--- old/src/hotspot/share/logging/logStream.cpp	2020-02-24 07:47:43.621099908 +0000
+++ new/src/hotspot/share/logging/logStream.cpp	2020-02-24 07:47:43.361098486 +0000
@@ -25,6 +25,8 @@
 #include "precompiled.hpp"
 #include "logging/log.hpp"
 #include "logging/logStream.hpp"
+#include "logging/logMessageBuffer.hpp"
+#include "logging/logAsyncFlusher.hpp"
 
 LogStream::LineBuffer::LineBuffer()
  : _buf(_smallbuf), _cap(sizeof(_smallbuf)), _pos(0)
@@ -104,20 +106,44 @@
 void LogStream::write(const char* s, size_t len) {
   if (len > 0 && s[len - 1] == '\n') {
     _current_line.append(s, len - 1); // omit the newline.
-    _log_handle.print("%s", _current_line.buffer());
+    if (!_async_log) {
+      _log_handle.print("%s", _current_line.buffer());
+    } else {
+      if (!_async_buffer) {
+        _async_buffer = new (mtLogging)LogMessageBuffer();
+      }
+      _async_buffer->write_n(_log_handle.level(), _current_line.buffer(), _current_line.size());
+    }
     _current_line.reset();
   } else {
     _current_line.append(s, len);
   }
+
   update_position(s, len);
 }
 
 // Destructor writes any unfinished output left in the line buffer.
 LogStream::~LogStream() {
-  if (_current_line.is_empty() == false) {
-    _log_handle.print("%s", _current_line.buffer());
+  if (!_current_line.is_empty()) {
+    if (!_async_log) {
+      _log_handle.print("%s", _current_line.buffer());
+    }
+    else {
+      if (!_async_buffer) {
+        _async_buffer = new (mtLogging)LogMessageBuffer();
+      }
+      _async_buffer->write_n(_log_handle.level(), _current_line.buffer(), _current_line.size());
+    }
     _current_line.reset();
   }
-}
 
+  if (_async_log && _async_buffer) {
+    LogAsyncFlusher* flusher = LogAsyncFlusher::instance();
+    flusher->enqueue(_log_handle.tagset(), _async_buffer);
+  }
+}
 
+void LogStream::create_async_buffer() {
+  Arena* arena  = new (mtLogging)Arena(mtLogging, LogMessageBuffer::initial_buffer_size());
+  _async_buffer = new (mtLogging)LogMessageBuffer(arena);
+}