CurrentMetrics/Increment: Introduce add()

src/Common/CurrentMetrics.h

@@ -100,6 +100,12 @@ namespace CurrentMetrics
             amount -= value;
         }
 
+        void add(Value value = 1)
+        {
+            what->fetch_add(value, std::memory_order_relaxed);
+            amount += value;
+        }
+
         /// Subtract value before destructor.
         void destroy()
         {

src/Storages/Distributed/DirectoryMonitor.cpp

@@ -758,8 +758,7 @@ bool StorageDistributedDirectoryMonitor::addAndSchedule(size_t file_size, size_t
 
     {
         std::lock_guard metrics_lock(metrics_mutex);
-        /// TODO: extend CurrentMetrics::Increment
-        metric_pending_files.sub(-1);
+        metric_pending_files.add();
         bytes_count += file_size;
         ++files_count;
     }