12315: Tidy up test params.
[arvados.git] / sdk / python / arvados / arvfile.py
index 95dcea0ad3dc28596fc7857256ef5aafc96583b5..aa6bdad90bea0551f7043fbdd0889f6dea2ff6a8 100644 (file)
@@ -1,21 +1,41 @@
-import functools
-import os
-import zlib
+# Copyright (C) The Arvados Authors. All rights reserved.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+from __future__ import absolute_import
+from __future__ import division
+from future import standard_library
+from future.utils import listitems, listvalues
+standard_library.install_aliases()
+from builtins import range
+from builtins import object
 import bz2
-import config
-import hashlib
-import threading
-import Queue
+import collections
 import copy
 import errno
+import functools
+import hashlib
+import logging
+import os
+import queue
 import re
+import sys
+import threading
+import uuid
+import zlib
 
+from . import config
 from .errors import KeepWriteError, AssertionError, ArgumentError
 from .keep import KeepLocator
 from ._normalize_stream import normalize_stream
-from ._ranges import locators_and_ranges, replace_range, Range
+from ._ranges import locators_and_ranges, replace_range, Range, LocatorAndRange
 from .retry import retry_method
 
+MOD = "mod"
+WRITE = "write"
+
+_logger = logging.getLogger('arvados.arvfile')
+
 def split(path):
     """split(path) -> streamname, filename
 
@@ -30,6 +50,12 @@ def split(path):
         stream_name, file_name = '.', path
     return stream_name, file_name
 
+
+class UnownedBlockError(Exception):
+    """Raised when there's an writable block without an owner on the BlockManager."""
+    pass
+
+
 class _FileLikeObjectBase(object):
     def __init__(self, name, mode):
         self.name = name
@@ -62,7 +88,10 @@ class _FileLikeObjectBase(object):
 class ArvadosFileReaderBase(_FileLikeObjectBase):
     def __init__(self, name, mode, num_retries=None):
         super(ArvadosFileReaderBase, self).__init__(name, mode)
-        self._filepos = 0L
+        self._binary = 'b' in mode
+        if sys.version_info >= (3, 0) and not self._binary:
+            raise NotImplementedError("text mode {!r} is not implemented".format(mode))
+        self._filepos = 0
         self.num_retries = num_retries
         self._readline_cache = (None, None)
 
@@ -82,17 +111,29 @@ class ArvadosFileReaderBase(_FileLikeObjectBase):
             pos += self._filepos
         elif whence == os.SEEK_END:
             pos += self.size()
-        self._filepos = min(max(pos, 0L), self.size())
+        if pos < 0:
+            raise IOError(errno.EINVAL, "Tried to seek to negative file offset.")
+        self._filepos = pos
+        return self._filepos
 
     def tell(self):
         return self._filepos
 
+    def readable(self):
+        return True
+
+    def writable(self):
+        return False
+
+    def seekable(self):
+        return True
+
     @_FileLikeObjectBase._before_close
     @retry_method
     def readall(self, size=2**20, num_retries=None):
         while True:
             data = self.read(size, num_retries=num_retries)
-            if data == '':
+            if len(data) == 0:
                 break
             yield data
 
@@ -102,28 +143,30 @@ class ArvadosFileReaderBase(_FileLikeObjectBase):
         cache_pos, cache_data = self._readline_cache
         if self.tell() == cache_pos:
             data = [cache_data]
+            self._filepos += len(cache_data)
         else:
-            data = ['']
+            data = [b'']
         data_size = len(data[-1])
-        while (data_size < size) and ('\n' not in data[-1]):
+        while (data_size < size) and (b'\n' not in data[-1]):
             next_read = self.read(2 ** 20, num_retries=num_retries)
             if not next_read:
                 break
             data.append(next_read)
             data_size += len(next_read)
-        data = ''.join(data)
+        data = b''.join(data)
         try:
-            nextline_index = data.index('\n') + 1
+            nextline_index = data.index(b'\n') + 1
         except ValueError:
             nextline_index = len(data)
         nextline_index = min(nextline_index, size)
+        self._filepos -= len(data) - nextline_index
         self._readline_cache = (self.tell(), data[nextline_index:])
-        return data[:nextline_index]
+        return data[:nextline_index].decode()
 
     @_FileLikeObjectBase._before_close
     @retry_method
     def decompress(self, decompress, size, num_retries=None):
-        for segment in self.readall(size, num_retries):
+        for segment in self.readall(size, num_retries=num_retries):
             data = decompress(segment)
             if data:
                 yield data
@@ -153,16 +196,16 @@ class ArvadosFileReaderBase(_FileLikeObjectBase):
             data_size += len(s)
             if data_size >= sizehint:
                 break
-        return ''.join(data).splitlines(True)
+        return b''.join(data).decode().splitlines(True)
 
     def size(self):
-        raise NotImplementedError()
+        raise IOError(errno.ENOSYS, "Not implemented")
 
     def read(self, size, num_retries=None):
-        raise NotImplementedError()
+        raise IOError(errno.ENOSYS, "Not implemented")
 
     def readfrom(self, start, size, num_retries=None):
-        raise NotImplementedError()
+        raise IOError(errno.ENOSYS, "Not implemented")
 
 
 class StreamFileReader(ArvadosFileReaderBase):
@@ -190,15 +233,15 @@ class StreamFileReader(ArvadosFileReaderBase):
     def read(self, size, num_retries=None):
         """Read up to 'size' bytes from the stream, starting at the current file position"""
         if size == 0:
-            return ''
+            return b''
 
