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Oct 3, 2017
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Synchronize WeakHashSet with scalac #3218

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41 changes: 20 additions & 21 deletions compiler/src/dotty/tools/dotc/util/WeakHashSet.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -6,17 +6,16 @@ package dotty.tools.dotc.util

import java.lang.ref.{WeakReference, ReferenceQueue}
import scala.annotation.tailrec
import scala.collection.generic.Clearable
import scala.collection.mutable.{Set => MSet}

/**
* A HashSet where the elements are stored weakly. Elements in this set are elligible for GC if no other
* A HashSet where the elements are stored weakly. Elements in this set are eligible for GC if no other
* hard references are associated with them. Its primary use case is as a canonical reference
* identity holder (aka "hash-consing") via findEntryOrUpdate
*
* This Set implementation cannot hold null. Any attempt to put a null in it will result in a NullPointerException
*
* This set implmeentation is not in general thread safe without external concurrency control. However it behaves
* This set implementation is not in general thread safe without external concurrency control. However it behaves
* properly when GC concurrently collects elements in this set.
*/
final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadFactor: Double) extends Set[A] with Function1[A, Boolean] with MSet[A] {
Expand All @@ -29,7 +28,7 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF

/**
* queue of Entries that hold elements scheduled for GC
* the removeStaleEntries() method works through the queue to remeove
* the removeStaleEntries() method works through the queue to remove
* stale entries from the table
*/
private[this] val queue = new ReferenceQueue[A]
Expand All @@ -44,7 +43,7 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF
* power of two equal to or greater than the specified initial capacity
*/
private def computeCapacity = {
if (initialCapacity < 0) throw new IllegalArgumentException("initial capacity cannot be less than 0");
if (initialCapacity < 0) throw new IllegalArgumentException("initial capacity cannot be less than 0")
var candidate = 1
while (candidate < initialCapacity) {
candidate *= 2
Expand All @@ -60,12 +59,12 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF
/**
* the limit at which we'll increase the size of the hash table
*/
var threshhold = computeThreshHold
private[this] var threshold = computeThreshold

private[this] def computeThreshHold: Int = (table.size * loadFactor).ceil.toInt
private[this] def computeThreshold: Int = (table.size * loadFactor).ceil.toInt

/**
* find the bucket associated with an elements's hash code
* find the bucket associated with an element's hash code
*/
private[this] def bucketFor(hash: Int): Int = {
// spread the bits around to try to avoid accidental collisions using the
Expand Down Expand Up @@ -125,7 +124,7 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF
private[this] def resize(): Unit = {
val oldTable = table
table = new Array[Entry[A]](oldTable.size * 2)
threshhold = computeThreshHold
threshold = computeThreshold

@tailrec
def tableLoop(oldBucket: Int): Unit = if (oldBucket < oldTable.size) {
Expand Down Expand Up @@ -160,7 +159,7 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF
case null => null.asInstanceOf[A]
case _ => {
val entryElem = entry.get
if (elem == entryElem) entryElem
if (elem.equals(entryElem)) entryElem
else linkedListLoop(entry.tail)
}
}
Expand All @@ -180,7 +179,7 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF
def add() = {
table(bucket) = new Entry(elem, hash, oldHead, queue)
count += 1
if (count > threshhold) resize()
if (count > threshold) resize()
elem
}

Expand All @@ -189,7 +188,7 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF
case null => add()
case _ => {
val entryElem = entry.get
if (elem == entryElem) entryElem
if (elem.equals(entryElem)) entryElem
else linkedListLoop(entry.tail)
}
}
Expand All @@ -210,14 +209,14 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF
def add() = {
table(bucket) = new Entry(elem, hash, oldHead, queue)
count += 1
if (count > threshhold) resize()
if (count > threshold) resize()
}

@tailrec
def linkedListLoop(entry: Entry[A]): Unit = entry match {
case null => add()
case _ if (elem == entry.get) => ()
case _ => linkedListLoop(entry.tail)
case null => add()
case _ if elem.equals(entry.get) => ()
case _ => linkedListLoop(entry.tail)
}

linkedListLoop(oldHead)
Expand All @@ -227,7 +226,7 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF

def +=(elem: A) = this + elem

// from scala.reflect.interanl.Set
// from scala.reflect.internal.Set
override def addEntry(x: A) = { this += x }

// remove an element from this set and return this set
Expand All @@ -242,7 +241,7 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF
@tailrec
def linkedListLoop(prevEntry: Entry[A], entry: Entry[A]): Unit = entry match {
case null => ()
case _ if (elem == entry.get) => remove(bucket, prevEntry, entry)
case _ if elem.equals(entry.get) => remove(bucket, prevEntry, entry)
case _ => linkedListLoop(entry, entry.tail)
}

Expand All @@ -256,7 +255,7 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF
// empty this set
override def clear(): Unit = {
table = new Array[Entry[A]](table.size)
threshhold = computeThreshHold
threshold = computeThreshold
count = 0

// drain the queue - doesn't do anything because we're throwing away all the values anyway
Expand Down Expand Up @@ -375,13 +374,13 @@ final class WeakHashSet[A >: Null <: AnyRef](val initialCapacity: Int, val loadF
* Number of buckets that hold collisions. Useful for diagnosing performance issues.
*/
def collisionBucketsCount: Int =
(table filter (entry => entry != null && entry.tail != null)).size
(table count (entry => entry != null && entry.tail != null))

/**
* Number of buckets that are occupied in this hash table.
*/
def fullBucketsCount: Int =
(table filter (entry => entry != null)).size
(table count (entry => entry != null))

/**
* Number of buckets in the table
Expand Down