use global write thread pool.

cpp/src/common/global.cc

diff --git a/cpp/src/common/global.cc b/cpp/src/common/global.cc
index 859bb25..ea4bf12 100644
--- a/cpp/src/common/global.cc
+++ b/cpp/src/common/global.cc
@@ -26,11 +26,17 @@
 
 #include <thread>
 
+#ifdef ENABLE_THREADS
+#include "common/thread_pool.h"
+#endif
 #include "utils/injection.h"
 
 namespace common {
 
 ColumnSchema g_time_column_schema;
+#ifdef ENABLE_THREADS
+ThreadPool* g_write_thread_pool_ = nullptr;
+#endif
 ConfigValue g_config_value_;
 
 void init_config_value() {
@@ -137,6 +143,15 @@
     g_time_column_schema.encoding_ = PLAIN;
     g_time_column_schema.compression_ = UNCOMPRESSED;
     g_time_column_schema.column_name_ = storage::TIME_COLUMN_NAME;
+#ifdef ENABLE_THREADS
+    // (Re)create the global write thread pool with the configured size.
+    delete g_write_thread_pool_;
+    size_t pool_size =
+        g_config_value_.write_thread_count_ > 0
+            ? static_cast<size_t>(g_config_value_.write_thread_count_)
+            : size_t{1};
+    g_write_thread_pool_ = new ThreadPool(pool_size);
+#endif
     return ret;
 }
 

cpp/src/common/global.h

diff --git a/cpp/src/common/global.h b/cpp/src/common/global.h
index 3a4525b..ba5f4bd 100644
--- a/cpp/src/common/global.h
+++ b/cpp/src/common/global.h
@@ -173,14 +173,20 @@
 }
 
 // Set the number of threads for parallel writes.  Must be called before
-// constructing TsFileWriter instances — existing writers' thread pools
-// are not resized at runtime.
+// init_common() / libtsfile_init() — the global thread pool is created
+// during initialization and is not resized at runtime.
 FORCE_INLINE int set_write_thread_count(int32_t count) {
     if (count < 1 || count > 64) return E_INVALID_ARG;
     g_config_value_.write_thread_count_ = count;
     return E_OK;
 }
 
+#ifdef ENABLE_THREADS
+class ThreadPool;
+// Global write thread pool, created by init_common().
+extern ThreadPool* g_write_thread_pool_;
+#endif
+
 extern int init_common();
 extern bool is_timestamp_column_name(const char* time_col_name);
 extern void cols_to_json(ByteStream* byte_stream,

cpp/src/writer/tsfile_writer.cc

diff --git a/cpp/src/writer/tsfile_writer.cc b/cpp/src/writer/tsfile_writer.cc
index cee742f..35520c8 100644
--- a/cpp/src/writer/tsfile_writer.cc
+++ b/cpp/src/writer/tsfile_writer.cc
@@ -23,6 +23,9 @@
 
 #include "chunk_writer.h"
 #include "common/config/config.h"
+#ifdef ENABLE_THREADS
+#include "common/thread_pool.h"
+#endif
 #include "file/restorable_tsfile_io_writer.h"
 #include "file/tsfile_io_writer.h"
 #include "file/write_file.h"
@@ -50,6 +53,10 @@
 }
 
 void libtsfile_destroy() {
+#ifdef ENABLE_THREADS
+    delete common::g_write_thread_pool_;
+    common::g_write_thread_pool_ = nullptr;
+#endif
     ModStat::get_instance().destroy();
     libtsfile::g_s_is_inited = false;
 }
@@ -1262,7 +1269,7 @@
 #ifdef ENABLE_THREADS
         if (g_config_value_.parallel_write_enabled_) {
             std::vector<std::future<int>> futures;
-            futures.push_back(thread_pool_.submit(
+            futures.push_back(g_write_thread_pool_->submit(
                 [&write_time_in_segments, time_chunk_writer]() {
                     return write_time_in_segments(time_chunk_writer);
                 }));
@@ -1270,7 +1277,7 @@
                 ValueChunkWriter* vcw = value_chunk_writers[k];
                 if (IS_NULL(vcw)) continue;
                 uint32_t col_idx = field_columns[k];
-                futures.push_back(thread_pool_.submit(
+                futures.push_back(g_write_thread_pool_->submit(
                     [&write_value_in_segments, vcw, col_idx]() {
                         return write_value_in_segments(vcw, col_idx);
                     }));

cpp/src/writer/tsfile_writer.h

diff --git a/cpp/src/writer/tsfile_writer.h b/cpp/src/writer/tsfile_writer.h
index bf40987..cb1b952 100644
--- a/cpp/src/writer/tsfile_writer.h
+++ b/cpp/src/writer/tsfile_writer.h
@@ -33,9 +33,6 @@
 #include "common/record.h"
 #include "common/schema.h"
 #include "common/tablet.h"
-#ifdef ENABLE_THREADS
-#include "common/thread_pool.h"
-#endif
 
 namespace storage {
 class WriteFile;
@@ -198,13 +195,6 @@
     int64_t record_count_for_next_mem_check_;
     bool write_file_created_;
     bool io_writer_owned_;  // false when init(RestorableTsFileIOWriter*)
-#ifdef ENABLE_THREADS
-    static size_t get_thread_pool_size() {
-        int32_t count = common::g_config_value_.write_thread_count_;
-        return count > 0 ? static_cast<size_t>(count) : size_t{1};
-    }
-    common::ThreadPool thread_pool_{get_thread_pool_size()};
-#endif
 
     int write_typed_column(ValueChunkWriter* value_chunk_writer,
                            int64_t* timestamps, bool* col_values,