Method _checkout_write

src/proxy/logging/LogObject.cc:342–453

}

LogBuffer *
LogObject::_checkout_write(size_t *write_offset, size_t bytes_needed)
{
  LogBuffer::LB_ResultCode result_code;
  LogBuffer               *buffer;
  LogBuffer               *new_buffer = nullptr;
  bool                     retry      = true;
  head_p                   old_h;

  do {
    // To avoid a race condition, we keep a count of held references in
    // the pointer itself and add this to m_outstanding_references.

    // Increment the version of m_log_buffer, returning the previous version.
    head_p h = increment_pointer_version(&m_log_buffer);

    buffer           = static_cast<LogBuffer *>(FREELIST_POINTER(h));
    result_code      = buffer->checkout_write(write_offset, bytes_needed);
    bool decremented = false;

    switch (result_code) {
    case LogBuffer::LB_OK:
      // checkout succeeded
      retry = false;
      break;

    case LogBuffer::LB_FULL_ACTIVE_WRITERS:
    case LogBuffer::LB_FULL_NO_WRITERS:
      // no more room in current buffer, create a new one
      new_buffer = new LogBuffer(Log::config, this, Log::config->log_buffer_size);

      // swap the new buffer for the old one
      INK_WRITE_MEMORY_BARRIER;

      do {
        INK_QUEUE_LD(old_h, m_log_buffer);
        // we may depend on comparing the old pointer to the new pointer to detect buffer swaps
        // without worrying about pointer collisions because we always allocate a new LogBuffer
        // before freeing the old one
        if (FREELIST_POINTER(old_h) != FREELIST_POINTER(h)) {
          ink_atomic_increment(&buffer->m_references, -1);

          // another thread is already creating a new buffer,
          // so delete new_buffer and try again next loop iteration
          delete new_buffer;
          new_buffer = nullptr;
          break;
        }
      } while (write_pointer_version(&m_log_buffer, old_h, new_buffer, 0) == false);

      if (FREELIST_POINTER(old_h) == FREELIST_POINTER(h)) {
        ink_atomic_increment(&buffer->m_references, FREELIST_VERSION(old_h) - 1);

        int idx = m_buffer_manager_idx++ % m_flush_threads;
        Dbg(dbg_ctl_log_logbuffer, "adding buffer %d to flush list after checkout", buffer->get_id());
        m_buffer_manager[idx].add_to_flush_queue(buffer);
        Log::preproc_notify[idx].signal();
        buffer = nullptr;