-        data = ''
+        data = b''
         available_chunks = locators_and_ranges(self.segments, self._filepos, size)
         if available_chunks:
             lr = available_chunks[0]
             data = self._stream.readfrom(lr.locator+lr.segment_offset,
-                                          lr.segment_size,
-                                          num_retries=num_retries)
+                                         lr.segment_size,
+                                         num_retries=num_retries)
 
         self._filepos += len(data)
         return data
@@ -208,13 +251,13 @@ class StreamFileReader(ArvadosFileReaderBase):
     def readfrom(self, start, size, num_retries=None):
         """Read up to 'size' bytes from the stream, starting at 'start'"""
         if size == 0:
-            return ''
+            return b''
 
         data = []
         for lr in locators_and_ranges(self.segments, start, size):
             data.append(self._stream.readfrom(lr.locator+lr.segment_offset, lr.segment_size,
                                               num_retries=num_retries))
-        return ''.join(data)
+        return b''.join(data)
 
     def as_manifest(self):
         segs = []
@@ -230,6 +273,13 @@ def synchronized(orig_func):
             return orig_func(self, *args, **kwargs)
     return synchronized_wrapper
 
+
+class StateChangeError(Exception):
+    def __init__(self, message, state, nextstate):
+        super(StateChangeError, self).__init__(message)
+        self.state = state
+        self.nextstate = nextstate
+
 class _BufferBlock(object):
     """A stand-in for a Keep block that is in the process of being written.
 
@@ -253,6 +303,8 @@ class _BufferBlock(object):
     WRITABLE = 0
     PENDING = 1
     COMMITTED = 2
+    ERROR = 3
+    DELETED = 4
 
     def __init__(self, blockid, starting_capacity, owner):
         """
@@ -274,6 +326,8 @@ class _BufferBlock(object):
         self._locator = None
         self.owner = owner
         self.lock = threading.Lock()
+        self.wait_for_commit = threading.Event()
+        self.error = None
 
     @synchronized
     def append(self, data):
@@ -284,6 +338,8 @@ class _BufferBlock(object):
 
         """
         if self._state == _BufferBlock.WRITABLE:
+            if not isinstance(data, bytes) and not isinstance(data, memoryview):
+                data = data.encode()
             while (self.write_pointer+len(data)) > len(self.buffer_block):
                 new_buffer_block = bytearray(len(self.buffer_block) * 2)
                 new_buffer_block[0:self.write_pointer] = self.buffer_block[0:self.write_pointer]
@@ -295,17 +351,30 @@ class _BufferBlock(object):
         else:
             raise AssertionError("Buffer block is not writable")
 
+    STATE_TRANSITIONS = frozenset([
+            (WRITABLE, PENDING),
+            (PENDING, COMMITTED),
+            (PENDING, ERROR),
+            (ERROR, PENDING)])
+
     @synchronized
-    def set_state(self, nextstate, loc=None):
-        if ((self._state == _BufferBlock.WRITABLE and nextstate == _BufferBlock.PENDING) or
-            (self._state == _BufferBlock.PENDING and nextstate == _BufferBlock.COMMITTED)):
-            self._state = nextstate
-            if self._state == _BufferBlock.COMMITTED:
-                self._locator = loc
-                self.buffer_view = None
-                self.buffer_block = None
-        else:
-            raise AssertionError("Invalid state change from %s to %s" % (self.state, nextstate))
+    def set_state(self, nextstate, val=None):
+        if (self._state, nextstate) not in self.STATE_TRANSITIONS:
+            raise StateChangeError("Invalid state change from %s to %s" % (self._state, nextstate), self._state, nextstate)
+        self._state = nextstate
+
+        if self._state == _BufferBlock.PENDING:
+            self.wait_for_commit.clear()
+
+        if self._state == _BufferBlock.COMMITTED:
+            self._locator = val
+            self.buffer_view = None
+            self.buffer_block = None
+            self.wait_for_commit.set()
+
+        if self._state == _BufferBlock.ERROR:
+            self.error = val
+            self.wait_for_commit.set()
 
     @synchronized
     def state(self):
@@ -325,11 +394,61 @@ class _BufferBlock(object):
     @synchronized
     def clone(self, new_blockid, owner):
         if self._state == _BufferBlock.COMMITTED:
-            raise AssertionError("Can only duplicate a writable or pending buffer block")
+            raise AssertionError("Cannot duplicate committed buffer block")
         bufferblock = _BufferBlock(new_blockid, self.size(), owner)
         bufferblock.append(self.buffer_view[0:self.size()])
         return bufferblock
 
+    @synchronized
+    def clear(self):
+        self._state = _BufferBlock.DELETED
+        self.owner = None
+        self.buffer_block = None
+        self.buffer_view = None
+
+    @synchronized
+    def repack_writes(self):
+        """Optimize buffer block by repacking segments in file sequence.
+
+        When the client makes random writes, they appear in the buffer block in
+        the sequence they were written rather than the sequence they appear in
+        the file.  This makes for inefficient, fragmented manifests.  Attempt
+        to optimize by repacking writes in file sequence.
+
+        """
+        if self._state != _BufferBlock.WRITABLE:
+            raise AssertionError("Cannot repack non-writable block")
+
+        segs = self.owner.segments()
+
+        # Collect the segments that reference the buffer block.
+        bufferblock_segs = [s for s in segs if s.locator == self.blockid]
+
+        # Collect total data referenced by segments (could be smaller than
+        # bufferblock size if a portion of the file was written and
+        # then overwritten).
+        write_total = sum([s.range_size for s in bufferblock_segs])
+
+        if write_total < self.size() or len(bufferblock_segs) > 1:
+            # If there's more than one segment referencing this block, it is
+            # due to out-of-order writes and will produce a fragmented
+            # manifest, so try to optimize by re-packing into a new buffer.
+            contents = self.buffer_view[0:self.write_pointer].tobytes()
+            new_bb = _BufferBlock(None, write_total, None)
+            for t in bufferblock_segs:
+                new_bb.append(contents[t.segment_offset:t.segment_offset+t.range_size])
+                t.segment_offset = new_bb.size() - t.range_size
+
+            self.buffer_block = new_bb.buffer_block
+            self.buffer_view = new_bb.buffer_view
+            self.write_pointer = new_bb.write_pointer
+            self._locator = None
+            new_bb.clear()
+            self.owner.set_segments(segs)
+
+    def __repr__(self):
+        return "<BufferBlock %s>" % (self.blockid)
+
 
