# Copyright Mercurial Contributors
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
from __future__ import annotations
import contextlib
from ..i18n import _
from .. import (
error,
util,
)
_MAX_CACHED_CHUNK_SIZE = 1048576 # 1 MiB
PARTIAL_READ_MSG = _(
b'partial read of revlog %s; expected %d bytes from offset %d, got %d'
)
def _is_power_of_two(n):
return (n & (n - 1) == 0) and n != 0
class appender:
"""the changelog index must be updated last on disk, so we use this class
to delay writes to it"""
def __init__(self, vfs, name, mode, buf):
self.data = buf
fp = vfs(name, mode)
self.fp = fp
self.offset = fp.tell()
self.size = vfs.fstat(fp).st_size
self._end = self.size
def end(self):
return self._end
def tell(self):
return self.offset
def flush(self):
pass
@property
def closed(self):
return self.fp.closed
def close(self):
self.fp.close()
def seek(self, offset, whence=0):
'''virtual file offset spans real file and data'''
if whence == 0:
self.offset = offset
elif whence == 1:
self.offset += offset
elif whence == 2:
self.offset = self.end() + offset
if self.offset < self.size:
self.fp.seek(self.offset)
def read(self, count=-1):
'''only trick here is reads that span real file and data'''
ret = b""
if self.offset < self.size:
s = self.fp.read(count)
ret = s
self.offset += len(s)
if count > 0:
count -= len(s)
if count != 0:
doff = self.offset - self.size
self.data.insert(0, b"".join(self.data))
del self.data[1:]
s = self.data[0][doff : doff + count]
self.offset += len(s)
ret += s
return ret
def write(self, s):
self.data.append(bytes(s))
self.offset += len(s)
self._end += len(s)
def __enter__(self):
self.fp.__enter__()
return self
def __exit__(self, *args):
return self.fp.__exit__(*args)
class randomaccessfile:
"""Accessing arbitrary chuncks of data within a file, with some caching"""
def __init__(
self,
opener,
filename,
default_cached_chunk_size,
initial_cache=None,
):
# Required by bitwise manipulation below
assert _is_power_of_two(default_cached_chunk_size)
self.opener = opener
self.filename = filename
self.default_cached_chunk_size = default_cached_chunk_size
self.writing_handle = None # This is set from revlog.py
self.reading_handle = None
self._cached_chunk = b''
self._cached_chunk_position = 0 # Offset from the start of the file
if initial_cache:
self._cached_chunk_position, self._cached_chunk = initial_cache
def clear_cache(self):
self._cached_chunk = b''
self._cached_chunk_position = 0
@property
def is_open(self):
"""True if any file handle is being held
Used for assert and debug in the python code"""
return (
self.reading_handle is not None or self.writing_handle is not None
)
def _open(self, mode=b'r'):
"""Return a file object"""
return self.opener(self.filename, mode=mode)
@contextlib.contextmanager
def _read_handle(self):
"""File object suitable for reading data"""
# Use a file handle being actively used for writes, if available.
# There is some danger to doing this because reads will seek the
# file. However, revlog._writeentry performs a SEEK_END before all
# writes, so we should be safe.
if self.writing_handle:
yield self.writing_handle
elif self.reading_handle:
yield self.reading_handle
# Otherwise open a new file handle.
else:
with self._open() as fp:
yield fp
@contextlib.contextmanager
def reading(self):
"""Context manager that keeps the file open for reading"""
if (
self.reading_handle is None
and self.writing_handle is None
and self.filename is not None
):
with self._open() as fp:
self.reading_handle = fp
try:
yield
finally:
self.reading_handle = None
else:
yield
def read_chunk(self, offset, length):
"""Read a chunk of bytes from the file.
Accepts an absolute offset, length to read.
Returns a str or buffer of raw byte data.
Raises if the requested number of bytes could not be read.
"""
end = offset + length
cache_start = self._cached_chunk_position
cache_end = cache_start + len(self._cached_chunk)
# Is the requested chunk within the cache?
if cache_start <= offset and end <= cache_end:
if cache_start == offset and end == cache_end:
return self._cached_chunk # avoid a copy
relative_start = offset - cache_start
return util.buffer(self._cached_chunk, relative_start, length)
return self._read_and_update_cache(offset, length)
def _read_and_update_cache(self, offset, length):
# Cache data both forward and backward around the requested
# data, in a fixed size window. This helps speed up operations
# involving reading the revlog backwards.
real_offset = offset & ~(self.default_cached_chunk_size - 1)
real_length = (
(offset + length + self.default_cached_chunk_size)
& ~(self.default_cached_chunk_size - 1)
) - real_offset
with self._read_handle() as file_obj:
file_obj.seek(real_offset)
data = file_obj.read(real_length)
self._add_cached_chunk(real_offset, data)
relative_offset = offset - real_offset
got = len(data) - relative_offset
if got < length:
message = PARTIAL_READ_MSG % (self.filename, length, offset, got)
raise error.RevlogError(message)
if offset != real_offset or real_length != length:
return util.buffer(data, relative_offset, length)
return data
def _add_cached_chunk(self, offset, data):
"""Add to or replace the cached data chunk.
Accepts an absolute offset and the data that is at that location.
"""
if (
self._cached_chunk_position + len(self._cached_chunk) == offset
and len(self._cached_chunk) + len(data) < _MAX_CACHED_CHUNK_SIZE
):
# add to existing cache
self._cached_chunk += data
else:
self._cached_chunk = data
self._cached_chunk_position = offset