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/* =========================================================================================
* Copyright © 2013-2017 the kamon project <http://kamon.io/>
*
* Licensed 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 kamon.context
import kamon.context.Storage.ThreadLocal.ContextHolder
trait Storage {
def current(): Context
def store(context: Context): Storage.Scope
}
object Storage {
trait Scope {
def context: Context
def close(): Unit
}
/**
* Wrapper that implements optimized {@link ThreadLocal} access pattern ideal for heavily used
* ThreadLocals.
*
* It is faster to use a mutable holder object and always perform ThreadLocal.get() and never use
* ThreadLocal.set(), because the value is more likely to be found in the ThreadLocalMap direct hash
* slot and avoid the slow path ThreadLocalMap.getEntryAfterMiss().
*
* Important: this thread local will live in ThreadLocalMap forever, so use with care.
*/
class ThreadLocal extends Storage {
private val tls = new java.lang.ThreadLocal[ContextHolder]() {
override def initialValue() = new ContextHolder(Context.Empty)
}
override def current(): Context =
get()
override def store(context: Context): Scope = {
val newContext = context
val previousContext = get()
set(newContext)
new Scope {
override def context: Context = newContext
override def close(): Unit = set(previousContext)
}
}
private def get():Context =
tls.get().value
private def set(value:Context) : Unit =
tls.get().value = value
}
object ThreadLocal {
def apply(): ThreadLocal = new ThreadLocal()
final class ContextHolder(var value:Context)
}
}
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