Add a failing, somewhat contrived spec to demonstrate EXISTS keys bei…

…ng orphaned. We share redis clients between threads (redis obj is threadsafe) and because of this the 2nd thread will be blocking, waiting for the AVAILABLE key and thus the first thread is unable to finish cleanup. Eventually the AVAILABLE key expires but the EXISTS key does not. The failure to succeed with the signal() call could be due to loss of network connection, process crash, etc. Leaving an unexpiring EXISTS key but no AVAILABLE key means that a retry will believe the semaphore exists and wait for the AVAILABLE which never comes.

spec/semaphore_spec.rb

@@ -148,6 +148,31 @@
       sleep 3.0
       expect(@redis.keys.count).to eq(original_key_size)
     end
+
+    it "does not leave an exists key without an expiration when an expiration is specified" do
+      original_key_size = @redis.keys.count
+      queue = Queue.new
+      threads = 2.times.collect do
+        Thread.new do
+          Redis::Semaphore.new(:my_semaphore, :redis => @redis, :expiration => 3).lock(5) do
+            sleep 1
+          end
+        end
+      end
+      sleep 4.0
+      @redis2 = Redis.new :db => 15
+      threads.each{|t| t.kill } #ensure signal step fails
+      expect(@redis2.ttl("SEMAPHORE:my_semaphore:EXISTS").to_s).to_not eql("-1")
+      sleep 4.0 #allow blpop timeout to occur
+      thrd = Thread.new do
+        Redis::Semaphore.new(:my_semaphore, :redis => @redis2, :expiration => 3).lock(5) do
+          queue << "work"
+        end
+      end
+      thrd.join(3)
+      expect(queue.size).to eql(1)
+      expect(@redis.ttl("SEMAPHORE:my_semaphore:EXISTS").to_s).to_not eql("-1")
+    end
   end
 
   describe "semaphore without staleness checking" do