Synchronizing Repositories with the async-Pipeline¶
To accomplish the steps outlined in Synchronizing in an efficient way, pulp provides a high
level api to construct a pipeline of stages. Those stages work in parallel like an assembly line
using pythons async feature in combination with the asyncio library. Each stage takes
designated content units from an incoming queue of type
asyncio.Queue and performes an
individual task on them before passing them to the outgoing queue that is connected to the next
The anathomy of a stage is that it inherits
pulpcore.plugin.stages.Stage and overwrites
its asynchronous callback
run() it can retrieve incoming declarative content individually via the asynchronous
self.items() or in batches via
It can pass on declarative content with
The sync pipeline is headed by a first_stage, that is supposed to download upstream metadata
and iterate over all upstream content references. For each such reference, it creates a
pulpcore.plugin.stages.DeclarativeContent that contains a prefilled but unsaved instance
of a subclass of
pulpcore.plugin.content.Content, as well as a list of
pulpcore.plugin.stages.DeclarativeArtifact. The latter combine an unsaved instance of
pulpcore.plugin.content.Artifact with a url to retrieve it.
pulpcore.plugin.stages.DeclarativeContent objects, that describe, what a content will
look like when properly downloaded and saved to the database, are passed one by one to the next
The responsibility of providing this first_stage lies completely in the plugins domain, since
this is the part of the pipeline specific to the repository type.
The pulp plugin api provides the following stages which also comprise the default pipeline in the following order:
If the mirror=True optional parameter is passed to DeclarativeVersion the pipeline also runs
pulpcore.plugin.stages.ContentUnassociation at the end.
Multiple level discovery¶
Plugins like pulp_deb and pulp_container use content artifacts to enumerate more content.
To support this pattern, the declarative content allows to be associated with a
asyncio.Future, that is resolved when the content reaches the
By awaiting this Future, one can implement an informational back loop into earlier stages.
In order to prevent deadlocks, be sure that you mark the declarative content with does_batch=False, and that you do not drop it without resolving the future.
If you need downloaded artifacts of this content for further discovery, make sure to
provide deferred_download=False to the