 class NoopLock(object):
     def __enter__(self):
@@ -349,7 +468,7 @@ def must_be_writable(orig_func):
     @functools.wraps(orig_func)
     def must_be_writable_wrapper(self, *args, **kwargs):
         if not self.writable():
-            raise IOError((errno.EROFS, "Collection must be writable."))
+            raise IOError(errno.EROFS, "Collection is read-only.")
         return orig_func(self, *args, **kwargs)
     return must_be_writable_wrapper
 
@@ -361,19 +480,29 @@ class _BlockManager(object):
     Collection of ArvadosFiles.
 
     """
-    def __init__(self, keep):
+
+    DEFAULT_PUT_THREADS = 2
+    DEFAULT_GET_THREADS = 2
+
+    def __init__(self, keep, copies=None, put_threads=None):
         """keep: KeepClient object to use"""
         self._keep = keep
-        self._bufferblocks = {}
+        self._bufferblocks = collections.OrderedDict()
         self._put_queue = None
-        self._put_errors = None
         self._put_threads = None
         self._prefetch_queue = None
         self._prefetch_threads = None
         self.lock = threading.Lock()
         self.prefetch_enabled = True
-        self.num_put_threads = 2
-        self.num_get_threads = 2
+        if put_threads:
+            self.num_put_threads = put_threads
+        else:
+            self.num_put_threads = _BlockManager.DEFAULT_PUT_THREADS
+        self.num_get_threads = _BlockManager.DEFAULT_GET_THREADS
+        self.copies = copies
+        self._pending_write_size = 0
+        self.threads_lock = threading.Lock()
+        self.padding_block = None
 
     @synchronized
     def alloc_bufferblock(self, blockid=None, starting_capacity=2**14, owner=None):
@@ -389,8 +518,11 @@ class _BlockManager(object):
           ArvadosFile that owns this block
 
         """
+        return self._alloc_bufferblock(blockid, starting_capacity, owner)
+
+    def _alloc_bufferblock(self, blockid=None, starting_capacity=2**14, owner=None):
         if blockid is None:
-            blockid = "bufferblock%i" % len(self._bufferblocks)
+            blockid = str(uuid.uuid4())
         bufferblock = _BufferBlock(blockid, starting_capacity=starting_capacity, owner=owner)
         self._bufferblocks[bufferblock.blockid] = bufferblock
         return bufferblock
@@ -406,7 +538,7 @@ class _BlockManager(object):
           ArvadosFile that owns the new block
 
         """
-        new_blockid = "bufferblock%i" % len(self._bufferblocks)
+        new_blockid = str(uuid.uuid4())
         bufferblock = block.clone(new_blockid, owner)
         self._bufferblocks[bufferblock.blockid] = bufferblock
         return bufferblock
@@ -415,6 +547,72 @@ class _BlockManager(object):
     def is_bufferblock(self, locator):
         return locator in self._bufferblocks
 
+    def _commit_bufferblock_worker(self):
+        """Background uploader thread."""
+
+        while True:
+            try:
+                bufferblock = self._put_queue.get()
+                if bufferblock is None:
+                    return
+
+                if self.copies is None:
+                    loc = self._keep.put(bufferblock.buffer_view[0:bufferblock.write_pointer].tobytes())
+                else:
+                    loc = self._keep.put(bufferblock.buffer_view[0:bufferblock.write_pointer].tobytes(), copies=self.copies)
+                bufferblock.set_state(_BufferBlock.COMMITTED, loc)
+            except Exception as e:
+                bufferblock.set_state(_BufferBlock.ERROR, e)
+            finally:
+                if self._put_queue is not None:
+                    self._put_queue.task_done()
+
+    def start_put_threads(self):
+        with self.threads_lock:
+            if self._put_threads is None:
+                # Start uploader threads.
+
+                # If we don't limit the Queue size, the upload queue can quickly
+                # grow to take up gigabytes of RAM if the writing process is
+                # generating data more quickly than it can be send to the Keep
+                # servers.
+                #
+                # With two upload threads and a queue size of 2, this means up to 4
+                # blocks pending.  If they are full 64 MiB blocks, that means up to
+                # 256 MiB of internal buffering, which is the same size as the
+                # default download block cache in KeepClient.
+                self._put_queue = queue.Queue(maxsize=2)
+
+                self._put_threads = []
+                for i in range(0, self.num_put_threads):
+                    thread = threading.Thread(target=self._commit_bufferblock_worker)
+                    self._put_threads.append(thread)
+                    thread.daemon = True
+                    thread.start()
+
+    def _block_prefetch_worker(self):
+        """The background downloader thread."""
+        while True:
+            try:
+                b = self._prefetch_queue.get()
+                if b is None:
+                    return
+                self._keep.get(b)
+            except Exception:
+                _logger.exception("Exception doing block prefetch")
+
+    @synchronized
+    def start_get_threads(self):
+        if self._prefetch_threads is None:
+            self._prefetch_queue = queue.Queue()
+            self._prefetch_threads = []
+            for i in range(0, self.num_get_threads):
+                thread = threading.Thread(target=self._block_prefetch_worker)
+                self._prefetch_threads.append(thread)
+                thread.daemon = True
+                thread.start()
+
+
     @synchronized
     def stop_threads(self):
         """Shut down and wait for background upload and download threads to finish."""
@@ -426,7 +624,6 @@ class _BlockManager(object):
                 t.join()
         self._put_threads = None
         self._put_queue = None
-        self._put_errors = None
 
