zkutil: add Increment [#METR-15299]

███████████: write clicks to cloud [#METR-15299]

libs/libzkutil/include/zkutil/Increment.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include <zkutil/ZooKeeper.h>
+
+namespace zkutil 
+{
+	
+class Increment
+{
+public:
+	Increment(ZooKeeperPtr zk_, const std::string & path_) 
+	: zk(zk_), path(path_)
+	{
+	}
+	
+	size_t get()
+	{
+		LOG_TRACE(log, "Get increment");
+		
+		size_t result = 0;
+		std::string result_str;
+		zkutil::Stat stat;
+		
+		bool success = false;
+		do
+		{
+			if (zk->tryGet(path, result_str, &stat))
+			{
+				result = std::stol(result_str) + 1;
+				success = zk->trySet(path, std::to_string(result), stat.version) == ZOK;
+			}
+			else
+			{
+				success = zk->tryCreate(path, std::to_string(result), zkutil::CreateMode::Persistent) == ZOK;
+			}
+		} 
+		while(!success);
+		
+		return result;
+	}
+private:
+	zkutil::ZooKeeperPtr zk;
+	std::string path;
+	Logger * log = &Logger::get("zkutil::Increment");
+};
+
+}