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AsynchronousPool.scala
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AsynchronousPool.scala
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package com.thoughtworks.raii
import java.util.concurrent.atomic.AtomicReference
import com.thoughtworks.continuation._
import scala.util.{Failure, Success, Try}
import com.thoughtworks.tryt.covariant._
import com.thoughtworks.raii.asynchronous._
import com.thoughtworks.raii.covariant._
import scala.annotation.tailrec
import scala.collection.immutable.Queue
import scalaz.Free.Trampoline
import scalaz.{Monoid, Trampoline}
import scalaz.syntax.all._
/** The namespace that contains the implementation of the asynchronous resource pool.
*
* @example Given a factory that creates resources,
*
* {{{
* import scalaz.Tags.Parallel
* import scalaz._
* import scalaz.syntax.tag._
* import scalaz.syntax.all._
* import com.thoughtworks.future._
* import com.thoughtworks.raii.asynchronous._
* import com.thoughtworks.raii.AsynchronousPool
* import java.lang.AutoCloseable
*
* trait MyResource extends AutoCloseable {
* def inUse(): Unit
* }
*
* val myResourceStub0 = stub[MyResource]
* val myResourceStub1 = stub[MyResource]
* val myResourceStub2 = stub[MyResource]
*
* val myResourceFactoryMock = mockFunction[MyResource]
* myResourceFactoryMock.expects().returns(myResourceStub0)
* myResourceFactoryMock.expects().returns(myResourceStub1)
* myResourceFactoryMock.expects().returns(myResourceStub2)
* }}}
*
* then it can be converted to a resource pool, which holds some instances of `MyResource`.
*
* {{{
* val myResourcePool: Do[Do[MyResource]] = AsynchronousPool.fixed(
* resourceFactory = Do.autoCloseable(myResourceFactoryMock()),
* poolSize = 3
* )
* }}}
*
* When some clients are using the resource pool,
*
* {{{
* def client(acquire: Do[MyResource], operationsPerClient: Int): Do[Unit] = {
* Do.nested[Unit](acquire.flatMap { myResource =>
* Do.execute {
* myResource.inUse
* }
* .replicateM_(operationsPerClient)
* })
* }
* def allClients(acquire: Do[MyResource], numberOfClients: Int, operationsPerClient: Int): ParallelDo[Unit] = {
* implicit def keepLastException = new Semigroup[Throwable] {
* override def append(f1: Throwable, f2: => Throwable) = f2
* }
* Applicative[ParallelDo].replicateM_(numberOfClients, Parallel(client(acquire, operationsPerClient)))
* }
* def usingPool(numberOfClients: Int, operationsPerClient: Int) = {
* myResourcePool.flatMap { acquire =>
* allClients(acquire, numberOfClients, operationsPerClient).unwrap
* }
* }
* }}}
*
* then the operations from these clients should be distributed on those `MyResource`s,
* and those `MyResource`s should be closed after being used.
*
* {{{
* usingPool(numberOfClients = 10, operationsPerClient = 10).run.map { _: Unit =>
* ((myResourceStub0.inUse _): () => Unit).verify().repeated(30 to 40)
* ((myResourceStub0.close _): () => Unit).verify().once()
*
* ((myResourceStub1.inUse _): () => Unit).verify().repeated(30 to 40)
* ((myResourceStub1.close _): () => Unit).verify().once()
*
* ((myResourceStub2.inUse _): () => Unit).verify().repeated(30 to 40)
* ((myResourceStub2.close _): () => Unit).verify().once()
*
* succeed
* }.toScalaFuture
* }}}
*/
object AsynchronousPool {
private[AsynchronousPool] sealed trait State[A]
private[AsynchronousPool] sealed trait DisableAcquire[A] extends State[A]
private[AsynchronousPool] final case class Available[A](availableResources: List[A]) extends State[A]
private[AsynchronousPool] final case class Queued[A](
tasks: Queue[Resource[UnitContinuation, Try[A]] => Trampoline[Unit]])
extends State[A]
private[AsynchronousPool] final case class Flushing[A](
tasks: Queue[Resource[UnitContinuation, Try[A]] => Trampoline[Unit]],
shutDownHandler: Unit => Trampoline[Unit])
extends DisableAcquire[A]
private[AsynchronousPool] final case class ShuttingDown[A](numberOfShuttedDownResources: Int,
shutDownHandler: Unit => Trampoline[Unit])
extends DisableAcquire[A]
private[AsynchronousPool] final case class ShuttedDown[A]() extends DisableAcquire[A]
final class ClosedPoolException(message: String = "This pool has been closed.", cause: Throwable = null)
extends IllegalStateException(message, cause)
