5476: Better implementation of connection timeout scaling. Updated docstring
[arvados.git] / sdk / python / arvados / collection.py
index a0eda1175a3b089f723fa150c3b43bf974d4e824..3d48652dd53afe4eecc3bc35628646e427a8ac73 100644 (file)
@@ -3,17 +3,24 @@ import logging
 import os
 import re
 import errno
 import os
 import re
 import errno
+import hashlib
+import time
+import threading
 
 from collections import deque
 from stat import *
 
 
 from collections import deque
 from stat import *
 
-from .arvfile import ArvadosFileBase, split, ArvadosFile, ArvadosFileWriter, ArvadosFileReader, BlockManager
-from keep import *
-from .stream import StreamReader, normalize_stream, locator_block_size
-from .ranges import Range, LocatorAndRange
+from .arvfile import split, _FileLikeObjectBase, ArvadosFile, ArvadosFileWriter, ArvadosFileReader, _BlockManager, synchronized, must_be_writable, NoopLock
+from keep import KeepLocator, KeepClient
+from .stream import StreamReader
+from ._normalize_stream import normalize_stream
+from ._ranges import Range, LocatorAndRange
+from .safeapi import ThreadSafeApiCache
 import config
 import errors
 import util
 import config
 import errors
 import util
+import events
+from arvados.retry import retry_method
 
 _logger = logging.getLogger('arvados.collection')
 
 
 _logger = logging.getLogger('arvados.collection')
 
@@ -31,7 +38,8 @@ class CollectionBase(object):
         return self._keep_client
 
     def stripped_manifest(self):
         return self._keep_client
 
     def stripped_manifest(self):
-        """
+        """Get the manifest with locator hints stripped.
+
         Return the manifest for the current collection with all
         non-portable hints (i.e., permission signatures and other
         hints other than size hints) removed from the locators.
         Return the manifest for the current collection with all
         non-portable hints (i.e., permission signatures and other
         hints other than size hints) removed from the locators.
@@ -50,197 +58,7 @@ class CollectionBase(object):
         return ''.join(clean)
 
 
         return ''.join(clean)
 
 
-class CollectionReader(CollectionBase):
-    def __init__(self, manifest_locator_or_text, api_client=None,
-                 keep_client=None, num_retries=0):
-        """Instantiate a CollectionReader.
-
-        This class parses Collection manifests to provide a simple interface
-        to read its underlying files.
-
-        Arguments:
-        * manifest_locator_or_text: One of a Collection UUID, portable data
-          hash, or full manifest text.
-        * api_client: The API client to use to look up Collections.  If not
-          provided, CollectionReader will build one from available Arvados
-          configuration.
-        * keep_client: The KeepClient to use to download Collection data.
-          If not provided, CollectionReader will build one from available
-          Arvados configuration.
-        * num_retries: The default number of times to retry failed
-          service requests.  Default 0.  You may change this value
-          after instantiation, but note those changes may not
-          propagate to related objects like the Keep client.
-        """
-        self._api_client = api_client
-        self._keep_client = keep_client
-        self.num_retries = num_retries
-        if re.match(util.keep_locator_pattern, manifest_locator_or_text):
-            self._manifest_locator = manifest_locator_or_text
-            self._manifest_text = None
-        elif re.match(util.collection_uuid_pattern, manifest_locator_or_text):
-            self._manifest_locator = manifest_locator_or_text
-            self._manifest_text = None
-        elif re.match(util.manifest_pattern, manifest_locator_or_text):
-            self._manifest_text = manifest_locator_or_text
-            self._manifest_locator = None
-        else:
-            raise errors.ArgumentError(
-                "Argument to CollectionReader must be a manifest or a collection UUID")
-        self._api_response = None
-        self._streams = None
-
-    def _populate_from_api_server(self):
-        # As in KeepClient itself, we must wait until the last
-        # possible moment to instantiate an API client, in order to
-        # avoid tripping up clients that don't have access to an API
-        # server.  If we do build one, make sure our Keep client uses
-        # it.  If instantiation fails, we'll fall back to the except
-        # clause, just like any other Collection lookup
-        # failure. Return an exception, or None if successful.
-        try:
-            if self._api_client is None:
-                self._api_client = arvados.api('v1')
-                self._keep_client = None  # Make a new one with the new api.
-            self._api_response = self._api_client.collections().get(
-                uuid=self._manifest_locator).execute(
-                num_retries=self.num_retries)
-            self._manifest_text = self._api_response['manifest_text']
-            return None
-        except Exception as e:
-            return e
-
-    def _populate_from_keep(self):
-        # Retrieve a manifest directly from Keep. This has a chance of
-        # working if [a] the locator includes a permission signature
-        # or [b] the Keep services are operating in world-readable
-        # mode. Return an exception, or None if successful.
-        try:
-            self._manifest_text = self._my_keep().get(
-                self._manifest_locator, num_retries=self.num_retries)
-        except Exception as e:
-            return e
-
-    def _populate(self):
-        error_via_api = None
-        error_via_keep = None
-        should_try_keep = ((self._manifest_text is None) and
-                           util.keep_locator_pattern.match(
-                self._manifest_locator))
-        if ((self._manifest_text is None) and
-            util.signed_locator_pattern.match(self._manifest_locator)):
-            error_via_keep = self._populate_from_keep()
-        if self._manifest_text is None:
-            error_via_api = self._populate_from_api_server()
-            if error_via_api is not None and not should_try_keep:
-                raise error_via_api
-        if ((self._manifest_text is None) and
-            not error_via_keep and
-            should_try_keep):
-            # Looks like a keep locator, and we didn't already try keep above
-            error_via_keep = self._populate_from_keep()
-        if self._manifest_text is None:
-            # Nothing worked!
-            raise arvados.errors.NotFoundError(
-                ("Failed to retrieve collection '{}' " +
-                 "from either API server ({}) or Keep ({})."
-                 ).format(
-                    self._manifest_locator,
-                    error_via_api,
-                    error_via_keep))
-        self._streams = [sline.split()
-                         for sline in self._manifest_text.split("\n")
-                         if sline]
-
-    def _populate_first(orig_func):
-        # Decorator for methods that read actual Collection data.
-        @functools.wraps(orig_func)
-        def wrapper(self, *args, **kwargs):
-            if self._streams is None:
-                self._populate()
-            return orig_func(self, *args, **kwargs)
-        return wrapper
-
-    @_populate_first
-    def api_response(self):
-        """api_response() -> dict or None
-
-        Returns information about this Collection fetched from the API server.
-        If the Collection exists in Keep but not the API server, currently
-        returns None.  Future versions may provide a synthetic response.
-        """
-        return self._api_response
-
-    @_populate_first
-    def normalize(self):
-        # Rearrange streams
-        streams = {}
-        for s in self.all_streams():
-            for f in s.all_files():
-                streamname, filename = split(s.name() + "/" + f.name())
-                if streamname not in streams:
-                    streams[streamname] = {}
-                if filename not in streams[streamname]:
-                    streams[streamname][filename] = []
-                for r in f.segments:
-                    streams[streamname][filename].extend(s.locators_and_ranges(r.locator, r.range_size))
-
-        self._streams = [normalize_stream(s, streams[s])
-                         for s in sorted(streams)]
-
-        # Regenerate the manifest text based on the normalized streams
-        self._manifest_text = ''.join(
-            [StreamReader(stream, keep=self._my_keep()).manifest_text()
-             for stream in self._streams])
-
-    @_populate_first
-    def open(self, streampath, filename=None):
-        """open(streampath[, filename]) -> file-like object
-
-        Pass in the path of a file to read from the Collection, either as a
-        single string or as two separate stream name and file name arguments.
-        This method returns a file-like object to read that file.
-        """
-        if filename is None:
-            streampath, filename = split(streampath)
-        keep_client = self._my_keep()
-        for stream_s in self._streams:
-            stream = StreamReader(stream_s, keep_client,
-                                  num_retries=self.num_retries)
-            if stream.name() == streampath:
-                break
-        else:
-            raise ValueError("stream '{}' not found in Collection".
-                             format(streampath))
-        try:
-            return stream.files()[filename]
-        except KeyError:
-            raise ValueError("file '{}' not found in Collection stream '{}'".
-                             format(filename, streampath))
-
-    @_populate_first
-    def all_streams(self):
-        return [StreamReader(s, self._my_keep(), num_retries=self.num_retries)
-                for s in self._streams]
-
-    def all_files(self):
-        for s in self.all_streams():
-            for f in s.all_files():
-                yield f
-
-    @_populate_first
-    def manifest_text(self, strip=False, normalize=False):
-        if normalize:
-            cr = CollectionReader(self.manifest_text())
-            cr.normalize()
-            return cr.manifest_text(strip=strip, normalize=False)
-        elif strip:
-            return self.stripped_manifest()
-        else:
-            return self._manifest_text
-
-
-class _WriterFile(ArvadosFileBase):
+class _WriterFile(_FileLikeObjectBase):
     def __init__(self, coll_writer, name):
         super(_WriterFile, self).__init__(name, 'wb')
         self.dest = coll_writer
     def __init__(self, coll_writer, name):
         super(_WriterFile, self).__init__(name, 'wb')
         self.dest = coll_writer
@@ -249,22 +67,22 @@ class _WriterFile(ArvadosFileBase):
         super(_WriterFile, self).close()
         self.dest.finish_current_file()
 
