set(null)
}
/**
* This is a factory method for creating actors.
*
* The following example demonstrates its usage:
*
* {{{
* import scala.actors.Actor._
* ...
* val a = actor {
* ...
* }
* }}}
*
* @param body the code block to be executed by the newly created actor
* @return the newly created actor. Note that it is automatically started.
*/
def actor(body: => Unit): Actor = {
val a = new Actor {
def act() = body
override final val scheduler: IScheduler = parentScheduler
}
a.start()
a
}
/**
* This is a factory method for creating actors whose
* body is defined using a `Responder`.
*
* The following example demonstrates its usage:
*
* {{{
* import scala.actors.Actor._
* import Responder.exec
* ...
* val a = reactor {
* for {
* res <- b !! MyRequest;
* if exec(println("result: "+res))
* } yield {}
* }
* }}}
*
* @param body the `Responder` to be executed by the newly created actor
* @return the newly created actor. Note that it is automatically started.
*/
def reactor(body: => Responder[Unit]): Actor = {
val a = new Actor {
def act() {
Responder.run(body)
}
override final val scheduler: IScheduler = parentScheduler
}
a.start()
a
}
/**
* Receives the next message from the mailbox of the current actor
* self.
*/
def ? : Any = self.?
/**
* Receives a message from the mailbox of
* self. Blocks if no message matching any of the
* cases of f can be received.
*
* @param f a partial function specifying patterns and actions
* @return the result of processing the received message
*/
def receive[A](f: PartialFunction[Any, A]): A =
self.receive(f)
/**
* Receives a message from the mailbox of
* self. Blocks at most msec
* milliseconds if no message matching any of the cases of
* f can be received. If no message could be
* received the TIMEOUT action is executed if
* specified.
*
* @param msec the time span before timeout
* @param f a partial function specifying patterns and actions
* @return the result of processing the received message
*/
def receiveWithin[R](msec: Long)(f: PartialFunction[Any, R]): R =
self.receiveWithin(msec)(f)
/**
* Lightweight variant of receive.
*
* Actions in f have to contain the rest of the
* computation of self, as this method will never
* return.
*
* @param f a partial function specifying patterns and actions
* @return this function never returns
*/
def react(f: PartialFunction[Any, Unit]): Nothing =
rawSelf.react(f)
/**
* Lightweight variant of receiveWithin.
*
* Actions in f have to contain the rest of the
* computation of self, as this method will never
* return.
*
* @param msec the time span before timeout
* @param f a partial function specifying patterns and actions
* @return this function never returns
*/
def reactWithin(msec: Long)(f: PartialFunction[Any, Unit]): Nothing =
self.reactWithin(msec)(f)
def eventloop(f: PartialFunction[Any, Unit]): Nothing =
rawSelf.react(new RecursiveProxyHandler(rawSelf, f))
private class RecursiveProxyHandler(a: ReplyReactor, f: PartialFunction[Any, Unit])
extends PartialFunction[Any, Unit] {
def isDefinedAt(m: Any): Boolean =
true // events are immediately removed from the mailbox
def apply(m: Any) {
if (f.isDefinedAt(m)) f(m)
a.react(this)
}
}
/**
* Returns the actor which sent the last received message.
*/
def sender: OutputChannel[Any] =
rawSelf.sender
/**
* Send msg to the actor waiting in a call to
* !?.
*/
def reply(msg: Any): Unit =
rawSelf.reply(msg)
/**
* Send () to the actor waiting in a call to
* !?.
*/
def reply(): Unit =
rawSelf.reply(())
/**
* Returns the number of messages in self's mailbox
*
* @return the number of messages in self's mailbox
*/
def mailboxSize: Int = rawSelf.mailboxSize
/**
* Converts a synchronous event-based operation into
* an asynchronous `Responder`.
*
* The following example demonstrates its usage:
*
* {{{
* val adder = reactor {
* for {
* _ <- respondOn(react) { case Add(a, b) => reply(a+b) }
* } yield {}
* }
* }}}
*/
def respondOn[A, B](fun: PartialFunction[A, Unit] => Nothing):
PartialFunction[A, B] => Responder[B] =
(caseBlock: PartialFunction[A, B]) => new Responder[B] {
def respond(k: B => Unit) = fun(caseBlock andThen k)
}
private[actors] trait Body[a] {
def andThen[b](other: => b): Unit
}
implicit def mkBody[a](body: => a) = new Body[a] {
def andThen[b](other: => b): Unit = rawSelf.seq(body, other)
}
/**
* Links self to actor to.
*
* @param to the actor to link to
* @return the parameter actor
*/
def link(to: AbstractActor): AbstractActor = self.link(to)
/**
* Links self to the actor defined by body.
