Set to true if cache stores should be instrumented. Default is false.

# File activesupport/lib/active_support/cache.rb, line 183
def self.instrument=(boolean)
  Thread.current[:instrument_cache_store] = boolean
end

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.

# File activesupport/lib/active_support/cache.rb, line 163
def initialize(options = nil)
  @options = options ? options.dup : {}
end

Cleanup the cache by removing expired entries.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

# File activesupport/lib/active_support/cache.rb, line 448
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.

The options hash is passed to the underlying cache implementation.

All implementations may not support this method.

# File activesupport/lib/active_support/cache.rb, line 458
def clear(options = nil)
  raise NotImplementedError.new("#{self.class.name} does not support clear")
end

Decrement an integer value in the cache.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

# File activesupport/lib/active_support/cache.rb, line 439
def decrement(name, amount = 1, options = nil)
  raise NotImplementedError.new("#{self.class.name} does not support decrement")
end

Deletes an entry in the cache. Returns true if an entry is deleted.

Options are passed to the underlying cache implementation.

# File activesupport/lib/active_support/cache.rb, line 396
def delete(name, options = nil)
  options = merged_options(options)

  instrument(:delete, name) do
    delete_entry(namespaced_key(name, options), options)
  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.

# File activesupport/lib/active_support/cache.rb, line 421
def delete_matched(matcher, options = nil)
  raise NotImplementedError.new("#{self.class.name} does not support delete_matched")
end

Returns true if the cache contains an entry for the given key.

Options are passed to the underlying cache implementation.

# File activesupport/lib/active_support/cache.rb, line 407
def exist?(name, options = nil)
  options = merged_options(options)

  instrument(:exist?, name) do
    entry = read_entry(namespaced_key(name, options), options)
    (entry && !entry.expired?) || false
  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.

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 passed the key and executed 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 force: true will force a cache miss:

cache.write('today', 'Monday')
cache.fetch('today', force: true)  # => nil

Setting :compress will store a large cache entry set by the call in a compressed format.

Setting :expires_in 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 :race_condition_ttl 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 several 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 :race_condition_ttl. 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 bit 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 :race_condition_ttl 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 :race_condition_ttl 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"

# File activesupport/lib/active_support/cache.rb, line 285
def fetch(name, options = nil)
  if block_given?
    options = merged_options(options)
    key = namespaced_key(name, options)

    cached_entry = find_cached_entry(key, name, options) unless options[:force]
    entry = handle_expired_entry(cached_entry, key, options)

    if entry
      get_entry_value(entry, name, options)
    else
      save_block_result_to_cache(name, options) { |_name| yield _name }
    end
  else
    read(name, options)
  end
end

Fetches data from the cache, using the given keys. If there is data in the cache with the given keys, then that data is returned. Otherwise, the supplied block is called for each key for which there was no data, and the result will be written to the cache and returned.

Options are passed to the underlying cache implementation.

Returns an array with the data for each of the names. For example:

cache.write("bim", "bam")
cache.fetch_multi("bim", "boom") {|key| key * 2 }
# => ["bam", "boomboom"]

# File activesupport/lib/active_support/cache.rb, line 366
def fetch_multi(*names)
  options = names.extract_options!
  options = merged_options(options)

  results = read_multi(*names, options)

  names.map do |name|
    results.fetch(name) do
      value = yield name
      write(name, value, options)
      value
    end
  end
end

Increment an integer value in the cache.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

# File activesupport/lib/active_support/cache.rb, line 430
def increment(name, amount = 1, options = nil)
  raise NotImplementedError.new("#{self.class.name} does not support increment")
end

Silence the logger within a block.

# File activesupport/lib/active_support/cache.rb, line 174
def mute
  previous_silence, @silence = defined?(@silence) && @silence, true
  yield
ensure
  @silence = previous_silence
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.

# File activesupport/lib/active_support/cache.rb, line 308
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.

# File activesupport/lib/active_support/cache.rb, line 335
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

Silence the logger.

# File activesupport/lib/active_support/cache.rb, line 168
def silence!
  @silence = true
  self
end

Writes the value to the cache, with the key.

Options are passed to the underlying cache implementation.

# File activesupport/lib/active_support/cache.rb, line 384
def write(name, value, options = nil)
  options = merged_options(options)

  instrument(:write, name, options) do
    entry = Entry.new(value, options)
    write_entry(namespaced_key(name, options), entry, options)
  end
end

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.

# File activesupport/lib/active_support/cache.rb, line 467
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