Index: lldb/include/lldb/Utility/Stream.h
===================================================================
--- lldb/include/lldb/Utility/Stream.h
+++ lldb/include/lldb/Utility/Stream.h
@@ -19,6 +19,7 @@
 #include <cstdarg>
 #include <cstddef>
 #include <cstdint>
+#include <mutex>
 #include <type_traits>
 
 namespace lldb_private {
@@ -44,7 +45,6 @@
     Stream *m_stream;
     /// Bytes we have written so far when ByteDelta was created.
     size_t m_start;
-
   public:
     ByteDelta(Stream &s) : m_stream(&s), m_start(s.GetWrittenBytes()) {}
     /// Returns the number of bytes written to the given Stream since this
@@ -412,6 +412,26 @@
   RawOstreamForward m_forwarder;
 };
 
+template <typename T, typename M = std::mutex> class LockableStream : public T {
+public:
+  using T::T;
+  ~LockableStream() = default;
+
+  void Flush() override {
+    std::lock_guard<M> guard(m_mutex);
+    T::Flush();
+  }
+
+protected:
+  size_t WriteImpl(const void *s, size_t length) override {
+    std::lock_guard<M> guard(m_mutex);
+    return T::WriteImpl(s, length);
+  }
+
+private:
+  M m_mutex;
+};
+
 /// Output an address value to this stream.
 ///
 /// Put an address \a addr out to the stream with optional \a prefix and \a
Index: lldb/source/Core/Debugger.cpp
===================================================================
--- lldb/source/Core/Debugger.cpp
+++ lldb/source/Core/Debugger.cpp
@@ -733,8 +733,10 @@
     : UserID(g_unique_id++),
       Properties(std::make_shared<OptionValueProperties>()),
       m_input_file_sp(std::make_shared<NativeFile>(stdin, false)),
-      m_output_stream_sp(std::make_shared<StreamFile>(stdout, false)),
-      m_error_stream_sp(std::make_shared<StreamFile>(stderr, false)),
+      m_output_stream_sp(
+          std::make_shared<LockableStream<StreamFile>>(stdout, false)),
+      m_error_stream_sp(
+          std::make_shared<LockableStream<StreamFile>>(stderr, false)),
       m_input_recorder(nullptr),
       m_broadcaster_manager_sp(BroadcasterManager::MakeBroadcasterManager()),
       m_terminal_state(), m_target_list(*this), m_platform_list(),