Python fcntl 模块，F_SETLKW 实例源码

def lock(self, cmd, owner, **kw):
            #return -EROFS
            # The code here is much rather just a demonstration of the locking
            # API than something which actually was seen to be useful.

            # Advisory file locking is pretty messy in Unix, and the Python
            # interface to this doesn't make it better.
            # We can't do fcntl(2)/F_GETLK from Python in a platfrom independent
            # way. The following implementation *might* work under Linux. 
            #
            # if cmd == fcntl.F_GETLK:
            #     import struct
            # 
            #     lockdata = struct.pack('hhQQi', kw['l_type'], os.SEEK_SET,
            #                            kw['l_start'], kw['l_len'], kw['l_pid'])
            #     ld2 = fcntl.fcntl(self.fd, fcntl.F_GETLK, lockdata)
            #     flockfields = ('l_type', 'l_whence', 'l_start', 'l_len', 'l_pid')
            #     uld2 = struct.unpack('hhQQi', ld2)
            #     res = {}
            #     for i in xrange(len(uld2)):
            #          res[flockfields[i]] = uld2[i]
            #  
            #     return fuse.Flock(**res)

            # Convert fcntl-ish lock parameters to Python's weird
            # lockf(3)/flock(2) medley locking API...
            op = { fcntl.F_UNLCK : fcntl.LOCK_UN,
                   fcntl.F_RDLCK : fcntl.LOCK_SH,
                   fcntl.F_WRLCK : fcntl.LOCK_EX }[kw['l_type']]
            if cmd == fcntl.F_GETLK:
                return -EOPNOTSUPP
            elif cmd == fcntl.F_SETLK:
                if op != fcntl.LOCK_UN:
                    op |= fcntl.LOCK_NB
            elif cmd == fcntl.F_SETLKW:
                pass
            else:
                return -EINVAL

            fcntl.lockf(self.fd, op, kw['l_start'], kw['l_len'])

def lock_files(self, lock_type=None, offset=0, length=0):
        """Lock all files opened by open_files()."""
        if lock_type is None:
            lock_type = self.lock_type
        ret = []
        mode_str = 'WRITE' if lock_type == fcntl.F_WRLCK else 'READ'
        lockdata = struct.pack('hhllhh', lock_type, 0, long(offset), long(length), 0, 0)
        for fd in self.rfds + self.wfds:
            try:
                self.dprint('DBG3', "Lock file F_SETLKW (%s)" % mode_str)
                rv = fcntl.fcntl(fd, fcntl.F_SETLKW, lockdata)
                ret.append(rv)
            except Exception, e:
                self.warning("Unable to get lock on file: %r" % e)
        return ret