From a565a937409120993cdc450884ff1ac8915086d5 Mon Sep 17 00:00:00 2001
From: shuchaome <shuchaome@gmail.com>
Date: Mon, 28 Mar 2022 12:23:51 +0800
Subject: [PATCH] reduce mutex scope when setenv LIBHDFS3_CONF

---
 src/Storages/HDFS/HDFSCommon.cpp         | 23 ++++++++++++++---------
 src/Storages/HDFS/ReadBufferFromHDFS.cpp |  8 --------
 2 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/src/Storages/HDFS/HDFSCommon.cpp b/src/Storages/HDFS/HDFSCommon.cpp
index b186808a2db..da08f429457 100644
--- a/src/Storages/HDFS/HDFSCommon.cpp
+++ b/src/Storages/HDFS/HDFSCommon.cpp
@@ -25,6 +25,8 @@ namespace ErrorCodes
 const String HDFSBuilderWrapper::CONFIG_PREFIX = "hdfs";
 const String HDFS_URL_REGEXP = "^hdfs://[^/]*/.*";
 
+std::once_flag init_libhdfs3_conf_flag;
+
 void HDFSBuilderWrapper::loadFromConfig(const Poco::Util::AbstractConfiguration & config,
     const String & prefix, bool isUser)
 {
@@ -123,19 +125,22 @@ HDFSBuilderWrapper createHDFSBuilder(const String & uri_str, const Poco::Util::A
         throw Exception("Illegal HDFS URI: " + uri.toString(), ErrorCodes::BAD_ARGUMENTS);
 
     // Shall set env LIBHDFS3_CONF *before* HDFSBuilderWrapper construction.
-    String libhdfs3_conf = config.getString(HDFSBuilderWrapper::CONFIG_PREFIX + ".libhdfs3_conf", "");
-    if (!libhdfs3_conf.empty())
+    std::call_once(init_libhdfs3_conf_flag, [&config]()
     {
-        if (std::filesystem::path{libhdfs3_conf}.is_relative() && !std::filesystem::exists(libhdfs3_conf))
+        String libhdfs3_conf = config.getString(HDFSBuilderWrapper::CONFIG_PREFIX + ".libhdfs3_conf", "");
+        if (!libhdfs3_conf.empty())
         {
-            const String config_path = config.getString("config-file", "config.xml");
-            const auto config_dir = std::filesystem::path{config_path}.remove_filename();
-            if (std::filesystem::exists(config_dir / libhdfs3_conf))
-                libhdfs3_conf = std::filesystem::absolute(config_dir / libhdfs3_conf);
+            if (std::filesystem::path{libhdfs3_conf}.is_relative() && !std::filesystem::exists(libhdfs3_conf))
+            {
+                const String config_path = config.getString("config-file", "config.xml");
+                const auto config_dir = std::filesystem::path{config_path}.remove_filename();
+                if (std::filesystem::exists(config_dir / libhdfs3_conf))
+                    libhdfs3_conf = std::filesystem::absolute(config_dir / libhdfs3_conf);
+            }
+            setenv("LIBHDFS3_CONF", libhdfs3_conf.c_str(), 1);
         }
+    });
 
-        setenv("LIBHDFS3_CONF", libhdfs3_conf.c_str(), 1);
-    }
     HDFSBuilderWrapper builder;
     if (builder.get() == nullptr)
         throw Exception("Unable to create builder to connect to HDFS: " +
diff --git a/src/Storages/HDFS/ReadBufferFromHDFS.cpp b/src/Storages/HDFS/ReadBufferFromHDFS.cpp
index 902307fc828..1bafa49e55b 100644
--- a/src/Storages/HDFS/ReadBufferFromHDFS.cpp
+++ b/src/Storages/HDFS/ReadBufferFromHDFS.cpp
@@ -22,8 +22,6 @@ ReadBufferFromHDFS::~ReadBufferFromHDFS() = default;
 
 struct ReadBufferFromHDFS::ReadBufferFromHDFSImpl : public BufferWithOwnMemory<SeekableReadBuffer>
 {
-    /// HDFS create/open functions are not thread safe
-    static std::mutex hdfs_init_mutex;
 
     String hdfs_uri;
     String hdfs_file_path;
@@ -46,8 +44,6 @@ struct ReadBufferFromHDFS::ReadBufferFromHDFSImpl : public BufferWithOwnMemory<S
         , builder(createHDFSBuilder(hdfs_uri_, config_))
         , read_until_position(read_until_position_)
     {
-        std::lock_guard lock(hdfs_init_mutex);
-
         fs = createHDFSFS(builder.get());
         fin = hdfsOpenFile(fs.get(), hdfs_file_path.c_str(), O_RDONLY, 0, 0, 0);
 
@@ -59,7 +55,6 @@ struct ReadBufferFromHDFS::ReadBufferFromHDFSImpl : public BufferWithOwnMemory<S
 
     ~ReadBufferFromHDFSImpl() override
     {
-        std::lock_guard lock(hdfs_init_mutex);
         hdfsCloseFile(fs.get(), fin);
     }
 
@@ -124,9 +119,6 @@ struct ReadBufferFromHDFS::ReadBufferFromHDFSImpl : public BufferWithOwnMemory<S
     }
 };
 
-
-std::mutex ReadBufferFromHDFS::ReadBufferFromHDFSImpl::hdfs_init_mutex;
-
 ReadBufferFromHDFS::ReadBufferFromHDFS(
         const String & hdfs_uri_,
         const String & hdfs_file_path_,