1 # lock.py - simple locking scheme for mercurial

     2 #

     3 # Copyright 2005 Matt Mackall <mpm@selenic.com>

     4 #

     5 # This software may be used and distributed according to the terms

     6 # of the GNU General Public License, incorporated herein by reference.

     7 

     8 import os, time

     9 

    10 class LockHeld(Exception):

    11     pass

    12 

    13 class lock:

    14     def __init__(self, file, wait = 1):

    15         self.f = file

    16         self.held = 0

    17         self.wait = wait

    18         self.lock()

    19 

    20     def __del__(self):

    21         self.release()

    22 

    23     def lock(self):

    24         while 1:

    25             try:

    26                 self.trylock()

    27                 return 1

    28             except LockHeld, inst:

    29                 if self.wait:

    30                     time.sleep(1)

    31                     continue

    32                 raise inst

    33         

    34     def trylock(self):

    35         pid = os.getpid()

    36         try:

    37             os.symlink(str(pid), self.f)

    38             self.held = 1

    39         except:

    40             raise LockHeld(os.readlink(self.f))

    41 

    42     def release(self):

    43         if self.held:

    44             self.held = 0

    45             os.unlink(self.f)

    46