mirror of
https://github.com/thegeeklab/ansible-later.git
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399 lines
12 KiB
Python
399 lines
12 KiB
Python
# Copyright (C) 2010, 2011 Sebastian Thiel (byronimo@gmail.com) and contributors
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#
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# This module is part of GitDB and is released under
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# the New BSD License: http://www.opensource.org/licenses/bsd-license.php
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import binascii
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import os
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import mmap
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import sys
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import time
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import errno
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from io import BytesIO
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from smmap import (
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StaticWindowMapManager,
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SlidingWindowMapManager,
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SlidingWindowMapBuffer
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)
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# initialize our global memory manager instance
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# Use it to free cached (and unused) resources.
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mman = SlidingWindowMapManager()
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# END handle mman
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import hashlib
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try:
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from struct import unpack_from
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except ImportError:
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from struct import unpack, calcsize
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__calcsize_cache = dict()
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def unpack_from(fmt, data, offset=0):
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try:
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size = __calcsize_cache[fmt]
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except KeyError:
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size = calcsize(fmt)
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__calcsize_cache[fmt] = size
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# END exception handling
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return unpack(fmt, data[offset: offset + size])
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# END own unpack_from implementation
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#{ Aliases
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hex_to_bin = binascii.a2b_hex
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bin_to_hex = binascii.b2a_hex
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# errors
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ENOENT = errno.ENOENT
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# os shortcuts
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exists = os.path.exists
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mkdir = os.mkdir
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chmod = os.chmod
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isdir = os.path.isdir
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isfile = os.path.isfile
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rename = os.rename
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dirname = os.path.dirname
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basename = os.path.basename
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join = os.path.join
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read = os.read
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write = os.write
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close = os.close
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fsync = os.fsync
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def _retry(func, *args, **kwargs):
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# Wrapper around functions, that are problematic on "Windows". Sometimes
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# the OS or someone else has still a handle to the file
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if sys.platform == "win32":
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for _ in range(10):
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try:
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return func(*args, **kwargs)
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except Exception:
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time.sleep(0.1)
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return func(*args, **kwargs)
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else:
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return func(*args, **kwargs)
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def remove(*args, **kwargs):
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return _retry(os.remove, *args, **kwargs)
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# Backwards compatibility imports
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from gitdb.const import (
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NULL_BIN_SHA,
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NULL_HEX_SHA
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)
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#} END Aliases
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#{ compatibility stuff ...
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class _RandomAccessBytesIO(object):
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"""Wrapper to provide required functionality in case memory maps cannot or may
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not be used. This is only really required in python 2.4"""
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__slots__ = '_sio'
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def __init__(self, buf=''):
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self._sio = BytesIO(buf)
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def __getattr__(self, attr):
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return getattr(self._sio, attr)
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def __len__(self):
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return len(self.getvalue())
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def __getitem__(self, i):
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return self.getvalue()[i]
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def __getslice__(self, start, end):
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return self.getvalue()[start:end]
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def byte_ord(b):
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"""
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Return the integer representation of the byte string. This supports Python
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3 byte arrays as well as standard strings.
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"""
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try:
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return ord(b)
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except TypeError:
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return b
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#} END compatibility stuff ...
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#{ Routines
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def make_sha(source=''.encode("ascii")):
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"""A python2.4 workaround for the sha/hashlib module fiasco
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**Note** From the dulwich project """
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try:
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return hashlib.sha1(source)
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except NameError:
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import sha
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sha1 = sha.sha(source)
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return sha1
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def allocate_memory(size):
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""":return: a file-protocol accessible memory block of the given size"""
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if size == 0:
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return _RandomAccessBytesIO(b'')
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# END handle empty chunks gracefully
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try:
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return mmap.mmap(-1, size) # read-write by default
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except EnvironmentError:
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# setup real memory instead
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# this of course may fail if the amount of memory is not available in
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# one chunk - would only be the case in python 2.4, being more likely on
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# 32 bit systems.
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return _RandomAccessBytesIO(b"\0" * size)
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# END handle memory allocation
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def file_contents_ro(fd, stream=False, allow_mmap=True):
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""":return: read-only contents of the file represented by the file descriptor fd
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:param fd: file descriptor opened for reading
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:param stream: if False, random access is provided, otherwise the stream interface
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is provided.
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:param allow_mmap: if True, its allowed to map the contents into memory, which
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allows large files to be handled and accessed efficiently. The file-descriptor
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will change its position if this is False"""
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try:
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if allow_mmap:
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# supports stream and random access
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try:
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return mmap.mmap(fd, 0, access=mmap.ACCESS_READ)
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except EnvironmentError:
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# python 2.4 issue, 0 wants to be the actual size
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return mmap.mmap(fd, os.fstat(fd).st_size, access=mmap.ACCESS_READ)
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# END handle python 2.4
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except OSError:
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pass
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# END exception handling
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# read manully
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contents = os.read(fd, os.fstat(fd).st_size)
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if stream:
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return _RandomAccessBytesIO(contents)
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return contents
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def file_contents_ro_filepath(filepath, stream=False, allow_mmap=True, flags=0):
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"""Get the file contents at filepath as fast as possible
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:return: random access compatible memory of the given filepath
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:param stream: see ``file_contents_ro``
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:param allow_mmap: see ``file_contents_ro``
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:param flags: additional flags to pass to os.open
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:raise OSError: If the file could not be opened
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**Note** for now we don't try to use O_NOATIME directly as the right value needs to be
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shared per database in fact. It only makes a real difference for loose object
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databases anyway, and they use it with the help of the ``flags`` parameter"""
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fd = os.open(filepath, os.O_RDONLY | getattr(os, 'O_BINARY', 0) | flags)
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try:
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return file_contents_ro(fd, stream, allow_mmap)
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finally:
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close(fd)
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# END assure file is closed
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def sliding_ro_buffer(filepath, flags=0):
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"""
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:return: a buffer compatible object which uses our mapped memory manager internally
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ready to read the whole given filepath"""
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return SlidingWindowMapBuffer(mman.make_cursor(filepath), flags=flags)
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def to_hex_sha(sha):
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""":return: hexified version of sha"""
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if len(sha) == 40:
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return sha
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return bin_to_hex(sha)
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def to_bin_sha(sha):
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if len(sha) == 20:
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return sha
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return hex_to_bin(sha)
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#} END routines
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#{ Utilities
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class LazyMixin(object):
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"""
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Base class providing an interface to lazily retrieve attribute values upon
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first access. If slots are used, memory will only be reserved once the attribute
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is actually accessed and retrieved the first time. All future accesses will
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return the cached value as stored in the Instance's dict or slot.