         if self._prefetch_threads is not None:
             for t in self._prefetch_threads:
@@ -436,63 +633,141 @@ class _BlockManager(object):
         self._prefetch_threads = None
         self._prefetch_queue = None
 
-    def commit_bufferblock(self, block):
-        """Initiate a background upload of a bufferblock.
+    def __enter__(self):
+        return self
 
-        This will block if the upload queue is at capacity, otherwise it will
-        return immediately.
+    def __exit__(self, exc_type, exc_value, traceback):
+        self.stop_threads()
 
-        """
+    @synchronized
+    def repack_small_blocks(self, force=False, sync=False, closed_file_size=0):
+        """Packs small blocks together before uploading"""
 
-        def commit_bufferblock_worker(self):
-            """Background uploader thread."""
+        self._pending_write_size += closed_file_size
 
-            while True:
-                try:
-                    bufferblock = self._put_queue.get()
-                    if bufferblock is None:
-                        return
-                    loc = self._keep.put(bufferblock.buffer_view[0:bufferblock.write_pointer].tobytes())
-                    bufferblock.set_state(_BufferBlock.COMMITTED, loc)
+        # Check if there are enough small blocks for filling up one in full
+        if not (force or (self._pending_write_size >= config.KEEP_BLOCK_SIZE)):
+            return
 
-                except Exception as e:
-                    self._put_errors.put((bufferblock.locator(), e))
-                finally:
-                    if self._put_queue is not None:
-                        self._put_queue.task_done()
+        # Search blocks ready for getting packed together before being
+        # committed to Keep.
+        # A WRITABLE block always has an owner.
+        # A WRITABLE block with its owner.closed() implies that its
+        # size is <= KEEP_BLOCK_SIZE/2.
+        try:
+            small_blocks = [b for b in listvalues(self._bufferblocks)
+                            if b.state() == _BufferBlock.WRITABLE and b.owner.closed()]
+        except AttributeError:
+            # Writable blocks without owner shouldn't exist.
+            raise UnownedBlockError()
+
+        if len(small_blocks) <= 1:
+            # Not enough small blocks for repacking
+            return
 
-        with self.lock:
-            if self._put_threads is None:
-                # Start uploader threads.
+        for bb in small_blocks:
+            bb.repack_writes()
 
-                # If we don't limit the Queue size, the upload queue can quickly
-                # grow to take up gigabytes of RAM if the writing process is
-                # generating data more quickly than it can be send to the Keep
-                # servers.
-                #
-                # With two upload threads and a queue size of 2, this means up to 4
-                # blocks pending.  If they are full 64 MiB blocks, that means up to
-                # 256 MiB of internal buffering, which is the same size as the
-                # default download block cache in KeepClient.
-                self._put_queue = Queue.Queue(maxsize=2)
-                self._put_errors = Queue.Queue()
+        # Update the pending write size count with its true value, just in case
+        # some small file was opened, written and closed several times.
+        self._pending_write_size = sum([b.size() for b in small_blocks])
 
-                self._put_threads = []
-                for i in xrange(0, self.num_put_threads):
-                    thread = threading.Thread(target=commit_bufferblock_worker, args=(self,))
-                    self._put_threads.append(thread)
-                    thread.daemon = True
-                    thread.start()
+        if self._pending_write_size < config.KEEP_BLOCK_SIZE and not force:
+            return
 
-        if block.state() == _BufferBlock.WRITABLE:
+        new_bb = self._alloc_bufferblock()
+        new_bb.owner = []
+        files = []
+        while len(small_blocks) > 0 and (new_bb.write_pointer + small_blocks[0].size()) <= config.KEEP_BLOCK_SIZE:
+            bb = small_blocks.pop(0)
+            new_bb.owner.append(bb.owner)
+            self._pending_write_size -= bb.size()
+            new_bb.append(bb.buffer_view[0:bb.write_pointer].tobytes())
+            files.append((bb, new_bb.write_pointer - bb.size()))
+
+        self.commit_bufferblock(new_bb, sync=sync)
+
+        for bb, new_bb_segment_offset in files:
+            newsegs = bb.owner.segments()
+            for s in newsegs:
+                if s.locator == bb.blockid:
+                    s.locator = new_bb.blockid
+                    s.segment_offset = new_bb_segment_offset+s.segment_offset
+            bb.owner.set_segments(newsegs)
+            self._delete_bufferblock(bb.blockid)
+
+    def commit_bufferblock(self, block, sync):
+        """Initiate a background upload of a bufferblock.
+
+        :block:
+          The block object to upload
+
+        :sync:
+          If `sync` is True, upload the block synchronously.
+          If `sync` is False, upload the block asynchronously.  This will
+          return immediately unless the upload queue is at capacity, in
+          which case it will wait on an upload queue slot.
+
+        """
+        try:
             # Mark the block as PENDING so to disallow any more appends.
             block.set_state(_BufferBlock.PENDING)
+        except StateChangeError as e:
+            if e.state == _BufferBlock.PENDING:
+                if sync:
+                    block.wait_for_commit.wait()
+                else:
+                    return
+            if block.state() == _BufferBlock.COMMITTED:
+                return
+            elif block.state() == _BufferBlock.ERROR:
+                raise block.error
+            else:
+                raise
+
+        if sync:
+            try:
+                if self.copies is None:
+                    loc = self._keep.put(block.buffer_view[0:block.write_pointer].tobytes())
+                else:
+                    loc = self._keep.put(block.buffer_view[0:block.write_pointer].tobytes(), copies=self.copies)
+                block.set_state(_BufferBlock.COMMITTED, loc)
+            except Exception as e:
+                block.set_state(_BufferBlock.ERROR, e)
+                raise
+        else:
+            self.start_put_threads()
             self._put_queue.put(block)
 
