SyncDefer

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A Node.js module for synchronous waiting execution proxy based on LRUCache and Promise to handle asynchronous processing across multiple services.

Why?

Scenario: We have a service A that needs to make a synchronous request to service B. Service B needs to process this request by sending the task to service C. This task also needs to go through the processing of services D and E, and finally, service E will send the processed task result to service B. Once service B receives the processing result, it returns it to service A.

The problem that arises is: After service E submits the result to service B, how can service B return the result to service A?

Before solving the problem, let's break down the steps.

We divide this process into two steps, namely sync and defer. We mark the steps waiting for task processing as defer and the steps of sending task results as sync, as shown in the diagram:

The sync-defer module abstracts and encapsulates these two steps and make them independent.

The core design uses LRUCache to cache task IDs, allowing matching between sending requests and receiving results based on ID. It uses Promise to wait for processing and resolves or rejects the received results, thereby achieving synchronous waiting execution.

Getting Started

Install Dependencies

npm i sync-defer

Dependency Import

// for commonjs
const { SyncDefer } = require('sync-defer')
// for esm
import { SyncDefer } from 'sync-defer'

new SyncDefer(options)

const syncDefer = new SyncDefer({
  ttl: 500, // Cache expiration time in milliseconds, default is 5 minutes
  max: 10 // Maximum cache count, default is 500
})

defer()

Wait for the result returned by the sync method.

const result = await syncDefer.defer('id')

sync()

Synchronize normal results:

syncDefer.sync('id', { result: true })

Synchronize exceptional results:

syncDefer.sync('id', null, new Error())

Deferred

// for commonjs
const { Deferred } = require('sync-defer')
// for esm
import { Deferred } from 'sync-defer'

const deferred = new Deferred()

deferred.resolve({ bool: true })
deferred.reject(new Error())
const res = await deferred.promise

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You can check the test code for a complete usage example.

License

Released under the MIT License.