Make built-in spanProcessor extendable

[Jay Han]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is.
The implementations of SpanProcessor are final class, we cannot extend it.

Describe the solution you'd like
A clear and concise description of what you want to happen.
Make them extendable.

[John Watson]

Can you explain what your use-case is, and why you need to extend, rather than just create a wrapper that delegates some functionality to the underlying SpanProcessor?

[Jay Han]

I want BatchSpanProcessor to skip executing forceFlush when shutdown. It's impossible to create a wrapper that delegates the shutdown because it's a private method of the inner class Worker.

[John Watson]

Seems easy enough to have your delegate keep track of the shutdown state, and just use that to make forceFlush a no-op after shutdown has been called. Am I missing something?

[Jay Han]

Seems easy enough to have your delegate keep track of the shutdown state, and just use that to make forceFlush a no-op after shutdown has been called. Am I missing something?

Sorry, I can't get it. Would you please show me a code example?

[John Watson]

Seems easy enough to have your delegate keep track of the shutdown state, and just use that to make forceFlush a no-op after shutdown has been called. Am I missing something?

Sorry, I can't get it. Would you please show me a code example?

public class DelegatingSpanProcessor implements SpanProcessor {
  private final SpanProcessor delegate;
  private final AtomicBoolean isShutdown = new AtomicBoolean();

  public DelegatingSpanProcessor(SpanProcessor delegate) {this.delegate = delegate;}

  @Override
  public CompletableResultCode shutdown() {
    CompletableResultCode shutdown = delegate.shutdown();
    isShutdown.set(true);
    return shutdown;
  }

  @Override
  public CompletableResultCode forceFlush() {
    if (isShutdown.get()) {
      return CompletableResultCode.ofSuccess();
    }
    return delegate.forceFlush();
  }

  @Override
  public void onStart(Context parentContext, ReadWriteSpan span) {
    delegate.onStart(parentContext, span);
  }

  @Override
  public boolean isStartRequired() {
    return delegate.isStartRequired();
  }

  @Override
  public void onEnd(ReadableSpan span) {
    delegate.onEnd(span);
  }

  @Override
  public boolean isEndRequired() {
    return delegate.isEndRequired();
  }

  @Override
  public void close() {
    delegate.close();
  }
}

[Jay Han]

delegate.shutdown() calls worker.shutdown(), and then the worker will flush itself. The forceFlush of BatchSpanProcessor itself doesn't make sense.
Let's see the implementation of the forceFlush of BatchSpanProcessor:

@Override
public CompletableResultCode shutdown() {
  if (isShutdown.getAndSet(true)) {
    return CompletableResultCode.ofSuccess();
  }
  return worker.shutdown(); // <=== I want to skip this flush
}

[John Watson]

Why do you want to skip the controlled shutdown of the worker?

[Jay Han]

I don't want to flush spans when shutdown.

[John Watson]

Making the BatchSpanProcessor extendable wouldn't solve your issue, then, since we will still need to shut down the worker thread, even if it doesn't flush its spans before doing so.

I recommend making a copy of the BatchSpanProcessor code and modifying it to your liking. If you need this as a first-class feature (skipping the flushing of the spans on shutdown), I recommend creating an issue in the specification for it, as this is required behavior from the BatchSpanProcessor. See here for the specific requirement.