From 6248bd89b7d6805e6215c20fd114eb3f69a05594 Mon Sep 17 00:00:00 2001
From: vanshaj2023 <vanshaj2023@users.noreply.github.com>
Date: Mon, 16 Feb 2026 17:50:58 +0530
Subject: [PATCH] GH-49272: [C++][CI] Fix intermittent segfault in
 arrow-json-test on MinGW

---
 cpp/src/arrow/json/reader_test.cc | 45 +++++++++++++++++++++++++++++++
 cpp/src/arrow/util/task_group.cc  |  4 +--
 cpp/src/arrow/util/thread_pool.cc | 29 ++++++++++++++++++--
 3 files changed, 74 insertions(+), 4 deletions(-)

diff --git a/cpp/src/arrow/json/reader_test.cc b/cpp/src/arrow/json/reader_test.cc
index a52626413d6..8a01820e7cb 100644
--- a/cpp/src/arrow/json/reader_test.cc
+++ b/cpp/src/arrow/json/reader_test.cc
@@ -34,6 +34,25 @@
 #include "arrow/type_fwd.h"
 #include "arrow/util/vector.h"
 
+// On MinGW, install a crash handler to log the exception address for debugging
+// intermittent segfaults. See https://github.com/apache/arrow/issues/49272
+#if defined(__MINGW32__) || defined(__MINGW64__)
+#  include <cstdio>
+#  include <windows.h>
+namespace {
+LONG WINAPI ArrowCrashHandler(EXCEPTION_POINTERS* ep) {
+  fprintf(stderr, "CRASH: code=0x%lx addr=%p\n",
+          ep->ExceptionRecord->ExceptionCode,
+          ep->ExceptionRecord->ExceptionAddress);
+  fflush(stderr);
+  return EXCEPTION_CONTINUE_SEARCH;
+}
+struct CrashHandlerInstaller {
+  CrashHandlerInstaller() { SetUnhandledExceptionFilter(ArrowCrashHandler); }
+} g_crash_handler;
+}  // namespace
+#endif
+
 namespace arrow {
 namespace json {
 
@@ -290,6 +309,32 @@ TEST(ReaderTest, MultipleChunksParallel) {
   AssertTablesEqual(*serial, *threaded);
 }
 
+// Stress test for intermittent threading crashes on MinGW.
+// See https://github.com/apache/arrow/issues/49272
+TEST(ReaderTest, MultipleChunksParallelStress) {
+  constexpr int kTrials = 20;
+  for (int trial = 0; trial < kTrials; ++trial) {
+    int64_t count = 1 << 10;
+    ParseOptions parse_options;
+    parse_options.unexpected_field_behavior = UnexpectedFieldBehavior::InferType;
+    ReadOptions read_options;
+    read_options.block_size = static_cast<int>(count / 2);
+    read_options.use_threads = true;
+
+    std::string json;
+    for (int i = 0; i < count; ++i) {
+      json += "{\"a\":" + std::to_string(i) + "}\n";
+    }
+
+    std::shared_ptr<io::InputStream> input;
+    ASSERT_OK(MakeStream(json, &input));
+    ASSERT_OK_AND_ASSIGN(auto reader, TableReader::Make(default_memory_pool(), input,
+                                                        read_options, parse_options));
+    ASSERT_OK_AND_ASSIGN(auto table, reader->Read());
+    ASSERT_EQ(table->num_rows(), count);
+  }
+}
+
 TEST(ReaderTest, ListArrayWithFewValues) {
   // ARROW-7647
   ParseOptions parse_options;
diff --git a/cpp/src/arrow/util/task_group.cc b/cpp/src/arrow/util/task_group.cc
index 27cd1ba3971..980ca84de83 100644
--- a/cpp/src/arrow/util/task_group.cc
+++ b/cpp/src/arrow/util/task_group.cc
@@ -99,7 +99,7 @@ class ThreadedTaskGroup : public TaskGroup {
     // The hot path is unlocked thanks to atomics
     // Only if an error occurs is the lock taken
     if (ok_.load(std::memory_order_acquire)) {
-      nremaining_.fetch_add(1, std::memory_order_acquire);
+      nremaining_.fetch_add(1, std::memory_order_acq_rel);
 
       auto self = checked_pointer_cast<ThreadedTaskGroup>(shared_from_this());
 
@@ -176,7 +176,7 @@ class ThreadedTaskGroup : public TaskGroup {
 
   void OneTaskDone() {
     // Can be called unlocked thanks to atomics
-    auto nremaining = nremaining_.fetch_sub(1, std::memory_order_release) - 1;
+    auto nremaining = nremaining_.fetch_sub(1, std::memory_order_acq_rel) - 1;
     DCHECK_GE(nremaining, 0);
     if (nremaining == 0) {
       // Take the lock so that ~ThreadedTaskGroup cannot destroy cv
diff --git a/cpp/src/arrow/util/thread_pool.cc b/cpp/src/arrow/util/thread_pool.cc
index bf107006f8b..7f8806a38a1 100644
--- a/cpp/src/arrow/util/thread_pool.cc
+++ b/cpp/src/arrow/util/thread_pool.cc
@@ -630,9 +630,34 @@ void ThreadPool::CollectFinishedWorkersUnlocked() {
   state_->finished_workers_.clear();
 }
 
+// MinGW's __emutls implementation for C++ thread_local has known race conditions
+// during thread creation that can cause segfaults. Use native Win32 TLS instead.
+// See https://github.com/apache/arrow/issues/49272
+#if defined(__MINGW32__) || defined(__MINGW64__)
+#  include <windows.h>
+
+namespace {
+DWORD GetPoolTlsIndex() {
+  static DWORD index = TlsAlloc();
+  return index;
+}
+}  // namespace
+
+static ThreadPool* GetCurrentThreadPool() {
+  return static_cast<ThreadPool*>(TlsGetValue(GetPoolTlsIndex()));
+}
+
+static void SetCurrentThreadPool(ThreadPool* pool) {
+  TlsSetValue(GetPoolTlsIndex(), pool);
+}
+#else
 thread_local ThreadPool* current_thread_pool_ = nullptr;
 
-bool ThreadPool::OwnsThisThread() { return current_thread_pool_ == this; }
+static ThreadPool* GetCurrentThreadPool() { return current_thread_pool_; }
+static void SetCurrentThreadPool(ThreadPool* pool) { current_thread_pool_ = pool; }
+#endif
+
+bool ThreadPool::OwnsThisThread() { return GetCurrentThreadPool() == this; }
 
 void ThreadPool::LaunchWorkersUnlocked(int threads) {
   std::shared_ptr<State> state = sp_state_;
@@ -641,7 +666,7 @@ void ThreadPool::LaunchWorkersUnlocked(int threads) {
     state_->workers_.emplace_back();
     auto it = --(state_->workers_.end());
     *it = std::thread([this, state, it] {
-      current_thread_pool_ = this;
+      SetCurrentThreadPool(this);
       WorkerLoop(state, it);
     });
   }