@yadah/service-critical-section v0.2.0

Yadah Critical Section mixin

A mixin for Yadah Service classes that provides a way to run asynchronous code which will be allowed to complete prior to a process exiting. This helps to ensure that data will be consistent across different services even in the event that a service is being restarted.

Usage

Add the mixin to a service class and provide a callback function to the criticalSection() method. During a process shutdown, the service class shutdown() method won't resolve until the callback resolves.

import CriticalSectionMixin from "@yadah/service-critical-section";
import { Service } from "@yadah/data-manager";

class MyService extends (Service |> CriticalSectionMixin(%)) {
  async performRemoteMutation() {
    await this.criticalSection(async () => {
      const result = await remoteMutation();
      await localMutation(result);
    });
  }
}

In this example, the remoteMutation() function may take some time to complete, and when it does the result will be stored somewhere using the localMutation() method. It's desired to ensure that both functions will complete even if the nodejs process is stopped (eg. via nodemon or ECS task replacement).

The callback function may be a generator function returning an async iterable. The service class shutdown() method won't resolve until the iterator has resolved.

import CriticalSectionMixin from "@yadah/service-critical-section";
import { Service } from "@yadah/data-manager";

class MyService extends (Service |> CriticalSectionMixin(%)) {
  async performRemoteMutation(list) {
    async function* generator() {
      for await (const item of list) {
        yield await remoteMutation(item);
      }
    }
    const iterable = this.criticalSection(generator);
    for await (const result of iterable) {
      await localMutation(result);
    }
  }
}

A Promise may also be passed to criticalSection(). Again, the shutdown() method won't resolve until the promise is resolved.

import CriticalSectionMixin from "@yadah/service-critical-section";
import { Service } from "@yadah/data-manager";

class MyService extends (Service |> CriticalSectionMixin(%)) {
  async performRemoteMutation() {
    const promise = remoteMutation().then((result) => localMutation(result));
    await this.criticalSection(promise);
  }
}