aboutsummaryrefslogtreecommitdiffstats
path: root/activesupport/lib/active_support/cache.rb
blob: 55791bfa56699a4a1131e470d4dfe31c3876576f (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
require 'benchmark'
require 'zlib'
require 'active_support/core_ext/array/extract_options'
require 'active_support/core_ext/array/wrap'
require 'active_support/core_ext/benchmark'
require 'active_support/core_ext/exception'
require 'active_support/core_ext/class/attribute_accessors'
require 'active_support/core_ext/numeric/bytes'
require 'active_support/core_ext/numeric/time'
require 'active_support/core_ext/object/to_param'
require 'active_support/core_ext/string/inflections'

module ActiveSupport
  # See ActiveSupport::Cache::Store for documentation.
  module Cache
    autoload :FileStore, 'active_support/cache/file_store'
    autoload :MemoryStore, 'active_support/cache/memory_store'
    autoload :MemCacheStore, 'active_support/cache/mem_cache_store'
    autoload :NullStore, 'active_support/cache/null_store'

    # These options mean something to all cache implementations. Individual cache
    # implementations may support additional options.
    UNIVERSAL_OPTIONS = [:namespace, :compress, :compress_threshold, :expires_in, :race_condition_ttl]

    module Strategy
      autoload :LocalCache, 'active_support/cache/strategy/local_cache'
    end

    class << self
      # Creates a new CacheStore object according to the given options.
      #
      # If no arguments are passed to this method, then a new
      # ActiveSupport::Cache::MemoryStore object will be returned.
      #
      # If you pass a Symbol as the first argument, then a corresponding cache
      # store class under the ActiveSupport::Cache namespace will be created.
      # For example:
      #
      #   ActiveSupport::Cache.lookup_store(:memory_store)
      #   # => returns a new ActiveSupport::Cache::MemoryStore object
      #
      #   ActiveSupport::Cache.lookup_store(:mem_cache_store)
      #   # => returns a new ActiveSupport::Cache::MemCacheStore object
      #
      # Any additional arguments will be passed to the corresponding cache store
      # class's constructor:
      #
      #   ActiveSupport::Cache.lookup_store(:file_store, "/tmp/cache")
      #   # => same as: ActiveSupport::Cache::FileStore.new("/tmp/cache")
      #
      # If the first argument is not a Symbol, then it will simply be returned:
      #
      #   ActiveSupport::Cache.lookup_store(MyOwnCacheStore.new)
      #   # => returns MyOwnCacheStore.new
      def lookup_store(*store_option)
        store, *parameters = *Array.wrap(store_option).flatten

        case store
        when Symbol
          store_class_name = store.to_s.camelize
          store_class =
            begin
              require "active_support/cache/#{store}"
            rescue LoadError => e
              raise "Could not find cache store adapter for #{store} (#{e})"
            else
              ActiveSupport::Cache.const_get(store_class_name)
            end
          store_class.new(*parameters)
        when nil
          ActiveSupport::Cache::MemoryStore.new
        else
          store
        end
      end

      def expand_cache_key(key, namespace = nil)
        expanded_cache_key = namespace ? "#{namespace}/" : ""

        if prefix = ENV["RAILS_CACHE_ID"] || ENV["RAILS_APP_VERSION"]
          expanded_cache_key << "#{prefix}/"
        end

        expanded_cache_key << retrieve_cache_key(key)
        expanded_cache_key
      end

      private

      def retrieve_cache_key(key)
        case
        when key.respond_to?(:cache_key) then key.cache_key
        when key.is_a?(Array)            then key.map { |element| retrieve_cache_key(element) }.to_param
        when key.respond_to?(:to_a)      then retrieve_cache_key(key.to_a)
        else                                  key.to_param
        end.to_s
      end
    end

