code: public static ThreadManager getInstance() {
          if (thisClass == null) {
              thisClass = new ThreadManager();
  
              String useInheritableThreadLocalString = SSLConfigManager.getInstance().getGlobalProperty(Constants.SSLPROP_USE_INHERITABLE_THREAD_LOCAL);
              if (useInheritableThreadLocalString != null && (useInheritableThreadLocalString.equalsIgnoreCase("true") || useInheritableThreadLocalString.equalsIgnoreCase("yes"))) {
                  if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled())
                      Tr.debug(tc, "useInheritableThreadLocal is enabled.");
                  useInheritableThreadLocal = true;
              }
          }
  
          return thisClass;
      }
docs: Access the singleton instance of this class.
  
  @return ThreadManager