Using dbm locking one can not create values with nested creators

[sqlalchemy-bot]

Migrated issue, originally created by kaukas (kaukas)

Sometimes it is desired to cache not only the final result of the computation but the intermediate steps as well. Doing that you can invalidate the result of some of the steps and the final cache. The recomputation of the final result would then be faster because it would still use the rest of the cached values.

Example:

#!python

from dogpile.cache import make_region

region = make_region()
region.configure('dogpile.cache.dbm',
    arguments=dict(
        filename='file.dbm'
    )
)


def create_small_thing():
    def small_thing():
        return 'small '
    return region.get_or_create('small', creator=small_thing)


def create_big_thing():
    def big_thing():
        return create_small_thing() * 10
    return region.get_or_create('big', creator=big_thing)

create_big_thing()

The above code freezes - once the lock is acquired for the "big thing" you can not store "small things".

[sqlalchemy-bot]

Michael Bayer (zzzeek) wrote:

is that the file lock freezing ? OK we can make it re-entrant, perhaps beaker's did this already

[sqlalchemy-bot]

Michael Bayer (zzzeek) wrote:

oh, that's the dogpile. OK might want to put a reentrant decorator around the lock in a generic way....hooray latency

[sqlalchemy-bot]

Michael Bayer (zzzeek) wrote:

still thinking sorry ! the dbm backend's lock is across all keys. other locks dont. so maybe a reentrant proxy chosen by the backend depending on the type of lock.

[sqlalchemy-bot]

Changes by kaukas (kaukas):

• changed title from "Using dbm locking one can not create more than one" to "Using dbm locking one can not create values with n"

[sqlalchemy-bot]

Michael Bayer (zzzeek) wrote:

okey doke got something for this in [[https://bitbucket.org/zzzeek/dogpile.cache/changeset/c2e2571f326f5a990a52c75f4739800012c82493|c2e2571f326f5a990a52c75f4739800012c82493]]. Should be good to release 0.2.3.

[sqlalchemy-bot]

Changes by Michael Bayer (zzzeek):

• changed status to closed