Package org.elasticsearch.xpack.esql.datasources

Class ExternalSourceDrainUtils

java.lang.Object

org.elasticsearch.xpack.esql.datasources.ExternalSourceDrainUtils

public final class ExternalSourceDrainUtils
extends Object

Utility for draining pages from a CloseableIterator into an AsyncExternalSourceBuffer with non-blocking backpressure.

Runs synchronously while the buffer has space (hot path), yields the thread when the buffer is full, and resumes via the provided Executor when space is freed (cold path). No timeout is needed — cancellation propagates via AsyncExternalSourceBuffer.finish(boolean) setting noMoreInputs, which causes AsyncExternalSourceBuffer.waitForSpace() to return an already-completed listener so the drain loop exits promptly.

Method Summary

Modifier and Type	Method	Description
static void	drainPagesAsync(CloseableIterator<Page> pages, AsyncExternalSourceBuffer buffer, Executor executor, ActionListener<Void> listener)	Drains pages from iterator into buffer asynchronously.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

drainPagesAsync

public static void drainPagesAsync(CloseableIterator<Page> pages,
 AsyncExternalSourceBuffer buffer,
 Executor executor,
 ActionListener<Void> listener)

Drains pages from iterator into buffer asynchronously. Runs synchronously while the buffer has space; yields the thread when the buffer is full and resumes via executor when space is freed. Completion (success or failure) is reported via the listener.

Iterator ownership: This method does NOT close the iterator. The caller must close it regardless of outcome (e.g. via ActionListener.runAfter(org.elasticsearch.action.ActionListener<Response>, java.lang.Runnable)).

Executor contract: The executor must be a real thread-pool executor (e.g. generic), never DIRECT_EXECUTOR_SERVICE. Continuations resume on this executor to avoid running producer I/O on the Driver thread. The executor captures and restores thread context at submission time, so no explicit context-preserving wrapper is needed.

Cancellation: No timeout. Cancellation comes from buffer.finish(true) setting noMoreInputs, which causes waitForSpace() to return an already-completed listener.