Question

I want to pull multiple files from a queue and parse them simultaneously. However, my executor is only calling one thread:

private static ScheduledExecutorService parsingExec ;
protected static BlockingQueue<Path> queue = new LinkedBlockingQueue<>();
int threadPoolSize = 10;
parsingExec = Executors.newScheduledThreadPool(threadPoolSize);
parsingExec.scheduleAtFixedRate(new MyParser(queue), 0, 0, TimeUnit.MILLISECONDS);

Answer 1

From the Javadoc for scheduleWithFixedRate():

Creates and executes a periodic action that becomes enabled first
after the given initial delay, and subsequently with the given period;
that is executions will commence after initialDelay then
initialDelay+period, then initialDelay + 2 * period, and so on. If any
execution of the task encounters an exception, subsequent executions
are suppressed. Otherwise, the task will only terminate via
cancellation or termination of the executor. If any execution of this
task takes longer than its period, then subsequent executions may
start late, but will not concurrently execute.

This method is for scheduling a single task, to be executed multiple times. The key thing to note being that only one instance of your task will ever be executing at a time. If you want to execute multiple tasks simultaneously then you should be using, for example, a fixed thread pool instead.

final ExecutorService parsingExec = Executors.newFixedThreadPool(threadPoolSize);
for(final int i = 0; i < threadPoolSize; i++) {
    parsingExec.submit(new MyParser(queue));
}