[Lldb-commits] [lldb] [lldb] Always lock in StreamLogHandler::Write (PR #205771)

[Raphael Isemann via lldb-commits]

https://github.com/Teemperor updated https://github.com/llvm/llvm-project/pull/205771

>From 38ef5044eaf531bcf81e8a9f6a41dc4e1c7db516 Mon Sep 17 00:00:00 2001
From: Raphael Isemann <rise at apple.com>
Date: Thu, 25 Jun 2026 11:32:34 +0100
Subject: [PATCH] [lldb] Always lock in StreamLogHandler::Write

This code assumes that writing to an unbuffered raw_fd_ostream from
multiple threads is somehow safe. raw_fd_ostream doesn't make any
guarantees about this from what I can see.

The current raw_fd_ostream implementation also uses a looping write
call to write the content in chunks, and doing this from multiple
threads leads to interleaving log messages.

This patch unconditionally make us aquire the stream lock.
---
 lldb/source/Utility/Log.cpp | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/lldb/source/Utility/Log.cpp b/lldb/source/Utility/Log.cpp
index 1921573996196..6b077a3766e9f 100644
--- a/lldb/source/Utility/Log.cpp
+++ b/lldb/source/Utility/Log.cpp
@@ -378,12 +378,8 @@ void StreamLogHandler::Flush() {
 }
 
 void StreamLogHandler::Emit(llvm::StringRef message) {
-  if (m_stream.GetBufferSize() > 0) {
-    std::lock_guard<std::mutex> guard(m_mutex);
-    m_stream << message;
-  } else {
-    m_stream << message;
-  }
+  std::lock_guard<std::mutex> guard(m_mutex);
+  m_stream << message;
 }
 
 CallbackLogHandler::CallbackLogHandler(lldb::LogOutputCallback callback,