         super(_WriterFile, self).close()
         self.dest.finish_current_file()
 
-    @ArvadosFileBase._before_close
+    @_FileLikeObjectBase._before_close
     def write(self, data):
         self.dest.write(data)
 
     def write(self, data):
         self.dest.write(data)
 
-    @ArvadosFileBase._before_close
+    @_FileLikeObjectBase._before_close
     def writelines(self, seq):
         for data in seq:
             self.write(data)
 
     def writelines(self, seq):
         for data in seq:
             self.write(data)
 
-    @ArvadosFileBase._before_close
+    @_FileLikeObjectBase._before_close
     def flush(self):
         self.dest.flush_data()
 
 
 class CollectionWriter(CollectionBase):
     def flush(self):
         self.dest.flush_data()
 
 
 class CollectionWriter(CollectionBase):
-    def __init__(self, api_client=None, num_retries=0):
+    def __init__(self, api_client=None, num_retries=0, replication=None):
         """Instantiate a CollectionWriter.
 
         CollectionWriter lets you build a new Arvados Collection from scratch.
         """Instantiate a CollectionWriter.
 
         CollectionWriter lets you build a new Arvados Collection from scratch.
@@ -280,9 +98,13 @@ class CollectionWriter(CollectionBase):
           service requests.  Default 0.  You may change this value
           after instantiation, but note those changes may not
           propagate to related objects like the Keep client.
           service requests.  Default 0.  You may change this value
           after instantiation, but note those changes may not
           propagate to related objects like the Keep client.
+        * replication: The number of copies of each block to store.
+          If this argument is None or not supplied, replication is
+          the server-provided default if available, otherwise 2.
         """
         self._api_client = api_client
         self.num_retries = num_retries
         """
         self._api_client = api_client
         self.num_retries = num_retries
+        self.replication = (2 if replication is None else replication)
         self._keep_client = None
         self._data_buffer = []
         self._data_buffer_len = 0
         self._keep_client = None
         self._data_buffer = []
         self._data_buffer_len = 0
@@ -437,7 +259,9 @@ class CollectionWriter(CollectionBase):
         data_buffer = ''.join(self._data_buffer)
         if data_buffer:
             self._current_stream_locators.append(
         data_buffer = ''.join(self._data_buffer)
         if data_buffer:
             self._current_stream_locators.append(
-                self._my_keep().put(data_buffer[0:config.KEEP_BLOCK_SIZE]))
+                self._my_keep().put(
+                    data_buffer[0:config.KEEP_BLOCK_SIZE],
+                    copies=self.replication))
             self._data_buffer = [data_buffer[config.KEEP_BLOCK_SIZE:]]
             self._data_buffer_len = len(self._data_buffer[0])
 
             self._data_buffer = [data_buffer[config.KEEP_BLOCK_SIZE:]]
             self._data_buffer_len = len(self._data_buffer[0])
 
@@ -512,8 +336,16 @@ class CollectionWriter(CollectionBase):
         self._current_file_name = None
 
     def finish(self):
         self._current_file_name = None
 
     def finish(self):
-        # Store the manifest in Keep and return its locator.
-        return self._my_keep().put(self.manifest_text())
+        """Store the manifest in Keep and return its locator.
+
+        This is useful for storing manifest fragments (task outputs)
+        temporarily in Keep during a Crunch job.
+
+        In other cases you should make a collection instead, by
+        sending manifest_text() to the API server's "create
+        collection" endpoint.
+        """
+        return self._my_keep().put(self.manifest_text(), copies=self.replication)
 
     def portable_data_hash(self):
         stripped = self.stripped_manifest()
 
     def portable_data_hash(self):
         stripped = self.stripped_manifest()
@@ -547,10 +379,9 @@ class ResumableCollectionWriter(CollectionWriter):
                    '_data_buffer', '_dependencies', '_finished_streams',
                    '_queued_dirents', '_queued_trees']
 
                    '_data_buffer', '_dependencies', '_finished_streams',
                    '_queued_dirents', '_queued_trees']
 
-    def __init__(self, api_client=None, num_retries=0):
+    def __init__(self, api_client=None, **kwargs):
         self._dependencies = {}
         self._dependencies = {}
-        super(ResumableCollectionWriter, self).__init__(
-            api_client, num_retries=num_retries)
+        super(ResumableCollectionWriter, self).__init__(api_client, **kwargs)
 
     @classmethod
     def from_state(cls, state, *init_args, **init_kwargs):
 
     @classmethod
     def from_state(cls, state, *init_args, **init_kwargs):
@@ -640,37 +471,584 @@ class ResumableCollectionWriter(CollectionWriter):
         return super(ResumableCollectionWriter, self).write(data)
 
 
         return super(ResumableCollectionWriter, self).write(data)
 
 
-class Collection(CollectionBase):
-    '''An abstract Arvados collection, consisting of a set of files and
-    sub-collections.
-    '''
+ADD = "add"
+DEL = "del"
+MOD = "mod"
+FILE = "file"
+COLLECTION = "collection"
+
+class RichCollectionBase(CollectionBase):
+    """Base class for Collections and Subcollections.
+
+    Implements the majority of functionality relating to accessing items in the
+    Collection.
 
