Github user dragos commented on a diff in the pull request:
https://github.com/apache/spark/pull/7648#discussion_r35633081
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/scheduler/rate/PIDRateEstimator.scala
---
@@ -0,0 +1,91 @@
+/*
+ * 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.streaming.scheduler.rate
+
+/**
+ * Implements a proportional-integral-derivative (PID) controller which
acts on
+ * the speed of ingestion of elements into Spark Streaming.
+ *
+ * @param batchDurationMillis the batch duration, in milliseconds
+ * @param proportional how much the correction should depend on the current
+ * error,
+ * @param integral how much the correction should depend on the
accumulation
+ * of past errors,
+ * @param derivative how much the correction should depend on a prediction
+ * of future errors, based on current rate of change
+ */
+private[streaming] class PIDRateEstimator(
+ batchIntervalMillis: Long,
+ proportional: Double = -1D,
+ integral: Double = -.2D,
+ derivative: Double = 0D)
+ extends RateEstimator {
+
+ private var firstRun: Boolean = true
+ private var latestTime: Long = -1L
+ private var latestRate: Double = -1D
+ private var latestError: Double = -1L
+
+ require(
+ batchIntervalMillis > 0,
+ s"Specified batch interval $batchIntervalMillis in PIDRateEstimator is
invalid.")
+
+ def compute(time: Long, // in milliseconds
+ elements: Long,
+ processingDelay: Long, // in milliseconds
+ schedulingDelay: Long // in milliseconds
+ ): Option[Double] = {
+
+ this.synchronized {
--- End diff --
This may be called by different threads, either due to the streaming
listener bus being asynchronous, or the rate controller using a future when
calling this method. Probably it's unlikely to have concurrent runs, but at
least for visibility of updates we need some form of synchronization. We could
remove this and make all fields `volatile`, but I'm not 100% clear if there's
really no chance of running concurrently in some degenerate situation.
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