google.appengine.ext.ndb.SerialQueueFuture

Like QueueFuture but maintains the order of insertion.

Inherits From: Future, expected_type

google.appengine.ext.ndb.SerialQueueFuture(
    info=None
)

This class is used by Query operations.

Invariants:

  • At least one of _queue and _waiting is empty.
  • The Futures in _waiting are always pending.

(The Futures in _queue may be pending or completed.)

In the discussion below, add_dependent() is treated the same way as putq().

If putq() is ahead of getq(), the situation is like this:

                   putq()
                   v

_queue: [f1, f2, ...]; _waiting: [] ^ getq()

Here, putq() appends a Future to the right of _queue, and getq() removes one from the left.

If getq() is ahead of putq(), it's like this:

        putq()
        v

_queue: []; _waiting: [f1, f2, ...] ^ getq()

Here, putq() removes a Future from the left of _waiting, and getq() appends one to the right.

When both are empty, putq() appends a Future to the right of _queue, while getq() appends one to the right of _waiting.

The _full flag means that no more calls to putq() will be made; it is set by calling either complete() or set_exception().

Calling complete() signals that no more putq() calls will be made. If getq() is behind, subsequent getq() calls will eat up _queue until it is empty, and after that will return a Future that passes EOFError (note that getq() itself never raises EOFError). If getq() is ahead when complete() is called, the Futures in _waiting are all passed an EOFError exception (thereby eating up _waiting).

If, instead of complete(), set_exception() is called, the exception and traceback set there will be used instead of EOFError.

state

Methods

add_callback

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add_callback(
    callback, *args, **kwds
)

add_dependent

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add_dependent(
    fut
)

add_immediate_callback

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add_immediate_callback(
    callback, *args, **kwds
)

check_success

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check_success()

complete

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complete()

done

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done()

dump

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dump()

dump_stack

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dump_stack()

get_exception

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get_exception()

get_result

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get_result()

get_traceback

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get_traceback()

getq

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getq()

putq

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putq(
    value
)

set_exception

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set_exception(
    exc, tb=None
)

set_result

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set_result(
    result
)

wait

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wait()

wait_all

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@classmethod
wait_all(
    futures
)

wait_any

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@classmethod
wait_any(
    futures
)

FINISHING 2
IDLE 0
RUNNING 1