 
-    def __init__(self, manifest_locator_or_text=None, parent=None, api_client=None,
-                 keep_client=None, num_retries=0, block_manager=None):
-        '''manifest_locator_or_text: One of Arvados collection UUID, block locator of
-        a manifest, raw manifest text, or None (to create an empty collection).
+    """
 
 
-        parent: the parent Collection, may be None.
+    def __init__(self, parent=None):
+        self.parent = parent
+        self._modified = True
+        self._items = {}
 
 
-        api_client: The API client object to use for requests.  If None, use default.
+    def _my_api(self):
+        raise NotImplementedError()
 
 
-        keep_client: the Keep client to use for requests.  If None, use default.
+    def _my_keep(self):
+        raise NotImplementedError()
 
 
-        num_retries: the number of retries for API and Keep requests.
+    def _my_block_manager(self):
+        raise NotImplementedError()
 
 
-        block_manager: the block manager to use.  If None, create one.
-        '''
-        self.parent = parent
-        self._items = None
+    def writable(self):
+        raise NotImplementedError()
+
+    def root_collection(self):
+        raise NotImplementedError()
+
+    def notify(self, event, collection, name, item):
+        raise NotImplementedError()
+
+    def stream_name(self):
+        raise NotImplementedError()
+
+    @must_be_writable
+    @synchronized
+    def find_or_create(self, path, create_type):
+        """Recursively search the specified file path.
+
+        May return either a `Collection` or `ArvadosFile`.  If not found, will
+        create a new item at the specified path based on `create_type`.  Will
+        create intermediate subcollections needed to contain the final item in
+        the path.
+
+        :create_type:
+          One of `arvados.collection.FILE` or
+          `arvados.collection.COLLECTION`.  If the path is not found, and value
+          of create_type is FILE then create and return a new ArvadosFile for
+          the last path component.  If COLLECTION, then create and return a new
+          Collection for the last path component.
+
+        """
+
+        pathcomponents = path.split("/", 1)
+        if pathcomponents[0]:
+            item = self._items.get(pathcomponents[0])
+            if len(pathcomponents) == 1:
+                if item is None:
+                    # create new file
+                    if create_type == COLLECTION:
+                        item = Subcollection(self)
+                    else:
+                        item = ArvadosFile(self)
+                    self._items[pathcomponents[0]] = item
+                    self._modified = True
+                    self.notify(ADD, self, pathcomponents[0], item)
+                return item
+            else:
+                if item is None:
+                    # create new collection
+                    item = Subcollection(self)
+                    self._items[pathcomponents[0]] = item
+                    self._modified = True
+                    self.notify(ADD, self, pathcomponents[0], item)
+                if isinstance(item, RichCollectionBase):
+                    return item.find_or_create(pathcomponents[1], create_type)
+                else:
+                    raise IOError((errno.ENOTDIR, "Interior path components must be subcollection"))
+        else:
+            return self
+
+    @synchronized
+    def find(self, path):
+        """Recursively search the specified file path.
+
+        May return either a Collection or ArvadosFile.  Return None if not
+        found.
+
+        """
+        if not path:
+            raise errors.ArgumentError("Parameter 'path' must not be empty.")
+
+        pathcomponents = path.split("/", 1)
+        item = self._items.get(pathcomponents[0])
+        if len(pathcomponents) == 1:
+            return item
+        else:
+            if isinstance(item, RichCollectionBase):
+                if pathcomponents[1]:
+                    return item.find(pathcomponents[1])
+                else:
+                    return item
+            else:
+                raise IOError((errno.ENOTDIR, "Interior path components must be subcollection"))
+
+    def mkdirs(path):
+        """Recursive subcollection create.
+
+        Like `os.mkdirs()`.  Will create intermediate subcollections needed to
+        contain the leaf subcollection path.
+
+        """
+        return self.find_or_create(path, COLLECTION)
+
+    def open(self, path, mode="r"):
+        """Open a file-like object for access.
+
+        :path:
+          path to a file in the collection
+        :mode:
+          one of "r", "r+", "w", "w+", "a", "a+"
+          :"r":
+            opens for reading
+          :"r+":
+            opens for reading and writing.  Reads/writes share a file pointer.
+          :"w", "w+":
+            truncates to 0 and opens for reading and writing.  Reads/writes share a file pointer.
+          :"a", "a+":
+            opens for reading and writing.  All writes are appended to
+            the end of the file.  Writing does not affect the file pointer for
+            reading.
+        """
+        mode = mode.replace("b", "")
+        if len(mode) == 0 or mode[0] not in ("r", "w", "a"):
+            raise errors.ArgumentError("Bad mode '%s'" % mode)
+        create = (mode != "r")
+
+        if create and not self.writable():
+            raise IOError((errno.EROFS, "Collection is read only"))
+
+        if create:
+            arvfile = self.find_or_create(path, FILE)
+        else:
+            arvfile = self.find(path)
+
+        if arvfile is None:
+            raise IOError((errno.ENOENT, "File not found"))
+        if not isinstance(arvfile, ArvadosFile):
+            raise IOError((errno.EISDIR, "Path must refer to a file."))
+
+        if mode[0] == "w":
+            arvfile.truncate(0)
+
+        name = os.path.basename(path)
+
+        if mode == "r":
+            return ArvadosFileReader(arvfile, name, mode, num_retries=self.num_retries)
+        else:
+            return ArvadosFileWriter(arvfile, name, mode, num_retries=self.num_retries)
+
+    @synchronized
+    def modified(self):
+        """Test if the collection (or any subcollection or file) has been modified."""
+        if self._modified:
+            return True
+        for k,v in self._items.items():
+            if v.modified():
+                return True
+        return False
+
+    @synchronized
+    def set_unmodified(self):
+        """Recursively clear modified flag."""
+        self._modified = False
+        for k,v in self._items.items():
+            v.set_unmodified()
+
+    @synchronized
+    def __iter__(self):
+        """Iterate over names of files and collections contained in this collection."""
+        return iter(self._items.keys())
+
+    @synchronized
+    def __getitem__(self, k):
+        """Get a file or collection that is directly contained by this collection.
+
+        If you want to search a path, use `find()` instead.
+
+        """
+        return self._items[k]
+
+    @synchronized
+    def __contains__(self, k):
+        """Test if there is a file or collection a directly contained by this collection."""
+        return k in self._items
+
+    @synchronized
+    def __len__(self):
+        """Get the number of items directly contained in this collection."""
+        return len(self._items)
+
+    @must_be_writable
+    @synchronized
+    def __delitem__(self, p):
+        """Delete an item by name which is directly contained by this collection."""
+        del self._items[p]
+        self._modified = True
+        self.notify(DEL, self, p, None)
+
+    @synchronized
+    def keys(self):
+        """Get a list of names of files and collections directly contained in this collection."""
+        return self._items.keys()
+
+    @synchronized
+    def values(self):
+        """Get a list of files and collection objects directly contained in this collection."""
+        return self._items.values()
+
+    @synchronized
+    def items(self):
+        """Get a list of (name, object) tuples directly contained in this collection."""
+        return self._items.items()
+
+    def exists(self, path):
+        """Test if there is a file or collection at `path`."""
+        return self.find(path) is not None
+
+    @must_be_writable
+    @synchronized
+    def remove(self, path, recursive=False):
+        """Remove the file or subcollection (directory) at `path`.
+
+        :recursive:
+          Specify whether to remove non-empty subcollections (True), or raise an error (False).
+        """
+
+        if not path:
+            raise errors.ArgumentError("Parameter 'path' must not be empty.")
+
+        pathcomponents = path.split("/", 1)
+        item = self._items.get(pathcomponents[0])
+        if item is None:
+            raise IOError((errno.ENOENT, "File not found"))
+        if len(pathcomponents) == 1:
+            if isinstance(self._items[pathcomponents[0]], RichCollectionBase) and len(self._items[pathcomponents[0]]) > 0 and not recursive:
+                raise IOError((errno.ENOTEMPTY, "Subcollection not empty"))
+            deleteditem = self._items[pathcomponents[0]]
+            del self._items[pathcomponents[0]]
+            self._modified = True
+            self.notify(DEL, self, pathcomponents[0], deleteditem)
+        else:
+            item.remove(pathcomponents[1])
+
+    def _clonefrom(self, source):
+        for k,v in source.items():
+            self._items[k] = v.clone(self)
+
+    def clone(self):
+        raise NotImplementedError()
+
+    @must_be_writable
+    @synchronized
+    def add(self, source_obj, target_name, overwrite=False):
+        """Copy a file or subcollection to this collection.
+
+        :source_obj:
+          An ArvadosFile, or Subcollection object
+
+        :target_name:
+          Destination item name.  If the target name already exists and is a
+          file, this will raise an error unless you specify `overwrite=True`.
+
+        :overwrite:
+          Whether to overwrite target file if it already exists.
+
+        """
+
+        if target_name in self and not overwrite:
+            raise IOError((errno.EEXIST, "File already exists"))
+
+        modified_from = None
+        if target_name in self:
+            modified_from = self[target_name]
+
+        # Actually make the copy.
+        dup = source_obj.clone(self)
+        self._items[target_name] = dup
+        self._modified = True
+
+        if modified_from:
+            self.notify(MOD, self, target_name, (modified_from, dup))
+        else:
+            self.notify(ADD, self, target_name, dup)
+
+    @must_be_writable
+    @synchronized
+    def copy(self, source, target_path, source_collection=None, overwrite=False):
