[SPARK-8414] Ensure context cleaner periodic cleanups

Garbage collection triggers cleanups. If the driver JVM is huge and there is little memory pressure, we may never clean up shuffle files on executors. This is a problem for long-running applications (e.g. streaming).

Author: Andrew Or <andrew@databricks.com>

Closes #10070 from andrewor14/periodic-gc.

core/src/main/scala/org/apache/spark/ContextCleaner.scala

@@ -18,12 +18,13 @@
 package org.apache.spark
 
 import java.lang.ref.{ReferenceQueue, WeakReference}
+import java.util.concurrent.{TimeUnit, ScheduledExecutorService}
 
 import scala.collection.mutable.{ArrayBuffer, SynchronizedBuffer}
 
 import org.apache.spark.broadcast.Broadcast
 import org.apache.spark.rdd.{RDD, ReliableRDDCheckpointData}
-import org.apache.spark.util.Utils
+import org.apache.spark.util.{ThreadUtils, Utils}
 
 /**
  * Classes that represent cleaning tasks.
@@ -66,6 +67,20 @@ private[spark] class ContextCleaner(sc: SparkContext) extends Logging {
 
   private val cleaningThread = new Thread() { override def run() { keepCleaning() }}
 
+  private val periodicGCService: ScheduledExecutorService =
+    ThreadUtils.newDaemonSingleThreadScheduledExecutor("context-cleaner-periodic-gc")
+
+  /**
+   * How often to trigger a garbage collection in this JVM.
+   *
+   * This context cleaner triggers cleanups only when weak references are garbage collected.
+   * In long-running applications with large driver JVMs, where there is little memory pressure
+   * on the driver, this may happen very occasionally or not at all. Not cleaning at all may
+   * lead to executors running out of disk space after a while.
+   */
+  private val periodicGCInterval =
+    sc.conf.getTimeAsSeconds("spark.cleaner.periodicGC.interval", "30min")
+
   /**
    * Whether the cleaning thread will block on cleanup tasks (other than shuffle, which
    * is controlled by the `spark.cleaner.referenceTracking.blocking.shuffle` parameter).
@@ -104,6 +119,9 @@ private[spark] class ContextCleaner(sc: SparkContext) extends Logging {
     cleaningThread.setDaemon(true)
     cleaningThread.setName("Spark Context Cleaner")
     cleaningThread.start()
+    periodicGCService.scheduleAtFixedRate(new Runnable {
+      override def run(): Unit = System.gc()
+    }, periodicGCInterval, periodicGCInterval, TimeUnit.SECONDS)
   }
 
   /**
@@ -119,6 +137,7 @@ private[spark] class ContextCleaner(sc: SparkContext) extends Logging {
       cleaningThread.interrupt()
     }
     cleaningThread.join()
+    periodicGCService.shutdown()
   }
 
   /** Register a RDD for cleanup when it is garbage collected. */