{"action":"created","comment":{"url":"https://api.github.com/repos/apache/spark/pulls/comments/93087921","pull_request_review_id":13609533,"id":93087921,"diff_hunk":"@@ -432,6 +465,93 @@ private[spark] class Executor(\n   }\n \n   /**\n+   * Supervises the killing / cancellation of a task by sending the interrupted flag, optionally\n+   * sending a Thread.interrupt(), and monitoring the task until it finishes.\n+   */\n+  private class TaskReaper(\n+      taskRunner: TaskRunner,\n+      val interruptThread: Boolean)\n+    extends Runnable {\n+\n+    private[this] val taskId: Long = taskRunner.taskId\n+\n+    private[this] val killPollingIntervalMs: Long =\n+      conf.getTimeAsMs(\"spark.task.reaper.pollingInterval\", \"10s\")\n+\n+    private[this] val killTimeoutMs: Long = conf.getTimeAsMs(\"spark.task.reaper.killTimeout\", \"2m\")\n+\n+    private[this] val takeThreadDump: Boolean =\n+      conf.getBoolean(\"spark.task.reaper.threadDump\", true)\n+\n+    override def run(): Unit = {\n+      val startTimeMs = System.currentTimeMillis()\n+      def elapsedTimeMs = System.currentTimeMillis() - startTimeMs\n+      def timeoutExceeded(): Boolean = killTimeoutMs > 0 && elapsedTimeMs > killTimeoutMs\n+      try {\n+        // Only attempt to kill the task once. If interruptThread = false then a second kill\n+        // attempt would be a no-op and if interruptThread = true then it may not be safe or\n+        // effective to interrupt multiple times:\n+        taskRunner.kill(interruptThread = interruptThread)\n+        // Monitor the killed task until it exits:\n+        var finished: Boolean = false\n+        while (!finished && !timeoutExceeded()) {","path":"core/src/main/scala/org/apache/spark/executor/Executor.scala","position":136,"original_position":136,"commit_id":"7e7789d6a7dc260d7ad73e7c8e09e3f21ee0195a","original_commit_id":"7e7789d6a7dc260d7ad73e7c8e09e3f21ee0195a","user":{"login":"JoshRosen","id":50748,"avatar_url":"https://avatars.githubusercontent.com/u/50748?v=3","gravatar_id":"","url":"https://api.github.com/users/JoshRosen","html_url":"https://github.com/JoshRosen","followers_url":"https://api.github.com/users/JoshRosen/followers","following_url":"https://api.github.com/users/JoshRosen/following{/other_user}","gists_url":"https://api.github.com/users/JoshRosen/gists{/gist_id}","starred_url":"https://api.github.com/users/JoshRosen/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/JoshRosen/subscriptions","organizations_url":"https://api.github.com/users/JoshRosen/orgs","repos_url":"https://api.github.com/users/JoshRosen/repos","events_url":"https://api.github.com/users/JoshRosen/events{/privacy}","received_events_url":"https://api.github.com/users/JoshRosen/received_events","type":"User","site_admin":false},"body":"It's mentioned on line 495:\r\n\r\n> `// Monitor the killed task until it exits.`","created_at":"2016-12-19T18:17:07Z","updated_at":"2016-12-19T18:17:07Z","html_url":"https://github.com/apache/spark/pull/16189#discussion_r93087921","pull_request_url":"https://api.github.com/repos/apache/spark/pulls/16189","_links":{"self":{"href":"https://api.github.com/repos/apache/spark/pulls/comments/93087921"},"html":{"href":"https://github.com/apache/spark/pull/16189#discussion_r93087921"},"pull_request":{"href":"https://api.github.com/repos/apache/spark/pulls/16189"}}},"pull_request":{"url":"https://api.github.com/repos/apache/spark/pulls/16189","id":96866742,"html_url":"https://github.com/apache/spark/pull/16189","diff_url":"https://github.com/apache/spark/pull/16189.diff","patch_url":"https://github.com/apache/spark/pull/16189.patch","issue_url":"https://api.github.com/repos/apache/spark/issues/16189","number":16189,"state":"open","locked":false,"title":"[SPARK-18761][CORE] Introduce \"task reaper\" to oversee task killing in executors","user":{"login":"JoshRosen","id":50748,"avatar_url":"https://avatars.githubusercontent.com/u/50748?v=3","gravatar_id":"","url":"https://api.github.com/users/JoshRosen","html_url":"https://github.com/JoshRosen","followers_url":"https://api.github.com/users/JoshRosen/followers","following_url":"https://api.github.com/users/JoshRosen/following{/other_user}","gists_url":"https://api.github.com/users/JoshRosen/gists{/gist_id}","starred_url":"https://api.github.com/users/JoshRosen/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/JoshRosen/subscriptions","organizations_url":"https://api.github.com/users/JoshRosen/orgs","repos_url":"https://api.github.com/users/JoshRosen/repos","events_url":"https://api.github.com/users/JoshRosen/events{/privacy}","received_events_url":"https://api.github.com/users/JoshRosen/received_events","type":"User","site_admin":false},"body":"## What changes were proposed in this pull request?\r\n\r\nSpark's current task cancellation / task killing mechanism is \"best effort\" because some tasks may not be interruptible or may not respond to their \"killed\" flags being set. If a significant fraction of a cluster's task slots are occupied by tasks that have been marked as killed but remain running then this can lead to a situation where new jobs and tasks are starved of resources that are being used by these zombie tasks.\r\n\r\nThis patch aims to address this problem by adding a \"task reaper\" mechanism to executors. At a high-level, task killing now launches a new thread which attempts to kill the task and then watches the task and periodically checks whether it has been killed. The TaskReaper will periodically re-attempt to call `TaskRunner.kill()` and will log warnings if the task keeps running. I modified TaskRunner to rename its thread at the start of the task, allowing TaskReaper to take a thread dump and filter it in order to log stacktraces from the exact task thread that we are waiting to finish. If the task has not stopped after a configurable timeout then the TaskReaper will throw an exception to trigger executor JVM death, thereby forcibly freeing any resources consumed by the zombie tasks.\r\n\r\nThis feature is flagged off by default and is controlled by four new configurations under the `spark.task.reaper.*` namespace. See the updated `configuration.md` doc for details.\r\n\r\n## How was this patch tested?\r\n\r\nTested via a new test case in `JobCancellationSuite`, plus manual testing. 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