+        """Copy a file or subcollection to a new path in this collection.
+
+        :source:
+          A string with a path to source file or subcollection, or an actual ArvadosFile or Subcollection object.
+
+        :target_path:
+          Destination file or path.  If the target path already exists and is a
+          subcollection, the item will be placed inside the subcollection.  If
+          the target path already exists and is a file, this will raise an error
+          unless you specify `overwrite=True`.
+
+        :source_collection:
+          Collection to copy `source_path` from (default `self`)
+
+        :overwrite:
+          Whether to overwrite target file if it already exists.
+        """
+        if source_collection is None:
+            source_collection = self
+
+        # Find the object to copy
+        if isinstance(source, basestring):
+            source_obj = source_collection.find(source)
+            if source_obj is None:
+                raise IOError((errno.ENOENT, "File not found"))
+            sourcecomponents = source.split("/")
+        else:
+            source_obj = source
+            sourcecomponents = None
+
+        # Find parent collection the target path
+        targetcomponents = target_path.split("/")
+
+        # Determine the name to use.
+        target_name = targetcomponents[-1] if targetcomponents[-1] else (sourcecomponents[-1] if sourcecomponents else None)
+
+        if not target_name:
+            raise errors.ArgumentError("Target path is empty and source is an object.  Cannot determine destination filename to use.")
+
+        target_dir = self.find_or_create("/".join(targetcomponents[0:-1]), COLLECTION)
+
+        if target_name in target_dir and isinstance(self[target_name], RichCollectionBase) and sourcecomponents:
+            target_dir = target_dir[target_name]
+            target_name = sourcecomponents[-1]
+
+        target_dir.add(source_obj, target_name, overwrite)
+
+    @synchronized
+    def manifest_text(self, stream_name=".", strip=False, normalize=False):
+        """Get the manifest text for this collection, sub collections and files.
+
+        :stream_name:
+          Name of the stream (directory)
+
+        :strip:
+          If True, remove signing tokens from block locators if present.
+          If False (default), block locators are left unchanged.
+
+        :normalize:
+          If True, always export the manifest text in normalized form
+          even if the Collection is not modified.  If False (default) and the collection
+          is not modified, return the original manifest text even if it is not
+          in normalized form.
+
+        """
+
+        if self.modified() or self._manifest_text is None or normalize:
+            stream = {}
+            buf = []
+            sorted_keys = sorted(self.keys())
+            for filename in [s for s in sorted_keys if isinstance(self[s], ArvadosFile)]:
+                # Create a stream per file `k`
+                arvfile = self[filename]
+                filestream = []
+                for segment in arvfile.segments():
+                    loc = segment.locator
+                    if arvfile.parent._my_block_manager().is_bufferblock(loc):
+                        loc = arvfile.parent._my_block_manager().get_bufferblock(loc).locator()
+                    if strip:
+                        loc = KeepLocator(loc).stripped()
+                    filestream.append(LocatorAndRange(loc, KeepLocator(loc).size,
+                                         segment.segment_offset, segment.range_size))
+                stream[filename] = filestream
+            if stream:
+                buf.append(" ".join(normalize_stream(stream_name, stream)) + "\n")
+            for dirname in [s for s in sorted_keys if isinstance(self[s], RichCollectionBase)]:
+                buf.append(self[dirname].manifest_text(stream_name=os.path.join(stream_name, dirname), strip=strip))
+            return "".join(buf)
+        else:
+            if strip:
+                return self.stripped_manifest()
+            else:
+                return self._manifest_text
+
+    @synchronized
+    def diff(self, end_collection, prefix=".", holding_collection=None):
+        """Generate list of add/modify/delete actions.
+
+        When given to `apply`, will change `self` to match `end_collection`
+
+        """
+        changes = []
+        if holding_collection is None:
+            holding_collection = Collection(api_client=self._my_api(), keep_client=self._my_keep())
+        for k in self:
+            if k not in end_collection:
+               changes.append((DEL, os.path.join(prefix, k), self[k].clone(holding_collection)))
+        for k in end_collection:
+            if k in self:
+                if isinstance(end_collection[k], Subcollection) and isinstance(self[k], Subcollection):
+                    changes.extend(self[k].diff(end_collection[k], os.path.join(prefix, k), holding_collection))
+                elif end_collection[k] != self[k]:
+                    changes.append((MOD, os.path.join(prefix, k), self[k].clone(holding_collection), end_collection[k].clone(holding_collection)))
+            else:
+                changes.append((ADD, os.path.join(prefix, k), end_collection[k].clone(holding_collection)))
+        return changes
+
+    @must_be_writable
+    @synchronized
+    def apply(self, changes):
+        """Apply changes from `diff`.
+
+        If a change conflicts with a local change, it will be saved to an
+        alternate path indicating the conflict.
+
+        """
+        for change in changes:
+            event_type = change[0]
+            path = change[1]
+            initial = change[2]
+            local = self.find(path)
+            conflictpath = "%s~conflict-%s~" % (path, time.strftime("%Y-%m-%d-%H:%M:%S",
+                                                                    time.gmtime()))
+            if event_type == ADD:
+                if local is None:
+                    # No local file at path, safe to copy over new file
+                    self.copy(initial, path)
+                elif local is not None and local != initial:
+                    # There is already local file and it is different:
+                    # save change to conflict file.
+                    self.copy(initial, conflictpath)
+            elif event_type == MOD:
+                final = change[3]
+                if local == initial:
+                    # Local matches the "initial" item so it has not
+                    # changed locally and is safe to update.
+                    if isinstance(local, ArvadosFile) and isinstance(final, ArvadosFile):
+                        # Replace contents of local file with new contents
+                        local.replace_contents(final)
+                    else:
+                        # Overwrite path with new item; this can happen if
+                        # path was a file and is now a collection or vice versa
+                        self.copy(final, path, overwrite=True)
+                else:
+                    # Local is missing (presumably deleted) or local doesn't
+                    # match the "start" value, so save change to conflict file
+                    self.copy(final, conflictpath)
+            elif event_type == DEL:
+                if local == initial:
+                    # Local item matches "initial" value, so it is safe to remove.
+                    self.remove(path, recursive=True)
+                # else, the file is modified or already removed, in either
+                # case we don't want to try to remove it.
+
+    def portable_data_hash(self):
+        """Get the portable data hash for this collection's manifest."""
+        stripped = self.manifest_text(strip=True)
+        return hashlib.md5(stripped).hexdigest() + '+' + str(len(stripped))
+
+    @synchronized
+    def __eq__(self, other):
+        if other is self:
+            return True
+        if not isinstance(other, RichCollectionBase):
+            return False
+        if len(self._items) != len(other):
+            return False
+        for k in self._items:
+            if k not in other:
+                return False
+            if self._items[k] != other[k]:
+                return False
+        return True
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+
+class Collection(RichCollectionBase):
+    """Represents the root of an Arvados Collection.
+
+    This class is threadsafe.  The root collection object, all subcollections
+    and files are protected by a single lock (i.e. each access locks the entire
+    collection).
+
+    Brief summary of
+    useful methods:
+
+    :To read an existing file:
+      `c.open("myfile", "r")`
+
+    :To write a new file:
+      `c.open("myfile", "w")`
+
+    :To determine if a file exists:
+      `c.find("myfile") is not None`
+
+    :To copy a file:
+      `c.copy("source", "dest")`
+
+    :To delete a file:
+      `c.remove("myfile")`
+
+    :To save to an existing collection record:
+      `c.save()`
+
+    :To save a new collection record:
+    `c.save_new()`
+
+    :To merge remote changes into this object:
+      `c.update()`
+
+    Must be associated with an API server Collection record (during
+    initialization, or using `save_new`) to use `save` or `update`
+
+    """
+
+    def __init__(self, manifest_locator_or_text=None,
+                 api_client=None,
+                 keep_client=None,
+                 num_retries=None,
+                 parent=None,
+                 apiconfig=None,
+                 block_manager=None):
+        """Collection constructor.
+
+        :manifest_locator_or_text:
+          One of Arvados collection UUID, block locator of
+          a manifest, raw manifest text, or None (to create an empty collection).
+        :parent:
+          the parent Collection, may be None.
+        :apiconfig:
+          A dict containing keys for ARVADOS_API_HOST and ARVADOS_API_TOKEN.
+          Prefer this over supplying your own api_client and keep_client (except in testing).
+          Will use default config settings if not specified.
+        :api_client:
+          The API client object to use for requests.  If not specified, create one using `apiconfig`.
+        :keep_client:
+          the Keep client to use for requests.  If not specified, create one using `apiconfig`.
+        :num_retries:
+          the number of retries for API and Keep requests.
+        :block_manager:
+          the block manager to use.  If not specified, create one.
+
+        """
+        super(Collection, self).__init__(parent)
         self._api_client = api_client
         self._keep_client = keep_client
         self._block_manager = block_manager
 
