async-patterns

Async Patterns for GridGain/Ignite

From PR Mining (GridGain-9)

Key patterns from Continuous Query PRs #3565, #3588, #3592:

---

Pattern 1: CompletableFuture Chaining

prev.thenCompose(tmp -> cursorFut)
    .thenAcceptAsync(cursor -> {
        process(cursor);
        next.complete(result);
    }, exec)
    .exceptionally(t -> {
        next.completeExceptionally(t);
        return null;
    });

Key: Use thenCompose (not thenApply) for future chaining

---

Pattern 2: Channel-Based Producer-Consumer (from PR #3592)

var channel = Channel.CreateBounded<T>(new BoundedChannelOptions(capacity) {
    FullMode = BoundedChannelFullMode.Wait
});

// Producer with exception propagation
Task.Run(async () => {
    try {
        await foreach (var item in ScanPartition(partition)) {
            await channel.Writer.WriteAsync(item);
        }
    } catch (Exception ex) {
        channel.Writer.Complete(ex);  // Propagate error!
    }
});

---

Pattern 3: Protocol Feature Flags (from PR #3588)

public static final ClientProtocolFeature CQ_LONG_POLLING_WAIT_TIME =
    new ClientProtocolFeature(42);

public void serialize(PayloadWriter writer, ProtocolVersion version) {
    if (version.supports(CQ_LONG_POLLING_WAIT_TIME)) {
        writer.writeLong(longPollingWaitTimeMs);
    }
}

---

Pattern 4: Async Cancellation

public CompletableFuture<Void> cancelAsync() {
    if (!cancelled) {
        synchronized (lock) {
            if (!cancelled) {
                pendingFuture.completeExceptionally(new CancelledException());
                cancelled = true;
                cancelFut.complete(null);
            }
        }
    }
    return cancelFut;
}

---

Review Checklist

• Exceptions propagated through async chains
• thenCompose for future chaining, not thenApply
• Bounded channels/queues for backpressure
• Background tasks propagate errors
• Protocol features have version checks