httk.store.backend.mongo.leases¶

Cross-process writer and fsck leases for httk.store.backend.mongo.

The lease protocol deliberately uses MongoDB’s server clock. A writer first inserts itself and only then looks for the fsck singleton; fsck does the opposite half of that handshake by installing the singleton before draining fresh writers.

Exceptions¶

`StoreLockedError`	An fsck lease or a live writer prevents the requested operation.
`LeaseLostError`	A lease owner tried to refresh after its lease was displaced.

Classes¶

`LeaseTiming`	Server-clock lease timings.
`Lease`	Shared lease state and heartbeat operations for writer and fsck leases.
`WriterLease`	A writer registration plus the generation seen during acquisition.
`FsckLease`	The singleton fsck exclusion lease.

Functions¶

`acquire_writer`(database, *[, timing])	Insert a writer lease, then check fsck and observe the layout generation.
`acquire_fsck`(database, *[, force, timing])	Install the fsck singleton and drain fresh writer registrations.
`clear_stale_lock`(database, *[, timing])	Clear a stale fsck lock after an administrator verified its owner died.

Module Contents¶

exception httk.store.backend.mongo.leases.StoreLockedError¶

Bases: RuntimeError

An fsck lease or a live writer prevents the requested operation.

exception httk.store.backend.mongo.leases.LeaseLostError¶

Bases: StoreLockedError

A lease owner tried to refresh after its lease was displaced.

class httk.store.backend.mongo.leases.LeaseTiming¶

Server-clock lease timings.

Parameters:

refresh_interval – Maximum normal interval between heartbeats.
stale_multiplier – Number of refresh intervals before a writer is stale.
poll_initial – Initial fsck writer-drain sleep.
poll_max – Maximum fsck writer-drain sleep.

refresh_interval: float = 2.0¶

stale_multiplier: int = 4¶

poll_initial: float = 0.02¶

poll_max: float = 0.25¶

property stale_after: float¶

Return the age after which a writer heartbeat is stale.

class httk.store.backend.mongo.leases.Lease¶

Shared lease state and heartbeat operations for writer and fsck leases.

database: Any¶

identifier: str¶

owner: str¶

timing: LeaseTiming¶

refresh_heartbeat(*, force=False)¶

Refresh this lease using MongoDB’s $$NOW server timestamp.

release()¶

Remove this process’s lease document.

class httk.store.backend.mongo.leases.WriterLease¶

Bases: Lease

A writer registration plus the generation seen during acquisition.

generation: int = 0¶

class httk.store.backend.mongo.leases.FsckLease¶

Bases: Lease

The singleton fsck exclusion lease.

httk.store.backend.mongo.leases.acquire_writer(database, *, timing=DEFAULT_TIMING)¶

Insert a writer lease, then check fsck and observe the layout generation.

The ordering is the writer half of the insert-then-check handshake. A stale fsck lease intentionally still blocks writers: clearing it is an explicit administrative assertion that its owner is dead.

httk.store.backend.mongo.leases.acquire_fsck(database, *, force=False, timing=DEFAULT_TIMING)¶

Install the fsck singleton and drain fresh writer registrations.

force may replace a pre-existing fsck lease and may proceed past stale writer residue. It is an administrative assertion that those owners are dead; using it against a still-running owner can corrupt the store.

httk.store.backend.mongo.leases.clear_stale_lock(database, *, timing=DEFAULT_TIMING)¶

Clear a stale fsck lock after an administrator verified its owner died.

This has no fencing: clearing a merely slow fsck can corrupt the store.