ActiveSupport::Cache refactoring

All Caches

* Add default options to initializer that will be sent to all read, write, fetch, exist?, increment, and decrement
* Add support for the :expires_in option to fetch and write for all caches. Cache entries are stored with the create timestamp and a ttl so that expiration can be handled independently of the implementation.
* Add support for a :namespace option. This can be used to set a global prefix for cache entries.
* Deprecate expand_cache_key on ActiveSupport::Cache and move it to ActionController::Caching and ActionDispatch::Http::Cache since the logic in the method used some Rails specific environment variables and was only used by ActionPack classes. Not very DRY but there didn't seem to be a good shared spot and ActiveSupport really shouldn't be Rails specific.
* Add support for :race_condition_ttl to fetch. This setting can prevent race conditions on fetch calls where several processes try to regenerate a recently expired entry at once.
* Add support for :compress option to fetch and write which will compress any data over a configurable threshold.
* Nil values can now be stored in the cache and are distinct from cache misses for fetch.
* Easier API to create new implementations. Just need to implement the methods read_entry, write_entry, and delete_entry instead of overwriting existing methods.
* Since all cache implementations support storing objects, update the docs to state that ActiveCache::Cache::Store implementations should store objects. Keys, however, must be strings since some implementations require that.
* Increase test coverage.
* Document methods which are provided as convenience but which may not be universally available.

MemoryStore

* MemoryStore can now safely be used as the cache for single server sites.
* Make thread safe so that the default cache implementation used by Rails is thread safe. The overhead is minimal and it is still the fastest store available.
* Provide :size initialization option indicating the maximum size of the cache in memory (defaults to 32Mb).
* Add prune logic that removes the least recently used cache entries to keep the cache size from exceeding the max.
* Deprecated SynchronizedMemoryStore since it isn't needed anymore.

FileStore

* Escape key values so they will work as file names on all file systems, be consistent, and case sensitive
* Use a hash algorithm to segment the cache into sub directories so that a large cache doesn't exceed file system limits.
* FileStore can be slow so implement the LocalCache strategy to cache reads for the duration of a request.
* Add cleanup method to keep the disk from filling up with expired entries.
* Fix increment and decrement to use file system locks so they are consistent between processes.

MemCacheStore

* Support all keys. Previously keys with spaces in them would fail
* Deprecate CompressedMemCacheStore since it isn't needed anymore (use :compress => true)

[#4452 state:committed]

Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>

1 files changed, 102 insertions, 52 deletions

diff --git a/activesupport/lib/active_support/cache/strategy/local_cache.rb b/activesupport/lib/active_support/cache/strategy/local_cache.rb
index bbbd643736..8942587ac8 100644
--- a/activesupport/lib/active_support/cache/strategy/local_cache.rb
+++ b/activesupport/lib/active_support/cache/strategy/local_cache.rb
@@ -4,17 +4,54 @@ require 'active_support/core_ext/string/inflections'
 module ActiveSupport
   module Cache
     module Strategy
+      # Caches that implement LocalCache will be backed by an in memory cache for the
+      # duration of a block. Repeated calls to the cache for the same key will hit the
+      # in memory cache for faster access.
       module LocalCache
-        # this allows caching of the fact that there is nothing in the remote cache
-        NULL = 'remote_cache_store:null'
+        # Simple memory backed cache. This cache is not thread safe but is intended only
+        # for serving as a temporary memory cache for a single thread.
+        class LocalStore < Store
+          def initialize
+            super
+            @data = {}
+          end
+
+          # Since it isn't thread safe, don't allow synchronizing.
+          def synchronize # :nodoc:
+            yield
+          end
+
+          def clear(options = nil)
+            @data.clear
+          end
+
+          def read_entry(key, options)
+            @data[key]
+          end
 
+          def write_entry(key, value, options)
+            @data[key] = value
+            true
+          end
+
+          def delete_entry(key, options)
+            !!@data.delete(key)
+          end
+        end
+
+        # Use a local cache to front for the cache for the duration of a block.
         def with_local_cache
-          Thread.current[thread_local_key] = MemoryStore.new
-          yield
-        ensure
-          Thread.current[thread_local_key] = nil
+          save_val = Thread.current[thread_local_key]
+          begin
+            Thread.current[thread_local_key] = LocalStore.new
+            yield
+          ensure
+            Thread.current[thread_local_key] = save_val
+          end
         end
 
