Fix MSVC warning

cpp/src/arrow/python/python-test.cc

@@ -239,7 +239,8 @@ TEST(PandasConversionTest, TestObjectBlockWriteFails) {
   Py_BEGIN_ALLOW_THREADS;
   PandasOptions options;
   MemoryPool* pool = default_memory_pool();
-  ASSERT_RAISES(UnknownError, ConvertTableToPandas(options, table, 2, pool, &out));
+  ASSERT_RAISES(UnknownError,
+                ConvertTableToPandas(options, table, true /* use_threads */, pool, &out));
   Py_END_ALLOW_THREADS;
 }
 

cpp/src/arrow/util/thread-pool-test.cc

@@ -127,7 +127,7 @@ class TestThreadPool : public ::testing::Test {
 
   std::shared_ptr<ThreadPool> MakeThreadPool() { return MakeThreadPool(4); }
 
-  std::shared_ptr<ThreadPool> MakeThreadPool(size_t threads) {
+  std::shared_ptr<ThreadPool> MakeThreadPool(int threads) {
     std::shared_ptr<ThreadPool> pool;
     Status st = ThreadPool::Make(threads, &pool);
     return pool;
@@ -163,7 +163,7 @@ class TestThreadPool : public ::testing::Test {
 
 TEST_F(TestThreadPool, ConstructDestruct) {
   // Stress shutdown-at-destruction logic
-  for (size_t threads : {1, 2, 3, 8, 32, 70}) {
+  for (int threads : {1, 2, 3, 8, 32, 70}) {
     auto pool = this->MakeThreadPool(threads);
   }
 }
@@ -285,7 +285,7 @@ TEST_F(TestThreadPool, Submit) {
 TEST(TestGlobalThreadPool, Capacity) {
   // Sanity check
   auto pool = GetCpuThreadPool();
-  size_t capacity = pool->GetCapacity();
+  int capacity = pool->GetCapacity();
   ASSERT_GT(capacity, 0);
   ASSERT_EQ(pool->GetActualCapacity(), capacity);
   ASSERT_EQ(GetCpuThreadPoolCapacity(), capacity);
@@ -293,7 +293,7 @@ TEST(TestGlobalThreadPool, Capacity) {
   // Exercise default capacity heuristic
   ASSERT_OK(DelEnvVar("OMP_NUM_THREADS"));
   ASSERT_OK(DelEnvVar("OMP_THREAD_LIMIT"));
-  size_t hw_capacity = std::thread::hardware_concurrency();
+  int hw_capacity = std::thread::hardware_concurrency();
   ASSERT_EQ(ThreadPool::DefaultCapacity(), hw_capacity);
   ASSERT_OK(SetEnvVar("OMP_NUM_THREADS", "13"));
   ASSERT_EQ(ThreadPool::DefaultCapacity(), 13);

cpp/src/arrow/util/thread-pool.cc

@@ -58,7 +58,7 @@ int ThreadPool::GetCapacity() {
 
 int ThreadPool::GetActualCapacity() {
   std::unique_lock<std::mutex> lock(mutex_);
-  return workers_.size();
+  return static_cast<int>(workers_.size());
 }
 
 Status ThreadPool::Shutdown(bool wait) {