EVOLUTION-MANAGER

Edit File: filelock.py

# Copyright 2010 Matt Chaput. All rights reserved.
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"""
This module contains classes implementing exclusive locks for platforms with
fcntl (UNIX and Mac OS X) and Windows. Whoosh originally used directory
creation as a locking method, but it had the problem that if the program
crashed the lock directory was left behind and would keep the index locked
until it was cleaned up. Using OS-level file locks fixes this.
"""

import errno
import os
import sys
import time

def try_for(fn, timeout=5.0, delay=0.1):
    """Calls ``fn`` every ``delay`` seconds until it returns True or
    ``timeout`` seconds elapse. Returns True if the lock was acquired, or False
    if the timeout was reached.

:param timeout: Length of time (in seconds) to keep retrying to acquire the
        lock. 0 means return immediately. Only used when blocking is False.
    :param delay: How often (in seconds) to retry acquiring the lock during
        the timeout period. Only used when blocking is False and timeout > 0.
    """

until = time.time() + timeout
    v = fn()
    while not v and time.time() < until:
        time.sleep(delay)
        v = fn()
    return v

class LockBase(object):
    """Base class for file locks.
    """

def __init__(self, filename):
        self.fd = None
        self.filename = filename
        self.locked = False

def __del__(self):
        if hasattr(self, "fd") and self.fd:
            try:
                self.release()
            except:
                pass

def acquire(self, blocking=False):
        """Acquire the lock. Returns True if the lock was acquired.

:param blocking: if True, call blocks until the lock is acquired.
            This may not be available on all platforms. On Windows, this is
            actually just a delay of 10 seconds, rechecking every second.
        """
        pass

def release(self):
        pass

class FcntlLock(LockBase):
    """File lock based on UNIX-only fcntl module.
    """

def acquire(self, blocking=False):
        import fcntl  # @UnresolvedImport

flags = os.O_CREAT | os.O_WRONLY
        self.fd = os.open(self.filename, flags)

mode = fcntl.LOCK_EX
        if not blocking:
            mode |= fcntl.LOCK_NB

try:
            fcntl.flock(self.fd, mode)
            self.locked = True
            return True
        except IOError:
            e = sys.exc_info()[1]
            if e.errno not in (errno.EAGAIN, errno.EACCES):
                raise
            os.close(self.fd)
            self.fd = None
            return False

def release(self):
        if self.fd is None:
            raise Exception("Lock was not acquired")

import fcntl  # @UnresolvedImport
        fcntl.flock(self.fd, fcntl.LOCK_UN)
        os.close(self.fd)
        self.fd = None

class MsvcrtLock(LockBase):
    """File lock based on Windows-only msvcrt module.
    """

def acquire(self, blocking=False):
        import msvcrt  # @UnresolvedImport

flags = os.O_CREAT | os.O_WRONLY
        mode = msvcrt.LK_NBLCK
        if blocking:
            mode = msvcrt.LK_LOCK

self.fd = os.open(self.filename, flags)
        try:
            msvcrt.locking(self.fd, mode, 1)
            return True
        except IOError:
            e = sys.exc_info()[1]
            if e.errno not in (errno.EAGAIN, errno.EACCES, errno.EDEADLK):
                raise
            os.close(self.fd)
            self.fd = None
            return False

def release(self):
        import msvcrt  # @UnresolvedImport

if self.fd is None:
            raise Exception("Lock was not acquired")
        msvcrt.locking(self.fd, msvcrt.LK_UNLCK, 1)
        os.close(self.fd)
        self.fd = None

if os.name == "nt":
    FileLock = MsvcrtLock
else:
    FileLock = FcntlLock