Analysis of Openflowplugin ContextChain Creation and Lifecycle Management

The article examines the second part of the Openflowplugin source code analysis, focusing on the core logic that creates the ContextChain for a newly connected switch after the handshake phase.

When a switch connects, ContextChainHolderImpl.deviceConnected invokes ContextChainHolderImpl.createContextChain, which builds a unique ContextChain object to manage the switch's lifecycle within Openflowplugin.

1. Create DeviceContext

The method calls deviceManager.createContext(connectionContext) to obtain a DeviceContext. It registers a mastership watcher, configures the packet‑in filter, creates an OutboundQueueHandler, a DeviceContextImpl, and an OpenflowProtocolListenerFullImpl to handle all messages from the switch.

final DeviceContext deviceContext = deviceManager.createContext(connectionContext);
deviceContext.registerMastershipWatcher(this);

2. Create RpcContext

Using the previously created deviceContext, the code calls rpcManager.createContext(deviceContext) to obtain an RpcContext and registers the same mastership watcher.

final RpcContext rpcContext = rpcManager.createContext(deviceContext);
rpcContext.registerMastershipWatcher(this);

3. Create StatisticsContext

The method creates a StatisticsContext via

statisticsManager.createContext(deviceContext, ownershipChangeListener.isReconciliationFrameworkRegistered())

, registers a watcher, and also creates a MultipartWriterProvider to write operational YANG data to the device.

final StatisticsContext statisticsContext = statisticsManager.createContext(deviceContext, ownershipChangeListener.isReconciliationFrameworkRegistered());
statisticsContext.registerMastershipWatcher(this);

4. Create RoleContext

A RoleContext is created with roleManager.createContext(deviceContext), a RoleContextImpl and a SalRoleServiceImpl are instantiated to manage master/slave role assignment.

final RoleContext roleContext = roleManager.createContext(deviceContext);
roleContext.registerMastershipWatcher(this);

5. Assemble ContextChain

After the four individual contexts are ready, a ContextChainImpl is instantiated. Each context is wrapped in a GuardedContextImpl and added via addContext. The chain registers a device‑removed handler, stores the chain in ContextChainHolderImpl.contextChainMap, and finally registers services with contextChain.registerServices(singletonServiceProvider).

@Override
public <T extends OFPContext> void addContext(@Nonnull final T context) {
    contexts.add(new GuardedContextImpl(context));
}

6. Master/Slave Election

The article notes that after the ContextChain is built, the next crucial step is the call to contextChain.registerServices, which triggers the master/slave role election among multiple controllers in a cluster.

Summary

In summary, once a switch completes the Openflow handshake, Openflowplugin creates four specialized contexts (Device, Rpc, Statistics, Role), aggregates them into a ContextChain, and prepares the switch for further operations, including high‑availability master/slave role election.