Source Code for Module instant.locking

  1  """File locking for the cache system, to avoid problems 
  2  when multiple processes work with the same module. 
  3  Only works on UNIX systems. 
  4   
  5  Two python libraries can be used: 
  6   
  7    flufl.lock : A nfs safe which can be downloaded from: 
  8   
  9                   https://launchpad.net/flufl.lock 
 10   
 11    fcntl      : A builtin Python module which only works on posix machines 
 12                 and it is does unfortunately not work on nfs 
 13   
 14  """ 
 15   
 16  __all__ = ["get_lock", "release_lock", "release_all_lock"] 
 17   
 18  import os.path 
 19  from .output import instant_error, instant_assert, instant_debug 
 20  from .paths import validate_cache_dir 
 21   
 22  try: 
 23      import flufl.lock 
 24      fcntl = None 
 25  except: 
 26      flufl = None 
 27      try: 
 28          import fcntl 
 29      except: 
 30          fcntl = None 
 31   
 32  # Keeping an overview of locks currently held, 
 33  # to avoid deadlocks within a single process. 
 34  _lock_names = {} # lock.fileno() -> lockname 
 35  _lock_files = {} # lockname -> lock 
 36  _lock_count = {} # lockname -> number of times this lock has been aquired and not yet released 
 37   
 38  if flufl: 
 39 -    def get_lock(cache_dir, module_name): 
 40          "Get a new file lock." 
 41           
 42          from flufl.lock import Lock 
 43          from datetime import timedelta 
 44           
 45          lockname = module_name + ".lock" 
 46          count = _lock_count.get(lockname, 0) 
 47           
 48          instant_debug("Acquiring lock %s, count is %d." % (lockname, count)) 
 49           
 50          cache_dir = validate_cache_dir(cache_dir) 
 51          lockname = os.path.join(cache_dir, lockname) 
 52          lock = Lock(lockname) 
 53          lock.lock() 
 54           
 55          return lock 
 56       
 57 -    def release_lock(lock): 
 58          "Release a lock currently held by Instant." 
 59          if lock.is_locked: 
 60              hostname, pid, lockname = lock.details 
 61              instant_debug("Releasing lock %s." % (lockname)) 
 62              lock.unlock() 
 63   
 64 -    def release_all_locks(): 
 65          pass 
 66   
 67  elif fcntl: 
 68 -    def get_lock(cache_dir, module_name): 
 69          "Get a new file lock." 
 70          global _lock_names, _lock_files, _lock_count 
 71           
 72          lockname = module_name + ".lock" 
 73          count = _lock_count.get(lockname, 0) 
 74           
 75          instant_debug("Acquiring lock %s, count is %d." % (lockname, count)) 
 76           
 77          if count == 0: 
 78              cache_dir = validate_cache_dir(cache_dir) 
 79              lock = open(os.path.join(cache_dir, lockname), "w") 
 80              fcntl.flock(lock.fileno(), fcntl.LOCK_EX) 
 81              _lock_names[lock.fileno()] = lockname 
 82              _lock_files[lockname] = lock 
 83          else: 
 84              lock = _lock_files[lockname] 
 85           
 86          _lock_count[lockname] = count + 1 
 87          return lock 
 88       
 89 -    def release_lock(lock): 
 90          "Release a lock currently held by Instant." 
 91          global _lock_names, _lock_files, _lock_count 
 92           
 93          lockname = _lock_names[lock.fileno()] 
 94          count = _lock_count[lockname] 
 95   
 96          instant_debug("Releasing lock %s, count is %d." % (lockname, count)) 
 97   
 98          instant_assert(count > 0, "Releasing lock that Instant is supposedly not holding.") 
 99          instant_assert(lock is _lock_files[lockname], "Lock mismatch, might be something wrong in locking logic.") 
100           
101          del _lock_files[lockname] 
102          del _lock_names[lock.fileno()] 
103          _lock_count[lockname] = count - 1 
104           
105          fcntl.flock(lock.fileno(), fcntl.LOCK_UN) 
106          lock.close() 
107       
108 -    def release_all_locks(): 
109          "Release all locks currently held by Instant." 
110          locks = list(_lock_files.values()) 
111          for lock in locks: 
112              release_lock(lock) 
113          instant_assert(all(_lock_count[lockname] == 0 for lockname in _lock_count), "Lock counts not zero after releasing all locks.") 
114   
115  else: 
116      # Windows systems have no fcntl, implement these otherwise if locking is needed on windows 
117 -    def get_lock(cache_dir, module_name): 
118          return None 
119       
120 -    def release_lock(lock): 
121          pass 
122   
123 -    def release_all_locks(): 
124          pass 
125