*
* @param body the body of the actor to link to
* @return the parameter actor
*/
def link(body: => Unit): Actor = self.link(body)
/**
* Unlinks self from actor from.
*
* @param from the actor to unlink from
*/
def unlink(from: AbstractActor): Unit = self.unlink(from)
/**
*
* Terminates execution of self with the following
* effect on linked actors:
*
*
* For each linked actor a with
* trapExit set to true, send message
* Exit(self, reason) to a.
*
*
* For each linked actor a with
* trapExit set to false (default),
* call a.exit(reason) if
* reason != 'normal.
*
*/
def exit(reason: AnyRef): Nothing = self.exit(reason)
/**
*
* Terminates execution of self with the following
* effect on linked actors:
*
*
* For each linked actor a with
* trapExit set to true, send message
* Exit(self, 'normal) to a.
*
*/
def exit(): Nothing = rawSelf.exit()
}
/**
*
* This trait provides lightweight, concurrent actors. Actors are
* created by extending the `Actor` trait (alternatively, one of the
* factory methods in its companion object can be used). The
* behavior of an `Actor` subclass is defined by implementing its
* `act` method:
*
* {{{
* class MyActor extends Actor {
* def act() {
* // actor behavior goes here
* }
* }
* }}}
*
* A new `Actor` instance is started by invoking its `start` method.
*
* '''Note:''' care must be taken when invoking thread-blocking methods
* other than those provided by the `Actor` trait or its companion
* object (such as `receive`). Blocking the underlying thread inside
* an actor may lead to starvation of other actors. This also
* applies to actors hogging their thread for a long time between
* invoking `receive`/`react`.
*
* If actors use blocking operations (for example, methods for
* blocking I/O), there are several options:
*
* - The run-time system can be configured to use a larger thread pool size
* (for example, by setting the `actors.corePoolSize` JVM property).
*
* - The `scheduler` method of the `Actor` trait can be overridden to return a
* `ResizableThreadPoolScheduler`, which resizes its thread pool to
* avoid starvation caused by actors that invoke arbitrary blocking methods.
*
* - The `actors.enableForkJoin` JVM property can be set to `false`, in which
* case a `ResizableThreadPoolScheduler` is used by default to execute actors.
*
*
*
* The main ideas of the implementation are explained in the two papers
*
* -
*
* Event-Based
* Programming without Inversion of Control,
* Philipp Haller and Martin Odersky, Proc. JMLC 2006, and
*
* -
*
* Actors that
* Unify Threads and Events,
* Philipp Haller and Martin Odersky, Proc. COORDINATION 2007.
*
*
*
*
* @author Philipp Haller
*
* @define actor actor
* @define channel actor's mailbox
*/
@serializable @SerialVersionUID(-781154067877019505L)
trait Actor extends AbstractActor with ReplyReactor with ActorCanReply with InputChannel[Any] {
/* The following two fields are only used when the actor
* suspends by blocking its underlying thread, for example,
* when waiting in a receive or synchronous send.
*/
@volatile
private var isSuspended = false
/* This field is used to communicate the received message from
* the invocation of send to the place where the thread of
* the receiving actor resumes inside receive/receiveWithin.
*/
@volatile
private var received: Option[Any] = None
protected[actors] override def scheduler: IScheduler = Scheduler
private[actors] override def startSearch(msg: Any, replyTo: OutputChannel[Any], handler: PartialFunction[Any, Any]) =
if (isSuspended) {
() => synchronized {
mailbox.append(msg, replyTo)
resumeActor()
}
} else super.startSearch(msg, replyTo, handler)
// we override this method to check `shouldExit` before suspending
private[actors] override def searchMailbox(startMbox: MQueue[Any],
handler: PartialFunction[Any, Any],
resumeOnSameThread: Boolean) {
var tmpMbox = startMbox
var done = false
while (!done) {
val qel = tmpMbox.extractFirst((msg: Any, replyTo: OutputChannel[Any]) => {
senders = List(replyTo)
handler.isDefinedAt(msg)
})
if (tmpMbox ne mailbox)
tmpMbox.foreach((m, s) => mailbox.append(m, s))
if (null eq qel) {
synchronized {
// in mean time new stuff might have arrived
if (!sendBuffer.isEmpty) {