         self._api_client = api_client
         self._keep_client = keep_client
         self._block_manager = block_manager
 
-        self.num_retries = num_retries
+        if apiconfig:
+            self._config = apiconfig
+        else:
+            self._config = config.settings()
+
+        self.num_retries = num_retries if num_retries is not None else 0
         self._manifest_locator = None
         self._manifest_text = None
         self._api_response = None
 
         self._manifest_locator = None
         self._manifest_text = None
         self._api_response = None
 
+        self.lock = threading.RLock()
+        self.callbacks = []
+        self.events = None
+
         if manifest_locator_or_text:
             if re.match(util.keep_locator_pattern, manifest_locator_or_text):
                 self._manifest_locator = manifest_locator_or_text
         if manifest_locator_or_text:
             if re.match(util.keep_locator_pattern, manifest_locator_or_text):
                 self._manifest_locator = manifest_locator_or_text
@@ -682,27 +1060,53 @@ class Collection(CollectionBase):
                 raise errors.ArgumentError(
                     "Argument to CollectionReader must be a manifest or a collection UUID")
 
                 raise errors.ArgumentError(
                     "Argument to CollectionReader must be a manifest or a collection UUID")
 
+            try:
+                self._populate()
+            except (IOError, errors.SyntaxError) as e:
+                raise errors.ArgumentError("Error processing manifest text: %s", e)
+
+    def root_collection(self):
+        return self
+
+    def stream_name(self):
+        return "."
+
+    def writable(self):
+        return True
+
+    @synchronized
+    @retry_method
+    def update(self, other=None, num_retries=None):
+        """Merge the latest collection on the API server with the current collection."""
+
+        if other is None:
+            if self._manifest_locator is None:
+                raise errors.ArgumentError("`other` is None but collection does not have a manifest_locator uuid")
+            response = self._my_api().collections().get(uuid=self._manifest_locator).execute(num_retries=num_retries)
+            other = CollectionReader(response["manifest_text"])
+        baseline = CollectionReader(self._manifest_text)
+        self.apply(baseline.diff(other))
+
+    @synchronized
     def _my_api(self):
         if self._api_client is None:
     def _my_api(self):
         if self._api_client is None:
-            if self.parent is not None:
-                return self.parent._my_api()
-            self._api_client = arvados.api('v1')
-            self._keep_client = None  # Make a new one with the new api.
+            self._api_client = ThreadSafeApiCache(self._config)
+            self._keep_client = self._api_client.keep
         return self._api_client
 
         return self._api_client
 
+    @synchronized
     def _my_keep(self):
         if self._keep_client is None:
     def _my_keep(self):
         if self._keep_client is None:
-            if self.parent is not None:
-                return self.parent._my_keep()
-            self._keep_client = KeepClient(api_client=self._my_api(),
-                                           num_retries=self.num_retries)
+            if self._api_client is None:
+                self._my_api()
+            else:
+                self._keep_client = KeepClient(api_client=self._api_client)
         return self._keep_client
 
         return self._keep_client
 
+    @synchronized
     def _my_block_manager(self):
         if self._block_manager is None:
     def _my_block_manager(self):
         if self._block_manager is None:
-            if self.parent is not None:
-                return self.parent._my_block_manager()
-            self._block_manager = BlockManager(self._my_keep())
+            self._block_manager = _BlockManager(self._my_keep())
         return self._block_manager
 
     def _populate_from_api_server(self):
         return self._block_manager
 
     def _populate_from_api_server(self):
@@ -734,14 +1138,13 @@ class Collection(CollectionBase):
             return e
 
     def _populate(self):
             return e
 
     def _populate(self):
-        self._items = {}
         if self._manifest_locator is None and self._manifest_text is None:
             return
         error_via_api = None
         error_via_keep = None
         should_try_keep = ((self._manifest_text is None) and
                            util.keep_locator_pattern.match(
         if self._manifest_locator is None and self._manifest_text is None:
             return
         error_via_api = None
         error_via_keep = None
         should_try_keep = ((self._manifest_text is None) and
                            util.keep_locator_pattern.match(
-                self._manifest_locator))
+                               self._manifest_locator))
         if ((self._manifest_text is None) and
             util.signed_locator_pattern.match(self._manifest_locator)):
             error_via_keep = self._populate_from_keep()
         if ((self._manifest_text is None) and
             util.signed_locator_pattern.match(self._manifest_locator)):
             error_via_keep = self._populate_from_keep()
@@ -756,7 +1159,7 @@ class Collection(CollectionBase):
             error_via_keep = self._populate_from_keep()
         if self._manifest_text is None:
             # Nothing worked!
             error_via_keep = self._populate_from_keep()
         if self._manifest_text is None:
             # Nothing worked!
-            raise arvados.errors.NotFoundError(
+            raise errors.NotFoundError(
                 ("Failed to retrieve collection '{}' " +
                  "from either API server ({}) or Keep ({})."
                  ).format(
                 ("Failed to retrieve collection '{}' " +
                  "from either API server ({}) or Keep ({})."
                  ).format(
@@ -764,375 +1167,359 @@ class Collection(CollectionBase):
                     error_via_api,
                     error_via_keep))
         # populate
                     error_via_api,
                     error_via_keep))
         # populate
-        import_manifest(self._manifest_text, self)
+        self._baseline_manifest = self._manifest_text
+        self._import_manifest(self._manifest_text)
 
 
-    def _populate_first(orig_func):
-        # Decorator for methods that read actual Collection data.
-        @functools.wraps(orig_func)
-        def wrapper(self, *args, **kwargs):
-            if self._items is None:
-                self._populate()
-            return orig_func(self, *args, **kwargs)
-        return wrapper
+
+    def _has_collection_uuid(self):
+        return self._manifest_locator is not None and re.match(util.collection_uuid_pattern, self._manifest_locator)
 
     def __enter__(self):
         return self
 
     def __exit__(self, exc_type, exc_value, traceback):
 
     def __enter__(self):
         return self
 
     def __exit__(self, exc_type, exc_value, traceback):
-        '''Support scoped auto-commit in a with: block'''
-        self.save(no_locator=True)
+        """Support scoped auto-commit in a with: block."""
+        if exc_type is not None:
+            if self.writable() and self._has_collection_uuid():
+                self.save()
         if self._block_manager is not None:
             self._block_manager.stop_threads()
 
         if self._block_manager is not None:
             self._block_manager.stop_threads()
 
-    @_populate_first
-    def find(self, path, create=False, create_collection=False):
-        '''Recursively search the specified file path.  May return either a Collection
-        or ArvadosFile.
+    @synchronized
+    def manifest_locator(self):
+        """Get the manifest locator, if any.
 