    # An abstract cache store class. There are multiple cache store
    # implementations, each having its own additional features. See the classes
    # under the ActiveSupport::Cache module, e.g.
    # ActiveSupport::Cache::MemCacheStore. MemCacheStore is currently the most
    # popular cache store for large production websites.
    #
    # Some implementations may not support all methods beyond the basic cache
    # methods of +fetch+, +write+, +read+, +exist?+, and +delete+.
    #
    # ActiveSupport::Cache::Store can store any serializable Ruby object.
    #
    #   cache = ActiveSupport::Cache::MemoryStore.new
    #
    #   cache.read("city")   # => nil
    #   cache.write("city", "Duckburgh")
    #   cache.read("city")   # => "Duckburgh"
    #
    # Keys are always translated into Strings and are case sensitive. When an
    # object is specified as a key and has a +cache_key+ method defined, this
    # method will be called to define the key.  Otherwise, the +to_param+
    # method will be called. Hashes and Arrays can also be used as keys. The
    # elements will be delimited by slashes, and the elements within a Hash
    # will be sorted by key so they are consistent.
    #
    #   cache.read("city") == cache.read(:city)   # => true
    #
    # Nil values can be cached.
    #
    # If your cache is on a shared infrastructure, you can define a namespace
    # for your cache entries. If a namespace is defined, it will be prefixed on
    # to every key. The namespace can be either a static value or a Proc. If it
    # is a Proc, it will be invoked when each key is evaluated so that you can
    # use application logic to invalidate keys.
    #
    #   cache.namespace = lambda { @last_mod_time }  # Set the namespace to a variable
    #   @last_mod_time = Time.now  # Invalidate the entire cache by changing namespace
    #
    #
    # Caches can also store values in a compressed format to save space and
    # reduce time spent sending data. Since there is overhead, values must be
    # large enough to warrant compression. To turn on compression either pass
    # <tt>:compress => true</tt> in the initializer or as an option to +fetch+
    # or +write+. To specify the threshold at which to compress values, set the
    # <tt>:compress_threshold</tt> option. The default threshold is 16K.
    class Store

      cattr_accessor :logger, :instance_writer => true

      attr_reader :silence, :options
      alias :silence? :silence

      # Create a new cache. The options will be passed to any write method calls except
      # for :namespace which can be used to set the global namespace for the cache.
      def initialize(options = nil)
        @options = options ? options.dup : {}
      end

      # Silence the logger.
      def silence!
        @silence = true
        self
      end

      # Silence the logger within a block.
      def mute
        previous_silence, @silence = defined?(@silence) && @silence, true
        yield
      ensure
        @silence = previous_silence
      end

      # Set to true if cache stores should be instrumented. Default is false.
      def self.instrument=(boolean)
        Thread.current[:instrument_cache_store] = boolean
      end

      def self.instrument
        Thread.current[:instrument_cache_store] || false
      end

