"lockfile" Module in Python, When and how to use that

The lockfile module in Python provides a simple way to lock files and ensure that only one process or thread can access the file at a time. This is useful for preventing race conditions and ensuring that multiple processes or threads don't interfere with each other.

To install lockfile

pip install lockfile

A Simple Example:

import lockfile

lock = lockfile.FileLock("file.lock")

try:
    lock.acquire(timeout=10)
    # Access the file here
    with Open("file.txt", "w") as f:
        # Do your write operation
finally:
    lock.release()

Here, You can name your lockfile anything you want, in our case, it is file.lock. This file will temporally create while acquiring the lock and it will automatically deleted after releasing the lock.

Another example of how you can use the lockfile module to lock a file for a specific duration:

import time
from lockfile import FileLock

lock = FileLock("file.lock")

with lock:
    # Access the file here
    with Open("file.txt", "w") as f:
        # Do your write operation
    time.sleep(10)

Another example (without lockfile) of how two Python scripts can write to the same file simultaneously and cause a race condition:

# Script 1
with open("samefile.txt", "w") as f:
    for line in range(10):
        f.write(f"Script 1: Line {line} \n")

# Script 2
with open("samefile.txt", "w") as f:
    for line in range(10):
        f.write(f"Script 2: Line {line} \n")

Here, both scripts open the file samefile.txt using the with statement and write 10 lines of text to the file. However, since both scripts open the file in write mode ("w"), they overwrite each other's changes and only one set of lines is written to the file. This is an example of a race condition, as the outcome of the scripts depends on which one finishes first.

To prevent this race condition, you can use a lock file to ensure that only one script can write to the file at a time:

import lockfile

# Script 1
lock = lockfile.FileLock("file.lock")
with lock:
    with open("samefile.txt", "a") as f:
        for line in range(10):
            f.write(f"Script 1: Line {line} \n")

# Script 2
lock = lockfile.FileLock("file.lock")
with lock:
    with open("samefile.txt", "a") as f:
        for line in range(10):
            f.write(f"Script 2: Line {line} \n")

Here, both scripts use the lockfile module to lock the file file.lock before writing to the file samefile.txt. The with statement is used to obtain the lock and automatically release it after the protected code has executed. This ensures that only one script can write to the file at a time and prevents the race condition.

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