Source code for taskflow.persistence.backends.impl_memory

# -*- coding: utf-8 -*-

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#    Copyright (C) 2013 Rackspace Hosting All Rights Reserved.
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

import contextlib
import copy
import itertools
import posixpath as pp

import fasteners

from taskflow import exceptions as exc
from taskflow.persistence import path_based
from taskflow.types import tree

[docs]class FakeInode(tree.Node): """A in-memory filesystem inode-like object.""" def __init__(self, item, path, value=None): super(FakeInode, self).__init__(item, path=path, value=value)
[docs]class FakeFilesystem(object): """An in-memory filesystem-like structure. This filesystem uses posix style paths **only** so users must be careful to use the ``posixpath`` module instead of the ``os.path`` one which will vary depending on the operating system which the active python is running in (the decision to use ``posixpath`` was to avoid the path variations which are not relevant in an implementation of a in-memory fake filesystem). **Not** thread-safe when a single filesystem is mutated at the same time by multiple threads. For example having multiple threads call into :meth:`~taskflow.persistence.backends.impl_memory.FakeFilesystem.clear` at the same time could potentially end badly. It is thread-safe when only :meth:`~taskflow.persistence.backends.impl_memory.FakeFilesystem.get` or other read-only actions (like calling into :meth:``) are occurring at the same time. Example usage: >>> from taskflow.persistence.backends import impl_memory >>> fs = impl_memory.FakeFilesystem() >>> fs.ensure_path('/a/b/c') >>> fs['/a/b/c'] = 'd' >>> print(fs['/a/b/c']) d >>> del fs['/a/b/c'] >>>"/a/b") [] >>> fs.get("/a/b/c", 'blob') 'blob' """ #: Root path of the in-memory filesystem. root_path = pp.sep
[docs] @classmethod def normpath(cls, path): """Return a normalized absolutized version of the pathname path.""" if not path: raise ValueError("This filesystem can only normalize paths" " that are not empty") if not path.startswith(cls.root_path): raise ValueError("This filesystem can only normalize" " paths that start with %s: '%s' is not" " valid" % (cls.root_path, path)) return pp.normpath(path)
#: Split a pathname into a tuple of ``(head, tail)``. split = staticmethod(pp.split)
[docs] @staticmethod def join(*pieces): """Join many path segments together.""" return pp.sep.join(pieces)
def __init__(self, deep_copy=True): self._root = FakeInode(self.root_path, self.root_path) self._reverse_mapping = { self.root_path: self._root, } if deep_copy: self._copier = copy.deepcopy else: self._copier = copy.copy
[docs] def ensure_path(self, path): """Ensure the path (and parents) exists.""" path = self.normpath(path) # Ignore the root path as we already checked for that; and it # will always exist/can't be removed anyway... if path == self._root.item: return node = self._root for piece in self._iter_pieces(path): child_node = node.find(piece, only_direct=True, include_self=False) if child_node is None: child_node = self._insert_child(node, piece) node = child_node
def _insert_child(self, parent_node, basename, value=None): child_path = self.join(parent_node.metadata['path'], basename) # This avoids getting '//a/b' (duplicated sep at start)... # # Which can happen easily if something like the following is given. # >>> x = ['/', 'b'] # >>> pp.sep.join(x) # '//b' if child_path.startswith(pp.sep * 2): child_path = child_path[1:] child_node = FakeInode(basename, child_path, value=value) parent_node.add(child_node) self._reverse_mapping[child_path] = child_node return child_node def _fetch_node(self, path, normalized=False): if not normalized: normed_path = self.normpath(path) else: normed_path = path try: return self._reverse_mapping[normed_path] except KeyError: raise exc.NotFound("Path '%s' not found" % path)
[docs] def get(self, path, default=None): """Fetch the value of given path (and return default if not found).""" try: return self._get_item(self.normpath(path)) except exc.NotFound: return default
def _get_item(self, path, links=None): node = self._fetch_node(path, normalized=True) if 'target' in node.metadata: # Follow the link (and watch out for loops)... path = node.metadata['target'] if links is None: links = [] if path in links: raise ValueError("Recursive link following not" " allowed (loop %s detected)" % (links + [path])) else: links.append(path) return self._get_item(path, links=links) else: return self._copier(node.metadata['value']) def _up_to_root_selector(self, root_node, child_node): # Build the path from the child to the root and stop at the # root, and then form a path string... path_pieces = [child_node.item] for parent_node in child_node.path_iter(include_self=False): if parent_node is root_node: break path_pieces.append(parent_node.item) if len(path_pieces) > 1: path_pieces.reverse() return self.join(*path_pieces) @staticmethod def _metadata_path_selector(root_node, child_node): return child_node.metadata['path']
