1# http://pyrocko.org - GPLv3
2#
3# The Pyrocko Developers, 21st Century
4# ---|P------/S----------~Lg----------
6import logging
8from pyrocko.guts import Object, Int
10logger = logging.getLogger('psq.cache')
13class ContentCacheStats(Object):
14 '''
15 Information about cache state.
16 '''
17 nentries = Int.T(
18 help='Number of items in the cache.')
19 naccessors = Int.T(
20 help='Number of accessors currently holding references to cache '
21 'items.')
24class ContentCache(object):
26 '''
27 Simple memory cache for file contents.
29 Squirrel manages data in small entities: nuts. Only the meta-data for each
30 nut is stored in the database, content data has to be read from file. This
31 cache helps to speed up data access for typical seismological access
32 patterns.
34 Content data for stations, channels and instrument responses is small in
35 size but slow to parse so it makes sense to cache these indefinitely once
36 read. Also, it is usually inefficient to read a single station from a
37 station file, so it is better to cache the contents of the complete file
38 even if only one station is requested (it is likely that other stations
39 from that file will be used anyway).
41 Content data for waveforms is large in size and we usually want to free the
42 memory allocated for them after processing. Typical processing schemes
43 require batches of waveforms to be available together (e.g.
44 cross-correlations between pairs of stations) and there may be overlap
45 between successive batches (e.g. sliding window processing schemes).
47 This cache implementation uses named accessors and batch window counting
48 for flexible content caching. Loaded contents are held in memory as long as
49 an accessor is holding a reference to it. For each accessor a batch counter
50 is maintained, which starts at 0 and is incremented using calls to
51 :py:meth:`advance_accessor`. Content accesses are tracked with calls to
52 :py:meth:`get`, which sets a "last access" attribute on the cached item to
53 the current value of the batch counter (each accessor has its own last
54 access attribute on the items it uses). References to items which have
55 not been accessed during the latest batch by the accessor in question are
56 released during :py:meth:`advance_accessor`. :py:meth:`put` inserts new
57 items into the cache. :py:meth:`has` checks if there already is content
58 cached for a given item. To remove all references held by a given accessor,
59 :py:meth:`clear_accessor` can be called.
61 **Example usage**
63 For meta-data content to be cached indefinitely, no calls to
64 :py:meth:`advance_accessor` or :py:meth:`clear_accessor` should be made.
65 For waveform content one would call :py:meth:`advance_accessor` after each
66 move of a sliding window or :py:meth:`clear_accessor` after each processed
67 event. For a process requiring data from two independent positions of
68 extraction, e.g. for cross-correlations between all possible pairs of a set
69 of events, two separate accessor names could be used.
70 '''
72 def __init__(self):
73 self._entries = {}
74 self._accessor_ticks = {}
76 def _prune_outdated(self, path, segment, nut_mtime):
77 try:
78 cache_mtime = self._entries[path, segment][0]
79 except KeyError:
80 return
82 if cache_mtime != nut_mtime:
83 logger.debug('Forgetting (outdated): %s %s' % (path, segment))
84 del self._entries[path, segment]
86 def put(self, nut):
87 '''
88 Insert a new/updated item into cache.
90 :param nut:
91 Content item with attached data object.
92 :type nut:
93 :py:class:`~pyrocko.squirrel.model.Nut`
94 '''
95 path, segment, element, mtime = nut.key
96 self._prune_outdated(path, segment, nut.file_mtime)
98 if (path, segment) not in self._entries:
99 self._entries[path, segment] = nut.file_mtime, {}, {}
101 self._entries[path, segment][1][element] = nut
103 def get(self, nut, accessor='default', model='squirrel'):
104 '''
105 Get a content item and track its access.
107 :param nut:
108 Content item.
109 :type nut:
110 :py:class:`~pyrocko.squirrel.model.Nut`
112 :param accessor:
113 Name of accessing consumer. Giving a new name initializes a new
114 accessor.
115 :type accessor:
116 str
118 :returns:
119 Content data object
120 '''
121 path, segment, element, mtime = nut.key
122 entry = self._entries[path, segment]
124 if accessor not in self._accessor_ticks:
125 self._accessor_ticks[accessor] = 0
127 entry[2][accessor] = self._accessor_ticks[accessor]
128 el = entry[1][element]
130 if model == 'squirrel':
131 return el.content
132 elif model.endswith('+'):
133 return el.content, el.raw_content[model[:-1]]
134 else:
135 return el.raw_content[model]
137 def has(self, nut):
138 '''
139 Check if item's content is currently in cache.
141 :param nut:
142 Content item.
143 :type nut:
144 :py:class:`~pyrocko.squirrel.model.Nut`
146 :returns:
147 :py:class:`bool`
149 '''
150 path, segment, element, nut_mtime = nut.key
152 try:
153 entry = self._entries[path, segment]
154 cache_mtime = entry[0]
155 entry[1][element]
156 except KeyError:
157 return False
159 return cache_mtime == nut_mtime
161 def advance_accessor(self, accessor='default'):
162 '''
163 Increment batch counter of an accessor.
165 :param accessor:
166 Name of accessing consumer. Giving a new name initializes a new
167 accessor.
168 :type accessor:
169 str
170 '''
171 if accessor not in self._accessor_ticks:
172 self._accessor_ticks[accessor] = 0
174 ta = self._accessor_ticks[accessor]
176 delete = []
177 for path_segment, entry in self._entries.items():
178 t = entry[2].get(accessor, ta)
179 if t < ta:
180 del entry[2][accessor]
181 if not entry[2]:
182 delete.append(path_segment)
184 for path_segment in delete:
185 logger.debug('Forgetting (advance): %s %s' % path_segment)
186 del self._entries[path_segment]
188 self._accessor_ticks[accessor] += 1
190 def clear_accessor(self, accessor='default'):
191 '''
192 Clear all references held by an accessor.
194 :param accessor:
195 Name of accessing consumer.
196 :type accessor:
197 str
198 '''
199 delete = []
200 for path_segment, entry in self._entries.items():
201 entry[2].pop(accessor, None)
202 if not entry[2]:
203 delete.append(path_segment)
205 for path_segment in delete:
206 logger.debug('Forgetting (clear): %s %s' % path_segment)
207 del self._entries[path_segment]
209 try:
210 del self._accessor_ticks[accessor]
211 except KeyError:
212 pass
214 def clear(self):
215 '''
216 Empty the cache.
217 '''
218 for accessor in list(self._accessor_ticks.keys()):
219 self.clear_accessor(accessor)
221 self._entries = {}
222 self._accessor_ticks = {}
224 def get_stats(self):
225 '''
226 Get information about cache state.
228 :returns: :py:class:`ContentCacheStats` object.
229 '''
230 return ContentCacheStats(
231 nentries=len(self._entries),
232 naccessors=len(self._accessor_ticks))