server: Add global LRU for routes with keys being the appname + path (#472)

* Add global lru for routes with keys being the appname + path

* minor comment fixes

* remove duplicate entires from THIRD_PARTY

* Make sure that we lock and unlock on get, refresh and delete on the cache

api/server/internal/routecache/lru.go

@@ -0,0 +1,88 @@
+// Package routecache is meant to assist in resolving the most used routes at
+// an application. Implemented as a LRU, it returns always its full context for
+// iteration at the router handler.
+package routecache
+
+// based on groupcache's LRU
+
+import (
+	"container/list"
+
+	"github.com/iron-io/functions/api/models"
+)
+
+// Cache holds an internal linkedlist for hotness management. It is not safe
+// for concurrent use, must be guarded externally.
+type Cache struct {
+	MaxEntries int
+
+	ll    *list.List
+	cache map[string]*list.Element
+}
+
+// New returns a route cache.
+func New(maxentries int) *Cache {
+	return &Cache{
+		MaxEntries: maxentries,
+		ll:         list.New(),
+		cache:      make(map[string]*list.Element),
+	}
+}
+
+// Refresh updates internal linkedlist either adding a new route to the front,
+// or moving it to the front when used. It will discard seldom used routes.
+func (c *Cache) Refresh(route *models.Route) {
+	if c.cache == nil {
+		return
+	}
+
+	if ee, ok := c.cache[route.AppName+route.Path]; ok {
+		c.ll.MoveToFront(ee)
+		ee.Value = route
+		return
+	}
+
+	ele := c.ll.PushFront(route)
+	c.cache[route.AppName+route.Path] = ele
+	if c.MaxEntries != 0 && c.ll.Len() > c.MaxEntries {
+		c.removeOldest()
+	}
+}
+
+// Get looks up a path's route from the cache.
+func (c *Cache) Get(appname, path string) (route *models.Route, ok bool) {
+	if c.cache == nil {
+		return
+	}
+	if ele, hit := c.cache[appname+path]; hit {
+		c.ll.MoveToFront(ele)
+		return ele.Value.(*models.Route), true
+	}
+	return
+}
+
+// Delete removes the element for the given appname and path from the cache.
+func (c *Cache) Delete(appname, path string) {
+	if ele, hit := c.cache[appname+path]; hit {
+		c.removeElement(ele)
+	}
+}
+
+func (c *Cache) removeOldest() {
+	if c.cache == nil {
+		return
+	}
+	if ele := c.ll.Back(); ele != nil {
+		c.removeElement(ele)
+	}
+}
+
+func (c *Cache) removeElement(e *list.Element) {
+	c.ll.Remove(e)
+	kv := e.Value.(*models.Route)
+	delete(c.cache, kv.AppName+kv.Path)
+}
+
+func (c *Cache) Len() int {
+	return len(c.cache)
+}