Source code for duck.utils.filelock

"""
File lock capabilities module.
"""

import os
import time
import platform


if platform.system() == "Windows":
    import msvcrt
else:
    try:
        import fcntl
    except ImportError:
        fcntl = None




def lock_file(file_descriptor, retries=5, wait=1):
    """
    Lock file when modifying or accessing critical sections to avoid race conditions.
    """
    if platform.system() == "Windows":
        for _ in range(retries):
            try:
                msvcrt.locking(
                    file_descriptor.fileno(),
                    msvcrt.LK_NBLCK,
                    os.path.getsize(file_descriptor.name),
                )
                return
            except OSError:
                time.sleep(wait)
        raise BlockingIOError(
            f"Could not acquire lock after {retries} retries")
    else:
        if not fcntl:
            return
        for _ in range(retries):
            try:
                fcntl.flock(file_descriptor, fcntl.LOCK_EX | fcntl.LOCK_NB)
                return
            except OSError:
                # Maybe the function is not implemented
                pass
            except BlockingIOError:
                time.sleep(wait)
        raise BlockingIOError(
            f"Could not acquire lock after {retries} retries")





def unlock_file(file_descriptor):
    """
    Unlock a locked file.
    """
    if platform.system() == "Windows":
        msvcrt.locking(
            file_descriptor.fileno(),
            msvcrt.LK_UNLCK,
            os.path.getsize(file_descriptor.name),
        )
    else:
        try:
            fcntl.flock(file_descriptor, fcntl.LOCK_UN)
        except OSError:
            # Maybe the function is unimplemented
            pass





def open_and_lock(filename, mode="r+", failsafe: bool = True):
    """
    Opens a file and acquires an exclusive lock.

    Args:
        filename: The name of the file to open.
        mode: The file open mode (default is 'r+').
        failsafe: Whether to continue if file locking fails.
        
    Returns:
        The opened file object.
    """
    fd = open(filename, mode)
    
    try:
        lock_file(fd)
    except Exception as e:
        if not failsafe:
            raise e # Reraise exception
    
    # Return the file descriptor
    return fd