 
-        create: If true, create path components (i.e. Collections) that are
-        missing.  If "create" is False, return None if a path component is not
-        found.
+        The manifest locator will be set when the collection is loaded from an
+        API server record or the portable data hash of a manifest.
 
 
-        create_collection: If the path is not found, "create" is True, and
-        "create_collection" is False, then create and return a new ArvadosFile
-        for the last path component.  If "create_collection" is True, then
-        create and return a new Collection for the last path component.
-        '''
-        p = path.split("/")
-        if p[0] == '.':
-            del p[0]
-
-        if len(p) > 0:
-            item = self._items.get(p[0])
-            if len(p) == 1:
-                # item must be a file
-                if item is None and create:
-                    # create new file
-                    if create_collection:
-                        item = Collection(parent=self, num_retries=self.num_retries)
-                    else:
-                        item = ArvadosFile(self)
-                    self._items[p[0]] = item
-                return item
-            else:
-                if item is None and create:
-                    # create new collection
-                    item = Collection(parent=self, num_retries=self.num_retries)
-                    self._items[p[0]] = item
-                del p[0]
-                return item.find("/".join(p), create=create)
+        The manifest locator will be None if the collection is newly created or
+        was created directly from manifest text.  The method `save_new()` will
+        assign a manifest locator.
+
+        """
+        return self._manifest_locator
+
+    @synchronized
+    def clone(self, new_parent=None, readonly=False, new_config=None):
+        if new_config is None:
+            new_config = self._config
+        if readonly:
+            newcollection = CollectionReader(parent=new_parent, apiconfig=new_config)
         else:
         else:
-            return self
+            newcollection = Collection(parent=new_parent, apiconfig=new_config)
+
+        newcollection._clonefrom(self)
+        return newcollection
 
 
-    @_populate_first
+    @synchronized
     def api_response(self):
     def api_response(self):
-        """api_response() -> dict or None
+        """Returns information about this Collection fetched from the API server.
 
 
-        Returns information about this Collection fetched from the API server.
         If the Collection exists in Keep but not the API server, currently
         returns None.  Future versions may provide a synthetic response.
         If the Collection exists in Keep but not the API server, currently
         returns None.  Future versions may provide a synthetic response.
+
         """
         return self._api_response
 
         """
         return self._api_response
 
-    def open(self, path, mode):
-        '''Open a file-like object for access.
+    def find_or_create(self, path, create_type):
+        """See `RichCollectionBase.find_or_create`"""
+        if path == ".":
+            return self
+        else:
+            return super(Collection, self).find_or_create(path[2:] if path.startswith("./") else path, create_type)
 
 
-        path: path to a file in the collection
+    def find(self, path):
+        """See `RichCollectionBase.find`"""
+        if path == ".":
+            return self
+        else:
+            return super(Collection, self).find(path[2:] if path.startswith("./") else path)
 
 
-        mode: one of "r", "r+", "w", "w+", "a", "a+"
-        "r" opens for reading
+    def remove(self, path, recursive=False):
+        """See `RichCollectionBase.remove`"""
+        if path == ".":
+            raise errors.ArgumentError("Cannot remove '.'")
+        else:
+            return super(Collection, self).remove(path[2:] if path.startswith("./") else path, recursive)
 
 
-        "r+" opens for reading and writing.  Reads/writes share a file pointer.
+    @must_be_writable
+    @synchronized
+    @retry_method
+    def save(self, merge=True, num_retries=None):
+        """Save collection to an existing collection record.
 
 
-        "w", "w+" truncates to 0 and opens for reading and writing.  Reads/writes share a file pointer.
+        Commit pending buffer blocks to Keep, merge with remote record (if
+        merge=True, the default), write the manifest to Keep, and update the
+        collection record.
 
 
-        "a", "a+" opens for reading and writing.  All writes are appended to the end of the file.  Writing does not affect the file pointer for reading.
-        '''
-        mode = mode.replace("b", "")
-        if len(mode) == 0 or mode[0] not in ("r", "w", "a"):
-            raise ArgumentError("Bad mode '%s'" % mode)
-        create = (mode != "r")
+        Will raise AssertionError if not associated with a collection record on
+        the API server.  If you want to save a manifest to Keep only, see
+        `save_new()`.
 
 
-        f = self.find(path, create=create)
-        if f is None:
-            raise IOError((errno.ENOENT, "File not found"))
-        if not isinstance(f, ArvadosFile):
-            raise IOError((errno.EISDIR, "Path must refer to a file."))
+        :merge:
+          Update and merge remote changes before saving.  Otherwise, any
+          remote changes will be ignored and overwritten.
 
 
-        if mode[0] == "w":
-            f.truncate(0)
+        :num_retries:
+          Retry count on API calls (if None,  use the collection default)
 
 
-        if mode == "r":
-            return ArvadosFileReader(f, path, mode)
-        else:
-            return ArvadosFileWriter(f, path, mode)
+        """
+        if self.modified():
+            if not self._has_collection_uuid():
+                raise AssertionError("Collection manifest_locator must be a collection uuid.  Use save_new() for new collections.")
+            self._my_block_manager().commit_all()
+            if merge:
+                self.update()
+            self._my_keep().put(self.manifest_text(strip=True), num_retries=num_retries)
+
+            text = self.manifest_text(strip=False)
+            self._api_response = self._my_api().collections().update(
+                uuid=self._manifest_locator,
+                body={'manifest_text': text}
+                ).execute(
+                    num_retries=num_retries)
+            self._manifest_text = self._api_response["manifest_text"]
+            self.set_unmodified()
 
 
-    @_populate_first
-    def modified(self):
-        '''Test if the collection (or any subcollection or file) has been modified
-        since it was created.'''
-        for k,v in self._items.items():
-            if v.modified():
-                return True
-        return False
 
 
-    @_populate_first
-    def set_unmodified(self):
-        '''Recursively clear modified flag'''
-        for k,v in self._items.items():
-            v.set_unmodified()
+    @must_be_writable
+    @synchronized
+    @retry_method
+    def save_new(self, name=None, create_collection_record=True, owner_uuid=None, ensure_unique_name=False, num_retries=None):
+        """Save collection to a new collection record.
 
 
-    @_populate_first
-    def __iter__(self):
-        '''Iterate over names of files and collections contained in this collection.'''
-        return self._items.iterkeys()
+        Commit pending buffer blocks to Keep, write the manifest to Keep, and
+        create a new collection record (if create_collection_record True).
+        After creating a new collection record, this Collection object will be
+        associated with the new record used by `save()`.
 
 
-    @_populate_first
-    def iterkeys(self):
-        '''Iterate over names of files and collections directly contained in this collection.'''
-        return self._items.iterkeys()
+        :name:
+          The collection name.
 
 
-    @_populate_first
-    def __getitem__(self, k):
-        '''Get a file or collection that is directly contained by this collection.  Use
-        find() for path serach.'''
-        return self._items[k]
+        :create_collection_record:
+          If True, create a collection record.  If False, only save the manifest to keep.
 
