hybrid time series buffer

[cboulay]

This is a proposal for a generalized buffer class that operates as follows:

• When add_message(message) is called, the new message is merely appended to a deque
• Synchronization between the deque and a circular buffer occurs...
  • Upon every add_message `if self._update_strategy == "immediate"
  • Upon some add_message calls elif self._update_strategy == "threshold" and len(q) > threshold
  • Upon get_data if self._update_strategy == "on_demand"
• When get_data(...) is called, it may synchronize the buffers (see previous point) then it will return a message with the requested data.
  • The data may be a view of the buffer if the requested interval was contiguous

Compared to a deque-only buffer, this has more efficient reads and minimal copies, especially when reads are less frequent than inserts or reads are likely to have overlaps.
Compared to a circular-only buffer, this has faster insertions.