preliminary work on DeletePrefix

bucket.go

@@ -1,6 +1,7 @@
 package ccache
 
 import (
+	"strings"
 	"sync"
 	"time"
 )
@@ -40,6 +41,45 @@ func (b *bucket) delete(key string) *Item {
 	return item
 }
 
+// This is an expensive operation, so we do what we can to optimize it and limit
+// the impact it has on concurrent operations. Specifically, we:
+// 1 - Do an initial iteration to collect matches. This allows us to do the
+//     "expensive" prefix check (on all values) using only a read-lock
+// 2 - Do a second iteration, under write lock, for the matched results to do
+//     the actual deletion
+
+// Also, this is the only place where the Bucket is aware of cache detail: the
+// deletables channel. Passing it here lets us avoid iterating over matched items
+// again in the cache. Further, we pass item to deletables BEFORE actually removing
+// the item from the map. I'm pretty sure this is 100% fine, but it is unique.
+// (We do this so that the write to the channel is under the read lock and not the
+// write lock)
+func (b *bucket) deletePrefix(prefix string, deletables chan *Item) int {
+	lookup := b.lookup
+	items := make([]*Item, 0, len(lookup)/10)
+
+	b.RLock()
+	for key, item := range lookup {
+		if strings.HasPrefix(key, prefix) {
+			deletables <- item
+			items = append(items, item)
+		}
+	}
+	b.RUnlock()
+
+	if len(items) == 0 {
+		// avoid the write lock if we can
+		return 0
+	}
+
+	b.Lock()
+	defer b.Unlock()
+	for _, item := range items {
+		delete(lookup, item.key)
+	}
+	return len(items)
+}
+
 func (b *bucket) clear() {
 	b.Lock()
 	defer b.Unlock()

cache.go

@@ -45,6 +45,14 @@ func (c *Cache) ItemCount() int {
 	return count
 }
 
+func (c *Cache) DeletePrefix(prefix string) int {
+	count := 0
+	for _, b := range c.buckets {
+		count += b.deletePrefix(prefix, c.deletables)
+	}
+	return count
+}
+
 // Get an item from the cache. Returns nil if the item wasn't found.
 // This can return an expired item. Use item.Expired() to see if the item
 // is expired and item.TTL() to see how long until the item expires (which

cache_test.go

@@ -28,6 +28,29 @@ func (_ CacheTests) DeletesAValue() {
 	Expect(cache.ItemCount()).To.Equal(1)
 }
 
+func (_ CacheTests) DeletesAPrefix() {
+	cache := New(Configure())
+	Expect(cache.ItemCount()).To.Equal(0)
+
+	cache.Set("aaa", "1", time.Minute)
+	cache.Set("aab", "2", time.Minute)
+	cache.Set("aac", "3", time.Minute)
+	cache.Set("ac", "4", time.Minute)
+	cache.Set("z5", "7", time.Minute)
+	Expect(cache.ItemCount()).To.Equal(5)
+
+	Expect(cache.DeletePrefix("9a")).To.Equal(0)
+	Expect(cache.ItemCount()).To.Equal(5)
+
+	Expect(cache.DeletePrefix("aa")).To.Equal(3)
+	Expect(cache.Get("aaa")).To.Equal(nil)
+	Expect(cache.Get("aab")).To.Equal(nil)
+	Expect(cache.Get("aac")).To.Equal(nil)
+	Expect(cache.Get("ac").Value()).To.Equal("4")
+	Expect(cache.Get("z5").Value()).To.Equal("7")
+	Expect(cache.ItemCount()).To.Equal(2)
+}
+
 func (_ CacheTests) OnDeleteCallbackCalled() {
 	onDeleteFnCalled := false
 	onDeleteFn := func(item *Item) {