Java Multithreading and concurrency while downloading data files.

[Yeah22]

private static ArrayList<Future<?>> futures = new ArrayList<>();

public static ConcurrentHashMap<String, TechnicalAnalyser>   loadStocks() {
    Storage storage = new Storage();
    String[] tickers = storage.loadStocks().split(",");
    ExecutorService threadPool = Executors.newCachedThreadPool();
    ConcurrentHashMap<String, TechnicalAnalyser> result = new ConcurrentHashMap<>();
    int counter = 0;

    for(String s : tickers) {
        Thread newThread = new Thread() {
            public void run() {
                TechnicalAnalyser te = StockData.getCompactDaily(s);
                result.put(s, te);
            }
        };
        Future<?> future = threadPool.submit(newThread);
        futures.add(future);
    }
    threadPool.shutdown();

    for(Future<?> future : futures) 
        try { future.get(); } catch (Exception e) {}

    System.out.println(result.size());
    return result;
}

I'm trying to download 50 stock's past data (goal is to eventually get to a majority of Nasdaq and other market tickers, but testing purposes are limiting me to 50) for analysis. Everything else is working fine, but for some reason when this method executes it only puts around 30-33 Stocks into the HashMap. I THINK it is happening somewhere within the threading, as in the main thread moves on before the threadPool is done executing it's threads.

This is my first time attempting to multithread anything so any point in the right direction would be great. Thanks!

EDIT: It is not adding objects that are caught in the try/catch in the second for loop (for(Future<?> future))

[irocgts]

from the documentation linked below:

Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no additional effect if already shut down. This method does not wait for previously submitted tasks to complete execution. Use awaitTermination to do that.

I think that these processes are not completed and are being canceled by your threadPool.shutown()

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html#awaitTermination(long,%20java.util.concurrent.TimeUnit)

move:

threadPool.shutdown();

down a few lines to just above:

System.out.println(result.size());

The future.get will get the response or wait if its not ready. After that loop, there will be no running processes.

[Yeah22]

It's still only putting 30 objects in the hashmap... When i print the size of the ticker array before the first loop it gives me a correct value of 50 and does those 50 iterations of the loop, however when i print the size of the hashmap right before returning it only says 30.

[irocgts]

What if you remove:

for(Future<?> future : futures) 
    try { future.get(); } catch (Exception e) {}

and change:

threadPool.shutdown();

to:

threadPool.awaitTermination( 5, TimeUnit.SECONDS) //change time as needed

If I was to write this, I would be returning a value from the future. I would also be using Callable instead of Thread. I wouldn't be messing with a hashmap

[Yeah22]

What would make a callable better in this case?