tmpMbox = new MQueue[Any]("Temp")
drainSendBuffer(tmpMbox)
// keep going
} else {
// very important to check for `shouldExit` at this point
// since linked actors might have set it after we checked
// last time (e.g., at the beginning of `react`)
if (shouldExit) exit()
waitingFor = handler
// see Reactor.searchMailbox
throw Actor.suspendException
}
}
} else {
resumeReceiver((qel.msg, qel.session), handler, resumeOnSameThread)
done = true
}
}
}
private[actors] override def makeReaction(fun: () => Unit, handler: PartialFunction[Any, Any], msg: Any): Runnable =
new ActorTask(this, fun, handler, msg)
def receive[R](f: PartialFunction[Any, R]): R = {
assert(Actor.self(scheduler) == this, "receive from channel belonging to other actor")
synchronized {
if (shouldExit) exit() // links
drainSendBuffer(mailbox)
}
var done = false
while (!done) {
val qel = mailbox.extractFirst((m: Any, replyTo: OutputChannel[Any]) => {
senders = replyTo :: senders
val matches = f.isDefinedAt(m)
senders = senders.tail
matches
})
if (null eq qel) {
synchronized {
// in mean time new stuff might have arrived
if (!sendBuffer.isEmpty) {
drainSendBuffer(mailbox)
// keep going
} else {
waitingFor = f
isSuspended = true
scheduler.managedBlock(blocker)
drainSendBuffer(mailbox)
// keep going
}
}
} else {
received = Some(qel.msg)
senders = qel.session :: senders
done = true
}
}
val result = f(received.get)
received = None
senders = senders.tail
result
}
def receiveWithin[R](msec: Long)(f: PartialFunction[Any, R]): R = {
assert(Actor.self(scheduler) == this, "receive from channel belonging to other actor")
synchronized {
if (shouldExit) exit() // links
drainSendBuffer(mailbox)
}
// first, remove spurious TIMEOUT message from mailbox if any
mailbox.extractFirst((m: Any, replyTo: OutputChannel[Any]) => m == TIMEOUT)
val receiveTimeout = () => {
if (f.isDefinedAt(TIMEOUT)) {
received = Some(TIMEOUT)
senders = this :: senders
} else
error("unhandled timeout")
}
var done = false
while (!done) {
val qel = mailbox.extractFirst((m: Any, replyTo: OutputChannel[Any]) => {
senders = replyTo :: senders
val matches = f.isDefinedAt(m)
senders = senders.tail
matches
})
if (null eq qel) {
val todo = synchronized {
// in mean time new stuff might have arrived
if (!sendBuffer.isEmpty) {
drainSendBuffer(mailbox)
// keep going
() => {}
} else if (msec == 0L) {
done = true
receiveTimeout
} else {
waitingFor = f
received = None
isSuspended = true
val thisActor = this
onTimeout = Some(new TimerTask {
def run() { thisActor.send(TIMEOUT, thisActor) }
})
Actor.timer.schedule(onTimeout.get, msec)
scheduler.managedBlock(blocker)
drainSendBuffer(mailbox)
// keep going
() => {}
}
}
todo()
} else {
synchronized {
if (!onTimeout.isEmpty) {
onTimeout.get.cancel()
onTimeout = None
}
}
received = Some(qel.msg)
senders = qel.session :: senders
done = true
}
}
val result = f(received.get)
received = None
senders = senders.tail
result
}
override def react(handler: PartialFunction[Any, Unit]): Nothing = {
synchronized {
if (shouldExit) exit()
}
super.react(handler)
}
override def reactWithin(msec: Long)(handler: PartialFunction[Any, Unit]): Nothing = {
synchronized {
if (shouldExit) exit()
}
super.reactWithin(msec)(handler)
}
def ? : Any = receive {
case x => x
}
// guarded by lock of this
// never throws SuspendActorControl
private[actors] override def scheduleActor(f: PartialFunction[Any, Any], msg: Any) =
if (f eq null) {
// do nothing (timeout is handled instead)
}
else {
val task = new ActorTask(this, null, f, msg)
scheduler executeFromActor task
}
/* Used for notifying scheduler when blocking inside receive/receiveWithin. */
private object blocker extends scala.concurrent.ManagedBlocker {
def block() = {
Actor.this.suspendActor()
true
}
def isReleasable =
!Actor.this.isSuspended
}
private def suspendActor() = synchronized {
while (isSuspended) {
try {
wait()
} catch {
case _: InterruptedException =>
}
}
// links: check if we should exit
if (shouldExit) exit()
}
private def resumeActor() {
isSuspended = false
notify()
}
private[actors] override def exiting = synchronized {
_state == Actor.State.Terminated
}
// guarded by this
private[actors] override def dostart() {
// Reset various flags.
