diff --git a/lib/private/Memcache/CADTrait.php b/lib/private/Memcache/CADTrait.php
index d0f6611c4f3..d5c0d8174d0 100644
--- a/lib/private/Memcache/CADTrait.php
+++ b/lib/private/Memcache/CADTrait.php
@@ -7,6 +7,9 @@
  */
 namespace OC\Memcache;
 
+/**
+ * CAD/NCAD implementations for cache backends that lack their own.
+ */
 trait CADTrait {
 	abstract public function get($key);
 
@@ -15,42 +18,77 @@ trait CADTrait {
 	abstract public function add($key, $value, $ttl = 0);
 
 	/**
-	 * Compare and delete
+	 * Compare-and-delete.
+  	 *
+	 * If $key's current value is equal to $expectedValue, delete $key.
+  	 * Note may return false for reasons other than not meeting condition.
+	 *
+	 * Implements CAD using simple locking (only requiring backend add/remove support).
 	 *
 	 * @param string $key
-	 * @param mixed $old
-	 * @return bool
+	 * @param mixed $expectedValue
+	 * @return bool True if key was deleted; False if no deletion occurred
 	 */
-	public function cad($key, $old) {
-		//no native cas, emulate with locking
-		if ($this->add($key . '_lock', true)) {
-			if ($this->get($key) === $old) {
-				$this->remove($key);
-				$this->remove($key . '_lock');
-				return true;
-			} else {
-				$this->remove($key . '_lock');
-				return false;
-			}
+	public function cad($key, $expectedValue) {
+		if (!$this->acquireLock($key)) {
+			return false;
+		}
+		$currentValue = $this->get($key);
+		// Check condition		
+		if ($currentValue === $expectedValue) {
+			// Matches condition
+			$this->remove($key);
+			$this->releaseLock($key);
+			return true;
 		} else {
+			// Fails condition
+			$this->releaseLock($key);
+			// TODO: consider throwing if release fails
 			return false;
 		}
 	}
 
-	public function ncad(string $key, mixed $old): bool {
-		//no native cad, emulate with locking
-		if ($this->add($key . '_lock', true)) {
-			$value = $this->get($key);
-			if ($value !== null && $value !== $old) {
-				$this->remove($key);
-				$this->remove($key . '_lock');
-				return true;
-			} else {
-				$this->remove($key . '_lock');
-				return false;
-			}
+	/**
+ 	 * Nonequal-compare-and-delete.
+   	 *
+	 * If $key's current value is not equal to $expectedValue, delete $key.
+	 * Note may return false for reasons other than not meeting condition.
+	 *
+	 * Implements NCAD using simple locking (only requiring backend add/remove support).
+  	 *
+	 * @param string $key
+	 * @param mixed $expectedValue
+	 * @return bool True if key was deleted; False if no deletion occurred
+	 */
+	public function ncad(string $key, mixed $expectedValue): bool {
+		if (!$this->acquireLock($key)) {
+			return false;
+		}
+		$currentValue = $this->get($key);
+		// Check condition
+		if ($currentValue !== null && $currentValue !== $expectedValue) {
+			// Matches condition
+			$this->remove($key);
+			$this->releaseLock($key);
+			return true;
 		} else {
+			// Fails condition
+			$this->releaseLock($key);
+			// TODO: consider throwing if release fails
 			return false;
 		}
 	}
+
+	//
+	// Utilities
+	//
+
+	private function acquireLock(string $key): bool {
+		// TODO: an actual TTL would be clearer
+		return $this->add($key . '_lock', true);
+	}
+	
+	private function releaseLock(string $key): bool {
+		return $this->remove($key . '_lock');
+	}
 }