[docs] def ls_r(self, path, absolute=False): """Return list of all children of the given path (recursively).""" node = self._fetch_node(path) if absolute: selector_func = self._metadata_path_selector else: selector_func = self._up_to_root_selector return [selector_func(node, child_node) for child_node in node.bfs_iter()]
[docs] def ls(self, path, absolute=False): """Return list of all children of the given path (not recursive).""" node = self._fetch_node(path) if absolute: selector_func = self._metadata_path_selector else: selector_func = self._up_to_root_selector child_node_it = iter(node) return [selector_func(node, child_node) for child_node in child_node_it]
[docs] def clear(self): """Remove all nodes (except the root) from this filesystem.""" self._reverse_mapping = { self.root_path: self._root, } for node in list(self._root.reverse_iter()): node.disassociate()
[docs] def delete(self, path, recursive=False): """Deletes a node (optionally its children) from this filesystem.""" path = self.normpath(path) node = self._fetch_node(path, normalized=True) if node is self._root and not recursive: raise ValueError("Can not delete '%s'" % self._root.item) if recursive: child_paths = (child.metadata['path'] for child in node.bfs_iter()) else: node_child_count = node.child_count() if node_child_count: raise ValueError("Can not delete '%s', it has %s children" % (path, node_child_count)) child_paths = [] if node is self._root: # Don't drop/pop the root... paths = child_paths drop_nodes = [] else: paths = itertools.chain([path], child_paths) drop_nodes = [node] for path in paths: self._reverse_mapping.pop(path, None) for node in drop_nodes: node.disassociate()
def _iter_pieces(self, path, include_root=False): if path == self._root.item: # Check for this directly as the following doesn't work with # split correctly: # # >>> path = "/" # path.split(pp.sep) # ['', ''] parts = [] else: parts = path.split(pp.sep)[1:] if include_root: parts.insert(0, self._root.item) for piece in parts: yield piece def __delitem__(self, path): self.delete(path, recursive=True) @staticmethod def _stringify_node(node): if 'target' in node.metadata: return "%s (link to %s)" % (node.item, node.metadata['target']) else: return str(node.item)
[docs] def pformat(self): """Pretty format this in-memory filesystem.""" return self._root.pformat(stringify_node=self._stringify_node)
def __getitem__(self, path): return self._get_item(self.normpath(path)) def __setitem__(self, path, value): path = self.normpath(path) value = self._copier(value) try: node = self._fetch_node(path, normalized=True) node.metadata.update(value=value) except exc.NotFound: parent_path, basename = self.split(path) parent_node = self._fetch_node(parent_path, normalized=True) self._insert_child(parent_node, basename, value=value)
[docs]class MemoryBackend(path_based.PathBasedBackend): """A in-memory (non-persistent) backend. This backend writes logbooks, flow details, and atom details to a in-memory filesystem-like structure (rooted by the ``memory`` instance variable). This backend does *not* provide true transactional semantics. It does guarantee that there will be no inter-thread race conditions when writing and reading by using a read/write locks. """ #: Default path used when none is provided. DEFAULT_PATH = pp.sep def __init__(self, conf=None): super(MemoryBackend, self).__init__(conf) self.memory = FakeFilesystem(deep_copy=self._conf.get('deep_copy', True)) self.lock = fasteners.ReaderWriterLock()
[docs] def get_connection(self): return Connection(self)
[docs] def close(self): pass
[docs]class Connection(path_based.PathBasedConnection): def __init__(self, backend): super(Connection, self).__init__(backend) self.upgrade() @contextlib.contextmanager def _memory_lock(self, write=False): if write: lock = self.backend.lock.write_lock else: lock = self.backend.lock.read_lock with lock(): try: yield except exc.TaskFlowException: raise except Exception: exc.raise_with_cause(exc.StorageFailure, "Storage backend internal error") def _join_path(self, *parts): return pp.join(*parts) def _get_item(self, path): with self._memory_lock(): return self.backend.memory[path] def _set_item(self, path, value, transaction): self.backend.memory[path] = value def _del_tree(self, path, transaction): del self.backend.memory[path] def _get_children(self, path): with self._memory_lock(): return def _ensure_path(self, path): with self._memory_lock(write=True): self.backend.memory.ensure_path(path) def _create_link(self, src_path, dest_path, transaction): self.backend.memory.symlink(src_path, dest_path) @contextlib.contextmanager def _transaction(self): """This just wraps a global write-lock.""" with self._memory_lock(write=True): yield
[docs] def validate(self): pass