channeldb/channel_cache: add channelCache w/ randomized eviction

channeldb/channel_cache.go

@@ -0,0 +1,50 @@
+package channeldb
+
+// channelCache is an in-memory cache used to improve the performance of
+// ChanUpdatesInHorizon. It caches the chan info and edge policies for a
+// particular channel.
+type channelCache struct {
+	n        int
+	channels map[uint64]ChannelEdge
+}
+
+// newChannelCache creates a new channelCache with maximum capacity of n
+// channels.
+func newChannelCache(n int) *channelCache {
+	return &channelCache{
+		n:        n,
+		channels: make(map[uint64]ChannelEdge),
+	}
+}
+
+// get returns the channel from the cache, if it exists.
+func (c *channelCache) get(chanid uint64) (ChannelEdge, bool) {
+	channel, ok := c.channels[chanid]
+	return channel, ok
+}
+
+// insert adds the entry to the channel cache. If an entry for chanid already
+// exists, it will be replaced with the new entry. If the entry doesn't exist,
+// it will be inserted to the cache, performing a random eviction if the cache
+// is at capacity.
+func (c *channelCache) insert(chanid uint64, channel ChannelEdge) {
+	// If entry exists, replace it.
+	if _, ok := c.channels[chanid]; ok {
+		c.channels[chanid] = channel
+		return
+	}
+
+	// Otherwise, evict an entry at random and insert.
+	if len(c.channels) == c.n {
+		for id := range c.channels {
+			delete(c.channels, id)
+			break
+		}
+	}
+	c.channels[chanid] = channel
+}
+
+// remove deletes an edge for chanid from the cache, if it exists.
+func (c *channelCache) remove(chanid uint64) {
+	delete(c.channels, chanid)
+}