From a53ad5bba37199047ba20194933e122bf6b0252f Mon Sep 17 00:00:00 2001
From: Nahum Wild <nahum.wild@gmail.com>
Date: Thu, 15 Jan 2009 21:28:10 -0600
Subject: Added in a local per request cache to MemCacheStore. It acts as a
 buffer to stop unneccessary requests being sent through to memcache [#1653
 state:resolved] Signed-off-by: Joshua Peek <josh@joshpeek.com>

---
 .../lib/active_support/cache/mem_cache_store.rb    | 65 ++++++++++++++++++++--
 1 file changed, 61 insertions(+), 4 deletions(-)

(limited to 'activesupport/lib/active_support/cache/mem_cache_store.rb')

diff --git a/activesupport/lib/active_support/cache/mem_cache_store.rb b/activesupport/lib/active_support/cache/mem_cache_store.rb
index f9a7fb1440..eed9faac6d 100644
--- a/activesupport/lib/active_support/cache/mem_cache_store.rb
+++ b/activesupport/lib/active_support/cache/mem_cache_store.rb
@@ -13,6 +13,7 @@ module ActiveSupport
     #   server goes down, then MemCacheStore will ignore it until it goes back
     #   online.
     # - Time-based expiry support. See #write and the +:expires_in+ option.
+    # - Per-request in memory cache for all communication with the MemCache server(s).
     class MemCacheStore < Store
       module Response # :nodoc:
         STORED      = "STORED\r\n"
@@ -22,6 +23,24 @@ module ActiveSupport
         DELETED     = "DELETED\r\n"
       end
 
+      # this allows caching of the fact that there is nothing in the remote cache
+      NULL = 'mem_cache_store:null'
+
+      THREAD_LOCAL_KEY = :mem_cache_store_cache
+
+      class LocalCache
+        def initialize(app)
+          @app = app
+        end
+
+        def call(env)
+          Thread.current[THREAD_LOCAL_KEY] = MemoryStore.new
+          @app.call(env)
+        ensure
+          Thread.current[THREAD_LOCAL_KEY] = nil
+        end
+      end
+
       attr_reader :addresses
 
       # Creates a new MemCacheStore object, with the given memcached server
@@ -42,7 +61,18 @@ module ActiveSupport
 
       def read(key, options = nil) # :nodoc:
         super
-        @data.get(key, raw?(options))
+
+        value = local_cache && local_cache.read(key)
+        if value == NULL
+          nil
+        elsif value.nil?
+          value = @data.get(key, raw?(options))
+          local_cache.write(key, value || NULL) if local_cache
+          value
+        else
+          # forcing the value to be immutable
+          value.dup
+        end
       rescue MemCache::MemCacheError => e
         logger.error("MemCacheError (#{e}): #{e.message}")
         nil
@@ -61,6 +91,7 @@ module ActiveSupport
         # memcache-client will break the connection if you send it an integer
         # in raw mode, so we convert it to a string to be sure it continues working.
         value = value.to_s if raw?(options)
+        local_cache.write(key, value || NULL) if local_cache
         response = @data.send(method, key, value, expires_in(options), raw?(options))
         response == Response::STORED
       rescue MemCache::MemCacheError => e
@@ -70,6 +101,7 @@ module ActiveSupport
 
       def delete(key, options = nil) # :nodoc:
         super
+        local_cache.write(key, NULL) if local_cache
         response = @data.delete(key, expires_in(options))
         response == Response::DELETED
       rescue MemCache::MemCacheError => e
@@ -80,14 +112,27 @@ module ActiveSupport
       def exist?(key, options = nil) # :nodoc:
         # Doesn't call super, cause exist? in memcache is in fact a read
         # But who cares? Reading is very fast anyway
-        !read(key, options).nil?
+        # Local cache is checked first, if it doesn't know then memcache itself is read from
+        value = local_cache.read(key) if local_cache
+        if value == NULL
+          false
+        elsif value
+          true
+        else
+          !read(key, options).nil?
+        end
       end
 
       def increment(key, amount = 1) # :nodoc:
         log("incrementing", key, amount)
 
         response = @data.incr(key, amount)
-        response == Response::NOT_FOUND ? nil : response
+        unless response == Response::NOT_FOUND
+          local_cache.write(key, response.to_s) if local_cache
+          response
+        else
+          nil
+        end
       rescue MemCache::MemCacheError
         nil
       end
@@ -96,17 +141,25 @@ module ActiveSupport
         log("decrement", key, amount)
 
         response = @data.decr(key, amount)
-        response == Response::NOT_FOUND ? nil : response
+        unless response == Response::NOT_FOUND
+          local_cache.write(key, response.to_s) if local_cache
+          response
+        else
+          nil
+        end
       rescue MemCache::MemCacheError
         nil
       end
 
       def delete_matched(matcher, options = nil) # :nodoc:
+        # don't do any local caching at present, just pass
+        # through and let the error happen
         super
         raise "Not supported by Memcache"
       end
 
       def clear
+        local_cache.clear if local_cache
         @data.flush_all
       end
 
@@ -115,6 +168,10 @@ module ActiveSupport
       end
 
       private
+        def local_cache
+          Thread.current[THREAD_LOCAL_KEY]
+        end
+
         def expires_in(options)
           (options && options[:expires_in]) || 0
         end
-- 
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