Mercurial > personal > weather-server

annotate weather_server/logfile.py @ 1:f66df122f18d

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get the skeleton of a webserver up?
author Paul Fisher <paul@pfish.zone>
date Sun, 29 Sep 2019 00:52:13 -0400
parents efe7a1eff167
children beb42c835c52
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efe7a1eff167 Create initial logger for weather server.
Paul Fisher <paul@pfish.zone>
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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 fcntl
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5 import os
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6 import threading
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7 import typing as t
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8
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9 import bson
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10
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11 from . import common
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12 from . import types
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13
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14
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15 class Logger:
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16 """Logger which handles reading/writing a temperature log for one process.
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17 """
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18
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19 instance_lock = threading.Lock()
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20 instances: t.Dict[str, 'Logger'] = {}
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21
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22 @classmethod
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23 def create(cls, filename: str) -> 'Logger':
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24 """Creates a single shared instance of a logger for the given file."""
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25 try:
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26 return cls.instances[filename]
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27 except KeyError:
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28 with cls.instance_lock:
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29 try:
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30 return cls.instances[filename]
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31 except KeyError:
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32 cls.instances[filename] = Logger(filename)
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33 return cls.instances[filename]
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34
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35 def __init__(self, filename: str):
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36 """You should probably call .create() instead."""
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37 self._file = _open_or_create(filename)
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38 self._data: t.Tuple[types.Reading] = ()
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39 self._last_size = 0
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40 self._maybe_read_data()
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41 self._lock = threading.Lock()
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42
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43 def _maybe_read_data(self) -> None:
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44 """Reads data and advances the file pointer to the end of the file."""
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45 # This must be called with both the file lock and _lock held.
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46 size = self._size()
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47 if size == self._last_size:
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48 return
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49 last_good = self._file.tell()
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50 data = list(self._data)
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51 try:
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52 items = bson.decode_file_iter(
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53 self._file, codec_options=common.BSON_OPTIONS)
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54 for item in items:
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55 last_good = self._file.tell()
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56 try:
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57 data.append(types.Reading(**item))
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58 except TypeError:
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59 pass # Skip this item.
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60 except bson.InvalidBSON:
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61 pass # We have reached the last valid document. Bail.
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62 # Seek back to immediately after the end of the last valid doc.
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63 self._data = tuple(data)
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64 self._file.truncate(last_good)
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65 self._last_size = last_good
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66 self._file.seek(last_good, os.SEEK_SET)
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67
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68 def write_rows(self, readings: t.Iterable[types.Reading]) -> None:
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69 """Write a sorted series of readings, ignoring old ones."""
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70 with self._lock:
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71 fcntl.flock(self._file.fileno(), fcntl.LOCK_EX)
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72 try:
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73 self._maybe_read_data()
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74 self._file.truncate(self._file.tell())
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75 data = list(self._data)
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76 if not data:
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77 last_time = None
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78 else:
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79 last_time = data[-1].sample_time
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80 for reading in readings:
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81 if not last_time or last_time < reading.sample_time:
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82 self._file.write(common.bson_encode(reading.as_dict()))
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83 data.append(reading)
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84 self._data = tuple(data)
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85 finally:
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86 self._file.flush()
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87 self._last_size = self._size()
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88 fcntl.flock(self, fcntl.LOCK_UN)
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89
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90 def fileno(self) -> int:
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91 return self._file.fileno()
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92
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93 def close(self):
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94 self._file.close()
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95
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96 @property
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97 def data(self) -> t.Tuple[types.Reading, ...]:
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98 if self._size() != self._last_size:
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99 fcntl.flock(self, fcntl.LOCK_SH)
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100 try:
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101 with self._lock:
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102 self._maybe_read_data()
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103 finally:
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104 fcntl.flock(self, fcntl.LOCK_UN)
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105 return self._data
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106
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107 def _size(self) -> int:
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108 return os.stat(self.fileno()).st_size
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109
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110
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111 def _open_or_create(path: str) -> t.BinaryIO:
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112 while True:
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113 try:
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114 return open(path, 'r+b')
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115 except FileNotFoundError:
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116 pass
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117 try:
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118 return open(path, 'x+b')
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119 except FileExistsError:
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120 pass