 
-    @_populate_first
-    def __contains__(self, k):
-        '''If there is a file or collection a directly contained by this collection
-        with name "k".'''
-        return k in self._items
+        :owner_uuid:
+          the user, or project uuid that will own this collection.
+          If None, defaults to the current user.
 
 
-    @_populate_first
-    def __len__(self):
-        '''Get the number of items directly contained in this collection'''
-        return len(self._items)
+        :ensure_unique_name:
+          If True, ask the API server to rename the collection
+          if it conflicts with a collection with the same name and owner.  If
+          False, a name conflict will result in an error.
 
 
-    @_populate_first
-    def __delitem__(self, p):
-        '''Delete an item by name which is directly contained by this collection.'''
-        del self._items[p]
+        :num_retries:
+          Retry count on API calls (if None,  use the collection default)
 
 
-    @_populate_first
-    def keys(self):
-        '''Get a list of names of files and collections directly contained in this collection.'''
-        return self._items.keys()
+        """
+        self._my_block_manager().commit_all()
+        self._my_keep().put(self.manifest_text(strip=True), num_retries=num_retries)
+        text = self.manifest_text(strip=False)
 
 
-    @_populate_first
-    def values(self):
-        '''Get a list of files and collection objects directly contained in this collection.'''
-        return self._items.values()
+        if create_collection_record:
+            if name is None:
+                name = "Collection created %s" % (time.strftime("%Y-%m-%d %H:%M:%S %Z", time.localtime()))
 
 
-    @_populate_first
-    def items(self):
-        '''Get a list of (name, object) tuples directly contained in this collection.'''
-        return self._items.items()
+            body = {"manifest_text": text,
+                    "name": name}
+            if owner_uuid:
+                body["owner_uuid"] = owner_uuid
 
 
-    @_populate_first
-    def exists(self, path):
-        '''Test if there is a file or collection at "path"'''
-        return self.find(path) != None
-
-    @_populate_first
-    def remove(self, path):
-        '''Test if there is a file or collection at "path"'''
-        p = path.split("/")
-        if p[0] == '.':
-            del p[0]
-
-        if len(p) > 0:
-            item = self._items.get(p[0])
-            if item is None:
-                raise IOError((errno.ENOENT, "File not found"))
-            if len(p) == 1:
-                del self._items[p[0]]
-            else:
-                del p[0]
-                item.remove("/".join(p))
-        else:
-            raise IOError((errno.ENOENT, "File not found"))
+            self._api_response = self._my_api().collections().create(ensure_unique_name=ensure_unique_name, body=body).execute(num_retries=num_retries)
+            text = self._api_response["manifest_text"]
 
 
-    @_populate_first
-    def manifest_text(self, strip=False, normalize=False):
-        '''Get the manifest text for this collection, sub collections and files.
+            self._manifest_locator = self._api_response["uuid"]
 
 
-        strip: If True, remove signing tokens from block locators if present.
-        If False, block locators are left unchanged.
+        self._manifest_text = text
+        self.set_unmodified()
 
 
-        normalize: If True, always export the manifest text in normalized form
-        even if the Collection is not modified.  If False and the collection is
-        not modified, return the original manifest text even if it is not in
-        normalized form.
-        '''
-        if self.modified() or self._manifest_text is None or normalize:
-            return export_manifest(self, stream_name=".", portable_locators=strip)
-        else:
-            if strip:
-                return self.stripped_manifest()
-            else:
-                return self._manifest_text
+    @synchronized
+    def subscribe(self, callback):
+        self.callbacks.append(callback)
 
 
-    def portable_data_hash(self):
-        '''Get the portable data hash for this collection's manifest.'''
-        stripped = self.manifest_text(strip=True)
-        return hashlib.md5(stripped).hexdigest() + '+' + str(len(stripped))
+    @synchronized
+    def unsubscribe(self, callback):
+        self.callbacks.remove(callback)
 
 
-    @_populate_first
-    def save(self, no_locator=False):
-        '''Commit pending buffer blocks to Keep, write the manifest to Keep, and
-        update the collection record to Keep.
+    @synchronized
+    def notify(self, event, collection, name, item):
+        for c in self.callbacks:
+            c(event, collection, name, item)
 
 
-        no_locator: If False and there is no collection uuid associated with
-        this Collection, raise an error.  If True, do not raise an error.
-        '''
-        if self.modified():
-            self._my_block_manager().commit_all()
-            self._my_keep().put(self.manifest_text(strip=True))
-            if self._manifest_locator is not None and re.match(util.collection_uuid_pattern, self._manifest_locator):
-                self._api_response = self._my_api().collections().update(
-                    uuid=self._manifest_locator,
-                    body={'manifest_text': self.manifest_text(strip=False)}
-                    ).execute(
-                        num_retries=self.num_retries)
-            elif not no_locator:
-                raise AssertionError("Collection manifest_locator must be a collection uuid.  Use save_as() for new collections.")
-            self.set_unmodified()
+    @synchronized
+    def _import_manifest(self, manifest_text):
+        """Import a manifest into a `Collection`.
 
 
-    @_populate_first
-    def save_as(self, name, owner_uuid=None, ensure_unique_name=False):
-        '''Save a new collection record.
+        :manifest_text:
+          The manifest text to import from.
 
 
-        name: The collection name.
+        """
+        if len(self) > 0:
+            raise ArgumentError("Can only import manifest into an empty collection")
 
 
-        owner_uuid: the user, or project uuid that will own this collection.
-        If None, defaults to the current user.
+        STREAM_NAME = 0
+        BLOCKS = 1
+        SEGMENTS = 2
+
+        stream_name = None
+        state = STREAM_NAME
+
+        for token_and_separator in re.finditer(r'(\S+)(\s+|$)', manifest_text):
+            tok = token_and_separator.group(1)
+            sep = token_and_separator.group(2)
+
+            if state == STREAM_NAME:
+                # starting a new stream
+                stream_name = tok.replace('\\040', ' ')
+                blocks = []
+                segments = []
+                streamoffset = 0L
+                state = BLOCKS
+                continue
+
+            if state == BLOCKS:
+                block_locator = re.match(r'[0-9a-f]{32}\+(\d+)(\+\S+)*', tok)
+                if block_locator:
+                    blocksize = long(block_locator.group(1))
+                    blocks.append(Range(tok, streamoffset, blocksize))
+                    streamoffset += blocksize
+                else:
+                    state = SEGMENTS
+
+            if state == SEGMENTS:
+                file_segment = re.search(r'^(\d+):(\d+):(\S+)', tok)
+                if file_segment:
+                    pos = long(file_segment.group(1))
+                    size = long(file_segment.group(2))
+                    name = file_segment.group(3).replace('\\040', ' ')
+                    filepath = os.path.join(stream_name, name)
+                    afile = self.find_or_create(filepath, FILE)
+                    if isinstance(afile, ArvadosFile):
+                        afile.add_segment(blocks, pos, size)
+                    else:
+                        raise errors.SyntaxError("File %s conflicts with stream of the same name.", filepath)
+                else:
+                    # error!
+                    raise errors.SyntaxError("Invalid manifest format")
+
+            if sep == "\n":
+                stream_name = None
+                state = STREAM_NAME
 
 
-        ensure_unique_name: If True, ask the API server to rename the
-        collection if it conflicts with a collection with the same name and
-        owner.  If False, a name conflict will result in an error.
-        '''
-        self._my_block_manager().commit_all()
-        self._my_keep().put(self.manifest_text(strip=True))
-        body = {"manifest_text": self.manifest_text(strip=False),
-                "name": name}
-        if owner_uuid:
-            body["owner_uuid"] = owner_uuid
-        self._api_response = self._my_api().collections().create(ensure_unique_name=ensure_unique_name, body=body).execute(num_retries=self.num_retries)
-        self._manifest_locator = self._api_response["uuid"]
         self.set_unmodified()
 
 
         self.set_unmodified()
 
 
-def import_manifest(manifest_text, into_collection=None, api_client=None, keep=None, num_retries=None):
-    '''Import a manifest into a Collection.
+class Subcollection(RichCollectionBase):
+    """This is a subdirectory within a collection that doesn't have its own API
+    server record.
 
