sbt.inc.FileValueCache.scala Maven / Gradle / Ivy

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package sbt
package inc

	import java.io.File
	import java.util.concurrent.ConcurrentHashMap

sealed trait FileValueCache[T]
{
	def clear(): Unit
	def get: File => T
}

private[this] final class FileValueCache0[T](getStamp: File => Stamp, make: File => T)(implicit equiv: Equiv[Stamp]) extends FileValueCache[T]
{
	private[this] val backing = new ConcurrentHashMap[File, FileCache]

	def clear(): Unit = backing.clear()
	def get = file => {
		val ifAbsent = new FileCache(file)
		val cache = backing.putIfAbsent(file, ifAbsent)
		(if(cache eq null) ifAbsent else cache).get()
	}

	private[this] final class FileCache(file: File)
	{
		private[this] var stampedValue: Option[(Stamp,T)] = None
		def get(): T = synchronized
		{
			val latest = getStamp(file)
			stampedValue match
			{
				case Some( (stamp, value) ) if(equiv.equiv(latest, stamp)) => value
				case _ => update(latest)
			}
		}

		private[this] def update(stamp: Stamp): T =
		{
			val value = make(file)
			stampedValue = Some((stamp, value))
			value
		}
	}
}
object FileValueCache
{
	def apply[T](f: File => T): FileValueCache[T] = make(Stamp.lastModified)(f)
	def make[T](stamp: File => Stamp)(f: File => T): FileValueCache[T] = new FileValueCache0[T](stamp, f)
}