HDDS-1969. Implement OM GetDelegationToken request to use Cache and DoubleBuffer.

[bharatviswa504]

No description provided.

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Comment
0	reexec	43	Docker mode activated.
		_ Prechecks _
+1	dupname	1	No case conflicting files found.
+1	@author	0	The patch does not contain any @author tags.
-1	test4tests	0	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.
		_ trunk Compile Tests _
0	mvndep	14	Maven dependency ordering for branch
+1	mvninstall	602	trunk passed
+1	compile	365	trunk passed
+1	checkstyle	62	trunk passed
+1	mvnsite	0	trunk passed
+1	shadedclient	836	branch has no errors when building and testing our client artifacts.
+1	javadoc	149	trunk passed
0	spotbugs	420	Used deprecated FindBugs config; considering switching to SpotBugs.
+1	findbugs	616	trunk passed
		_ Patch Compile Tests _
0	mvndep	27	Maven dependency ordering for patch
+1	mvninstall	566	the patch passed
+1	compile	367	the patch passed
+1	cc	367	the patch passed
+1	javac	367	the patch passed
+1	checkstyle	71	the patch passed
+1	mvnsite	0	the patch passed
+1	whitespace	0	The patch has no whitespace issues.
+1	shadedclient	665	patch has no errors when building and testing our client artifacts.
+1	javadoc	159	the patch passed
+1	findbugs	638	the patch passed
		_ Other Tests _
+1	unit	284	hadoop-hdds in the patch passed.
-1	unit	1653	hadoop-ozone in the patch failed.
+1	asflicense	52	The patch does not generate ASF License warnings.
		7359

Reason	Tests
Failed junit tests	hadoop.ozone.client.rpc.TestWatchForCommit
	hadoop.ozone.client.rpc.TestOzoneAtRestEncryption
	hadoop.ozone.client.rpc.TestOzoneClientRetriesOnException

Subsystem	Report/Notes
Docker	Client=19.03.1 Server=19.03.1 base: https://builds.apache.org/job/hadoop-multibranch/job/PR-1296/1/artifact/out/Dockerfile
GITHUB PR	#1296
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient findbugs checkstyle cc
uname	Linux b85568b6c30b 4.4.0-138-generic #164-Ubuntu SMP Tue Oct 2 17:16:02 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	personality/hadoop.sh
git revision	trunk / 167acd8
Default Java	1.8.0_222
unit	https://builds.apache.org/job/hadoop-multibranch/job/PR-1296/1/artifact/out/patch-unit-hadoop-ozone.txt
Test Results	https://builds.apache.org/job/hadoop-multibranch/job/PR-1296/1/testReport/
Max. process+thread count	5403 (vs. ulimit of 5500)
modules	C: hadoop-ozone/common hadoop-ozone/ozone-manager U: hadoop-ozone
Console output	https://builds.apache.org/job/hadoop-multibranch/job/PR-1296/1/console
versions	git=2.7.4 maven=3.3.9 findbugs=3.1.0-RC1
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[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Comment
0	reexec	55	Docker mode activated.
		_ Prechecks _
+1	dupname	1	No case conflicting files found.
+1	@author	0	The patch does not contain any @author tags.
-1	test4tests	0	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.
		_ trunk Compile Tests _
0	mvndep	13	Maven dependency ordering for branch
+1	mvninstall	586	trunk passed
+1	compile	350	trunk passed
+1	checkstyle	59	trunk passed
+1	mvnsite	0	trunk passed
+1	shadedclient	800	branch has no errors when building and testing our client artifacts.
+1	javadoc	154	trunk passed
0	spotbugs	413	Used deprecated FindBugs config; considering switching to SpotBugs.
+1	findbugs	616	trunk passed
		_ Patch Compile Tests _
0	mvndep	16	Maven dependency ordering for patch
+1	mvninstall	532	the patch passed
+1	compile	366	the patch passed
+1	cc	366	the patch passed
+1	javac	366	the patch passed
+1	checkstyle	73	the patch passed
+1	mvnsite	0	the patch passed
+1	whitespace	0	The patch has no whitespace issues.
+1	shadedclient	638	patch has no errors when building and testing our client artifacts.
+1	javadoc	149	the patch passed
+1	findbugs	626	the patch passed
		_ Other Tests _
+1	unit	302	hadoop-hdds in the patch passed.
-1	unit	1841	hadoop-ozone in the patch failed.
+1	asflicense	39	The patch does not generate ASF License warnings.
		7361

Reason	Tests
Failed junit tests	hadoop.ozone.om.TestScmSafeMode
	hadoop.ozone.client.rpc.TestBlockOutputStreamWithFailures

Subsystem	Report/Notes
Docker	Client=19.03.1 Server=19.03.1 base: https://builds.apache.org/job/hadoop-multibranch/job/PR-1296/2/artifact/out/Dockerfile
GITHUB PR	#1296
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient findbugs checkstyle cc
uname	Linux 00a46a5c70c6 4.4.0-138-generic #164-Ubuntu SMP Tue Oct 2 17:16:02 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	personality/hadoop.sh
git revision	trunk / 9b8359b
Default Java	1.8.0_212
unit	https://builds.apache.org/job/hadoop-multibranch/job/PR-1296/2/artifact/out/patch-unit-hadoop-ozone.txt
Test Results	https://builds.apache.org/job/hadoop-multibranch/job/PR-1296/2/testReport/
Max. process+thread count	4832 (vs. ulimit of 5500)
modules	C: hadoop-ozone/common hadoop-ozone/ozone-manager U: hadoop-ozone
Console output	https://builds.apache.org/job/hadoop-multibranch/job/PR-1296/2/console
versions	git=2.7.4 maven=3.3.9 findbugs=3.1.0-RC1
Powered by	Apache Yetus 0.10.0 http://yetus.apache.org

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[arp7]

+1 with request to add a few explanatory comments.

[bharatviswa504]

Thank You @arp7 for the review.
Fixed review comments.

[bharatviswa504]

Thank You @arp7 for the review.
I will commit this to the trunk. 2nd PR changes are only code comment changes. Committing this, as previous CI test failures are not related to this PR.