Merge pull request #158 from sergiud/zero-allocation

[RFC] reduce heap memory allocations to zero

1 files changed, 31 insertions, 0 deletions

diff --git a/src/logging.cc b/src/logging.cc
index 46a0f5a..0d9aad8 100644
--- a/src/logging.cc
+++ b/src/logging.cc
@@ -331,6 +331,7 @@ const size_t LogMessage::kMaxLogMessageLen = 30000;
 
 struct LogMessage::LogMessageData  {
   LogMessageData();
+  void reset();
 
   int preserved_errno_;      // preserved errno
   // Buffer space; contains complete message text.
@@ -1145,10 +1146,22 @@ static bool fatal_msg_exclusive = true;
 static LogMessage::LogMessageData fatal_msg_data_exclusive;
 static LogMessage::LogMessageData fatal_msg_data_shared;
 
+#ifdef GLOG_THREAD_LOCAL_STORAGE
+// Static thread-local log data space to use, because typically at most one
+// LogMessageData object exists (in this case glog makes zero heap memory
+// allocations).
+static GLOG_THREAD_LOCAL_STORAGE bool thread_data_available = true;
+static GLOG_THREAD_LOCAL_STORAGE LogMessage::LogMessageData thread_msg_data;
+#endif // defined(GLOG_THREAD_LOCAL_STORAGE)
+
 LogMessage::LogMessageData::LogMessageData()
   : stream_(message_text_, LogMessage::kMaxLogMessageLen, 0) {
 }
 
+void LogMessage::LogMessageData::reset() {
+    stream_.reset();
+}
+
 LogMessage::LogMessage(const char* file, int line, LogSeverity severity,
                        int ctr, void (LogMessage::*send_method)())
     : allocated_(NULL) {
@@ -1201,8 +1214,22 @@ void LogMessage::Init(const char* file,
                       void (LogMessage::*send_method)()) {
   allocated_ = NULL;
   if (severity != GLOG_FATAL || !exit_on_dfatal) {
+#ifdef GLOG_THREAD_LOCAL_STORAGE
+    // No need for locking, because this is thread local.
+    if (thread_data_available) {
+      thread_data_available = false;
+      data_ = &thread_msg_data;
+      // Make sure to clear log data since it may have been used and filled with
+      // data. We do not want to append the new message to the previous one.
+      data_->reset();
+    } else {
+      allocated_ = new LogMessageData();
+      data_ = allocated_;
+    }
+#else // !defined(GLOG_THREAD_LOCAL_STORAGE)
     allocated_ = new LogMessageData();
     data_ = allocated_;
+#endif // defined(GLOG_THREAD_LOCAL_STORAGE)
     data_->first_fatal_ = false;
   } else {
     MutexLock l(&fatal_msg_lock);
@@ -1271,6 +1298,10 @@ void LogMessage::Init(const char* file,
 
 LogMessage::~LogMessage() {
   Flush();
+#ifdef GLOG_THREAD_LOCAL_STORAGE
+  if (data_ == &thread_msg_data)
+    thread_data_available = true;
+#endif // defined(GLOG_THREAD_LOCAL_STORAGE)
   delete allocated_;
 }