spark EpochTracker 源码
spark EpochTracker 代码
文件路径：/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/continuous/EpochTracker.scala
/*
* 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.sql.execution.streaming.continuous
import java.util.concurrent.atomic.AtomicLong
/**
* Tracks the current continuous processing epoch within a task. Call
* EpochTracker.getCurrentEpoch to get the current epoch.
*/
object EpochTracker {
// The current epoch. Note that this is a shared reference; ContinuousWriteRDD.compute() will
// update the underlying AtomicLong as it finishes epochs. Other code should only read the value.
private val currentEpoch: InheritableThreadLocal[AtomicLong] = {
new InheritableThreadLocal[AtomicLong] {
override def childValue(parent: AtomicLong): AtomicLong = {
// Note: make another instance so that changes in the parent epoch aren't reflected in
// those in the children threads. This is required at `ContinuousCoalesceRDD`.
new AtomicLong(parent.get)
}
override def initialValue() = new AtomicLong(-1)
}
}
/**
* Get the current epoch for the current task, or None if the task has no current epoch.
*/
def getCurrentEpoch: Option[Long] = {
currentEpoch.get().get() match {
case n if n < 0 => None
case e => Some(e)
}
}
/**
* Increment the current epoch for this task thread. Should be called by [[ContinuousWriteRDD]]
* between epochs.
*/
def incrementCurrentEpoch(): Unit = {
currentEpoch.get().incrementAndGet()
}
/**
* Initialize the current epoch for this task thread. Should be called by [[ContinuousWriteRDD]]
* at the beginning of a task.
*/
def initializeCurrentEpoch(startEpoch: Long): Unit = {
currentEpoch.get().set(startEpoch)
}
}
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