Implementation:Apache Shardingsphere ShowProcessListHandler Handle

Knowledge Sources	Apache_Shardingsphere
Domains	Cluster, Process_Management
Last Updated	2026-02-10 00:00 GMT

Overview

ShowProcessListHandler handles distributed show process list events by collecting local process information for matching cluster instances.

Description

ShowProcessListHandler implements GlobalDataChangedEventHandler and subscribes to ShowProcessListTriggerNodePath for ADDED and DELETED event types. On an ADDED event, it extracts the instance ID and process ID (task ID) from the event path. If the local instance matches, it delegates to ClusterProcessPersistCoordinator.reportLocalProcesses to persist local process information into the shared repository under the task ID. On a DELETED event, it notifies ProcessOperationLockRegistry to release any waiting locks, signaling the requesting node that process collection is complete.

Usage

This handler is auto-loaded via SPI in cluster mode. When a SHOW PROCESSLIST command is executed, trigger paths are persisted for all online instances. Each instance's handler responds by reporting its local processes, enabling the requesting node to aggregate results from all cluster members.

Code Reference

Source Location

• Repository: Apache_Shardingsphere
• File: ShowProcessListHandler.java
• Lines: 1-67

Signature

public final class ShowProcessListHandler implements GlobalDataChangedEventHandler {

    public NodePath getSubscribedNodePath()

    public Collection<Type> getSubscribedTypes()

    public void handle(final ContextManager contextManager, final DataChangedEvent event)
}

Import

import org.apache.shardingsphere.mode.manager.cluster.dispatch.handler.global.node.process.ShowProcessListHandler;

I/O Contract

Inputs

Name	Type	Required	Description
contextManager	ContextManager	Yes	Provides access to instance context and persist services
event	DataChangedEvent	Yes	Contains the event key (path), value, and type (ADDED/DELETED)

Outputs

Name	Type	Description
void	void	Side effects: reports local processes to the shared repository or notifies lock registry

Usage Examples

// Trigger show process list by persisting trigger paths for all online instances:
String triggerPath = NodePathGenerator.toPath(
    new ShowProcessListTriggerNodePath(new InstanceProcessNodeValue(instanceId, taskId)));
repository.persist(triggerPath, "");
// Each instance's ShowProcessListHandler reports its local processes under the taskId path.

Related Pages

• Principle:Apache_Shardingsphere_Cluster_Metadata_Synchronization