Merge branch 'redis-connection-pool' into 'master'

Redis connection pool

Split from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3232

Having an easily accessible Redis connection pool allows us to do more
cool stuff with Redis in GitLab (instead of having to go through e.g.
the Rails cache).

See merge request !3521

4 files changed, 64 insertions, 43 deletions

diff --git a/lib/gitlab/exclusive_lease.rb b/lib/gitlab/exclusive_lease.rb
index c73eca832d7..c2260a5f7ac 100644
--- a/lib/gitlab/exclusive_lease.rb
+++ b/lib/gitlab/exclusive_lease.rb
@@ -43,7 +43,9 @@ module Gitlab
     # false if the lease is already taken.
     def try_obtain
       # Performing a single SET is atomic
-      !!redis.set(redis_key, '1', nx: true, ex: @timeout)
+      Gitlab::Redis.with do |redis|
+        !!redis.set(redis_key, '1', nx: true, ex: @timeout)
+      end
     end
 
     # No #cancel method. See comments above!
diff --git a/lib/gitlab/redis.rb b/lib/gitlab/redis.rb
new file mode 100644
index 00000000000..319447669dc
--- /dev/null
+++ b/lib/gitlab/redis.rb
@@ -0,0 +1,48 @@
+module Gitlab
+  class Redis
+    CACHE_NAMESPACE = 'cache:gitlab'
+
+    attr_reader :url
+
+    # To be thread-safe we must be careful when writing the class instance
+    # variables @url and @pool. Because @pool depends on @url we need two
+    # mutexes to prevent deadlock.
+    URL_MUTEX = Mutex.new
+    POOL_MUTEX = Mutex.new
+    private_constant :URL_MUTEX, :POOL_MUTEX
+
+    def self.url
+      @url || URL_MUTEX.synchronize { @url = new.url }
+    end
+
+    def self.with
+      if @pool.nil?
+        POOL_MUTEX.synchronize do
+          @pool = ConnectionPool.new { ::Redis.new(url: url) }
+        end
+      end
+      @pool.with { |redis| yield redis }
+    end
+    
+    def self.redis_store_options
+      url = new.url
+      redis_config_hash = ::Redis::Store::Factory.extract_host_options_from_uri(url)
+      # Redis::Store does not handle Unix sockets well, so let's do it for them
+      redis_uri = URI.parse(url)
+      if redis_uri.scheme == 'unix'
+        redis_config_hash[:path] = redis_uri.path
+      end
+      redis_config_hash
+    end
+
+    def initialize(rails_env=nil)
+      rails_env ||= Rails.env
+      config_file = File.expand_path('../../../config/resque.yml', __FILE__)
+  
+      @url = "redis://localhost:6379"
+      if File.exists?(config_file)
+        @url =YAML.load_file(config_file)[rails_env]
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/redis_config.rb b/lib/gitlab/redis_config.rb
deleted file mode 100644
index 4949c6db539..00000000000
--- a/lib/gitlab/redis_config.rb
+++ /dev/null
@@ -1,30 +0,0 @@
-module Gitlab
-  class RedisConfig
-    attr_reader :url
-
-    def self.url
-      new.url
-    end
-    
-    def self.redis_store_options
-      url = new.url
-      redis_config_hash = Redis::Store::Factory.extract_host_options_from_uri(url)
-      # Redis::Store does not handle Unix sockets well, so let's do it for them
-      redis_uri = URI.parse(url)
-      if redis_uri.scheme == 'unix'
-        redis_config_hash[:path] = redis_uri.path
-      end
-      redis_config_hash
-    end
-
-    def initialize(rails_env=nil)
-      rails_env ||= Rails.env
-      config_file = File.expand_path('../../../config/resque.yml', __FILE__)
-  
-      @url = "redis://localhost:6379"
-      if File.exists?(config_file)
-        @url =YAML.load_file(config_file)[rails_env]
-      end
-    end
-  end
-end
diff --git a/lib/tasks/cache.rake b/lib/tasks/cache.rake
index 51e746ef923..2214f855200 100644
--- a/lib/tasks/cache.rake
+++ b/lib/tasks/cache.rake
@@ -4,18 +4,19 @@ namespace :cache do
 
   desc "GitLab | Clear redis cache"
   task :clear => :environment do
-    redis = Redis.new(url: Gitlab::RedisConfig.url)
-    cursor = REDIS_SCAN_START_STOP
-    loop do
-      cursor, keys = redis.scan(
-        cursor,
-        match: "#{Gitlab::REDIS_CACHE_NAMESPACE}*", 
-        count: CLEAR_BATCH_SIZE
-      )
-
-      redis.del(*keys) if keys.any?
-
-      break if cursor == REDIS_SCAN_START_STOP
+    Gitlab::Redis.with do |redis|
+      cursor = REDIS_SCAN_START_STOP
+      loop do
+        cursor, keys = redis.scan(
+          cursor,
+          match: "#{Gitlab::Redis::CACHE_NAMESPACE}*", 
+          count: CLEAR_BATCH_SIZE
+        )
+  
+        redis.del(*keys) if keys.any?
+  
+        break if cursor == REDIS_SCAN_START_STOP
+      end
     end
   end
 end