Can you provide more details so that someone else can duplicate the problem you're reporting?

I run a Jenkins instance with 30 or more agents, several thousand jobs, and intentional stress tests running many bug check jobs did not exceed 600 threads running at a time

I suspect that there is something in your pipeline shared library that is different than the pipeline shared libraries that I use in my environment.

Most issues won't get attention from maintainers until there is a precise set of steps that will show the problem. If you'd like more attention on this issue, you'll need to provide step by step instructions that will allow someone else to see the problem in their environment.

Thanks Mark for you response 

we are  using around: 10-15  agent and its running around  75 jobs ,we are also using grrovy shared library for ci pipeline. threads of master   is keeping increasing  not get  down till  restart the jenkins.  please  find below high level threads and all threds details in attached pdf  JavaMelody_nodes_9_17_20.pdf

please find attached  thread dumps also thredd dumps.txt

*on 18 sep- 2020 master agent has *
Threads on masterjenkins: Number = 626, Maximum = 669, Total started = 24,437 Details
*on 21 sep- 2020 master agent has *
Threads on masterjenkins: Number = 819, Maximum = 842, Total started = 47,800 Details

all waiting threads has below details and we are using jdk 11 is there any issue with jdk 11

"Thread-4214" daemon prio=5 WAITING
java.base@11.0.4/java.lang.Object.wait(Native Method)
java.base@11.0.4/java.lang.Object.wait(Object.java:328)
java.naming@11.0.4/com.sun.jndi.ldap.Connection.pauseReader(Connection.java:790)
java.naming@11.0.4/com.sun.jndi.ldap.Connection.run(Connection.java:930)
java.base@11.0.4/java.lang.Thread.run(Thread.java:834)

"Thread-4219" daemon prio=5 WAITING
java.base@11.0.4/java.lang.Object.wait(Native Method)
java.base@11.0.4/java.lang.Object.wait(Object.java:328)
java.naming@11.0.4/com.sun.jndi.ldap.Connection.pauseReader(Connection.java:790)
java.naming@11.0.4/com.sun.jndi.ldap.Connection.run(Connection.java:930)
java.base@11.0.4/java.lang.Thread.run(Thread.java:834)

I'm not aware of any issue that is specific to Java 11 and threads in Jenkins. There are issues that are specific to Java 11, but I'm not aware of any Java 11 issues that are related to threading. My first guess is that you would be likely to see the same problem on Java 8 as you are seeing on Java 11. The biggest challenge is to identify what is different in your environment compared to other environments.