Examples with MPSequence com.questdb.mp.MPSequence used on opensource projects

Example 1 with MPSequence

use of com.questdb.mp.MPSequence in project questdb by bluestreak01.

the class AppendObjectConcurrent method main.

/**
 * Multiple threads append to same journal concurrently.
 * <p>
 * Single append thread receives data from multiple publishers via circular queue using QuestDB's thread messaging mechanism.
 * Please refer to my blog post: http://blog.questdb.org/2016/08/the-art-of-thread-messaging.html for more details.
 */
public static void main(String[] args) throws JournalException, InterruptedException {
    if (args.length != 1) {
        System.out.println("Usage: " + AppendObjectConcurrent.class.getName() + " <path>");
        System.exit(1);
    }
    // 
    RingQueue<Quote> queue = new RingQueue<>(Quote::new, 4096);
    // publisher sequence
    final MPSequence pubSequence = new MPSequence(queue.getCapacity());
    final SCSequence subSequence = new SCSequence();
    // create circular dependency between sequences
    pubSequence.then(subSequence).then(pubSequence);
    // run configuration
    int nThreads = 2;
    int nMessages = 1000000;
    JournalConfiguration configuration = ModelConfiguration.CONFIG.build(args[0]);
    try (Factory factory = new Factory(configuration, 1000, 1, 0)) {
        // start publishing threads
        for (int i = 0; i < nThreads; i++) {
            new Thread(new Publisher(queue, pubSequence, nMessages)).start();
        }
        // consume messages in main thread
        int count = 0;
        int deadline = nMessages * nThreads;
        try (JournalWriter<Quote> writer = factory.writer(Quote.class)) {
            while (count < deadline) {
                long cursor = subSequence.next();
                if (cursor < 0) {
                    LockSupport.parkNanos(1);
                    continue;
                }
                long available = subSequence.available();
                while (cursor < available) {
                    Quote q = queue.get(cursor++);
                    q.setTimestamp(System.currentTimeMillis());
                    try {
                        writer.append(q);
                    } catch (JournalException e) {
                        // append may fail, log and continue
                        // N.B. this logging uses builder pattern to construct message. Building finishes with $() call.
                        LOG.error().$("Sequence failed: ").$(cursor - 1).$(e).$();
                    }
                    count++;
                }
                subSequence.done(available - 1);
                try {
                    writer.commit();
                } catch (JournalException e) {
                    // something serious, attempt to rollback
                    LOG.error().$("Batch commit() failed [").$(available - 1).$(']').$(e).$();
                }
            }
        }
        LOG.info().$("Writer done").$();
    }
}