public static synchronized  void addTotalThreads(int thisGroup) 
{
        totalThreads += thisGroup;
}

Update the total number of threads

 public static synchronized  void clearTotalThreads() 
{
        totalThreads = 0;
}

Set total threads to zero

 static synchronized  void decrNumberOfThreads() 
{
        numberOfActiveThreads--;
}

Decrement number of active threads.

 public static synchronized  void endTest() 
{
        testStart = 0;
}

Called by MainFrame#testEnded(). Clears start time field.

 public static JMeterContext getContext() 
{
        return (JMeterContext) threadContext.get();
}

Gives access to the current thread context.

 public static synchronized int getNumberOfThreads() 
{
        return numberOfActiveThreads;
}

Get the number of currently active threads

 public static synchronized long getTestStartTime() 
{
// NOT USED
        return testStart;
}

 public static synchronized int getTotalThreads() 
{
        return totalThreads;
}

Get the total number of threads (>= active)

 static synchronized  void incrNumberOfThreads() 
{
        numberOfActiveThreads++;
}

Increment number of active threads.

 public static synchronized  void startTest() 
{
        if (testStart == 0) {
            numberOfActiveThreads = 0;
            testStart = System.currentTimeMillis();
            JMeterUtils.setProperty("TESTSTART.MS",Long.toString(testStart));// $NON-NLS-1$
        }
}

Method is called by the JMeterEngine class when a test run is started. Zeroes numberOfActiveThreads. Saves current time in a field and in the JMeter property "TESTSTART.MS"