class Sprockets::Cache
Public: Wrapper
interface to backend cache stores. Ensures a consistent API even when the backend uses get/set or read/write.
Public cache interface
Always assign the backend store instance to Environment#cache=
.
environment.cache = Sprockets::Cache::MemoryStore.new(1000)
Environment#cache
will always return a wrapped Cache
interface. See the methods marked public on this class.
Backend cache interface
The Backend cache store must implement two methods.
get(key)
key - An opaque String with a length less than 250 characters. Returns an JSON serializable object.
set(key, value)
Will only be called once per key. Setting a key "foo" with value "bar", then later key "foo" with value "baz" is an undefined behavior. key - An opaque String with a length less than 250 characters. value - A JSON serializable object. Returns argument value.
clear(options)
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.
Constants
- PEEK_SIZE
- VERSION
Internal:
Cache
key version for this class. Rarely should have to change unless the cache format radically changes. Will be bump on major version releases though.
Public Class Methods
# File lib/sprockets/cache.rb, line 56 def self.default_logger logger = Logger.new($stderr) logger.level = Logger::FATAL logger end
Internal: Wrap a backend cache store.
Always assign a backend cache store instance to Environment#cache=
and use Environment#cache
to retrieve a wrapped interface.
cache - A compatible backend cache store instance.
# File lib/sprockets/cache.rb, line 68 def initialize(cache = nil, logger = self.class.default_logger) @cache_wrapper = get_cache_wrapper(cache) @fetch_cache = Cache::MemoryStore.new(1024) @logger = logger end
Public Instance Methods
Public: Clear cache
Returns truthy on success, potentially raises exception on failure
# File lib/sprockets/cache.rb, line 156 def clear(options=nil) @cache_wrapper.clear @fetch_cache.clear end
Public: Prefer API to retrieve and set values in the cache store.
key - JSON serializable key block -
Must return a consistent JSON serializable object for the given key.
Examples
cache.fetch("foo") { "bar" }
Returns a JSON serializable object.
# File lib/sprockets/cache.rb, line 85 def fetch(key) start = Time.now.to_f expanded_key = expand_key(key) value = @fetch_cache.get(expanded_key) if value.nil? value = @cache_wrapper.get(expanded_key) if value.nil? value = yield @cache_wrapper.set(expanded_key, value) @logger.debug do ms = "(#{((Time.now.to_f - start) * 1000).to_i}ms)" "Sprockets Cache miss #{peek_key(key)} #{ms}" end end @fetch_cache.set(expanded_key, value) end value end
Public: Low level API to retrieve item directly from the backend cache store.
This API may be used publicly, but may have undefined behavior depending on the backend store being used. Prefer the Cache#fetch
API over using this.
key - JSON serializable key local - Check local cache first (default: false)
Returns a JSON serializable object or nil if there was a cache miss.
# File lib/sprockets/cache.rb, line 115 def get(key, local = false) expanded_key = expand_key(key) if local && value = @fetch_cache.get(expanded_key) return value end value = @cache_wrapper.get(expanded_key) @fetch_cache.set(expanded_key, value) if local value end
Public: Pretty inspect
Returns String.
# File lib/sprockets/cache.rb, line 149 def inspect "#<#{self.class} local=#{@fetch_cache.inspect} store=#{@cache_wrapper.cache.inspect}>" end
Public: Low level API to set item directly to the backend cache store.
This API may be used publicly, but may have undefined behavior depending on the backend store being used. Prefer the Cache#fetch
API over using this.
key - JSON serializable key value - A consistent JSON serializable object for the given key. Setting
a different value for the given key has undefined behavior.
local - Set on local cache (default: false)
Returns the value argument.
# File lib/sprockets/cache.rb, line 140 def set(key, value, local = false) expanded_key = expand_key(key) @fetch_cache.set(expanded_key, value) if local @cache_wrapper.set(expanded_key, value) end
Private Instance Methods
Internal: Expand object cache key into a short String key.
The String should be under 250 characters so its compatible with Memcache.
key - JSON serializable key
Returns a String with a length less than 250 characters.
# File lib/sprockets/cache.rb, line 170 def expand_key(key) digest_key = DigestUtils.pack_urlsafe_base64digest(DigestUtils.digest(key)) namespace = digest_key[0, 2] "sprockets/v#{VERSION}/#{namespace}/#{digest_key}" end
# File lib/sprockets/cache.rb, line 196 def get_cache_wrapper(cache) if cache.is_a?(Cache) cache # `Cache#get(key)` for Memcache elsif cache.respond_to?(:get) GetWrapper.new(cache) # `Cache#[key]` so `Hash` can be used elsif cache.respond_to?(:[]) HashWrapper.new(cache) # `Cache#read(key)` for `ActiveSupport::Cache` support elsif cache.respond_to?(:read) ReadWriteWrapper.new(cache) else cache = Sprockets::Cache::NullStore.new GetWrapper.new(cache) end end
Internal: Show first 100 characters of cache key for logging purposes.
Returns a String with a length less than 100 characters.
# File lib/sprockets/cache.rb, line 181 def peek_key(key) case key when Integer key.to_s when String key[0, PEEK_SIZE].inspect when Array str = [] key.each { |k| str << peek_key(k) } str.join(':')[0, PEEK_SIZE] else peek_key(DigestUtils.pack_urlsafe_base64digest(DigestUtils.digest(key))) end end