file_io.py 文件源码

def _getlock(self, name, fd, lock_type=None, offset=0, length=0, lock=None, tlock=False):
        """Get byte range lock on file given by file descriptor"""
        rn = self.random.randint(0,9999)
        stype = fcntl.F_SETLK
        if lock_type == fcntl.F_UNLCK:
            lstr = "UNLOCK"
            if not lock or rn >= 100*self.unlock:
                # Do not unlock file
                return
            self.nunlock += 1
        else:
            if tlock:
                # Just do TLOCK
                lstr = "TLOCK "
                stype = fcntl.F_GETLK
                if rn >= 100*self.tlock:
                    # No lock, so no tlock
                    return
                self.ntlock += 1
            else:
                lstr = "LOCK  "
                if rn >= 100*self.lock:
                    # No lock
                    return
                self.nlock += 1
            if lock_type is None:
                # Choose lock: read or write
                if self._percent(50):
                    lock_type = fcntl.F_RDLCK
                else:
                    lock_type = fcntl.F_WRLCK
            if not tlock:
                # LOCK is requested, but do TLOCK before actual lock
                self._getlock(name, fd, lock_type=lock_type, offset=offset, length=length, lock=lock, tlock=True)
        fstr = ""
        if offset == 0 and length == 0 and lstr == "LOCK  ":
            fstr = " full file"
        self._dprint("DBG4", "%s  %s %d @ %d (%s)%s" % (lstr, name, length, offset, LOCKMAP[lock_type], fstr))
        lockdata = struct.pack('hhllhh', lock_type, 0, offset, length, 0, 0)
        return fcntl.fcntl(fd, stype, lockdata)