/** Returns a resource pool from preloaded resoures. */
def preloaded[A](preloadedResources: Seq[A]): Resource[UnitContinuation, Do[A]] = {
val pool = new AsynchronousPool[A](preloadedResources)
Resource(pool.acquire, pool.shutdown)
}
/** Returns a factory of fixed sized resource pool. */
def fixed[A](resourceFactory: Do[A], poolSize: Int): Do[Do[A]] = {
resourceFactory.replicateM(poolSize).flatMap { resources: List[A] =>
Do.resource[Do[A]](AsynchronousPool.preloaded[A](resources))
}
}
}
import AsynchronousPool._
private final class AsynchronousPool[A](resources: Seq[A])
extends AtomicReference[State[A]](Available(resources.toList))
with ((Resource[UnitContinuation, Try[A]] => Trampoline[Unit]) => Trampoline[Unit]) {
private val poolSize = resources.length
@tailrec
def apply(task: Resource[UnitContinuation, Try[A]] => Trampoline[Unit]): Trampoline[Unit] = {
super.get() match {
case oldState @ Available(head :: tail) =>
if (super.compareAndSet(oldState, Available(tail))) {
Trampoline.suspend {
task(borrowed(head))
}
} else {
apply(task)
}
case oldState @ Available(Nil) =>
if (super.compareAndSet(oldState, Queued(Queue(task)))) {
Trampoline.done(())
} else {
apply(task)
}
case oldState @ Queued(tasks) =>
if (super.compareAndSet(oldState, Queued(tasks.enqueue(task)))) {
Trampoline.done(())
} else {
apply(task)
}
case _: DisableAcquire[_] =>
Trampoline.suspend {
task(Resource.now(Failure(new ClosedPoolException)))
}
}
}
private def borrowed(head: A) = {
Resource(Success(head), UnitContinuation(release(head)))
}
@tailrec
private def release(a: A)(continue: Unit => Trampoline[Unit]): Trampoline[Unit] = {
super.get() match {
case oldState @ Queued(tasks) =>
if (tasks.nonEmpty) {
val (head, tail) = tasks.dequeue
if (super.compareAndSet(oldState, Queued(tail))) {
Trampoline.suspend {
continue(()) >> head(borrowed(a))
}
} else {
release(a)(continue)
}
} else {
if (super.compareAndSet(oldState, Available(a :: Nil))) {
Trampoline.suspend(continue(()))
} else {
release(a)(continue)
}
}
case oldState @ Available(rest) =>
if (super.compareAndSet(oldState, Available(a :: rest))) {
Trampoline.suspend(continue(()))
} else {
release(a)(continue)
}
case oldState @ Flushing(tasks, shutDownHandler) =>
if (tasks.nonEmpty) {
val (head, tail) = tasks.dequeue
if (super.compareAndSet(oldState, Flushing(tail, shutDownHandler))) {
Trampoline.suspend {
continue(()) >> head(borrowed(a))
}
} else {
release(a)(continue)
}
} else {
if (poolSize == 1) {
if (super.compareAndSet(oldState, ShuttedDown())) {
Trampoline.suspend {
continue(()) >> shutDownHandler(())
}
} else {
release(a)(continue)
}
} else {
if (super.compareAndSet(oldState, ShuttingDown(1, shutDownHandler))) {
Trampoline.suspend(continue(()))
} else {
release(a)(continue)
}
}
}
case oldState @ ShuttingDown(oldNumberOfShuttedDownResources, shutDownHandler) =>
val newNumberOfShuttedDownResources = oldNumberOfShuttedDownResources + 1
if (poolSize == newNumberOfShuttedDownResources) {
if (super.compareAndSet(oldState, ShuttedDown())) {
Trampoline.suspend {
continue(()) >> shutDownHandler(())
}
} else {
release(a)(continue)
}
} else {
if (super.compareAndSet(oldState, ShuttingDown(newNumberOfShuttedDownResources, shutDownHandler))) {
Trampoline.suspend(continue(()))
} else {
release(a)(continue)
}
}
case ShuttedDown() =>
throw new ClosedPoolException()
}
}
def shutdown: UnitContinuation[Unit] = {
@tailrec
def retry(continue: Unit => Trampoline[Unit]): Trampoline[Unit] = {
super.get() match {
case oldState @ Available(availableResources) =>
val numberOfAvailableResources = availableResources.length
if (numberOfAvailableResources == poolSize) {
if (super.compareAndSet(oldState, ShuttedDown())) {
Trampoline.suspend {
continue(())
}
} else {
retry(continue)
}
} else {
if (super.compareAndSet(oldState, ShuttingDown(numberOfAvailableResources, continue))) {
Trampoline.done(())
} else {
retry(continue)
}
}
case oldState @ Queued(tasks) =>
if (super.compareAndSet(oldState, Flushing(tasks, continue))) {
Trampoline.done(())
} else {
retry(continue)
}
case _: DisableAcquire[_] =>
throw new ClosedPoolException()
}
}
UnitContinuation(retry)
}
def acquire: Do[A] = Do(TryT(ResourceT(UnitContinuation(this))))
}