     @synchronized
     def get_bufferblock(self, locator):
         return self._bufferblocks.get(locator)
 
+    @synchronized
+    def get_padding_block(self):
+        """Get a bufferblock 64 MB in size consisting of all zeros, used as padding
+        when using truncate() to extend the size of a file.
+
+        For reference (and possible future optimization), the md5sum of the
+        padding block is: 7f614da9329cd3aebf59b91aadc30bf0+67108864
+
+        """
+
+        if self.padding_block is None:
+            self.padding_block = self._alloc_bufferblock(starting_capacity=config.KEEP_BLOCK_SIZE)
+            self.padding_block.write_pointer = config.KEEP_BLOCK_SIZE
+            self.commit_bufferblock(self.padding_block, False)
+        return self.padding_block
+
+    @synchronized
+    def delete_bufferblock(self, locator):
+        self._delete_bufferblock(locator)
+
+    def _delete_bufferblock(self, locator):
+        bb = self._bufferblocks[locator]
+        bb.clear()
+        del self._bufferblocks[locator]
+
     def get_block_contents(self, locator, num_retries, cache_only=False):
         """Fetch a block.
 
@@ -515,30 +790,47 @@ class _BlockManager(object):
     def commit_all(self):
         """Commit all outstanding buffer blocks.
 
-        Unlike commit_bufferblock(), this is a synchronous call, and will not
-        return until all buffer blocks are uploaded.  Raises
-        KeepWriteError() if any blocks failed to upload.
+        This is a synchronous call, and will not return until all buffer blocks
+        are uploaded.  Raises KeepWriteError() if any blocks failed to upload.
 
         """
+        self.repack_small_blocks(force=True, sync=True)
+
         with self.lock:
-            items = self._bufferblocks.items()
+            items = listitems(self._bufferblocks)
 
         for k,v in items:
-            v.owner.flush()
+            if v.state() != _BufferBlock.COMMITTED and v.owner:
+                # Ignore blocks with a list of owners, as if they're not in COMMITTED
+                # state, they're already being committed asynchronously.
+                if isinstance(v.owner, ArvadosFile):
+                    v.owner.flush(sync=False)
 
         with self.lock:
             if self._put_queue is not None:
                 self._put_queue.join()
 
-                if not self._put_errors.empty():
-                    err = []
-                    try:
-                        while True:
-                            err.append(self._put_errors.get(False))
-                    except Queue.Empty:
-                        pass
+                err = []
+                for k,v in items:
+                    if v.state() == _BufferBlock.ERROR:
+                        err.append((v.locator(), v.error))
+                if err:
                     raise KeepWriteError("Error writing some blocks", err, label="block")
 
+        for k,v in items:
+            # flush again with sync=True to remove committed bufferblocks from
+            # the segments.
+            if v.owner:
+                if isinstance(v.owner, ArvadosFile):
+                    v.owner.flush(sync=True)
+                elif isinstance(v.owner, list) and len(v.owner) > 0:
+                    # This bufferblock is referenced by many files as a result
+                    # of repacking small blocks, so don't delete it when flushing
+                    # its owners, just do it after flushing them all.
+                    for owner in v.owner:
+                        owner.flush(sync=True)
+                    self.delete_bufferblock(k)
+
     def block_prefetch(self, locator):
         """Initiate a background download of a block.
 
@@ -552,28 +844,14 @@ class _BlockManager(object):
         if not self.prefetch_enabled:
             return
 
-        def block_prefetch_worker(self):
-            """The background downloader thread."""
-            while True:
-                try:
-                    b = self._prefetch_queue.get()
-                    if b is None:
-                        return
-                    self._keep.get(b)
-                except Exception:
-                    pass
+        if self._keep.get_from_cache(locator) is not None:
+            return
 
         with self.lock:
             if locator in self._bufferblocks:
                 return
-            if self._prefetch_threads is None:
-                self._prefetch_queue = Queue.Queue()
-                self._prefetch_threads = []
-                for i in xrange(0, self.num_get_threads):
-                    thread = threading.Thread(target=block_prefetch_worker, args=(self,))
-                    self._prefetch_threads.append(thread)
-                    thread.daemon = True
-                    thread.start()
+
+        self.start_get_threads()
         self._prefetch_queue.put(locator)
 
 
@@ -588,7 +866,7 @@ class ArvadosFile(object):
 
     """
 
-    def __init__(self, parent, stream=[], segments=[]):
+    def __init__(self, parent, name, stream=[], segments=[]):
         """
         ArvadosFile constructor.
 