 
-    manifest_text: The manifest text to import from.
+    It falls under the umbrella of the root collection.
 
 
-    into_collection: The Collection that will be initialized (must be empty).
-    If None, create a new Collection object.
+    """
 
 
-    api_client: The API client object that will be used when creating a new Collection object.
+    def __init__(self, parent):
+        super(Subcollection, self).__init__(parent)
+        self.lock = self.root_collection().lock
+        self._manifest_text = None
 
 
-    keep: The keep client object that will be used when creating a new Collection object.
+    def root_collection(self):
+        return self.parent.root_collection()
 
 
-    num_retries: the default number of api client and keep retries on error.
-    '''
-    if into_collection is not None:
-        if len(into_collection) > 0:
-            raise ArgumentError("Can only import manifest into an empty collection")
-        c = into_collection
-    else:
-        c = Collection(api_client=api_client, keep_client=keep, num_retries=num_retries)
-
-    STREAM_NAME = 0
-    BLOCKS = 1
-    SEGMENTS = 2
-
-    stream_name = None
-    state = STREAM_NAME
-
-    for n in re.finditer(r'(\S+)(\s+|$)', manifest_text):
-        tok = n.group(1)
-        sep = n.group(2)
-
-        if state == STREAM_NAME:
-            # starting a new stream
-            stream_name = tok.replace('\\040', ' ')
-            blocks = []
-            segments = []
-            streamoffset = 0L
-            state = BLOCKS
-            continue
-
-        if state == BLOCKS:
-            s = re.match(r'[0-9a-f]{32}\+(\d+)(\+\S+)*', tok)
-            if s:
-                blocksize = long(s.group(1))
-                blocks.append(Range(tok, streamoffset, blocksize))
-                streamoffset += blocksize
-            else:
-                state = SEGMENTS
-
-        if state == SEGMENTS:
-            s = re.search(r'^(\d+):(\d+):(\S+)', tok)
-            if s:
-                pos = long(s.group(1))
-                size = long(s.group(2))
-                name = s.group(3).replace('\\040', ' ')
-                f = c.find("%s/%s" % (stream_name, name), create=True)
-                f.add_segment(blocks, pos, size)
-            else:
-                # error!
-                raise errors.SyntaxError("Invalid manifest format")
-
-        if sep == "\n":
-            stream_name = None
-            state = STREAM_NAME
-
-    c.set_unmodified()
-    return c
-
-def export_manifest(item, stream_name=".", portable_locators=False):
-    '''Create a manifest for "item" (must be a Collection or ArvadosFile).  If
-    "item" is a is a Collection, this will also export subcollections.
-
-    stream_name: the name of the stream when exporting "item".
-
-    portable_locators: If True, strip any permission hints on block locators.
-    If False, use block locators as-is.
-    '''
-    buf = ""
-    if isinstance(item, Collection):
-        stream = {}
-        sorted_keys = sorted(item.keys())
-        for k in [s for s in sorted_keys if isinstance(item[s], ArvadosFile)]:
-            v = item[k]
-            st = []
-            for s in v.segments:
-                loc = s.locator
-                if loc.startswith("bufferblock"):
-                    loc = v.parent._my_block_manager()._bufferblocks[loc].locator()
-                if portable_locators:
-                    loc = KeepLocator(loc).stripped()
-                st.append(LocatorAndRange(loc, locator_block_size(loc),
-                                     s.segment_offset, s.range_size))
-            stream[k] = st
-        if stream:
-            buf += ' '.join(normalize_stream(stream_name, stream))
-            buf += "\n"
-        for k in [s for s in sorted_keys if isinstance(item[s], Collection)]:
-            buf += export_manifest(item[k], stream_name=os.path.join(stream_name, k), portable_locators=portable_locators)
-    elif isinstance(item, ArvadosFile):
-        st = []
-        for s in item.segments:
-            loc = s.locator
-            if loc.startswith("bufferblock"):
-                loc = item._bufferblocks[loc].calculate_locator()
-            if portable_locators:
-                loc = KeepLocator(loc).stripped()
-            st.append(LocatorAndRange(loc, locator_block_size(loc),
-                                 s.segment_offset, s.range_size))
-        stream[stream_name] = st
-        buf += ' '.join(normalize_stream(stream_name, stream))
-        buf += "\n"
-    return buf
+    def writable(self):
+        return self.root_collection().writable()
+
+    def _my_api(self):
+        return self.root_collection()._my_api()
+
+    def _my_keep(self):
+        return self.root_collection()._my_keep()
+
+    def _my_block_manager(self):
+        return self.root_collection()._my_block_manager()
+
+    def notify(self, event, collection, name, item):
+        return self.root_collection().notify(event, collection, name, item)
+
+    def stream_name(self):
+        for k, v in self.parent.items():
+            if v is self:
+                return os.path.join(self.parent.stream_name(), k)
+        return '.'
+
+    @synchronized
+    def clone(self, new_parent):
+        c = Subcollection(new_parent)
+        c._clonefrom(self)
+        return c
+
+
+class CollectionReader(Collection):
+    """A read-only collection object.
+
+    Initialize from an api collection record locator, a portable data hash of a
+    manifest, or raw manifest text.  See `Collection` constructor for detailed
+    options.
+
+    """
+    def __init__(self, manifest_locator_or_text, *args, **kwargs):
+        self._in_init = True
+        super(CollectionReader, self).__init__(manifest_locator_or_text, *args, **kwargs)
+        self._in_init = False
+
+        # Forego any locking since it should never change once initialized.
+        self.lock = NoopLock()
+
+        # Backwards compatability with old CollectionReader
+        # all_streams() and all_files()
+        self._streams = None
+
+    def writable(self):
+        return self._in_init
+
+    def _populate_streams(orig_func):
+        @functools.wraps(orig_func)
+        def populate_streams_wrapper(self, *args, **kwargs):
+            # Defer populating self._streams until needed since it creates a copy of the manifest.
+            if self._streams is None:
+                if self._manifest_text:
+                    self._streams = [sline.split()
+                                     for sline in self._manifest_text.split("\n")
+                                     if sline]
+                else:
+                    self._streams = []
+            return orig_func(self, *args, **kwargs)
+        return populate_streams_wrapper
+
+    @_populate_streams
+    def normalize(self):
+        """Normalize the streams returned by `all_streams`.
+
+        This method is kept for backwards compatability and only affects the
+        behavior of `all_streams()` and `all_files()`
+
+        """
+
+        # Rearrange streams
+        streams = {}
+        for s in self.all_streams():
+            for f in s.all_files():
+                streamname, filename = split(s.name() + "/" + f.name())
+                if streamname not in streams:
+                    streams[streamname] = {}
+                if filename not in streams[streamname]:
+                    streams[streamname][filename] = []
+                for r in f.segments:
+                    streams[streamname][filename].extend(s.locators_and_ranges(r.locator, r.range_size))
+
+        self._streams = [normalize_stream(s, streams[s])
+                         for s in sorted(streams)]
+    @_populate_streams
+    def all_streams(self):
+        return [StreamReader(s, self._my_keep(), num_retries=self.num_retries)
+                for s in self._streams]
+
+    @_populate_streams
+    def all_files(self):
+        for s in self.all_streams():
+            for f in s.all_files():
+                yield f