      # Fetches data from the cache, using the given key. If there is data in
      # the cache with the given key, then that data is returned.
      #
      # If there is no such data in the cache (a cache miss), then nil will be
      # returned. However, if a block has been passed, that block will be run
      # in the event of a cache miss. The return value of the block will be
      # written to the cache under the given cache key, and that return value
      # will be returned.
      #
      #   cache.write("today", "Monday")
      #   cache.fetch("today")  # => "Monday"
      #
      #   cache.fetch("city")   # => nil
      #   cache.fetch("city") do
      #     "Duckburgh"
      #   end
      #   cache.fetch("city")   # => "Duckburgh"
      #
      # You may also specify additional options via the +options+ argument.
      # Setting <tt>:force => true</tt> will force a cache miss:
      #
      #   cache.write("today", "Monday")
      #   cache.fetch("today", :force => true)  # => nil
      #
      # Setting <tt>:compress</tt> will store a large cache entry set by the call
      # in a compressed format.
      #
      #
      # Setting <tt>:expires_in</tt> will set an expiration time on the cache.
      # All caches support auto-expiring content after a specified number of
      # seconds. This value can be specified as an option to the constructor
      # (in which case all entries will be affected), or it can be supplied to
      # the +fetch+ or +write+ method to effect just one entry.
      #
      #   cache = ActiveSupport::Cache::MemoryStore.new(:expires_in => 5.minutes)
      #   cache.write(key, value, :expires_in => 1.minute)  # Set a lower value for one entry
      #
      # Setting <tt>:race_condition_ttl</tt> is very useful in situations where a cache entry
      # is used very frequently and is under heavy load. If a cache expires and due to heavy load
      # seven different processes will try to read data natively and then they all will try to
      # write to cache. To avoid that case the first process to find an expired cache entry will
      # bump the cache expiration time by the value set in <tt>:race_condition_ttl</tt>. Yes
      # this process is extending the time for a stale value by another few seconds. Because
      # of extended life of the previous cache, other processes will continue to use slightly
      # stale data for a just a big longer. In the meantime that first process will go ahead
      # and will write into cache the new value. After that all the processes will start
      # getting new value. The key is to keep <tt>:race_condition_ttl</tt> small.
      #
      # If the process regenerating the entry errors out, the entry will be regenerated
      # after the specified number of seconds. Also note that the life of stale cache is
      # extended only if it expired recently. Otherwise a new value is generated and
      # <tt>:race_condition_ttl</tt> does not play any role.
      #
      #   # Set all values to expire after one minute.
      #   cache = ActiveSupport::Cache::MemoryStore.new(:expires_in => 1.minute)
      #
      #   cache.write("foo", "original value")
      #   val_1 = nil
      #   val_2 = nil
      #   sleep 60
      #
      #   Thread.new do
      #     val_1 = cache.fetch("foo", :race_condition_ttl => 10) do
      #       sleep 1
      #       "new value 1"
      #     end
      #   end
      #
      #   Thread.new do
      #     val_2 = cache.fetch("foo", :race_condition_ttl => 10) do
      #       "new value 2"
      #     end
      #   end
      #
      #   # val_1 => "new value 1"
      #   # val_2 => "original value"
      #   # sleep 10 # First thread extend the life of cache by another 10 seconds
      #   # cache.fetch("foo") => "new value 1"
      #
      # Other options will be handled by the specific cache store implementation.
      # Internally, #fetch calls #read_entry, and calls #write_entry on a cache miss.
      # +options+ will be passed to the #read and #write calls.
      #
      # For example, MemCacheStore's #write method supports the +:raw+
      # option, which tells the memcached server to store all values as strings.
      # We can use this option with #fetch too:
      #
      #   cache = ActiveSupport::Cache::MemCacheStore.new
      #   cache.fetch("foo", :force => true, :raw => true) do
      #     :bar
      #   end
      #   cache.fetch("foo")  # => "bar"
      def fetch(name, options = nil)
        if block_given?
          options = merged_options(options)
          key = namespaced_key(name, options)
          unless options[:force]
            entry = instrument(:read, name, options) do |payload|
              payload[:super_operation] = :fetch if payload
              read_entry(key, options)
            end
          end
          if entry && entry.expired?
            race_ttl = options[:race_condition_ttl].to_i
            if race_ttl and Time.now.to_f - entry.expires_at <= race_ttl
              entry.expires_at = Time.now + race_ttl
              write_entry(key, entry, :expires_in => race_ttl * 2)
            else
              delete_entry(key, options)
            end
            entry = nil
          end

          if entry
            instrument(:fetch_hit, name, options) { |payload| }
            entry.value
          else
            result = instrument(:generate, name, options) do |payload|
              yield
            end
            write(name, result, options)
            result
          end
        else
          read(name, options)
        end
      end

      # Fetches data from the cache, using the given key. If there is data in
      # the cache with the given key, then that data is returned. Otherwise,
      # nil is returned.
      #
      # Options are passed to the underlying cache implementation.
      def read(name, options = nil)
        options = merged_options(options)
        key = namespaced_key(name, options)
        instrument(:read, name, options) do |payload|
          entry = read_entry(key, options)
          if entry
            if entry.expired?
              delete_entry(key, options)
              payload[:hit] = false if payload
              nil
            else
              payload[:hit] = true if payload
              entry.value
            end
          else
            payload[:hit] = false if payload
            nil
          end
        end
      end

