sync_files.py

# -*- coding: utf-8 -*-
import os
import pickle
import shutil
import time

class SyncFileException(Exception):
    pass


notyet = '.notyet'

def touch(fpath):
    try:
        with open(fpath, 'w') as sgf:
            sgf.write('hi')
            sgf.flush()
            os.fsync(sgf.fileno())
    except OSError as e:
        if e.errno != EEXIST:
            raise e

def write_sync_file(fpath, contents):
    with open(fpath+notyet, 'w') as sgf:
        sgf.write(contents)
        sgf.flush()
        os.fsync(sgf.fileno())  # file should close when you exit block
        os.rename(fpath+notyet, fpath)


def write_pickle(fpath, obj):
    with open(fpath+notyet, 'wb') as result_file:
        pickle.dump(obj, result_file)
        result_file.flush()
        os.fsync(result_file.fileno())  # or else reader may not see data
        os.rename(fpath+notyet, fpath)


# create directory if it's not already there

def ensure_dir_exists(dirpath):
    if not os.path.exists(dirpath):
        parent_path = os.path.dirname(dirpath)
        if parent_path == dirpath:
            raise SMFSyncFileException('ensure_dir_exists: ' +
                            'cannot obtain parent path ' +
                            'of non-existent path: ' +
                            dirpath)
        ensure_dir_exists(parent_path)
        try:
            os.mkdir(dirpath)
        except os.error as e:
            if e.errno != errno.EEXIST:  # workaround for filesystem bug
                raise e
    else:
        if not os.path.isdir(dirpath):
            raise SMFSyncFileException('%s already exists and is not a directory!'
                            % dirpath)


# avoid exception if file we wish to delete is not there

def ensure_deleted(fn):
    try:
        if os.path.lexists(fn):
            os.unlink(fn)
    except Exception as e:
        # could be race condition with other client processes/hosts
        # if was race condition, file will no longer be there
        if os.path.exists(fn):
            raise SMFSyncFileException('exception while ensuring %s deleted: %s'
                            % (fn, str(e)))