# Optional mutex implementation.

from struct import pack, unpack

# This controls how big our mutex handles are.
encoded_format = "=L"

# These are all determined by encoded_format, don't touch.

encoded_length = len(pack(encoded_format, 0))
encoded_type   = CK_BYTE * encoded_length
handle_max     = unpack(encoded_format, chr(0xff) * encoded_length)[0]

class Mutex(object):

  def __init__(self, handle):
    from threading import Lock
    self.encoded = encoded_type(*handle)
    self.lock    = Lock()

def p11_callback(func):
  from threading import ThreadError
  def wrapper(self, arg):
    try:
      func(self, arg)
    except ThreadError:
      return CKR_MUTEX_NOT_LOCKED
    except:
      return CKR_FUNCTION_FAILED
    else:
      return CKR_OK
  return wrapper

class MutexDB(object):

  def __init__(self):
    self.mutexes = {}
    self.next_handle = 0

  def find_free_handle(self):
    if len(self.mutexes) > handle_max:
      raise RuntimeError
    while self.next_handle in self.mutexes:
      self.next_handle = (self.next_handle + 1) & handle_max
    return pack(encoded_format, self.next_handle)

  @p11_callback
  def create(self, handle_ptr):
    handle = self.find_free_handle()
    self.mutexes[handle] = self.mutex_type(handle)
    handle_ptr[0] = self.mutexes[handle].encoded

  @p11_callback
  def destroy(self, handle):
    del self.mutexes[handle[:encoded_length]]

  @p11_callback
  def lock(self, handle):
    self.mutexes[handle[:encoded_length]].lock.acquire()

  @p11_callback
  def unlock(self, handle):
    self.mutexes[handle[:encoded_length]].lock.release()