//
// Note that we do *not* reset `trapExit`. The reason is that
// users should be able to set the field in the constructor
// and before `act` is called.
exitReason = 'normal
shouldExit = false
super.dostart()
}
override def start(): Actor = synchronized {
super.start()
this
}
override def getState: Actor.State.Value = synchronized {
if (isSuspended) {
if (onTimeout.isEmpty)
Actor.State.Blocked
else
Actor.State.TimedBlocked
} else
super.getState
}
// guarded by this
private[actors] var links: List[AbstractActor] = Nil
/**
* Links self to actor to.
*
* @param to the actor to link to
* @return the parameter actor
*/
def link(to: AbstractActor): AbstractActor = {
assert(Actor.self(scheduler) == this, "link called on actor different from self")
this linkTo to
to linkTo this
to
}
/**
* Links self to the actor defined by body.
*
* @param body the body of the actor to link to
* @return the parameter actor
*/
def link(body: => Unit): Actor = {
assert(Actor.self(scheduler) == this, "link called on actor different from self")
val a = new Actor {
def act() = body
override final val scheduler: IScheduler = Actor.this.scheduler
}
link(a)
a.start()
a
}
private[actors] def linkTo(to: AbstractActor) = synchronized {
links = to :: links
}
/**
* Unlinks self from actor from.
*/
def unlink(from: AbstractActor) {
assert(Actor.self(scheduler) == this, "unlink called on actor different from self")
this unlinkFrom from
from unlinkFrom this
}
private[actors] def unlinkFrom(from: AbstractActor) = synchronized {
links = links.filterNot(from.==)
}
@volatile
var trapExit = false
// guarded by this
private var exitReason: AnyRef = 'normal
// guarded by this
private[actors] var shouldExit = false
/**
*
* Terminates execution of self with the following
* effect on linked actors:
*
*
* For each linked actor a with
* trapExit set to true, send message
* Exit(self, reason) to a.
*
*
* For each linked actor a with
* trapExit set to false (default),
* call a.exit(reason) if
* reason != 'normal.
*
*/
protected[actors] def exit(reason: AnyRef): Nothing = {
synchronized {
exitReason = reason
}
exit()
}
/**
* Terminates with exit reason 'normal.
*/
protected[actors] override def exit(): Nothing = {
val todo = synchronized {
if (!links.isEmpty)
exitLinked()
else
() => {}
}
todo()
super.exit()
}
// Assume !links.isEmpty
// guarded by this
private[actors] def exitLinked(): () => Unit = {
_state = Actor.State.Terminated
// reset waitingFor, otherwise getState returns Suspended
waitingFor = Reactor.waitingForNone
// remove this from links
val mylinks = links.filterNot(this.==)
// unlink actors
mylinks.foreach(unlinkFrom(_))
// return closure that locks linked actors
() => {
mylinks.foreach((linked: AbstractActor) => {
linked.synchronized {
if (!linked.exiting)
linked.exit(this, exitReason)
}
})
}
}
// Assume !links.isEmpty
// guarded by this
private[actors] def exitLinked(reason: AnyRef): () => Unit = {
exitReason = reason
exitLinked()
}
// Assume !this.exiting
private[actors] def exit(from: AbstractActor, reason: AnyRef) {
if (trapExit) {
this ! Exit(from, reason)
}
else if (reason != 'normal)
synchronized {
shouldExit = true
exitReason = reason
// resume this Actor in a way that
// causes it to exit
// (because shouldExit == true)
if (isSuspended)
resumeActor()
else if (waitingFor ne Reactor.waitingForNone) {
waitingFor = Reactor.waitingForNone
// it doesn't matter what partial function we are passing here
scheduleActor(waitingFor, null)
/* Here we should not throw a SuspendActorControl,
since the current method is called from an actor that
is in the process of exiting.
Therefore, the contract for scheduleActor is that
it never throws a SuspendActorControl.
*/
}
}
}
/* Requires qualified private, because RemoteActor must
* register a termination handler.
*/
private[actors] def onTerminate(f: => Unit) {
scheduler.onTerminate(this) { f }
}
}
/**
* This object is used as the timeout pattern in
*
* receiveWithin and
*
* reactWithin.
*
*
* The following example demonstrates its usage:
*
* receiveWithin(500) {
* case (x, y) => ...
* case TIMEOUT => ...
* }
*
* @author Philipp Haller
*/
case object TIMEOUT
/** An `Exit` message (an instance of this class) is sent to an actor
* with `trapExit` set to `true` whenever one of its linked actors
* terminates.
*
* @param from the actor that terminated
* @param reason the reason that caused the actor to terminate
*/
case class Exit(from: AbstractActor, reason: AnyRef)
/**
* This class is used to manage control flow of actor
* executions.
*
*
* @author Philipp Haller
*/
private[actors] class SuspendActorControl extends ControlThrowable
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