Source Code for Module dimer.filelock

  1  # Copyright (c) 2009, Evan Fosmark 
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 27    
 28  import os 
 29  import time 
 30  import errno 
 31    
 32 -class FileLockException(Exception): 
 33      pass 
 34    
 35 -class FileLock(object): 
 36      """ A file locking mechanism that has context-manager support so  
 37          you can use it in a with statement. This should be relatively cross 
 38          compatible as it doesn't rely on msvcrt or fcntl for the locking. 
 39      """ 
 40    
 41 -    def __init__(self, file_name, timeout=10, delay=.05): 
 42          """ Prepare the file locker. Specify the file to lock and optionally 
 43              the maximum timeout and the delay between each attempt to lock. 
 44          """ 
 45          self.is_locked = False 
 46          self.lockfile = os.path.join(os.getcwd(), "%s.lock" % file_name) 
 47          self.file_name = file_name 
 48          self.timeout = timeout 
 49          self.delay = delay 
 50    
 51    
 52 -    def acquire(self): 
 53          """ Acquire the lock, if possible. If the lock is in use, it check again 
 54              every `wait` seconds. It does this until it either gets the lock or 
 55              exceeds `timeout` number of seconds, in which case it throws  
 56              an exception. 
 57          """ 
 58          start_time = time.time() 
 59          while True: 
 60              try: 
 61                  self.fd = os.open(self.lockfile, os.O_CREAT|os.O_EXCL|os.O_RDWR) 
 62                  break; 
 63              except OSError as e: 
 64                  if e.errno != errno.EEXIST: 
 65                      raise  
 66                  if (time.time() - start_time) >= self.timeout: 
 67                      raise FileLockException("Timeout occured.") 
 68                  time.sleep(self.delay) 
 69          self.is_locked = True 
 70    
 71    
 72 -    def release(self): 
 73          """ Get rid of the lock by deleting the lockfile.  
 74              When working in a `with` statement, this gets automatically  
 75              called at the end. 
 76          """ 
 77          if self.is_locked: 
 78              os.close(self.fd) 
 79              os.unlink(self.lockfile) 
 80              self.is_locked = False 
 81    
 82    
 83 -    def __enter__(self): 
 84          """ Activated when used in the with statement.  
 85              Should automatically acquire a lock to be used in the with block. 
 86          """ 
 87          if not self.is_locked: 
 88              self.acquire() 
 89          return self 
 90    
 91    
 92 -    def __exit__(self, type, value, traceback): 
 93          """ Activated at the end of the with statement. 
 94              It automatically releases the lock if it isn't locked. 
 95          """ 
 96          if self.is_locked: 
 97              self.release() 
 98    
 99    
100 -    def __del__(self): 
101          """ Make sure that the FileLock instance doesn't leave a lockfile 
102              lying around. 
103          """ 
104          self.release() 
105