Observation of life cycle events

There are life cycle events associated with an application, typically start and stop. Life cycle observers allows various types of artifacts to participate in the application life cycles.

You can make use of the life cycle observer generator to create observers easily.

How is cache maintained

In the CachingService, there is a time-to-live (ttl) setting for each cache items. That means when the cache item is expired, it will be removed from the cache.

The life cycle observer provides a way to look at the in-memory caching as part of the application life cycle and remove the ones that are expired. See the cache.observer.ts as an example.

During the start of the application, the observer calls CachingService.start() which does the sweeping periodically.

async start(): Promise<void> {
  debug('Starting caching service');
  await this.clear();
  const ttl = await this.getTTL();
  debug('TTL: %d', ttl);
  this.timer = setInterval(() => {
    this.sweep().catch(console.warn);
  }, ttl);
}

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