yyds-lock

中文文档

yyds-lock is a lightweight, zero-dependency Python library for single-instance execution of cooperating scripts, processes, threads, and asyncio tasks using operating-system advisory file locks. It is designed for cron jobs, automation scripts, schedulers, and local background daemons.

Key Features

• 🛡️ Immunity to Crashes / Force Kills: Unlike PID files or stale lock files that cause permanent lockups if a process is terminated forcefully (kill -9, crash, or power loss), yyds-lock binds the lock to the process file descriptor. The OS automatically and instantly releases the lock as soon as the process ends.
• 🪶 Zero Dependencies: 100% Python standard library with no runtime packages to install.
• 🎛️ Dual Modes: Supports both "Instant Exit" (non-blocking, terminates immediately if another instance is running) and "Queue / Wait" (blocking, waits for the existing instance to finish).
• 🧵 Thread-Safety & Isolation: Safe to use in multi-threaded programs. Different threads running under the same process are isolated and will block or raise conflicts on the same lock.
• ⚡ Async-Safe Waiting: force_single_async and asynchronous decorators wait without blocking the event loop and support finite timeouts.
• 🔱 Fork-Safety: Coordinates registry mutations with Unix fork() and closes both acquired and in-flight inherited descriptors in the child without unlocking the parent.
• 📁 Inaccessible Directory Fallback: If the home directory is read-only or unavailable, bare lock names fall back to a private per-user directory under the system temporary directory. An explicit base_dir never silently moves.
• 🧹 Automatic Cleanup: Registers an atexit cleanup hook to close file descriptors cleanly on interpreter shutdown, preventing python ResourceWarning.
• 💻 Cross-Platform: Seamlessly works on Linux, macOS (using fcntl.flock), and Windows (using msvcrt.locking).

Installation

pip install -U yyds-lock

Usage

You can protect your script using any of the following approaches:

Pattern A: Direct Call (Best for straightforward scripts / entrypoints)

Place this call at the very top of your entrypoint script. If another instance of the script is already running, the new instance will immediately print an error and exit with status code 1.

import time
import yyds_lock

# Force single-instance execution.
yyds_lock.force_single(lock_name="my_automation.lock", block=False)

print("Running heavy automation task...")
time.sleep(300)

Pattern B: Decorator with Dynamic Lock Names

Decorate your functions to enforce mutual exclusion. The lock_name parameter can also be a callable (e.g. lambda function) that dynamically generates the lock name based on function arguments.

import yyds_lock

# 1. Static lock name
@yyds_lock.single_decorator(lock_name="my_task.lock", block=False)
def main():
    print("Executing single instance task safely...")

# 2. Dynamic lock name based on arguments
@yyds_lock.single_decorator(lock_name=lambda job_id: f"job_{job_id}.lock", block=False)
def process_job(job_id):
    print(f"Processing job {job_id} exclusively...")

if __name__ == "__main__":
    main()
    process_job(42)

Pattern C: Handle Lock Conflict (Exception Raising)

If you prefer to handle the locking failure programmatically (e.g., to perform custom cleanups, log warnings, or run fallback logic) instead of immediately terminating the process, set raise_on_conflict=True to raise AlreadyLockedError:

import yyds_lock
from yyds_lock import AlreadyLockedError

try:
    yyds_lock.force_single(lock_name="my_automation.lock", block=False, raise_on_conflict=True)
except AlreadyLockedError:
    print("Failed to acquire lock. Running fallback script instead...")
    # Add custom fallback actions here

Operational failures such as permission errors or unsupported filesystem locking raise LockOperationError rather than being misreported as lock contention.

Pattern D: Context Manager

Use SingleInstanceLock when the lock should have an explicit lexical lifetime:

from yyds_lock import SingleInstanceLock

with SingleInstanceLock("my_task.lock", raise_on_conflict=True):
    run_task()

The decorator also preserves the lock for the full lifetime of coroutine, generator, and async-generator functions. Asynchronous decorators safely support block=True without blocking the event loop.

Pattern E: Async Waiting with a Timeout

Use force_single_async directly from the Task that will eventually release the lock:

from yyds_lock import LockTimeoutError, force_single_async, release_single

async def run_job():
    try:
        await force_single_async("my_async_job.lock", timeout=10)
    except LockTimeoutError:
        return

    try:
        await do_work()
    finally:
        release_single("my_async_job.lock")

Do not acquire in an executor and release from the event-loop Task: lock ownership belongs to the Thread or Task that performed the acquisition. If an executor is required, the complete acquire/work/release scope must run in one executor call.

Configuration / Arguments

force_single and single_decorator share the following core arguments:

• lock_name (str or os.PathLike): The filename/path of the lock. single_decorator additionally accepts a callable that returns the lock name from the decorated function's arguments.
  • If a simple filename is given (e.g. "my_job.lock"), it is automatically created in a hidden directory .yyds_lock under the user's home directory (~/.yyds_lock).
  • If an absolute or relative path is given (e.g., "/var/run/my_job.lock"), it is created at that specific path. The parent directories will be created automatically if they do not exist.
• block (bool):
  • False (default): Exit immediately (or raise) if the lock cannot be acquired.
  • True: Block and queue, waiting for the active process/thread to finish and release the lock.
• raise_on_conflict (bool):
  • False (default): Immediately log an error and call sys.exit(1) when the lock is already held.
  • True: Raise AlreadyLockedError when the lock is already held, allowing the caller to catch it.
• base_dir (str or os.PathLike, optional): Overrides the default folder (~/.yyds_lock) for simple filenames. Failure to use an explicit directory raises LockOperationError; it is not silently replaced.

force_single_async accepts lock_name and base_dir plus:

• timeout (float or None): Maximum wait in seconds. None waits indefinitely; expiration raises LockTimeoutError.
• poll_interval (float): Delay between non-blocking attempts, defaulting to 0.05 seconds.

For coroutine and async-generator decorators, timeout and poll_interval configure async waiting when block=True.

Logging

yyds-lock uses Python's standard logging library. All lock conflicts and warning outputs are logged using:

import logging
logger = logging.getLogger("yyds_lock")

If an effective handler is configured, conflicts are emitted once through logging. Otherwise, yyds-lock prints one message to sys.stderr (colored only when stderr is a terminal).

How It Works Under the Hood

1. Linux / macOS: Uses fcntl.flock(fd, fcntl.LOCK_EX) for exclusive advisory locking.
2. Windows: Uses interruptible polling around msvcrt.LK_NBLCK to lock the first byte, giving block=True true wait-until-available behavior instead of the CRT's bounded retry window.
3. Thread / Task Safety: Tracks the owning live Thread or asyncio Task object, supports same-owner reentrancy, and serializes local path transitions before calling the OS lock.
4. Fork-Safety: Uses all three os.register_at_fork phases. A fork gate snapshots registry mutations, and the child replaces inherited synchronization primitives after closing acquired and in-flight descriptors.
5. Clean Reclamation: Locks are released when:
   • An explicit release_single call is executed.
   • The decorated function finishes execution.
   • Python exit handlers run (atexit).
   • The process terminates or is killed, prompting the operating system to reclaim all file descriptors and release the locks.

Scope and Limitations

• Locks are advisory: every participant must cooperate by locking the same canonical file path.
• Mutual exclusion is local to processes that share the same underlying filesystem. Separate containers, hosts, or non-shared temporary directories require a distributed lock instead.
• Network filesystems may implement flock differently; validate the target filesystem before relying on it for critical coordination.
• sys.exit(1) raises SystemExit in the calling execution context. In libraries and worker threads, raise_on_conflict=True is usually the safer integration mode.