Function ExampleNewAutoRefreshCache

flytestdlib/utils/auto_refresh_example_test.go:43–96

()

}

func ExampleNewAutoRefreshCache() {
	// This auto-refresh cache can be used for cases where keys are created by caller but processed by
	// an external service and we want to asynchronously keep track of its progress.
	exampleService := newExampleService()

	// define a sync method that the cache can use to auto-refresh in background
	syncItemCb := func(ctx context.Context, obj CacheItem) (CacheItem, CacheSyncAction, error) {
		oldItem := obj.(*ExampleCacheItem)
		newItem := exampleService.getStatus(oldItem.ID())
		if newItem.status != oldItem.status {
			return newItem, Update, nil
		}
		return newItem, Unchanged, nil
	}

	// define resync period as time duration we want cache to refresh. We can go as low as we want but cache
	// would still be constrained by time it takes to run Sync call for each item.
	resyncPeriod := time.Millisecond

	// Since number of items in the cache is dynamic, rate limiter is our knob to control resources we spend on
	// sync.
	rateLimiter := NewRateLimiter("ExampleRateLimiter", 10000, 1)

	// since cache refreshes itself asynchronously, it may not notice that an object has been deleted immediately,
	// so users of the cache should have the delete logic aware of this shortcoming (eg. not-exists may be a valid
	// error during removal if based on status in cache).
	cache, err := NewAutoRefreshCache(syncItemCb, rateLimiter, resyncPeriod, 100, nil)
	if err != nil {
		panic(err)
	}

	// start the cache with a context that would be to stop the cache by cancelling the context
	ctx, cancel := context.WithCancel(context.Background())
	cache.Start(ctx)

	// creating objects that go through a couple of state transitions to reach the final state.
	item1 := &ExampleCacheItem{status: ExampleStatusNotStarted, id: "item1"}
	item2 := &ExampleCacheItem{status: ExampleStatusNotStarted, id: "item2"}
	_, err1 := cache.GetOrCreate(item1)
	_, err2 := cache.GetOrCreate(item2)
	if err1 != nil || err2 != nil {
		fmt.Printf("unexpected error in create; err1: %v, err2: %v", err1, err2)
	}

	// wait for the cache to go through a few refresh cycles and then check status
	time.Sleep(resyncPeriod * 10)
	fmt.Printf("Current status for item1 is %v", cache.Get(item1.ID()).(*ExampleCacheItem).status)

	// stop the cache
	cancel()

	// Output:
	// Current status for item1 is Completed
}