      # Read multiple values at once from the cache. Options can be passed
      # in the last argument.
      #
      # Some cache implementation may optimize this method.
      #
      # Returns a hash mapping the names provided to the values found.
      def read_multi(*names)
        options = names.extract_options!
        options = merged_options(options)
        results = {}
        names.each do |name|
          key = namespaced_key(name, options)
          entry = read_entry(key, options)
          if entry
            if entry.expired?
              delete_entry(key, options)
            else
              results[name] = entry.value
            end
          end
        end
        results
      end

      # Writes the value to the cache, with the key.
      #
      # Options are passed to the underlying cache implementation.
      def write(name, value, options = nil)
        options = merged_options(options)
        instrument(:write, name, options) do |payload|
          entry = Entry.new(value, options)
          write_entry(namespaced_key(name, options), entry, options)
        end
      end

      # Deletes an entry in the cache. Returns +true+ if an entry is deleted.
      #
      # Options are passed to the underlying cache implementation.
      def delete(name, options = nil)
        options = merged_options(options)
        instrument(:delete, name) do |payload|
          delete_entry(namespaced_key(name, options), options)
        end
      end

      # Return true if the cache contains an entry for the given key.
      #
      # Options are passed to the underlying cache implementation.
      def exist?(name, options = nil)
        options = merged_options(options)
        instrument(:exist?, name) do |payload|
          entry = read_entry(namespaced_key(name, options), options)
          entry && !entry.expired?
        end
      end

      # Delete all entries with keys matching the pattern.
      #
      # Options are passed to the underlying cache implementation.
      #
      # All implementations may not support this method.
      def delete_matched(matcher, options = nil)
        raise NotImplementedError.new("#{self.class.name} does not support delete_matched")
      end

      # Increment an integer value in the cache.
      #
      # Options are passed to the underlying cache implementation.
      #
      # All implementations may not support this method.
      def increment(name, amount = 1, options = nil)
        raise NotImplementedError.new("#{self.class.name} does not support increment")
      end

      # Increment an integer value in the cache.
      #
      # Options are passed to the underlying cache implementation.
      #
      # All implementations may not support this method.
      def decrement(name, amount = 1, options = nil)
        raise NotImplementedError.new("#{self.class.name} does not support decrement")
      end

      # Cleanup the cache by removing expired entries.
      #
      # Options are passed to the underlying cache implementation.
      #
      # All implementations may not support this method.
      def cleanup(options = nil)
        raise NotImplementedError.new("#{self.class.name} does not support cleanup")
      end

      # Clear the entire cache. Be careful with this method since it could
      # affect other processes if shared cache is being used.
      #
      # Options are passed to the underlying cache implementation.
      #
      # All implementations may not support this method.
      def clear(options = nil)
        raise NotImplementedError.new("#{self.class.name} does not support clear")
      end

      protected
        # Add the namespace defined in the options to a pattern designed to match keys.
        # Implementations that support delete_matched should call this method to translate
        # a pattern that matches names into one that matches namespaced keys.
        def key_matcher(pattern, options)
          prefix = options[:namespace].is_a?(Proc) ? options[:namespace].call : options[:namespace]
          if prefix
            source = pattern.source
            if source.start_with?('^')
              source = source[1, source.length]
            else
              source = ".*#{source[0, source.length]}"
            end
            Regexp.new("^#{Regexp.escape(prefix)}:#{source}", pattern.options)
          else
            pattern
          end
        end

        # Read an entry from the cache implementation. Subclasses must implement this method.
        def read_entry(key, options) # :nodoc:
          raise NotImplementedError.new
        end

        # Write an entry to the cache implementation. Subclasses must implement this method.
        def write_entry(key, entry, options) # :nodoc:
          raise NotImplementedError.new
        end

        # Delete an entry from the cache implementation. Subclasses must implement this method.
        def delete_entry(key, options) # :nodoc:
          raise NotImplementedError.new
        end

      private
        # Merge the default options with ones specific to a method call.
        def merged_options(call_options) # :nodoc:
          if call_options
            options.merge(call_options)
          else
            options.dup
          end
        end