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"""
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__slots__ = tuple()
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def __getattr__(self, attr):
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"""
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Whenever an attribute is requested that we do not know, we allow it
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to be created and set. Next time the same attribute is reqeusted, it is simply
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returned from our dict/slots. """
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self._set_cache_(attr)
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# will raise in case the cache was not created
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return object.__getattribute__(self, attr)
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def _set_cache_(self, attr):
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"""
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This method should be overridden in the derived class.
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It should check whether the attribute named by attr can be created
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and cached. Do nothing if you do not know the attribute or call your subclass
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The derived class may create as many additional attributes as it deems
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necessary in case a git command returns more information than represented
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in the single attribute."""
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pass
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class LockedFD(object):
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"""
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This class facilitates a safe read and write operation to a file on disk.
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If we write to 'file', we obtain a lock file at 'file.lock' and write to
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that instead. If we succeed, the lock file will be renamed to overwrite
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the original file.
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When reading, we obtain a lock file, but to prevent other writers from
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succeeding while we are reading the file.
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This type handles error correctly in that it will assure a consistent state
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on destruction.
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**note** with this setup, parallel reading is not possible"""
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__slots__ = ("_filepath", '_fd', '_write')
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def __init__(self, filepath):
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"""Initialize an instance with the givne filepath"""
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self._filepath = filepath
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self._fd = None
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self._write = None # if True, we write a file
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def __del__(self):
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# will do nothing if the file descriptor is already closed
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if self._fd is not None:
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self.rollback()
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def _lockfilepath(self):
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return "%s.lock" % self._filepath
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def open(self, write=False, stream=False):
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"""
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Open the file descriptor for reading or writing, both in binary mode.
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:param write: if True, the file descriptor will be opened for writing. Other
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wise it will be opened read-only.
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:param stream: if True, the file descriptor will be wrapped into a simple stream
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object which supports only reading or writing
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:return: fd to read from or write to. It is still maintained by this instance
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and must not be closed directly
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:raise IOError: if the lock could not be retrieved
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:raise OSError: If the actual file could not be opened for reading
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**note** must only be called once"""
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if self._write is not None:
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raise AssertionError("Called %s multiple times" % self.open)
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self._write = write
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# try to open the lock file
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binary = getattr(os, 'O_BINARY', 0)
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lockmode = os.O_WRONLY | os.O_CREAT | os.O_EXCL | binary
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try:
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fd = os.open(self._lockfilepath(), lockmode, int("600", 8))
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if not write:
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os.close(fd)
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else:
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self._fd = fd
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# END handle file descriptor
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except OSError:
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raise IOError("Lock at %r could not be obtained" % self._lockfilepath())
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# END handle lock retrieval
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# open actual file if required
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if self._fd is None:
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# we could specify exlusive here, as we obtained the lock anyway
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try:
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self._fd = os.open(self._filepath, os.O_RDONLY | binary)
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except:
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# assure we release our lockfile
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remove(self._lockfilepath())
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raise
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# END handle lockfile
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# END open descriptor for reading
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if stream:
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# need delayed import
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from gitdb.stream import FDStream
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return FDStream(self._fd)
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else:
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return self._fd
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# END handle stream
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def commit(self):
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"""When done writing, call this function to commit your changes into the
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actual file.
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The file descriptor will be closed, and the lockfile handled.
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**Note** can be called multiple times"""
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self._end_writing(successful=True)
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def rollback(self):
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"""Abort your operation without any changes. The file descriptor will be
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closed, and the lock released.
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**Note** can be called multiple times"""
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self._end_writing(successful=False)
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def _end_writing(self, successful=True):
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"""Handle the lock according to the write mode """
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if self._write is None:
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raise AssertionError("Cannot end operation if it wasn't started yet")
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if self._fd is None:
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return
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os.close(self._fd)
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self._fd = None
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lockfile = self._lockfilepath()
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if self._write and successful:
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# on windows, rename does not silently overwrite the existing one
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if sys.platform == "win32":
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if isfile(self._filepath):
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remove(self._filepath)
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# END remove if exists
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# END win32 special handling
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os.rename(lockfile, self._filepath)
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# assure others can at least read the file - the tmpfile left it at rw--
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# We may also write that file, on windows that boils down to a remove-
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# protection as well
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chmod(self._filepath, int("644", 8))
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else:
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# just delete the file so far, we failed
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remove(lockfile)
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# END successful handling
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#} END utilities
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