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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.spark
import java.util.UUID
import java.util.concurrent.locks.ReentrantReadWriteLock
import scala.collection.mutable
import scala.language.implicitConversions
/**
* Utility wrapper to "smuggle" objects into tasks while bypassing serialization.
* This is intended for testing purposes, primarily to make locks, semaphores, and
* other constructs that would not survive serialization available from within tasks.
* A Smuggle reference is itself serializable, but after being serialized and
* deserialized, it still refers to the same underlying "smuggled" object, as long
* as it was deserialized within the same JVM. This can be useful for tests that
* depend on the timing of task completion to be deterministic, since one can "smuggle"
* a lock or semaphore into the task, and then the task can block until the test gives
* the go-ahead to proceed via the lock.
*/
class Smuggle[T] private(val key: Symbol) extends Serializable {
def smuggledObject: T = Smuggle.get(key)
}
object Smuggle {
/**
* Wraps the specified object to be smuggled into a serialized task without
* being serialized itself.
*
* @param smuggledObject
* @tparam T
* @return Smuggle wrapper around smuggledObject.
*/
def apply[T](smuggledObject: T): Smuggle[T] = {
val key = Symbol(UUID.randomUUID().toString)
lock.writeLock().lock()
try {
smuggledObjects += key -> smuggledObject
} finally {
lock.writeLock().unlock()
}
new Smuggle(key)
}
private val lock = new ReentrantReadWriteLock
private val smuggledObjects = mutable.WeakHashMap.empty[Symbol, Any]
private def get[T](key: Symbol) : T = {
lock.readLock().lock()
try {
smuggledObjects(key).asInstanceOf[T]
} finally {
lock.readLock().unlock()
}
}
/**
* Implicit conversion of a Smuggle wrapper to the object being smuggled.
*
* @param smuggle the wrapper to unpack.
* @tparam T
* @return the smuggled object represented by the wrapper.
*/
implicit def unpackSmuggledObject[T](smuggle : Smuggle[T]): T = smuggle.smuggledObject
}
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