        # Expand key to be a consistent string value. Invoke +cache_key+ if
        # object responds to +cache_key+. Otherwise, to_param method will be
        # called. If the key is a Hash, then keys will be sorted alphabetically.
        def expanded_key(key) # :nodoc:
          return key.cache_key.to_s if key.respond_to?(:cache_key)

          case key
          when Array
            if key.size > 1
              key = key.collect{|element| expanded_key(element)}
            else
              key = key.first
            end
          when Hash
            key = key.sort_by { |k,_| k.to_s }.collect{|k,v| "#{k}=#{v}"}
          end

          key.to_param
        end

        # Prefix a key with the namespace. Namespace and key will be delimited with a colon.
        def namespaced_key(key, options)
          key = expanded_key(key)
          namespace = options[:namespace] if options
          prefix = namespace.is_a?(Proc) ? namespace.call : namespace
          key = "#{prefix}:#{key}" if prefix
          key
        end

        def instrument(operation, key, options = nil)
          log(operation, key, options)

          if self.class.instrument
            payload = { :key => key }
            payload.merge!(options) if options.is_a?(Hash)
            ActiveSupport::Notifications.instrument("cache_#{operation}.active_support", payload){ yield(payload) }
          else
            yield(nil)
          end
        end

        def log(operation, key, options = nil)
          return unless logger && logger.debug? && !silence?
          logger.debug("Cache #{operation}: #{key}#{options.blank? ? "" : " (#{options.inspect})"}")
        end
    end

    # Entry that is put into caches. It supports expiration time on entries and can compress values
    # to save space in the cache.
    class Entry
      attr_reader :created_at, :expires_in

      DEFAULT_COMPRESS_LIMIT = 16.kilobytes

      class << self
        # Create an entry with internal attributes set. This method is intended to be
        # used by implementations that store cache entries in a native format instead
        # of as serialized Ruby objects.
        def create(raw_value, created_at, options = {})
          entry = new(nil)
          entry.instance_variable_set(:@value, raw_value)
          entry.instance_variable_set(:@created_at, created_at.to_f)
          entry.instance_variable_set(:@compressed, options[:compressed])
          entry.instance_variable_set(:@expires_in, options[:expires_in])
          entry
        end
      end

      # Create a new cache entry for the specified value. Options supported are
      # +:compress+, +:compress_threshold+, and +:expires_in+.
      def initialize(value, options = {})
        @compressed = false
        @expires_in = options[:expires_in]
        @expires_in = @expires_in.to_f if @expires_in
        @created_at = Time.now.to_f
        if value.nil?
          @value = nil
        else
          @value = Marshal.dump(value)
          if should_compress?(@value, options)
            @value = Zlib::Deflate.deflate(@value)
            @compressed = true
          end
        end
      end

      # Get the raw value. This value may be serialized and compressed.
      def raw_value
        @value
      end

      # Get the value stored in the cache.
      def value
        # If the original value was exactly false @value is still true because
        # it is marshalled and eventually compressed. Both operations yield
        # strings.
        if @value
          Marshal.load(compressed? ? Zlib::Inflate.inflate(@value) : @value)
        end
      end

      def compressed?
        @compressed
      end

      # Check if the entry is expired. The +expires_in+ parameter can override the
      # value set when the entry was created.
      def expired?
        @expires_in && @created_at + @expires_in <= Time.now.to_f
      end

      # Set a new time when the entry will expire.
      def expires_at=(time)
        if time
          @expires_in = time.to_f - @created_at
        else
          @expires_in = nil
        end
      end

      # Seconds since the epoch when the entry will expire.
      def expires_at
        @expires_in ? @created_at + @expires_in : nil
      end

      # Returns the size of the cached value. This could be less than value.size
      # if the data is compressed.
      def size
        if @value.nil?
          0
        else
          @value.bytesize
        end
      end

      private
        def should_compress?(serialized_value, options)
          if options[:compress]
            compress_threshold = options[:compress_threshold] || DEFAULT_COMPRESS_LIMIT
            return true if serialized_value.size >= compress_threshold
          end
          false
        end
    end
  end
end