code: static boolean agentIsAvailable() {
          try {
              if (instrumentation == null) {
                  instrumentation = (Instrumentation)System.getProperties().get(INSTRUMENTATION_INSTANCE_SYSTEM_PROPERTY_NAME);
              }
              if (instrumentation == null) {
                  Class<?> sizeOfAgentClass = ClassLoader.getSystemClassLoader().loadClass(SIZEOF_AGENT_CLASSNAME);
                  Method getInstrumentationMethod = sizeOfAgentClass.getMethod("getInstrumentation");
                  instrumentation = (Instrumentation)getInstrumentationMethod.invoke(sizeOfAgentClass);
              }
              return instrumentation != null;
          } catch (SecurityException e) {
              LOGGER.warn("Couldn't access the system classloader because of the security policies applied by " +
                          "the security manager. You either want to loosen these, so ClassLoader.getSystemClassLoader() and " +
                          "reflection API calls are permitted or the sizing will be done using some other mechanism.\n" +
                          "Alternatively, set the system property org.ehcache.sizeof.agent.instrumentationSystemProperty to true " +
                          "to have the agent put the required instances in the System Properties for the loader to access.");
              return false;
          } catch (Throwable e) {
              return false;
          }
      }
docs: Checks whether the agent is available
  
  @return true if available