The processor counters fail to execute multiple threads. The programming is not safe since they are not atomic operations. They are using a volatile instance variable accessed by multiple threads when onTrigger is called. The solution is to declare those local variables to onTrigger. Perform several tests with millions of records and the counter does not work correctly when it is executed with more than one task.
The problem is in the declaration of these instance variables:
private volatile int lineCount;
private volatile int lineNonEmptyCount;
private volatile int wordCount;
private volatile int characterCount;
This is not safe to perform atomic operations on these variables. As a result the counters register less amount of lines when executed with multiple threads.
I propose the following solution: