mapserver/mapblockaccessor/get.go

package mapblockaccessor

import (
	"mapserver/coords"
	"mapserver/eventbus"
	"mapserver/types"
	"sync"

	"github.com/minetest-go/mapparser"
	cache "github.com/patrickmn/go-cache"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/sirupsen/logrus"
)

var lock = &sync.RWMutex{}

func (a *MapBlockAccessor) GetMapBlock(pos *coords.MapBlockCoords) (*mapparser.MapBlock, error) {
	cache_enabled := a.maxcount > 0
	key := getKey(pos)

	if cache_enabled {

		//maintenance
		cacheBlocks.Set(float64(a.blockcache.ItemCount()))
		if a.blockcache.ItemCount() > a.maxcount {
			//flush cache
			fields := logrus.Fields{
				"cached items": a.blockcache.ItemCount(),
				"maxcount":     a.maxcount,
			}
			logrus.WithFields(fields).Debug("Flushing cache")

			a.blockcache.Flush()
		}

		//read section
		lock.RLock()

		cachedblock, found := a.blockcache.Get(key)
		if found {
			defer lock.RUnlock()

			getCacheHitCount.Inc()
			if cachedblock == nil {
				return nil, nil
			} else {
				return cachedblock.(*mapparser.MapBlock), nil
			}
		}

		//end read
		lock.RUnlock()

		timer := prometheus.NewTimer(dbGetDuration)
		defer timer.ObserveDuration()

		//write section
		lock.Lock()
		defer lock.Unlock()

		//try read
		cachedblock, found = a.blockcache.Get(key)
		if found {
			getCacheHitCount.Inc()
			if cachedblock == nil {
				return nil, nil
			} else {
				return cachedblock.(*mapparser.MapBlock), nil
			}
		}

	}

	block, err := a.accessor.GetBlock(pos)
	if err != nil {
		return nil, err
	}

	if block == nil {
		//no mapblock here
		if cache_enabled {
			cacheBlockCount.Inc()
			a.blockcache.Set(key, nil, cache.DefaultExpiration)
		}
		return nil, nil
	}

	if cache_enabled {
		getCacheMissCount.Inc()
	}

	mapblock, err := mapparser.Parse(block.Data)
	if err != nil {
		return nil, err
	}

	a.Eventbus.Emit(eventbus.MAPBLOCK_RENDERED, types.NewParsedMapblock(mapblock, pos))

	if cache_enabled {
		cacheBlockCount.Inc()
		a.blockcache.Set(key, mapblock, cache.DefaultExpiration)
	}

	return mapblock, nil
}