Implementation:Apache Kafka CoordinatorRuntime ScheduleReadOperation

Knowledge Sources	Apache Kafka
Domains	Distributed_Systems, State_Management
Last Updated	2026-02-09 12:00 GMT

Overview

Concrete tool for scheduling coordinator state queries provided by the CoordinatorRuntime framework.

Description

The scheduleReadOperation method creates a CoordinatorReadEvent and enqueues it for processing. The event executes the read operation lambda against the coordinator's committed state and completes the returned future immediately with the result.

Usage

Called by coordinator service implementations for read-only queries like DescribeGroup, ListGroups, etc.

Code Reference

Source Location

Repository: Apache Kafka
File: coordinator-common/src/main/java/org/apache/kafka/coordinator/common/runtime/CoordinatorRuntime.java
Lines: L2207-2217

Signature

public <T> CompletableFuture<T> scheduleReadOperation(
    String name,
    TopicPartition tp,
    CoordinatorReadOperation<S, T> op
)

Import

import org.apache.kafka.coordinator.common.runtime.CoordinatorRuntime;
import org.apache.kafka.common.TopicPartition;
import java.util.concurrent.CompletableFuture;

I/O Contract

Inputs

Name	Type	Required	Description
name	String	Yes	Operation name for logging
tp	TopicPartition	Yes	The coordinator's topic-partition
op	CoordinatorReadOperation<S, T>	Yes	Lambda that reads from committed coordinator state

Outputs

Name	Type	Description
CompletableFuture<T>	future	Completes immediately with query result

Usage Examples

CompletableFuture<GroupDescription> future = coordinatorRuntime.scheduleReadOperation(
    "DescribeGroup",
    new TopicPartition("__consumer_offsets", 0),
    (coordinator) -> coordinator.describeGroup("my-consumer-group")
);

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