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| author | Mike Bayer <mike_mp@zzzcomputing.com> | 2019-08-02 23:20:06 -0400 |
|---|---|---|
| committer | Mike Bayer <mike_mp@zzzcomputing.com> | 2019-08-04 12:40:11 -0400 |
| commit | e22d2b089fad1f79d53bc6238626f32f0e796ad0 (patch) | |
| tree | 46997483eceb659d61b4bc00033624a7aef4b999 /lib/sqlalchemy/event | |
| parent | a4e0995dc817acda7d669b8925c9bc3defdb660b (diff) | |
| download | sqlalchemy-e22d2b089fad1f79d53bc6238626f32f0e796ad0.tar.gz | |
Strong reference listen function wrapped by "once"
Fixed issue in event system where using the ``once=True`` flag with
dynamically generated listener functions would cause event registration of
future events to fail if those listener functions were garbage collected
after they were used, due to an assumption that a listened function is
strongly referenced. The "once" wrapped is now modified to strongly
reference the inner function persistently, and documentation is updated
that using "once" does not imply automatic de-registration of listener
functions.
Fixes: #4794
Change-Id: I06388083d1633dcc89e8919eb1e51270f966df38
Diffstat (limited to 'lib/sqlalchemy/event')
| -rw-r--r-- | lib/sqlalchemy/event/api.py | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/lib/sqlalchemy/event/api.py b/lib/sqlalchemy/event/api.py index e7c30901f..260d6e86f 100644 --- a/lib/sqlalchemy/event/api.py +++ b/lib/sqlalchemy/event/api.py @@ -64,6 +64,13 @@ def listen(target, identifier, fn, *args, **kw): .. versionadded:: 0.9.4 Added ``once=True`` to :func:`.event.listen` and :func:`.event.listens_for`. + .. warning:: The ``once`` argument does not imply automatic de-registration + of the listener function after it has been invoked a first time; a + listener entry will remain associated with the target object. + Associating an arbitrarily high number of listeners without explictitly + removing them will cause memory to grow unbounded even if ``once=True`` + is specified. + .. note:: The :func:`.listen` function cannot be called at the same time @@ -124,6 +131,13 @@ def listens_for(target, identifier, *args, **kw): .. versionadded:: 0.9.4 Added ``once=True`` to :func:`.event.listen` and :func:`.event.listens_for`. + .. warning:: The ``once`` argument does not imply automatic de-registration + of the listener function after it has been invoked a first time; a + listener entry will remain associated with the target object. + Associating an arbitrarily high number of listeners without explictitly + removing them will cause memory to grow unbounded even if ``once=True`` + is specified. + .. seealso:: :func:`.listen` - general description of event listening |