Architecture of Web Worker

Certain modules, such as the formula engine, are naturally resource-intensive. To prevent them from blocking the main thread and degrading the interactive user experience, Univer supports running these modules within Web Workers.

A Univer codebase running within a Web Worker is essentially a separate Univer instance, and instances communicate with each other via the RPC mechanism provided by the @univerjs/rpc package. This plugin also offers a mechanism for synchronizing data and mutations between the two Univer instances.

Example

Utilizing Web Workers in Univer is quite simple.

In the main thread's Univer instance, import the @univerjs/rpc plugin, specify the path of the Web Worker entry file, and configure the formula plugin in the main thread to not compute formulas.

import type { IUniverRPCMainThreadConfig } from '@univerjs/rpc';
import { UniverRPCMainThread } from '@univerjs/rpc';
import { UniverSheetsFormula } from '@univerjs/sheets-formula';
 
// ...
 
univer.registerPlugin(UniverSheetsFormula, {
  notExecuteFormula: true,
})
 
univer.registerPlugin(UniverRPCMainThread, {
  workerURL: './worker.js',
  unsyncMutations: new Set([RichTextEditingMutation.id])
});

In the Web Worker's entry file, instantiate another Univer instance and register the required plugins.

import { UniverFormulaEngine } from '@univerjs/engine-formula';
import { UniverSheets } from '@univerjs/sheets';
import { LocaleType, Univer } from '@univerjs/core';
import { UniverRPCWorkerThreadPlugin } from '@univerjs/rpc';
import { UniverSheetsFormula } from '@univerjs/sheets-formula';
 
const univer = new Univer();
 
univer.registerPlugin(UniverRPCWorkerThreadPlugin);
univer.registerPlugin(UniverSheets);
univer.registerPlugin(UniverFormulaEngine);
univer.registerPlugin(UniverSheetsFormula);

After running the code, you will notice a Web Worker thread, and formula computations will occur within it.

For more information, please refer to examples/sheets (opens in a new tab).

Overall Architecture

The architecture of Univer's Web Worker is as follows:

Documents created and edits made in the main thread will be synchronized to the Web Worker through the following steps:

1. When a document is created in the main thread, the DataSyncPrimaryController in the main thread detects the event and calls the createInstance method of the IRemoteInstanceService in the Web Worker to create the same document instance.
2. When mutation occurs in the main thread, the DataSyncPrimaryController in the main thread detects the event and calls the syncMutation method of the IRemoteInstanceService in the Web Worker to apply the mutation to the Univer instance in the Web Worker.

The calculation results of the Web Worker's formula are written back to the main thread as follows:

1. When the Univer instance in the Web Worker completes formula calculation, it generates a mutation and references it. The DataSyncReplicaController in the Web Worker detects the event and calls the syncMutation method of the IRemoteSyncService in the main thread to apply the mutation to the Univer instance in the main thread.

RPC Mechanism

As shown in the previous explanation, modules of Univer in different threads appear to be able to directly call each other's methods, which is provided by the RPC mechanism of the @univerjs/rpc plugin.

As an example, let's consider the main thread calling the IRemoteInstanceService in the Web Worker thread. In the main thread, acting as a client, an IRemoteInstanceService interface needs to be declared as a dependency, and the specific implementation is provided by the toModule method of the RPC module. This method accepts a Channel as a parameter and returns an object that implements the IRemoteInstanceService interface. This object is actually a Proxy, and calls to its methods are intercepted by the Proxy. The channel name, method name, and arguments are serialized by the RPC module and sent to the Web Worker thread.

export class UniverRPCMainThread extends Plugin {
  override async onStarting(injector: Injector): Promise<void> {
    const worker = new Worker(this._config.workerURL);
    const messageProtocol = createWebWorkerMessagePortOnMain(worker);
    const client = new ChannelClient(messageProtocol);
    const server = new ChannelServer(messageProtocol);
 
    const dependencies: Dependency[] = [
        IRemoteInstanceService,
        { useFactory: () => toModule<IRemoteInstanceService>(client.getChannel(RemoteInstanceServiceName)) },
      ],
    ];
    dependencies.forEach((dependency) => injector.add(dependency));
  }
}

In the Web Worker thread, the IRemoteInstanceService interface must be implemented and registered to ChannelServer, so the RPC module in the Web Worker thread can forward RPC calls from the main thread to the implementation of IRemoteInstanceService in the Web Worker thread.

/**
 * This plugin is used to register the RPC services on the worker thread.
 */
export class UniverRPCWorkerThreadPlugin extends Plugin {
  override onStarting(injector: Injector): void {
    const messageProtocol = createWebWorkerMessagePortOnWorker();
    const server = new ChannelServer(messageProtocol);
 
    const dependencies: Dependency[] = [
      [IRemoteInstanceService, { useClass: RemoteInstanceReplicaService }],
    ];
    dependencies.forEach((dependency) => injector.add(dependency));
    server.registerChannel(RemoteInstanceServiceName, fromModule(injector.get(IRemoteInstanceService)));
  }
}

Indeed, the RPC mechanism provided by the @univerjs/rpc plugin can be used for communication between any two Univer instances, not limited to the main thread and Web Worker. Therefore, implementing server-side calculations or using multi-process with Electron is also straightforward. All that is needed is to implement the corresponding communication mechanism (messageProtocol) in the corresponding environment.