Removing copy to temp buffer in log flush.

src/xenia/base/logging.cc

@@ -104,9 +104,10 @@ class Logger {
       bool did_write = false;
       while (!ring_buffer_.empty()) {
         did_write = true;
+
+        // Read line header and write out the line prefix.
         LogLine line;
         ring_buffer_.Read(&line, sizeof(line));
-        ring_buffer_.Read(log_format_buffer_.data(), line.buffer_length);
         char prefix[] = {
             line.level_char,
             '>',
@@ -125,11 +126,23 @@ class Logger {
         std::snprintf(prefix + 3, sizeof(prefix) - 3, "%08" PRIX32 " ",
                       line.thread_id);
         fwrite(prefix, 1, sizeof(prefix) - 1, file_);
-        fwrite(log_format_buffer_.data(), 1, line.buffer_length, file_);
-        if (log_format_buffer_[line.buffer_length - 1] != '\n') {
+
+        // Get access to the line data - which may be split in the ring buffer -
+        // and write it out in parts.
+        auto line_range = ring_buffer_.BeginRead(line.buffer_length);
+        fwrite(line_range.first, 1, line_range.first_length, file_);
+        if (line_range.second_length) {
+          fwrite(line_range.second, 1, line_range.second_length, file_);
+        }
+        // Always ensure there is a newline.
+        char last_char = line_range.second
+                             ? line_range.second[line_range.second_length - 1]
+                             : line_range.first[line_range.first_length - 1];
+        if (last_char != '\n') {
           const char suffix[1] = {'\n'};
           fwrite(suffix, 1, sizeof(suffix), file_);
         }
+        ring_buffer_.EndRead(std::move(line_range));
       }
       mutex_.unlock();
       if (did_write) {

src/xenia/base/ring_buffer.cc

@@ -17,6 +17,28 @@ namespace xe {
 RingBuffer::RingBuffer(uint8_t* buffer, size_t capacity)
     : buffer_(buffer), capacity_(capacity) {}
 
+RingBuffer::ReadRange RingBuffer::BeginRead(size_t count) {
+  count = std::min(count, capacity_);
+  if (!count) {
+    return {0};
+  }
+  if (read_offset_ + count < capacity_) {
+    return {buffer_ + read_offset_, count, nullptr, 0};
+  } else {
+    size_t left_half = capacity_ - read_offset_;
+    size_t right_half = count - left_half;
+    return {buffer_ + read_offset_, left_half, buffer_, right_half};
+  }
+}
+
+void RingBuffer::EndRead(ReadRange read_range) {
+  if (read_range.second_length) {
+    read_offset_ = read_range.second_length;
+  } else {
+    read_offset_ += read_range.first_length;
+  }
+}
+
 size_t RingBuffer::Read(uint8_t* buffer, size_t count) {
   count = std::min(count, capacity_);
   if (!count) {

src/xenia/base/ring_buffer.h

@@ -48,6 +48,15 @@ class RingBuffer {
     }
   }
 
+  struct ReadRange {
+    const uint8_t* first;
+    size_t first_length;
+    const uint8_t* second;
+    size_t second_length;
+  };
+  ReadRange BeginRead(size_t count);
+  void EndRead(ReadRange read_range);
+
   size_t Read(uint8_t* buffer, size_t count);
   template <typename T>
   size_t Read(T* buffer, size_t count) {