1) use std::stringstream::view; 2) add comment to test

Author: pitrou

cpp/src/arrow/util/logging.cc

@@ -71,7 +71,7 @@ class CerrLog {
     if (has_logged_) {
       static std::mutex cerr_mutex;
       std::lock_guard<std::mutex> lock(cerr_mutex);
-      std::cerr << buffer_.str() << std::endl;
+      std::cerr << buffer_.view() << std::endl;
     }
     if (severity_ == ArrowLogLevel::ARROW_FATAL) {
       PrintBackTrace();

cpp/src/arrow/util/logging_test.cc

@@ -42,17 +42,11 @@ int64_t current_time_ms() {
 // This file just print some information using the logging macro.
 
 void PrintLog() {
-  ARROW_LOG(DEBUG) << "This is the"
-                   << " DEBUG"
-                   << " message";
-  ARROW_LOG(INFO) << "This is the"
-                  << " INFO message";
-  ARROW_LOG(WARNING) << "This is the"
-                     << " WARNING message";
-  ARROW_LOG(ERROR) << "This is the"
-                   << " ERROR message";
-  ARROW_CHECK(true) << "This is a ARROW_CHECK"
-                    << " message but it won't show up";
+  ARROW_LOG(DEBUG) << "This is the" << " DEBUG" << " message";
+  ARROW_LOG(INFO) << "This is the" << " INFO message";
+  ARROW_LOG(WARNING) << "This is the" << " WARNING message";
+  ARROW_LOG(ERROR) << "This is the" << " ERROR message";
+  ARROW_CHECK(true) << "This is a ARROW_CHECK" << " message but it won't show up";
   // The following 2 lines should not run since it will cause program failure.
   // ARROW_LOG(FATAL) << "This is the FATAL message";
   // ARROW_CHECK(false) << "This is a ARROW_CHECK message but it won't show up";
@@ -98,6 +92,8 @@ TEST(ArrowCheck, PayloadEvaluatedOnFailure) {
 }
 
 TEST(ArrowLog, MultiThreadedLogging) {
+  // This is mostly a visual test that logging from multiple threads produces
+  // a clean output without interleaving messages (GH-49433).
   constexpr int kNumThreads = 10;
   constexpr int kNumMessges = 10;
   std::vector<std::thread> threads;
@@ -107,7 +103,7 @@ TEST(ArrowLog, MultiThreadedLogging) {
   for (int i = 0; i < kNumThreads; ++i) {
     threads.emplace_back([i]() {
       for (int j = 0; j < kNumMessges; ++j) {
-        ARROW_LOG(INFO) << "Thread" << i << " message " << j
+        ARROW_LOG(INFO) << "Thread " << i << " message " << j
                         << " - testing thread safety.";
       }
     });