+        # Middleware class can be inserted as a Rack handler to use a local cache for the
+        # duration of a request.
         def middleware
           @middleware ||= begin
             klass = Class.new
@@ -24,7 +61,7 @@ module ActiveSupport
               end
 
               def call(env)
-                Thread.current[:#{thread_local_key}] = MemoryStore.new
+                Thread.current[:#{thread_local_key}] = LocalStore.new
                 @app.call(env)
               ensure
                 Thread.current[:#{thread_local_key}] = nil
@@ -39,73 +76,86 @@ module ActiveSupport
           end
         end
 
-        def read(key, options = nil)
-          value = local_cache && local_cache.read(key)
-          if value == NULL
-            nil
-          elsif value.nil?
-            value = super
-            local_cache.mute { local_cache.write(key, value || NULL) } if local_cache
-            value.duplicable? ? value.dup : value
-          else
-            # forcing the value to be immutable
-            value.duplicable? ? value.dup : value
-          end
-        end
-
-        def write(key, value, options = nil)
-          value = value.to_s if respond_to?(:raw?) && raw?(options)
-          local_cache.mute { local_cache.write(key, value || NULL) } if local_cache
+        def clear(options = nil) # :nodoc:
+          local_cache.clear(options) if local_cache
           super
         end
 
-        def delete(key, options = nil)
-          local_cache.mute { local_cache.write(key, NULL) } if local_cache
+        def cleanup(options = nil) # :nodoc:
+          local_cache.clear(options) if local_cache
           super
         end
 
-        def exist(key, options = nil)
-          value = local_cache.read(key) if local_cache
-          if value == NULL
-            false
-          elsif value
-            true
-          else
-            super
+        def increment(name, amount = 1, options = nil) # :nodoc:
+          value = bypass_local_cache{super}
+          if local_cache
+            local_cache.mute do
+              if value
+                local_cache.write(name, value, options)
+              else
+                local_cache.delete(name, options)
+              end
+            end
           end
+          value
         end
 
-        def increment(key, amount = 1)
-          if value = super
-            local_cache.mute { local_cache.write(key, value.to_s) } if local_cache
-            value
-          else
-            nil
+        def decrement(name, amount = 1, options = nil) # :nodoc:
+          value = bypass_local_cache{super}
+          if local_cache
+            local_cache.mute do
+              if value
+                local_cache.write(name, value, options)
+              else
+                local_cache.delete(name, options)
+              end
+            end
           end
+          value
         end
 
-        def decrement(key, amount = 1)
-          if value = super
-            local_cache.mute { local_cache.write(key, value.to_s) } if local_cache
-            value
-          else
-            nil
+        protected
+          def read_entry(key, options) # :nodoc:
+            if local_cache
+              entry = local_cache.read_entry(key, options)
+              unless entry
+                entry = super
+                local_cache.write_entry(key, entry, options)
+              end
+              entry
+            else
+              super
+            end
           end
-        end
 
-        def clear
-          local_cache.clear if local_cache
-          super
-        end
+          def write_entry(key, entry, options) # :nodoc:
+            local_cache.write_entry(key, entry, options) if local_cache
+            super
+          end
+
+          def delete_entry(key, options) # :nodoc:
+            local_cache.delete_entry(key, options) if local_cache
+            super
+          end
 
         private
           def thread_local_key
-            @thread_local_key ||= "#{self.class.name.underscore}_local_cache".gsub("/", "_").to_sym
+            @thread_local_key ||= "#{self.class.name.underscore}_local_cache_#{self.object_id}".gsub("/", "_").to_sym
           end
 
           def local_cache
             Thread.current[thread_local_key]
           end
+
+          def bypass_local_cache
+            save_cache = Thread.current[thread_local_key]
+            begin
+              Thread.current[thread_local_key] = nil
+              yield
+            ensure
+              Thread.current[thread_local_key] = save_cache
+            end
+          end
       end
     end
   end