Follower¶

Follower(live=False)

A reader that follows a form of logs live, one state per tree (streaming.md, Following a log).

receive(event) says what it did with each: "kept" (the next event), "duplicate", "stale" (a writer the log has left behind), "rewind" (a later writer continued the log from an event this reader holds: it drops what it has after that event, keeps the rest, and takes this one), "loss" (events were lost: resume from a source) or "unknown-format" (it stops following). It keeps the events it holds, since it may have to rewind; forget(tree) lets a tree go.

live=True: it follows a live form (the whole log, or a view of it that may show values the kept form lacks), given each event by the process of the event's writer; such a form it resumes in place only from the process that gave it every event it holds. The kept form (the default) is the same from every source.

Methods¶

can_resume_from¶

Follower.can_resume_from(tree, source)

Whether reading source after its last event keeps what it holds true: the source can give every event it holds, as it holds it (streaming.md, Resuming). source.writer is the writer whose process it is, or None for a store.

events¶

Follower.events(tree)

The events it holds of a tree, in order (copies).

forget¶

Follower.forget(tree)

Let a tree go: its events and state (a long-lived reader forgets the trees it is done with).

resume¶

Follower.resume(tree, source)

Read a tree again from source (anything with read(tree, after)): after its last event when it may resume in place, from the beginning when it may not or the source says event-unknown. Returns its reads, each (after, the events read or the EventRefused). It stops at an event of a format it does not know, as when following.

state¶

Follower.state(tree)

The replay of what it holds of a tree: {"calls", "finished"}.