configurable-redlock 1.0.0

Simplified Redlock API with configurable TTL and silent exception handling for deadlock prevention

configurable-redlock

A Python distributed lock built on top of pottery's Redlock implementation. It wraps pottery's Redlock with a simpler timeout API and adds two features that pottery cannot provide natively: silent skip (skip a with block body without try/except) and waiting statistics (Redis counters tracking how many processes are waiting per lock key).

Features

• Distributed locking via Redis — uses pottery's Redlock algorithm, safe across multiple processes and machines, with automatic TTL (auto_release_time, default 30 s) to prevent deadlocks on process crash.
• Simple timeout API — one timeout parameter: 0 = wait forever, -1 = skip if locked, N = wait up to N seconds.
• Silent skip — cl() + silence_object_lock_timeout=True skips the block body without try/except when the lock is not acquired.
• Waiting statistics — while a process waits for the lock, the number of waiters and the set of contended lock keys are tracked in Redis, allowing external monitoring of lock contention.
• Configurable Redis client — pass a single redis.Redis client or an iterable of clients for true multi-master Redlock quorum. Defaults to redis.Redis().
• Async support — ConfigurableAIOREDLock provides the same API for async with / await usage.

Documentation

Full documentation: https://docs.velis.si/configurable-redlock.html

Why not just use pottery's Redlock?

pottery's Redlock already covers distributed locking with TTL, timeout, and skip-if-taken. The two things ConfigurableREDLock adds are a cleaner API for single-Redis setups (one timeout parameter instead of context_manager_blocking + context_manager_timeout) and two features pottery cannot provide:

1. Silent skip — skip the with block body without a try/except around it (see below)
2. Waiting statistics — Redis counters tracking how many processes are waiting per lock key

The cl() call exists solely to enable silent skip: Python's context manager protocol does not allow __enter__ to skip the block body, and raising from __enter__ prevents __exit__ from running, which means the exception can never be silenced. By deferring the raise to cl() inside the block, __exit__ always runs and can swallow the exception.

Comparison with pottery Redlock

Timeout

pottery:

from pottery import Redlock
from pottery.exceptions import QuorumNotAchieved

try:
    with Redlock(key='res', masters={redis}, context_manager_blocking=True, context_manager_timeout=5):
        do_work()
except QuorumNotAchieved:
    pass  # lock not acquired within 5 seconds

ConfigurableREDLock:

from configurable_redlock import ConfigurableREDLock, ObjectLockTimeout

try:
    with ConfigurableREDLock(name='res', timeout=5) as cl:
        cl()
        do_work()
except ObjectLockTimeout:
    pass  # lock not acquired within 5 seconds

Silent skip (no try/except)

pottery — not possible without try/except:

from pottery.exceptions import QuorumNotAchieved

try:
    with Redlock(key='res', masters={redis}, context_manager_blocking=False):
        do_work()
except QuorumNotAchieved:
    pass  # must always handle explicitly

ConfigurableREDLock:

with ConfigurableREDLock(name='res', timeout=-1, silence_object_lock_timeout=True) as cl:
    cl()      # silently skips everything below if lock not acquired — no try/except needed
    do_work()

---

Installation

pip install configurable-redlock

Usage

from configurable_redlock import ConfigurableREDLock

ConfigurableREDLock is used as a context manager. The timeout parameter controls what happens when the lock is already held by another process.

timeout=0 — wait forever

The process blocks until the lock becomes available. No cl() call is needed.

with ConfigurableREDLock(name="my-resource") as cl:
    # lock is always acquired here
    do_work()

timeout=-1 — skip if locked

The idiomatic way to use timeout=-1 is together with silence_object_lock_timeout=True. With this combination, cl() raises ObjectLockTimeout when the lock is not acquired, and the exception is silently swallowed on exit — no try/except needed, the rest of the block is simply skipped.

with ConfigurableREDLock(name="my-resource", timeout=-1, silence_object_lock_timeout=True) as cl:
    cl()        # skips everything below if lock was not acquired
    do_work()

Moving cl() down allows some code to run before the skip — useful for logging that the context was entered regardless of whether the lock was acquired:

with ConfigurableREDLock(name="my-resource", timeout=-1, silence_object_lock_timeout=True) as cl:
    log.debug("entered my-resource block")
    cl()        # skips everything below if lock was not acquired
    do_work()

If you need to distinguish the "skipped" case from success, catch ObjectLockTimeout explicitly instead of using silence_object_lock_timeout:

from configurable_redlock import ObjectLockTimeout

try:
    with ConfigurableREDLock(name="my-resource", timeout=-1) as cl:
        cl()
        do_work()
except ObjectLockTimeout:
    log.debug("skipped: lock already held")

timeout=N — wait up to N seconds

The process waits at most N seconds. Call cl() as the first line — it raises ObjectLockTimeout if the lock could not be acquired within the given time.

from configurable_redlock import ObjectLockTimeout

try:
    with ConfigurableREDLock(name="my-resource", timeout=5) as cl:
        cl()  # raises ObjectLockTimeout if N seconds elapsed without acquiring
        do_work()
except ObjectLockTimeout:
    pass  # could not acquire within 5 seconds

Why is cl() needed for non-zero timeouts? Python's context manager protocol does not allow __enter__ to skip the body of a with block. Calling cl() as the first statement is the mechanism that skips the rest of the block when the lock was not acquired — it raises ObjectLockTimeout, which immediately exits the block. If you forget the call entirely, exiting the with block raises NoTimeoutCheck as a reminder.

Silencing ObjectLockTimeout on exit

If you want ObjectLockTimeout raised inside the block to not propagate out:

with ConfigurableREDLock(name="my-resource", timeout=-1, silence_object_lock_timeout=True) as cl:
    cl()
    raise ObjectLockTimeout()  # swallowed on exit

Parameters

Parameter	Default	Description
name	required	Lock identifier. Stored in Redis as ConfigurableLock.<name>.
timeout	0	0 = wait forever, -1 = skip if locked, N = wait up to N seconds.
auto_release_time	30.0	Lock TTL in seconds. The lock is automatically released after this time, preventing deadlocks if the process crashes.
silence_object_lock_timeout	False	If True, an ObjectLockTimeout raised inside the with block is suppressed on exit.
stats_name	name	Override the name used for waiting-process statistics in Redis.
redis_client	redis.Redis()	A single Redis client or an iterable of clients for multi-master Redlock. Defaults to a localhost connection.

Waiting statistics

While a process waits to acquire the lock, ConfigurableREDLock tracks the number of waiting processes in Redis:

• Waiting.ConfigurableLock.<name> — a counter of currently waiting processes
• ConfigurableLockKeys — a Redis list of all keys that have ever had waiters

This allows external monitoring of lock contention.

Exceptions

Exception	When raised
ObjectLockTimeout	Raised by cl() when the lock was not acquired (timeout=-1 or timeout=N expired).
NoTimeoutCheck	Raised on __exit__ when timeout != 0 and cl() was never called inside the block.