[
https://issues.apache.org/jira/browse/HADOOP-18217?focusedWorklogId=789706&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-789706
]
ASF GitHub Bot logged work on HADOOP-18217:
-------------------------------------------
Author: ASF GitHub Bot
Created on: 11/Jul/22 18:38
Start Date: 11/Jul/22 18:38
Worklog Time Spent: 10m
Work Description: HerCath commented on code in PR #4255:
URL: https://github.com/apache/hadoop/pull/4255#discussion_r918241764
##########
hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/TestExitUtil.java:
##########
@@ -0,0 +1,122 @@
+/**
+ * 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.hadoop.util;
+
+import static org.apache.hadoop.test.LambdaTestUtils.intercept;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+import org.apache.hadoop.util.ExitUtil.ExitException;
+import org.apache.hadoop.util.ExitUtil.HaltException;
+
+
+public class TestExitUtil {
+
+ @Test
+ public void testGetSetExitExceptions() throws Throwable {
+ // prepare states and exceptions
+ ExitUtil.disableSystemExit();
+ ExitUtil.resetFirstExitException();
+ ExitException ee1 = new ExitException(1, "TestExitUtil forged 1st
ExitException");
+ ExitException ee2 = new ExitException(2, "TestExitUtil forged 2nd
ExitException");
+ try {
+ // check proper initial settings
+ assertFalse("ExitUtil.terminateCalled initial value should be false",
+ ExitUtil.terminateCalled());
+ assertNull("ExitUtil.getFirstExitException initial value should be null",
+ ExitUtil.getFirstExitException());
+
+ // simulate/check 1st call
+ ExitException ee = intercept(ExitException.class,
()->ExitUtil.terminate(ee1));
+ assertSame("ExitUtil.terminate should have rethrown its ExitException
argument but it "
+ + "had thrown something else", ee1, ee);
+ assertTrue("ExitUtil.terminateCalled should be true after 1st
ExitUtil.terminate call",
+ ExitUtil.terminateCalled());
+ assertSame("ExitUtil.terminate should store its 1st call's
ExitException",
+ ee1, ExitUtil.getFirstExitException());
+
+ // simulate/check 2nd call not overwritting 1st one
+ ee = intercept(ExitException.class, ()->ExitUtil.terminate(ee2));
+ assertSame("ExitUtil.terminate should have rethrown its HaltException
argument but it "
+ + "had thrown something else", ee2, ee);
+ assertTrue("ExitUtil.terminateCalled should still be true after 2nd
ExitUtil.terminate call",
+ ExitUtil.terminateCalled());
+ // 2nd call rethrown the 2nd ExitException yet only the 1st only should
have been stored
+ assertSame("ExitUtil.terminate when called twice should only remember
1st call's "
+ + "ExitException", ee1, ExitUtil.getFirstExitException());
+
+ // simulate cleanup, also tries to make sure state is ok for all junit
still has to do
+ ExitUtil.resetFirstExitException();
+ assertFalse("ExitUtil.terminateCalled should be false after "
+ + "ExitUtil.resetFirstExitException call",
ExitUtil.terminateCalled());
+ assertNull("ExitUtil.getFirstExitException should be null after "
+ + "ExitUtil.resetFirstExitException call",
ExitUtil.getFirstExitException());
+ } finally {
+ // cleanup
+ ExitUtil.resetFirstExitException();
Review Comment:
I see that other tests in the util package use Before and After rather than
BeforeClass and AfterClass. TestExitUtil does not rely on having resources that
would benefit from being reserved only once for all the tests so i prefer to
stick with the package's habit : i'll use before and after, not beforeClass and
afterClass
Issue Time Tracking
-------------------
Worklog Id: (was: 789706)
Time Spent: 3h (was: 2h 50m)
> shutdownhookmanager should not be multithreaded (deadlock possible)
> -------------------------------------------------------------------
>
> Key: HADOOP-18217
> URL: https://issues.apache.org/jira/browse/HADOOP-18217
> Project: Hadoop Common
> Issue Type: Bug
> Components: util
> Affects Versions: 2.10.1
> Environment: linux, windows, any version
> Reporter: Catherinot Remi
> Priority: Minor
> Labels: pull-request-available
> Attachments: wtf.java
>
> Time Spent: 3h
> Remaining Estimate: 0h
>
> the ShutdownHookManager class uses an executor to run hooks to have a
> "timeout" notion around them. It does this using a single threaded executor.
> It can leads to deadlock leaving a never-shutting-down JVM with this
> execution flow:
> * JVM need to exit (only daemon threads remaining or someone called
> System.exit)
> * ShutdowHookManager kicks in
> * SHMngr executor start running some hooks
> * SHMngr executor thread kicks in and, as a side effect, run some code from
> one of the hook that calls System.exit (as a side effect from an external lib
> for example)
> * the executor thread is waiting for a lock because another thread already
> entered System.exit and has its internal lock, so the executor never returns.
> * SHMngr never returns
> * 1st call to System.exit never returns
> * JVM stuck
>
> using an executor with a single thread does "fake" timeouts (the task keeps
> running, you can interrupt it but until it stumble upon some piece of code
> that is interruptible (like an IO) it will keep running) especially since the
> executor is a single threaded one. So it has this bug for example :
> * caller submit 1st hook (bad one that would need 1 hour of runtime and that
> cannot be interrupted)
> * executor start 1st hook
> * caller of the future 1st hook result timeout
> * caller submit 2nd hook
> * bug : 1 hook still running, 2nd hook triggers a timeout but never got the
> chance to run anyway, so 1st faulty hook makes it impossible for any other
> hook to have a chance to run, so running hooks in a single separate thread
> does not allow to run other hooks in parallel to long ones.
>
> If we really really want to timeout the JVM shutdown, even accepting maybe
> dirty shutdown, it should rather handle the hooks inside the initial thread
> (not spawning new one(s) so not triggering the deadlock described on the 1st
> place) and if a timeout was configured, only spawn a single parallel daemon
> thread that sleeps the timeout delay, and then use Runtime.halt (which bypass
> the hook system so should not trigger the deadlock). If the normal
> System.exit ends before the timeout delay everything is fine. If the
> System.exit took to much time, the JVM is killed and so the reason why this
> multithreaded shutdown hook implementation was created is satisfied (avoding
> having hanging JVMs)
>
> Had the bug with both oracle and open jdk builds, all in 1.8 major version.
> hadoop 2.6 and 2.7 did not have the issue because they do not run hooks in
> another thread
>
> Another solution is of course to configure the timeout AND to have as many
> threads as needed to run the hooks so to have at least some gain to offset
> the pain of the dealock scenario
>
> EDIT: added some logs and reproduced the problem. in fact it is located after
> triggering all the hook entries and before shutting down the executor.
> Current code, after running the hooks, creates a new Configuration object and
> reads the configured timeout from it, applies this timeout to shutdown the
> executor. I sometimes run with a classloader doing remote classloading,
> Configuration loads its content using this classloader, so when shutting down
> the JVM and some network error occurs the classloader fails to load the
> ressources needed by Configuration. So the code crash before shutting down
> the executor and ends up inside the thread's default uncaught throwable
> handler, which was calling System.exit, so got stuck, so shutting down the
> executor never returned, so does the JVM.
> So, forget about the halt stuff (even if it is a last ressort very robust
> safety net). Still I'll do a small adjustement to the final executor shutdown
> code to be slightly more robust to even the strangest exceptions/errors it
> encounters.
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