From dfba5f289e31d2052d587f3ab8f63e5a94321c0d Mon Sep 17 00:00:00 2001
From: Stefan Geisbacher <stefan.geisbacher@gmail.com>
Date: Sun, 9 Dec 2018 16:47:30 +0100
Subject: [PATCH] added atomic list-append operation

---
 cache.go      | 21 +++++++++++++++++++++
 cache_test.go | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)

diff --git a/cache.go b/cache.go
index db88d2f..7a5ca77 100644
--- a/cache.go
+++ b/cache.go
@@ -81,6 +81,27 @@ func (c *cache) set(k string, x interface{}, d time.Duration) {
 	}
 }
 
+func (c *cache) Append(k string, x string) error {
+	c.mu.Lock()
+	v, found := c.items[k]
+	if !found || v.Expired() {
+		c.mu.Unlock()
+		return fmt.Errorf("Item %q not found", k)
+	}
+	rv, ok := v.Object.([]string)
+	if !ok {
+		c.mu.Unlock()
+		return fmt.Errorf("The value for %s is not an []string", k)
+	}
+	nv := append(rv, x)
+	v.Object = nv
+	c.items[k] = v
+	// TODO: Calls to mu.Unlock are currently not deferred because defer
+	// adds ~200 ns (as of go1.)
+	c.mu.Unlock()
+	return nil
+}
+
 // Add an item to the cache, replacing any existing item, using the default
 // expiration.
 func (c *cache) SetDefault(k string, x interface{}) {
diff --git a/cache_test.go b/cache_test.go
index cb80b38..0e2e868 100644
--- a/cache_test.go
+++ b/cache_test.go
@@ -68,6 +68,53 @@ func TestCache(t *testing.T) {
 	}
 }
 
+func TestAppend(t *testing.T) {
+	tc := New(NoExpiration, 0)
+	tc.Set("label1", []string{}, NoExpiration)
+	tc.Set("label2", []string{}, NoExpiration)
+	tc.Set("label3", []string{}, NoExpiration)
+
+	tc.Append("label1", "article1")
+	tc.Append("label1", "article2")
+	tc.Append("label2", "article1")
+	tc.Append("label2", "article3")
+	tc.Append("label2", "article4")
+	tc.Append("label3", "article2")
+
+	label1Articles, found := tc.Get("label1")
+	if !found {
+		t.Error("could not find key 'label1' after appending")
+	}
+	label2Articles, found := tc.Get("label2")
+	if !found {
+		t.Error("could not find key 'label2' after appending")
+	}
+	label3Articles, found := tc.Get("label3")
+	if !found {
+		t.Error("could not find key 'label3' after appending")
+	}
+
+	if l := len(label1Articles.([]string)); l != 2 {
+		t.Errorf("'label1' should have 2 articles but has: %d", l)
+	}
+	if l := len(label2Articles.([]string)); l != 3 {
+		t.Errorf("'label2' should have 3 articles but has: %d", l)
+	}
+	if l := len(label3Articles.([]string)); l != 1 {
+		t.Errorf("'label3' should have 1 articles but has: %d", l)
+	}
+
+	if v := label2Articles.([]string)[0]; v != "article1" {
+		t.Errorf("first article of label2 should be article1, but is: %s", v)
+	}
+	if v := label2Articles.([]string)[1]; v != "article3" {
+		t.Errorf("second article of label2 should be article3, but is: %s", v)
+	}
+	if v := label2Articles.([]string)[2]; v != "article4" {
+		t.Errorf("third article of label2 should be article4, but is: %s", v)
+	}
+}
+
 func TestCacheTimes(t *testing.T) {
 	var found bool