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/* =========================================================================================
* Copyright © 2013-2018 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
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.
*
* <p> 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().
*
* <p> Credit to @trask from the FastThreadLocal in glowroot.
*
* <p> One small change is that we don't use an kamon-defined holder object as that would prevent class unloading.
*
* */
class ThreadLocal extends Storage {
private val tls = new java.lang.ThreadLocal[Array[AnyRef]]() {
override def initialValue(): Array[AnyRef] =
Array(Context.Empty)
}
override def current(): Context =
tls.get()(0).asInstanceOf[Context]
override def store(newContext: Context): Scope = {
val ref = tls.get()
val previousContext = ref(0)
ref(0) = newContext
new Scope {
override def context: Context = newContext
override def close(): Unit = ref(0) = previousContext
}
}
}
object ThreadLocal {
def apply(): ThreadLocal = new ThreadLocal()
}
}
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