Huey

This section describes the changes in the 2.0.0 release. A detailed list of
changes can be found here: https://huey.readthedocs.io/en/latest/changes.html

Overview of changes:

* `always_eager` mode has been renamed to `immediate` mode. Unlike previous
versions, `immediate` mode involves the same code paths used by the consumer
process. This makes it easier to test features like task revocation and task
scheduling without needing to run a dedicated consumer process. Immediate
mode uses an in-memory storage layer by default, but can be configured to use
"live" storage like Redis or Sqlite.
* The events stream API has been removed in favor of simpler callback-driven
[signals](https://huey.readthedocs.io/en/latest/signals.html) APIs. These
callbacks are executed synchronously within the huey consumer process.
* A new serialization format is used in 2.0.0, however consumers running 2.0
will continue to be able to read and deserialize messages enqueued by Huey
version 1.11.0 for backwards compatibility.
* Support for [task priorities](https://huey.readthedocs.io/en/latest/guide.html#task-priority).
* New `Serializer` abstraction allows users to customize the serialization
format used when reading and writing tasks.
* Huey consumer and scheduler can be more easily run within the application
process, if you prefer not to run a separate consumer process.
* Tasks can now specify an `on_error` handler, in addition to the
previously-supported `on_complete` handler.
* Task pipelines return a special `ResultGroup` object which simplifies reading
the results of a sequence of task executions.
* `SqliteHuey` has been promoted out of `contrib`, onto an equal footing with
`RedisHuey`. To simplify deployment, the dependency on
[peewee](https://github.com/coleifer/peewee) was removed and the Sqlite
storage engine uses the Python `sqlite3` driver directly.

[View commits](https://github.com/coleifer/huey/compare/1.11.0...2.0.0)

**Backwards-incompatible changes**

Previously, it was possible for certain tasks to be silently ignored if a task
with that name already existed in the registry. To fix this, I have made two
changes:

1. The task-name, when serialized, now consists of the task module and the name
of the decorated function. So, "queue_task_foo" becomes "myapp.tasks.foo".
2. An exception will be raised when attempting to register a task function with
the same module + name.

Together, these changes are intended to fix problems described in 386.

Because these changes will impact the serialization (and deserialization) of
messages, **it is important that you consume all tasks (including scheduled
tasks) before upgrading**.

**Always-eager mode changes**

In order to provide a more consistent API, tasks enqueued using `always_eager`
mode will now return a dummy `TaskResultWrapper` implementation that wraps the
return value of the task. This change is designed to provide the same API for
reading task result values, regardless of whether you are using always-eager
mode or not.

Previously, tasks executed with `always_eager` would return the Python value
directly from the task. When using Huey with the consumer, though, task results
are not available immediately, so a special wrapper `TaskResultWrapper` is
returned, which provides helper methods for retrieving the return value of the
task. Going forward, `always_eager` tasks will return `EagerTaskResultWrapper`,
which implements the same `get()` API that is typically used to retrieve task
return values.

[View commits](https://github.com/coleifer/huey/compare/1.10.5...1.11.0)

* Compatibility with redis-py 3.0, updated requirements / dependencies.
* Add pre-/post- hooks into the djhuey namespace.

[View commits](https://github.com/coleifer/huey/compare/1.10.4...1.10.5)

* Log time taken to execute tasks at default log level.
* Fix missing import in SQLite storage backend.
* Small refactoring in Redis storage backend to make it easier to override the
driver / client implementation.
* Fix failing tests for simpledb storage backend.

[View commits](https://github.com/coleifer/huey/compare/1.10.3...1.10.4)

* Fixed regression where in *always eager* mode exceptions within tasks were
being swallowed instead of raised.
* Added an API for registering hooks to run when each worker process starts-up.
This simplifies creating global/process-wide shared resources, such as a
connection pool or database client. [Documentation](https://huey.readthedocs.io/en/latest/api.html#Huey.on_startup).

[View commits](https://github.com/coleifer/huey/compare/1.10.2...1.10.3)

* More granular "extras" installation options.

[View commits](https://github.com/coleifer/huey/compare/1.10.1...1.10.2)