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google.appengine.ext.ndb.AutoBatcher

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

Inherits From: expected_type

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

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add

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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

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flush

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run_queue

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Actually run the _todo_tasklet.