lacing.store.locking

Named exclusive locks for stores: the mechanisms behind store.lock(key).

IntervalAnnotationStore.lock(key) is an exclusive context manager scoped to one store (for PostgresStore: one (owner, project)). Each backend picks the narrowest mechanism that excludes every holder that can reach the same data: a process-local lock for MemoryStore, a file lock beside the database for SqliteStore (excludes other processes on the host too), a Postgres advisory lock for PostgresStore (excludes other hosts).

Locks are not re-entrant: taking a lock you already hold blocks forever.

Module Attributes

KEY_DIGEST_BYTES

Bytes of the blake2b digest used to name a key (file name / advisory id).

Functions

advisory_lock_id(*parts)	A signed 64-bit integer for parts: the argument of pg_advisory_lock.
file_lock(path)	Exclusive lock on path (created if missing), held for the with block.
key_digest(*parts)	Stable digest of parts (length-prefixed, so ("a", "bc") != ("ab", "c")).
sidecar_lock_path(db_path, key)	Lock file for key beside the database at db_path.

Classes

NamedLocks()

Process-local named exclusive locks (a registry of threading.Lock).

lacing.store.locking.KEY_DIGEST_BYTES = 8

Bytes of the blake2b digest used to name a key (file name / advisory id).

class lacing.store.locking.NamedLocks

Bases: object

Process-local named exclusive locks (a registry of threading.Lock).

lacing.store.locking.advisory_lock_id(*parts)

A signed 64-bit integer for parts: the argument of pg_advisory_lock.

Return type:

int

>>> advisory_lock_id("o", "p", "k") == advisory_lock_id("o", "p", "k")
True
>>> advisory_lock_id("o", "p", "k") != advisory_lock_id("o", "p", "other")
True
>>> -2**63 <= advisory_lock_id("o", "p", "k") < 2**63
True

lacing.store.locking.file_lock(path)

Exclusive lock on path (created if missing), held for the with block.

A fresh file descriptor per call, so threads of one process exclude each other as well as other processes. The kernel drops the lock if the holder dies. The lock file is left in place (removing it would race a waiter).

Return type:

Iterator[None]

lacing.store.locking.key_digest(*parts)

Stable digest of parts (length-prefixed, so ("a", "bc") != ("ab", "c")).

Return type:

bytes

lacing.store.locking.sidecar_lock_path(db_path, key)

Lock file for key beside the database at db_path.

Return type:

str