[TEZ-4315] rectifying the potential risk of ConcurrentModificationException when getMatchingRequestWithoutPriority

[chenjunbiao001]

link to https://issues.apache.org/jira/projects/TEZ/issues/TEZ-4315

[hadoop-yetus]

:broken_heart: -1 overall

Vote	Subsystem	Runtime	Comment
+0 :ok:	reexec	14m 22s	Docker mode activated.
		_ Prechecks _
+1 :green_heart:	dupname	0m 0s	No case conflicting files found.
+1 :green_heart:	@author	0m 0s	The patch does not contain any @author tags.
-1 :x:	test4tests	0m 0s	The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
		_ master Compile Tests _
+1 :green_heart:	mvninstall	13m 10s	master passed
+1 :green_heart:	compile	0m 44s	master passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 :green_heart:	compile	0m 35s	master passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 :green_heart:	checkstyle	1m 17s	master passed
+1 :green_heart:	javadoc	0m 46s	master passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 :green_heart:	javadoc	0m 36s	master passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+0 :ok:	spotbugs	1m 44s	Used deprecated FindBugs config; considering switching to SpotBugs.
+1 :green_heart:	findbugs	1m 42s	master passed
		_ Patch Compile Tests _
+1 :green_heart:	mvninstall	0m 28s	the patch passed
+1 :green_heart:	compile	0m 31s	the patch passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 :green_heart:	javac	0m 31s	the patch passed
+1 :green_heart:	compile	0m 25s	the patch passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 :green_heart:	javac	0m 25s	the patch passed
+1 :green_heart:	checkstyle	0m 22s	tez-dag: The patch generated 0 new + 97 unchanged - 2 fixed = 97 total (was 99)
+1 :green_heart:	whitespace	0m 0s	The patch has no whitespace issues.
+1 :green_heart:	javadoc	0m 25s	the patch passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 :green_heart:	javadoc	0m 23s	the patch passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 :green_heart:	findbugs	1m 16s	the patch passed
		_ Other Tests _
+1 :green_heart:	unit	4m 29s	tez-dag in the patch passed.
+1 :green_heart:	asflicense	0m 14s	The patch does not generate ASF License warnings.
		42m 40s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-133/1/artifact/out/Dockerfile
GITHUB PR	https://github.com/apache/tez/pull/133
Optional Tests	dupname asflicense javac javadoc unit spotbugs findbugs checkstyle compile
uname	Linux 681a0071a93e 4.15.0-112-generic #113-Ubuntu SMP Thu Jul 9 23:41:39 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
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Default Java	Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
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Test Results	https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-133/1/testReport/
Max. process+thread count	188 (vs. ulimit of 5500)
modules	C: tez-dag U: tez-dag
Console output	https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-133/1/console
versions	git=2.25.1 maven=3.6.3 findbugs=3.0.1
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[jteagles]

How often have you observed the ConcurrentModificationException? When I look at the code base, the callers of those functions are synchronized at the function level. Please 1) attach a stack trace if possible or 2) create a test that shows how this is possible or 3) Explain the code path more precisely.

[jteagles]

@chenjunbiao001, can can provide a stack trace of the ConcurrentModificationException? I am unable to find a code path that will exercise the problem in practice.