@@ -599,7 +877,9 @@ class ArvadosFile(object):
           a list of Range objects representing segments
         """
         self.parent = parent
-        self._modified = True
+        self.name = name
+        self._writers = set()
+        self._committed = False
         self._segments = []
         self.lock = parent.root_collection().lock
         for s in segments:
@@ -609,14 +889,22 @@ class ArvadosFile(object):
     def writable(self):
         return self.parent.writable()
 
+    @synchronized
+    def permission_expired(self, as_of_dt=None):
+        """Returns True if any of the segment's locators is expired"""
+        for r in self._segments:
+            if KeepLocator(r.locator).permission_expired(as_of_dt):
+                return True
+        return False
+
     @synchronized
     def segments(self):
         return copy.copy(self._segments)
 
     @synchronized
-    def clone(self, new_parent):
+    def clone(self, new_parent, new_name):
         """Make a copy of this file."""
-        cp = ArvadosFile(new_parent)
+        cp = ArvadosFile(new_parent, new_name)
         cp.replace_contents(self)
         return cp
 
@@ -640,7 +928,7 @@ class ArvadosFile(object):
 
             self._segments.append(Range(new_loc, other_segment.range_start, other_segment.range_size, other_segment.segment_offset))
 
-        self._modified = True
+        self.set_committed(False)
 
     def __eq__(self, other):
         if other is self:
@@ -652,7 +940,7 @@ class ArvadosFile(object):
         with self.lock:
             if len(self._segments) != len(othersegs):
                 return False
-            for i in xrange(0, len(othersegs)):
+            for i in range(0, len(othersegs)):
                 seg1 = self._segments[i]
                 seg2 = othersegs[i]
                 loc1 = seg1.locator
@@ -676,23 +964,64 @@ class ArvadosFile(object):
         return not self.__eq__(other)
 
     @synchronized
-    def set_unmodified(self):
-        """Clear the modified flag"""
-        self._modified = False
+    def set_segments(self, segs):
+        self._segments = segs
+
+    @synchronized
+    def set_committed(self, value=True):
+        """Set committed flag.
+
+        If value is True, set committed to be True.
+
+        If value is False, set committed to be False for this and all parents.
+        """
+        if value == self._committed:
+            return
+        self._committed = value
+        if self._committed is False and self.parent is not None:
+            self.parent.set_committed(False)
+
+    @synchronized
+    def committed(self):
+        """Get whether this is committed or not."""
+        return self._committed
+
+    @synchronized
+    def add_writer(self, writer):
+        """Add an ArvadosFileWriter reference to the list of writers"""
+        if isinstance(writer, ArvadosFileWriter):
+            self._writers.add(writer)
 
     @synchronized
-    def modified(self):
-        """Test the modified flag"""
-        return self._modified
+    def remove_writer(self, writer, flush):
+        """
+        Called from ArvadosFileWriter.close(). Remove a writer reference from the list
+        and do some block maintenance tasks.
+        """
+        self._writers.remove(writer)
+
+        if flush or self.size() > config.KEEP_BLOCK_SIZE // 2:
+            # File writer closed, not small enough for repacking
+            self.flush()
+        elif self.closed():
+            # All writers closed and size is adequate for repacking
+            self.parent._my_block_manager().repack_small_blocks(closed_file_size=self.size())
+
+    def closed(self):
+        """
+        Get whether this is closed or not. When the writers list is empty, the file
+        is supposed to be closed.
+        """
+        return len(self._writers) == 0
 
     @must_be_writable
     @synchronized
     def truncate(self, size):
-        """Shrink the size of the file.
+        """Shrink or expand the size of the file.
 
         If `size` is less than the size of the file, the file contents after
         `size` will be discarded.  If `size` is greater than the current size
-        of the file, an IOError will be raised.
+        of the file, it will be filled with zero bytes.
 
         """
         if size < self.size():
@@ -711,10 +1040,19 @@ class ArvadosFile(object):
                     new_segs.append(r)
 
             self._segments = new_segs
-            self._modified = True
+            self.set_committed(False)
         elif size > self.size():
-            raise IOError("truncate() does not support extending the file size")
-
+            padding = self.parent._my_block_manager().get_padding_block()
+            diff = size - self.size()
+            while diff > config.KEEP_BLOCK_SIZE:
+                self._segments.append(Range(padding.blockid, self.size(), config.KEEP_BLOCK_SIZE, 0))
+                diff -= config.KEEP_BLOCK_SIZE
+            if diff > 0:
+                self._segments.append(Range(padding.blockid, self.size(), diff, 0))
+            self.set_committed(False)
+        else:
+            # size == self.size()
+            pass
 
     def readfrom(self, offset, size, num_retries, exact=False):
         """Read up to `size` bytes from the file starting at `offset`.
@@ -727,47 +1065,27 @@ class ArvadosFile(object):
 
         with self.lock:
             if size == 0 or offset >= self.size():
-                return ''
-            prefetch = locators_and_ranges(self._segments, offset, size + config.KEEP_BLOCK_SIZE)
+                return b''
             readsegs = locators_and_ranges(self._segments, offset, size)
+            prefetch = locators_and_ranges(self._segments, offset + size, config.KEEP_BLOCK_SIZE, limit=32)
 
-        for lr in prefetch:
-            self.parent._my_block_manager().block_prefetch(lr.locator)
-
+        locs = set()
         data = []
         for lr in readsegs:
             block = self.parent._my_block_manager().get_block_contents(lr.locator, num_retries=num_retries, cache_only=(bool(data) and not exact))
             if block:
-                data.append(block[lr.segment_offset:lr.segment_offset+lr.segment_size])
+                blockview = memoryview(block)
+                data.append(blockview[lr.segment_offset:lr.segment_offset+lr.segment_size].tobytes())
+                locs.add(lr.locator)
             else:
                 break
-        return ''.join(data)
-
-    def _repack_writes(self, num_retries):
-        """Test if the buffer block has more data than actual segments.
-
-        This happens when a buffered write over-writes a file range written in
-        a previous buffered write.  Re-pack the buffer block for efficiency
-        and to avoid leaking information.
 
