public void run()

in src/core/src/main/java/org/apache/jmeter/engine/StandardJMeterEngine.java [401:549]
111 lines of code
24 McCabe index (conditional complexity)

    public void run() {
        log.info("Running the test!");
        running = true;

        /*
         * Ensure that the sample variables are correctly initialised for each run.
         */
        SampleEvent.initSampleVariables();

        JMeterContextService.startTest();
        try {
            PreCompiler compiler = new PreCompiler();
            test.traverse(compiler);
        } catch (RuntimeException e) {
            log.error("Error occurred compiling the tree:",e);
            JMeterUtils.reportErrorToUser("Error occurred compiling the tree: - see log file", e);
            return; // no point continuing
        }
        /*
         * Notification of test listeners needs to happen after function
         * replacement, but before setting RunningVersion to true.
         */
        SearchByClass<TestStateListener> testListeners = new SearchByClass<>(TestStateListener.class); // TL - S&E
        test.traverse(testListeners);

        // Merge in any additional test listeners
        // currently only used by the function parser
        testListeners.getSearchResults().addAll(testList);
        testList.clear(); // no longer needed

        test.traverse(new TurnElementsOn());
        notifyTestListenersOfStart(testListeners);

        List<?> testLevelElements = new ArrayList<>(test.list(test.getArray()[0]));
        removeThreadGroups(testLevelElements);

        SearchByClass<SetupThreadGroup> setupSearcher = new SearchByClass<>(SetupThreadGroup.class);
        SearchByClass<AbstractThreadGroup> searcher = new SearchByClass<>(AbstractThreadGroup.class);
        SearchByClass<PostThreadGroup> postSearcher = new SearchByClass<>(PostThreadGroup.class);

        test.traverse(setupSearcher);
        test.traverse(searcher);
        test.traverse(postSearcher);

        TestCompiler.initialize();
        // for each thread group, generate threads
        // hand each thread the sampler controller
        // and the listeners, and the timer
        Iterator<SetupThreadGroup> setupIter = setupSearcher.getSearchResults().iterator();
        Iterator<AbstractThreadGroup> iter = searcher.getSearchResults().iterator();
        Iterator<PostThreadGroup> postIter = postSearcher.getSearchResults().iterator();

        ListenerNotifier notifier = new ListenerNotifier();

        int groupCount = 0;
        JMeterContextService.clearTotalThreads();

        if (setupIter.hasNext()) {
            log.info("Starting setUp thread groups");
            while (running && setupIter.hasNext()) {//for each setup thread group
                AbstractThreadGroup group = setupIter.next();
                groupCount++;
                String groupName = group.getName();
                log.info("Starting setUp ThreadGroup: {} : {} ", groupCount, groupName);
                startThreadGroup(group, groupCount, setupSearcher, testLevelElements, notifier);
                if (serialized && setupIter.hasNext()) {
                    log.info("Waiting for setup thread group: {} to finish before starting next setup group",
                            groupName);
                    group.waitThreadsStopped();
                }
            }
            log.info("Waiting for all setup thread groups to exit");
            //wait for all Setup Threads To Exit
            waitThreadsStopped();
            log.info("All Setup Threads have ended");
            groupCount=0;
            JMeterContextService.clearTotalThreads();
        }

        groups.clear(); // The groups have all completed now

        /*
         * Here's where the test really starts. Run a Full GC now: it's no harm
         * at all (just delays test start by a tiny amount) and hitting one too
         * early in the test can impair results for short tests.
         */
        JMeterUtils.helpGC();

        JMeterContextService.getContext().setSamplingStarted(true);
        boolean mainGroups = running; // still running at this point, i.e. setUp was not cancelled
        while (running && iter.hasNext()) {// for each thread group
            AbstractThreadGroup group = iter.next();
            //ignore Setup and Post here.  We could have filtered the searcher. but then
            //future Thread Group objects wouldn't execute.
            if (group instanceof SetupThreadGroup ||
                    group instanceof PostThreadGroup) {
                continue;
            }
            groupCount++;
            String groupName = group.getName();
            log.info("Starting ThreadGroup: {} : {}", groupCount, groupName);
            startThreadGroup(group, groupCount, searcher, testLevelElements, notifier);
            if (serialized && iter.hasNext()) {
                log.info("Waiting for thread group: {} to finish before starting next group", groupName);
                group.waitThreadsStopped();
            }
        } // end of thread groups
        if (groupCount == 0){ // No TGs found
            log.info("No enabled thread groups found");
        } else {
            if (running) {
                log.info("All thread groups have been started");
            } else {
                log.info("Test stopped - no more thread groups will be started");
            }
        }

        //wait for all Test Threads To Exit
        waitThreadsStopped();
        groups.clear(); // The groups have all completed now

        if (postIter.hasNext()){
            groupCount = 0;
            JMeterContextService.clearTotalThreads();
            log.info("Starting tearDown thread groups");
            if (mainGroups && !running) { // i.e. shutdown/stopped during main thread groups
                running = tearDownOnShutdown; // re-enable for tearDown if necessary
            }
            while (running && postIter.hasNext()) {//for each setup thread group
                AbstractThreadGroup group = postIter.next();
                groupCount++;
                String groupName = group.getName();
                log.info("Starting tearDown ThreadGroup: {} : {}", groupCount, groupName);
                startThreadGroup(group, groupCount, postSearcher, testLevelElements, notifier);
                if (serialized && postIter.hasNext()) {
                    log.info("Waiting for post thread group: {} to finish before starting next post group", groupName);
                    group.waitThreadsStopped();
                }
            }
            waitThreadsStopped(); // wait for Post threads to stop
        }

        notifyTestListenersOfEnd(testListeners);
        JMeterContextService.endTest();
        if (JMeter.isNonGUI() && SYSTEM_EXIT_FORCED) {
            log.info("Forced JVM shutdown requested at end of test");
            System.exit(0); // NOSONAR Intentional
        }
    }