gaborgsomogyi commented on a change in pull request #19096: [SPARK-21869][SS] A 
cached Kafka producer should not be closed if any task is using it - adds inuse 
tracking.
URL: https://github.com/apache/spark/pull/19096#discussion_r267259001
 
 

 ##########
 File path: 
external/kafka-0-10-sql/src/main/scala/org/apache/spark/sql/kafka010/CachedKafkaProducer.scala
 ##########
 @@ -40,81 +94,103 @@ private[kafka010] object CachedKafkaProducer extends 
Logging {
       "spark.kafka.producer.cache.timeout",
       s"${defaultCacheExpireTimeout}ms")).getOrElse(defaultCacheExpireTimeout)
 
-  private val cacheLoader = new CacheLoader[Seq[(String, Object)], Producer] {
-    override def load(config: Seq[(String, Object)]): Producer = {
-      val configMap = config.map(x => x._1 -> x._2).toMap.asJava
-      createKafkaProducer(configMap)
+  private val cacheLoader = new CacheLoader[Seq[(String, Object)], 
CachedKafkaProducer] {
+    override def load(params: Seq[(String, Object)]): CachedKafkaProducer = {
+      CachedKafkaProducer(kafkaParams = params)
     }
   }
 
-  private val removalListener = new RemovalListener[Seq[(String, Object)], 
Producer]() {
+  private val closeQueue = new ConcurrentLinkedQueue[CachedKafkaProducer]()
+
+  private val removalListener = new RemovalListener[Seq[(String, Object)], 
CachedKafkaProducer]() {
     override def onRemoval(
-        notification: RemovalNotification[Seq[(String, Object)], Producer]): 
Unit = {
-      val paramsSeq: Seq[(String, Object)] = notification.getKey
-      val producer: Producer = notification.getValue
-      logDebug(
-        s"Evicting kafka producer $producer params: $paramsSeq, due to 
${notification.getCause}")
-      close(paramsSeq, producer)
+        notification: RemovalNotification[Seq[(String, Object)], 
CachedKafkaProducer]): Unit = {
+      val producer: CachedKafkaProducer = notification.getValue
+      if (producer.inUse()) {
+        logDebug(s"Evicting kafka producer $producer, due to 
${notification.getCause}.")
+        // When `inuse` producer is evicted we wait for it to be released 
before finally closing it.
+        closeQueue.add(producer)
+        producer.unCache()
+      } else {
+        close(producer)
+      }
     }
   }
 
-  private lazy val guavaCache: LoadingCache[Seq[(String, Object)], Producer] =
+  private lazy val guavaCache: LoadingCache[Seq[(String, Object)], 
CachedKafkaProducer] =
     CacheBuilder.newBuilder().expireAfterAccess(cacheExpireTimeout, 
TimeUnit.MILLISECONDS)
       .removalListener(removalListener)
-      .build[Seq[(String, Object)], Producer](cacheLoader)
-
-  private def createKafkaProducer(producerConfiguration: ju.Map[String, 
Object]): Producer = {
-    val updatedKafkaProducerConfiguration =
-      KafkaConfigUpdater("executor", producerConfiguration.asScala.toMap)
-        .setAuthenticationConfigIfNeeded()
-        .build()
-    val kafkaProducer: Producer = new 
Producer(updatedKafkaProducerConfiguration)
-    logDebug(s"Created a new instance of KafkaProducer for 
$updatedKafkaProducerConfiguration.")
-    kafkaProducer
-  }
+      .build[Seq[(String, Object)], CachedKafkaProducer](cacheLoader)
 
   /**
    * Get a cached KafkaProducer for a given configuration. If matching 
KafkaProducer doesn't
    * exist, a new KafkaProducer will be created. KafkaProducer is thread safe, 
it is best to keep
    * one instance per specified kafkaParams.
    */
-  private[kafka010] def getOrCreate(kafkaParams: ju.Map[String, Object]): 
Producer = {
-    val paramsSeq: Seq[(String, Object)] = paramsToSeq(kafkaParams)
-    try {
-      guavaCache.get(paramsSeq)
-    } catch {
-      case e @ (_: ExecutionException | _: UncheckedExecutionException | _: 
ExecutionError)
-        if e.getCause != null =>
-        throw e.getCause
+  private[kafka010] def acquire(kafkaParamsMap: ju.Map[String, Object]): 
CachedKafkaProducer =
+    this.synchronized {
+      val paramsSeq: Seq[(String, Object)] = paramsToSeq(kafkaParamsMap)
+      try {
+        val cachedKafkaProducer: CachedKafkaProducer = 
guavaCache.get(paramsSeq)
+        val useCount = cachedKafkaProducer.inUseCount.incrementAndGet()
+        logDebug(s"Granted producer $cachedKafkaProducer, inuse-count: 
$useCount")
+        cachedKafkaProducer
+      } catch {
+        case e@(_: ExecutionException | _: UncheckedExecutionException | _: 
ExecutionError)
+          if e.getCause != null =>
+          throw e.getCause
+      }
     }
-  }
 
-  private def paramsToSeq(kafkaParams: ju.Map[String, Object]): Seq[(String, 
Object)] = {
-    val paramsSeq: Seq[(String, Object)] = kafkaParams.asScala.toSeq.sortBy(x 
=> x._1)
+  private def paramsToSeq(kafkaParamsMap: ju.Map[String, Object]): 
Seq[(String, Object)] = {
+    val paramsSeq: Seq[(String, Object)] = 
kafkaParamsMap.asScala.toSeq.sortBy(x => x._1)
     paramsSeq
   }
 
-  /** For explicitly closing kafka producer */
-  private[kafka010] def close(kafkaParams: ju.Map[String, Object]): Unit = {
-    val paramsSeq = paramsToSeq(kafkaParams)
-    guavaCache.invalidate(paramsSeq)
+  /* Release a kafka producer back to the kafka cache. We simple decrement 
it's inuse count. */
+  private[kafka010] def release(producer: CachedKafkaProducer, failing: 
Boolean): Unit = {
+    this.synchronized {
+      val inUseCount = producer.inUseCount.decrementAndGet()
+      logDebug(s"Released producer $producer, updated inuse count: 
$inUseCount")
+      if (failing) {
+        // If this producer is failing to write, we remove it from cache.
+        // So that it is re-created, eventually.
+        logDebug(s"Invalidated a failing producer: $producer.")
+        guavaCache.invalidate(producer.kafkaParams)
 
 Review comment:
   Good idea, additionally makes the code more simple compared to my suggestion 
[here](https://github.com/apache/spark/pull/19096#discussion_r266888173). My 
one can be resolved because this covers it.
   @ScrapCodes it would be good to cover this functionality with a unit test. 
Something like:
   ```
     test("Should not close already closed producer.") {
     ...
     }
   ```
   

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