-        """
-        segs = self._segments
-
-        # Sum up the segments to get the total bytes of the file referencing
-        # into the buffer block.
-        bufferblock_segs = [s for s in segs if s.locator == self._current_bblock.blockid]
-        write_total = sum([s.range_size for s in bufferblock_segs])
-
-        if write_total < self._current_bblock.size():
-            # There is more data in the buffer block than is actually accounted for by segments, so
-            # re-pack into a new buffer by copying over to a new buffer block.
-            contents = self.parent._my_block_manager().get_block_contents(self._current_bblock.blockid, num_retries)
-            new_bb = self.parent._my_block_manager().alloc_bufferblock(self._current_bblock.blockid, starting_capacity=write_total, owner=self)
-            for t in bufferblock_segs:
-                new_bb.append(contents[t.segment_offset:t.segment_offset+t.range_size])
-                t.segment_offset = new_bb.size() - t.range_size
+        for lr in prefetch:
+            if lr.locator not in locs:
+                self.parent._my_block_manager().block_prefetch(lr.locator)
+                locs.add(lr.locator)
 
-            self._current_bblock = new_bb
+        return b''.join(data)
 
     @must_be_writable
     @synchronized
@@ -778,11 +1096,13 @@ class ArvadosFile(object):
         necessary.
 
         """
+        if not isinstance(data, bytes) and not isinstance(data, memoryview):
+            data = data.encode()
         if len(data) == 0:
             return
 
         if offset > self.size():
-            raise ArgumentError("Offset is past the end of the file")
+            self.truncate(offset)
 
         if len(data) > config.KEEP_BLOCK_SIZE:
             # Chunk it up into smaller writes
@@ -793,26 +1113,59 @@ class ArvadosFile(object):
                 n += config.KEEP_BLOCK_SIZE
             return
 
-        self._modified = True
+        self.set_committed(False)
 
         if self._current_bblock is None or self._current_bblock.state() != _BufferBlock.WRITABLE:
             self._current_bblock = self.parent._my_block_manager().alloc_bufferblock(owner=self)
 
         if (self._current_bblock.size() + len(data)) > config.KEEP_BLOCK_SIZE:
-            self._repack_writes(num_retries)
+            self._current_bblock.repack_writes()
             if (self._current_bblock.size() + len(data)) > config.KEEP_BLOCK_SIZE:
-                self.parent._my_block_manager().commit_bufferblock(self._current_bblock)
+                self.parent._my_block_manager().commit_bufferblock(self._current_bblock, sync=False)
                 self._current_bblock = self.parent._my_block_manager().alloc_bufferblock(owner=self)
 
         self._current_bblock.append(data)
 
         replace_range(self._segments, offset, len(data), self._current_bblock.blockid, self._current_bblock.write_pointer - len(data))
 
+        self.parent.notify(WRITE, self.parent, self.name, (self, self))
+
+        return len(data)
+
     @synchronized
-    def flush(self, num_retries=0):
-        if self._current_bblock:
-            self._repack_writes(num_retries)
-            self.parent._my_block_manager().commit_bufferblock(self._current_bblock)
+    def flush(self, sync=True, num_retries=0):
+        """Flush the current bufferblock to Keep.
+
+        :sync:
+          If True, commit block synchronously, wait until buffer block has been written.
+          If False, commit block asynchronously, return immediately after putting block into
+          the keep put queue.
+        """
+        if self.committed():
+            return
+
+        if self._current_bblock and self._current_bblock.state() != _BufferBlock.COMMITTED:
+            if self._current_bblock.state() == _BufferBlock.WRITABLE:
+                self._current_bblock.repack_writes()
+            if self._current_bblock.state() != _BufferBlock.DELETED:
+                self.parent._my_block_manager().commit_bufferblock(self._current_bblock, sync=sync)
+
+        if sync:
+            to_delete = set()
+            for s in self._segments:
+                bb = self.parent._my_block_manager().get_bufferblock(s.locator)
+                if bb:
+                    if bb.state() != _BufferBlock.COMMITTED:
+                        self.parent._my_block_manager().commit_bufferblock(bb, sync=True)
+                    to_delete.add(s.locator)
+                    s.locator = bb.locator()
+            for s in to_delete:
+                # Don't delete the bufferblock if it's owned by many files. It'll be
+                # deleted after all of its owners are flush()ed.
+                if self.parent._my_block_manager().get_bufferblock(s).owner is self:
+                    self.parent._my_block_manager().delete_bufferblock(s)
+
+        self.parent.notify(MOD, self.parent, self.name, (self, self))
 
     @must_be_writable
     @synchronized
@@ -827,7 +1180,7 @@ class ArvadosFile(object):
 
     def _add_segment(self, blocks, pos, size):
         """Internal implementation of add_segment."""
-        self._modified = True
+        self.set_committed(False)
         for lr in locators_and_ranges(blocks, pos, size):
             last = self._segments[-1] if self._segments else Range(0, 0, 0, 0)
             r = Range(lr.locator, last.range_start+last.range_size, lr.segment_size, lr.segment_offset)
@@ -843,21 +1196,34 @@ class ArvadosFile(object):
             return 0
 
