google.appengine.ext.ndb.AutoBatcher

Batches multiple async calls if they share the same RPC options.

Inherits From: expected_type

google.appengine.ext.ndb.AutoBatcher(
    todo_tasklet, limit
)

Here is an example to explain what this class does.

Life of a key.get_async(options) API call:

  • Key gets the singleton Context instance and invokes Context.get.

  • Context.get calls Context._get_batcher.add(key, options). This returns a future fut as the return value of key.get_async. At this moment, key.get_async returns.

  • When more than "limit" number of _get_batcher.add() was called, _get_batcher invokes its self._todo_tasklet, Context._get_tasklet, with the list of keys seen so far.

  • Context._get_tasklet fires a MultiRPC and waits on it.

  • Upon MultiRPC completion, Context._get_tasklet passes on the results to the respective fut from key.get_async.

  • If user calls fut.get_result() before "limit" number of add() was called, fut.get_result() will repeatedly call eventloop.run1().

  • After processing immediate callbacks, eventloop will run idlers. AutoBatcher._on_idle is an idler.

  • _on_idle will run the todo_tasklet before the batch is full.

So the engine is todo_tasklet, which is a proxy tasklet that can combine arguments into batches and passes along results back to respective futures. This class is mainly a helper that invokes todo_tasklet with the right arguments at the right time.

todo_tasklet The tasklet that actually fires RPC and waits on a MultiRPC. It should take a list of (future, arg) pairs and an "options" as arguments. "options" are rpc options.
limit Max number of items to batch for each distinct value of "options".

Methods

action

View source

action()

add

View source

add(
    arg, options=None
)

Returns back an instance of future after adding an arg.

Args
arg One argument for _todo_tasklet.
options RPC options.

Return
An instance of future, representing the result of running _todo_tasklet without batching.

add_once

View source

add_once(
    arg, options=None
)

flush

View source

flush()

run_queue

View source

run_queue(
    options, todo
)

Actually run the _todo_tasklet.