Revert "Remove .via, not sure it's necessary."

This reverts commit dd798bb6be.

lib/sidekiq/worker.rb

@@ -34,6 +34,25 @@ module Sidekiq
       Sidekiq.logger
     end
 
+    # Allows sharding of jobs across any number of Redis instances.  All jobs
+    # defined within the block will use the given Redis connection pool.
+    #
+    #   pool = ConnectionPool.new { Redis.new }
+    #   Sidekiq::Worker.via(pool) do
+    #     SomeWorker.perform_async(1,2,3)
+    #     SomeOtherWorker.perform_async(1,2,3)
+    #   end
+    #
+    # Generally this is only needed for very large Sidekiq installs processing
+    # more than thousands jobs per second.
+    def self.via(pool)
+      raise ArgumentError, "No pool given" if pool.nil?
+      Thread.current[:sidekiq_via_pool] = pool
+      yield
+    ensure
+      Thread.current[:sidekiq_via_pool] = nil
+    end
+
     module ClassMethods
 
       def perform_async(*args)
@@ -81,7 +100,7 @@ module Sidekiq
       end
 
       def client_push(item) # :nodoc:
-        pool = get_sidekiq_options['pool'] || Sidekiq.redis_pool
+        pool = Thread.current[:sidekiq_via_pool] || get_sidekiq_options['pool'] || Sidekiq.redis_pool
         Sidekiq::Client.new(pool).push(item.stringify_keys)
       end
 

test/test_client.rb

@@ -247,6 +247,16 @@ class TestClient < Sidekiq::Test
       DWorker.perform_async(1,2,3)
       conn.verify
     end
+    it 'allows #via to point to different Redi' do
+      conn = MiniTest::Mock.new
+      conn.expect(:multi, [0, 1])
+      default = Sidekiq::Client.redis_pool
+      Sidekiq::Client.via(ConnectionPool.new(size: 1) { conn }) do
+        CWorker.perform_async(1,2,3)
+      end
+      assert_equal default, Sidekiq::Client.redis_pool
+      conn.verify
+    end
     it 'allows Resque helpers to point to different Redi' do
       conn = MiniTest::Mock.new
       conn.expect(:zadd, 1, [String, Array])