     @synchronized
-    def manifest_text(self, stream_name=".", portable_locators=False, normalize=False):
+    def manifest_text(self, stream_name=".", portable_locators=False,
+                      normalize=False, only_committed=False):
         buf = ""
         filestream = []
-        for segment in self.segments:
+        for segment in self._segments:
             loc = segment.locator
-            if loc.startswith("bufferblock"):
-                loc = self._bufferblocks[loc].calculate_locator()
+            if self.parent._my_block_manager().is_bufferblock(loc):
+                if only_committed:
+                    continue
+                loc = self.parent._my_block_manager().get_bufferblock(loc).locator()
             if portable_locators:
                 loc = KeepLocator(loc).stripped()
-            filestream.append(LocatorAndRange(loc, locator_block_size(loc),
+            filestream.append(LocatorAndRange(loc, KeepLocator(loc).size,
                                  segment.segment_offset, segment.range_size))
-        buf += ' '.join(normalize_stream(stream_name, {stream_name: filestream}))
+        buf += ' '.join(normalize_stream(stream_name, {self.name: filestream}))
         buf += "\n"
         return buf
 
+    @must_be_writable
+    @synchronized
+    def _reparent(self, newparent, newname):
+        self.set_committed(False)
+        self.flush(sync=True)
+        self.parent.remove(self.name)
+        self.parent = newparent
+        self.name = newname
+        self.lock = self.parent.root_collection().lock
+
 
 class ArvadosFileReader(ArvadosFileReaderBase):
     """Wraps ArvadosFile in a file-like object supporting reading only.
@@ -867,8 +1233,8 @@ class ArvadosFileReader(ArvadosFileReaderBase):
 
     """
 
-    def __init__(self, arvadosfile, name, mode="r", num_retries=None):
-        super(ArvadosFileReader, self).__init__(name, mode, num_retries=num_retries)
+    def __init__(self, arvadosfile, mode="r", num_retries=None):
+        super(ArvadosFileReader, self).__init__(arvadosfile.name, mode=mode, num_retries=num_retries)
         self.arvadosfile = arvadosfile
 
     def size(self):
@@ -879,16 +1245,32 @@ class ArvadosFileReader(ArvadosFileReaderBase):
 
     @_FileLikeObjectBase._before_close
     @retry_method
-    def read(self, size, num_retries=None):
-        """Read up to `size` bytes from the stream, starting at the current file position."""
-        data = self.arvadosfile.readfrom(self._filepos, size, num_retries, exact=True)
-        self._filepos += len(data)
-        return data
+    def read(self, size=None, num_retries=None):
+        """Read up to `size` bytes from the file and return the result.
+
+        Starts at the current file position.  If `size` is None, read the
+        entire remainder of the file.
+        """
+        if size is None:
+            data = []
+            rd = self.arvadosfile.readfrom(self._filepos, config.KEEP_BLOCK_SIZE, num_retries)
+            while rd:
+                data.append(rd)
+                self._filepos += len(rd)
+                rd = self.arvadosfile.readfrom(self._filepos, config.KEEP_BLOCK_SIZE, num_retries)
+            return b''.join(data)
+        else:
+            data = self.arvadosfile.readfrom(self._filepos, size, num_retries, exact=True)
+            self._filepos += len(data)
+            return data
 
     @_FileLikeObjectBase._before_close
     @retry_method
     def readfrom(self, offset, size, num_retries=None):
-        """Read up to `size` bytes from the stream, starting at the current file position."""
+        """Read up to `size` bytes from the stream, starting at the specified file offset.
+
+        This method does not change the file position.
+        """
         return self.arvadosfile.readfrom(offset, size, num_retries)
 
     def flush(self):
@@ -903,37 +1285,39 @@ class ArvadosFileWriter(ArvadosFileReader):
 
     """
 
-    def __init__(self, arvadosfile, name, mode, num_retries=None):
-        super(ArvadosFileWriter, self).__init__(arvadosfile, name, mode, num_retries=num_retries)
+    def __init__(self, arvadosfile, mode, num_retries=None):
+        super(ArvadosFileWriter, self).__init__(arvadosfile, mode=mode, num_retries=num_retries)
+        self.arvadosfile.add_writer(self)
+
+    def writable(self):
+        return True
 
     @_FileLikeObjectBase._before_close
     @retry_method
     def write(self, data, num_retries=None):
         if self.mode[0] == "a":
-            self.arvadosfile.writeto(self.size(), data, num_retries)
-        else:
-            self.arvadosfile.writeto(self._filepos, data, num_retries)
-            self._filepos += len(data)
+            self._filepos = self.size()
+        self.arvadosfile.writeto(self._filepos, data, num_retries)
+        self._filepos += len(data)
+        return len(data)
 
     @_FileLikeObjectBase._before_close
     @retry_method
     def writelines(self, seq, num_retries=None):
         for s in seq:
-            self.write(s, num_retries)
+            self.write(s, num_retries=num_retries)
 
     @_FileLikeObjectBase._before_close
     def truncate(self, size=None):
         if size is None:
             size = self._filepos
         self.arvadosfile.truncate(size)
-        if self._filepos > self.size():
-            self._filepos = self.size()
 
     @_FileLikeObjectBase._before_close
     def flush(self):
         self.arvadosfile.flush()
 
-    def close(self):
+    def close(self, flush=True):
         if not self.closed:
-            self.flush()
+            self.arvadosfile.remove_writer(self, flush)
             super(ArvadosFileWriter, self).close()