Mercurial > personal > weather-server

annotate weather_server/logfile.py @ 27:99b0759386b1

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index: Add meta-viewport declaration.
author Paul Fisher <paul@pfish.zone>
date Sun, 10 Nov 2019 23:48:38 -0500
parents 20c8ec56e447
children 9bc3687e1e5e
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1 """The part which handles writing things out and reading things in from CSV.
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2 """
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3
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4 import concurrent.futures as futures
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5 import contextlib
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6 import fcntl
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7 import os
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8 import queue
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9 import threading
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10 import typing as t
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11
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12 import bson
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13
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14 from . import common
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15
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16
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17 class _WriteRequest:
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18
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19 def __init__(self, entries: t.Iterable[t.Dict[str, t.Any]]):
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20 """Creates a request to write the given data to the log."""
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21 # The data to be written. We take ownership of all the dicts!
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22 self.entries = entries
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23 # Once written, a future that will resolve to None if successful.
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24 self.future = futures.Future()
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25
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26
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27 class _ReadRequest:
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28
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29 def __init__(self):
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30 # The future that will be set with the log's contnets.
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31 self.future = futures.Future()
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32
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33
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34 # Poison pill to tell a logger thread to stop.
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35 _POISON = object()
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36
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37
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38 class Logger:
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39 """Logger which handles reading/writing one temperature log file."""
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40
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41 def __init__(self, filename: str, *, sample_field: str):
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42 """Creates a new Logger for the given file.
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43
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44 Args:
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45 filename: The filename to open, or create if not already there.
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46 sample_field: The field name to use as the strictly-increasing
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47 value to ensure that no duplicate writes occur.
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48 """
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49 self._sample_field = sample_field
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50 self._queue = queue.SimpleQueue()
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51 # Create a Future that will be resolved once the file is opened
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52 # (or fails to be opened).
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53 writer_started = futures.Future()
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54 self._writer_thread = threading.Thread(
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55 name=f'{filename!r} writer thread',
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56 target=lambda: _writer_thread(
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57 filename, self._queue, sample_field, writer_started),
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58 daemon=True)
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59 self._writer_thread.start()
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60 writer_started.result()
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61
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62 @property
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63 def data(self) -> t.Tuple[t.Dict[str, t.Any], ...]:
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64 req = _ReadRequest()
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65 self._queue.put(req)
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66 return req.future.result()
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67
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68 def write_rows(self, entries: t.Iterable[t.Dict[str, t.Any]]):
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69 req = _WriteRequest(entries)
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70 self._queue.put(req)
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71 return req.future.result()
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72
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73 def __del__(self):
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74 self.close()
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75
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76 def close(self):
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77 self._queue.put(_POISON)
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78 self._writer_thread.join()
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79
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80
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81 def _writer_thread(
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82 filename: str,
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83 q: queue.Queue,
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84 sample_field: str,
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85 started: futures.Future,
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86 ) -> None:
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87 if not started.set_running_or_notify_cancel():
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88 return
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89 try:
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90 file = _open_or_create(filename)
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91 started.set_result(None)
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92 except BaseException as e:
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93 started.set_exception(e)
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94 return
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95 with file:
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96 running = True
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97 data: t.List[t.Dict[str, object]] = []
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98 while running:
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99 item = q.get()
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100 if item is _POISON:
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101 # None is the poison pill that makes us stop.
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102 running = False
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103 elif isinstance(item, _ReadRequest):
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104 if not item.future.set_running_or_notify_cancel():
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105 continue
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106 try:
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107 with _file_lock(file, fcntl.LOCK_SH):
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108 data.extend(_catch_up(file))
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109 except BaseException as x:
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110 item.future.set_exception(x)
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111 else:
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112 item.future.set_result(tuple(data))
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113 elif isinstance(item, _WriteRequest):
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114 if not item.future.set_running_or_notify_cancel():
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115 continue
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116 try:
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117 with _file_lock(file, fcntl.LOCK_EX):
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118 data.extend(_catch_up(file))
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119 # Since we're at the last good point, truncate after.
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120 file.truncate(file.tell())
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121 if not data:
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122 last = None
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123 else:
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124 last = data[-1][sample_field]
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125 for entry in item.entries:
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126 entry_key = entry[sample_field]
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127 if last is None or last < entry_key:
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128 file.write(common.bson_encode(entry))
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129 data.append(entry)
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130 last = entry_key
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131 file.flush()
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132 except BaseException as x:
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133 item.future.set_exception(x)
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134 else:
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135 item.future.set_result(None)
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136 else:
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137 raise AssertionError(
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138 'Unexpected item {!r} in the queue'.format(item))
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139
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140
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141 @contextlib.contextmanager
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142 def _file_lock(file: t.BinaryIO, operation: int) -> t.Iterator[None]:
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143 assert operation in (fcntl.LOCK_SH, fcntl.LOCK_EX), 'Invalid operation.'
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144 fcntl.flock(file, operation)
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145 try:
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146 yield
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147 finally:
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148 fcntl.flock(file, fcntl.LOCK_UN)
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149
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150
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151 def _size(file: t.BinaryIO) -> int:
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152 return os.stat(file.fileno()).st_size
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153
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154
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155 def _catch_up(file: t.BinaryIO) -> t.Iterable[t.Dict[str, object]]:
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156 """Reads data and advances the file pointer to the end of the file."""
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157 size = _size(file)
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158 pointer = file.tell()
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159 if size == pointer:
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160 return ()
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161 output: t.List[t.Dict[str, object]] = []
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162 try:
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163 items = bson.decode_file_iter(
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164 file, codec_options=common.BSON_OPTIONS)
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165 for item in items:
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166 pointer = file.tell()
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167 output.append(item)
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168 except bson.InvalidBSON:
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169 pass # We have reached the last valid document. Bail.
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170 # Seek back to immediately after the end of the last valid doc.
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171 file.seek(pointer, os.SEEK_SET)
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172 return output
21
beb42c835c52 Make weather server handle arbitrary data:
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diff changeset
173
0
efe7a1eff167 Create initial logger for weather server.
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parents:
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174
efe7a1eff167 Create initial logger for weather server.
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175 def _open_or_create(path: str) -> t.BinaryIO:
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parents:
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176 while True:
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177 try:
efe7a1eff167 Create initial logger for weather server.
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178 return open(path, 'r+b')
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179 except FileNotFoundError:
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180 pass
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181 try:
efe7a1eff167 Create initial logger for weather server.
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182 return open(path, 'x+b')
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183 except FileExistsError:
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184 pass