CompleteableFuture in a loop contruct in a private Ethereum Blockchain

Question

I have a private Ethereum blockchain set up with 5 machines mining on it. The size of the block chain [number of blocks] are as of now, 300. The processing is done on back-end Java.

I need to run the following loop construct in a asynchronous manner. The bottleneck of the loop is during the execution of the following command:

EthBlock eb = web3.ethGetBlockByNumber(new DefaultBlockParameterNumber(BigInteger.valueOf(i)), true).send();

The command can also return a Completablefuture<EthBlock> object by ending it with supplyAsync() given here https://github.com/web3j/web3j#start-sending-requests Just calling supplyAync().get() removes the parallelism aspect and makes it behave synchronously.

public void businessLogic() throws Exception {
        recentBlocks = new ArrayList<EthBlock.Block>();
        for (long i = 1; i <= 300000; i++) {
            EthBlock eb = web3.ethGetBlockByNumber(new DefaultBlockParameterNumber(BigInteger.valueOf(i)), true).send();
            if (eb == null || eb.getBlock() == null) {
                continue;
            }
            EthBlock.Block block = eb.getBlock();
            recentBlocks.add(block);
        }
    }

I not able to grasp the institution of translating the code into a way CompleteableFuture can operate on. Goal is to 'group' up multiple calls to web.ethGetBlockNumber(...).supplyAync() into a collection and call them all at once to update an array which will get filled by EthBlock objects ie recentBlocks .

This is what I came up with:

public void businessLogic() throws Exception {
    recentBlocks = new ArrayList<EthBlock.Block>();
    List<CompleteableFuture> compFutures = new ArrayList<>();
    for (long i = 0, i <= 300000, i++){
        CompleteableFuture<EthBlock> compFuture = eb3.ethGetBlockByNumber(new DefaultBlockParameterNumber(BigInteger.valueOf(i)), true).sendAsync();
        compFuture.thenAcceptAsync(eb -> // Doesn't look right
        EthBlock.Block block = eb.getBlock();
        recentBlock.add(block);)
        compFutures.add(compFuture);        
    }
    CompleteableFuture.allOf(compFutures).get();
}

---

Implementing IntStream

    long start = System.nanoTime();
    recentBlocks = IntStream.rangeClosed(0, 300_000)
             .parallel()
             .mapToObj(i -> {
                try {
                    System.out.println("Current Thread -> " + Thread.currentThread());
                    return web3.ethGetBlockByNumber(new DefaultBlockParameterNumber(BigInteger.valueOf(i)), true).send();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                return null;
            })
             .filter(Objects::nonNull)
             .map(EthBlock::getBlock)
             .filter(Objects::nonNull)
             .collect(Collectors.toList());
    long stop = System.nanoTime();
    System.out.println("Time Elapsed: " + TimeUnit.MICROSECONDS.convert(stop-start, TimeUnit.NANOSECONDS));

Answer 1

CompletableFuture contains an Override for get: get(long timeout, TimeUnit unit) . You can use this to poll by making the get timeout if it does not return within a specific time.

Answer 2

You might be able to benefit from a parallel stream instead of relying on CompletableFuture , assuming the order of the resulting List isn't important:

IntStream.rangeClosed(0, 300_000)
         .parallel()
         .mapToObj(i -> web3.ethGetBlockByNumber(new DefaultBlockParameterNumber(BigInteger.valueOf(i)), true).send())
         .filter(Objects::nonNull)
         .map(EthBlock::getBlock)
         .filter(Objects::nonNull)
         .collect(Collectors.toList());

Because you stated that didn't help, let's try an ExecutorService that utilizes a cached thread pool instead:

List<EthBlock.Block> blocks = Collections.synchronizedList(new ArrayList<>(300_000));

ExecutorService service = Executors.newCachedThreadPool();

for (int i = 0; i <= 300_000; i++) {
    BigInteger number = BigInteger.valueOf(i);

    service.execute(() -> {
        EthBlock eb = web3.ethGetBlockByNumber(new DefaultBlockParameterNumber(number), true).send();

        if (eb == null) {
            return;
        }

        EthBlock.Block block = eb.getBlock();

        if (block != null) {
            blocks.add(block);
        }
    });
}