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annotate mercurial/revlogutils/randomaccessfile.py @ 48946:642e31cb55f0

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py3: use class X: instead of class X(object): The inheritance from object is implied in Python 3. So this should be equivalent. This change was generated via an automated search and replace. So there may have been some accidental changes. Differential Revision: https://phab.mercurial-scm.org/D12352
author Gregory Szorc <gregory.szorc@gmail.com>
date Mon, 21 Feb 2022 13:08:28 -0700
parents 5fa083a5ff04
children 3314c41c3759
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 # Copyright Mercurial Contributors
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2 #
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3 # This software may be used and distributed according to the terms of the
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4 # GNU General Public License version 2 or any later version.
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5
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6 import contextlib
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7
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8 from ..i18n import _
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9 from .. import (
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10 error,
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11 util,
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12 )
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13
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14
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15 _MAX_CACHED_CHUNK_SIZE = 1048576 # 1 MiB
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16
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17 PARTIAL_READ_MSG = _(
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18 b'partial read of revlog %s; expected %d bytes from offset %d, got %d'
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19 )
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20
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21
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22 def _is_power_of_two(n):
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23 return (n & (n - 1) == 0) and n != 0
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24
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25
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26 class randomaccessfile:
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27 """Accessing arbitrary chuncks of data within a file, with some caching"""
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28
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29 def __init__(
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30 self,
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31 opener,
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32 filename,
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33 default_cached_chunk_size,
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34 initial_cache=None,
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35 ):
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36 # Required by bitwise manipulation below
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37 assert _is_power_of_two(default_cached_chunk_size)
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38
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39 self.opener = opener
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40 self.filename = filename
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41 self.default_cached_chunk_size = default_cached_chunk_size
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42 self.writing_handle = None # This is set from revlog.py
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43 self.reading_handle = None
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44 self._cached_chunk = b''
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45 self._cached_chunk_position = 0 # Offset from the start of the file
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46 if initial_cache:
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47 self._cached_chunk_position, self._cached_chunk = initial_cache
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48
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49 def clear_cache(self):
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50 self._cached_chunk = b''
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51 self._cached_chunk_position = 0
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52
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53 def _open(self, mode=b'r'):
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54 """Return a file object"""
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55 return self.opener(self.filename, mode=mode)
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56
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57 @contextlib.contextmanager
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58 def _open_read(self, existing_file_obj=None):
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59 """File object suitable for reading data"""
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60 # Use explicit file handle, if given.
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61 if existing_file_obj is not None:
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62 yield existing_file_obj
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63
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64 # Use a file handle being actively used for writes, if available.
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65 # There is some danger to doing this because reads will seek the
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66 # file. However, revlog._writeentry performs a SEEK_END before all
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67 # writes, so we should be safe.
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68 elif self.writing_handle:
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69 yield self.writing_handle
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70
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71 elif self.reading_handle:
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72 yield self.reading_handle
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73
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74 # Otherwise open a new file handle.
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75 else:
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76 with self._open() as fp:
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77 yield fp
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78
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79 @contextlib.contextmanager
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80 def reading(self):
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81 """Context manager that keeps the file open for reading"""
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82 if (
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83 self.reading_handle is None
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84 and self.writing_handle is None
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85 and self.filename is not None
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86 ):
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87 with self._open() as fp:
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88 self.reading_handle = fp
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89 try:
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90 yield
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91 finally:
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92 self.reading_handle = None
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93 else:
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94 yield
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95
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96 def read_chunk(self, offset, length, existing_file_obj=None):
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97 """Read a chunk of bytes from the file.
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98
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99 Accepts an absolute offset, length to read, and an optional existing
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100 file handle to read from.
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101
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102 If an existing file handle is passed, it will be seeked and the
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103 original seek position will NOT be restored.
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104
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105 Returns a str or buffer of raw byte data.
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106
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107 Raises if the requested number of bytes could not be read.
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108 """
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109 end = offset + length
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110 cache_start = self._cached_chunk_position
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111 cache_end = cache_start + len(self._cached_chunk)
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112 # Is the requested chunk within the cache?
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113 if cache_start <= offset and end <= cache_end:
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114 if cache_start == offset and end == cache_end:
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115 return self._cached_chunk # avoid a copy
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116 relative_start = offset - cache_start
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117 return util.buffer(self._cached_chunk, relative_start, length)
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118
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119 return self._read_and_update_cache(offset, length, existing_file_obj)
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120
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121 def _read_and_update_cache(self, offset, length, existing_file_obj=None):
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122 # Cache data both forward and backward around the requested
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123 # data, in a fixed size window. This helps speed up operations
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124 # involving reading the revlog backwards.
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125 real_offset = offset & ~(self.default_cached_chunk_size - 1)
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126 real_length = (
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127 (offset + length + self.default_cached_chunk_size)
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128 & ~(self.default_cached_chunk_size - 1)
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129 ) - real_offset
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130 with self._open_read(existing_file_obj) as file_obj:
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131 file_obj.seek(real_offset)
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132 data = file_obj.read(real_length)
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133
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134 self._add_cached_chunk(real_offset, data)
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135
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136 relative_offset = offset - real_offset
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137 got = len(data) - relative_offset
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138 if got < length:
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139 message = PARTIAL_READ_MSG % (self.filename, length, offset, got)
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140 raise error.RevlogError(message)
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141
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142 if offset != real_offset or real_length != length:
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143 return util.buffer(data, relative_offset, length)
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144 return data
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145
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146 def _add_cached_chunk(self, offset, data):
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147 """Add to or replace the cached data chunk.
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148
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149 Accepts an absolute offset and the data that is at that location.
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150 """
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151 if (
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152 self._cached_chunk_position + len(self._cached_chunk) == offset
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153 and len(self._cached_chunk) + len(data) < _MAX_CACHED_CHUNK_SIZE
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154 ):
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155 # add to existing cache
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156 self._cached_chunk += data
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157 else:
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158 self._cached_chunk = data
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159 self._cached_chunk_position = offset