lib/redis/lock.rb in redis-objects-0.2.2 vs lib/redis/lock.rb in redis-objects-0.2.3

@@ -29,19 +29,55 @@
     # (on any server) will spin waiting for the lock up to the :timeout
     # that was specified when the lock was defined.
     def lock(&block)
       start = Time.now
       gotit = false
+      expiration = nil
       while Time.now - start < @options[:timeout]
-        gotit = redis.setnx(key, 1)
+        expiration = generate_expiration
+        # Use the expiration as the value of the lock.
+        gotit = redis.setnx(key, expiration)
         break if gotit
+
+        # Lock is being held.  Now check to see if it's expired (if we're using
+        # lock expiration).
+        # See "Handling Deadlocks" section on http://code.google.com/p/redis/wiki/SetnxCommand
+        if !@options[:expiration].nil?
+          old_expiration = redis.get(key).to_f
+
+          if old_expiration < Time.now.to_f
+            # If it's expired, use GETSET to update it.
+            expiration = generate_expiration
+            old_expiration = redis.getset(key, expiration).to_f
+
+            # Since GETSET returns the old value of the lock, if the old expiration
+            # is still in the past, we know no one else has expired the locked
+            # and we now have it.
+            if old_expiration < Time.now.to_f
+              gotit = true
+              break
+            end
+          end
+        end
+
         sleep 0.1
       end
       raise LockTimeout, "Timeout on lock #{key} exceeded #{@options[:timeout]} sec" unless gotit
       begin
         yield
       ensure
-        redis.del(key)
+        # We need to be careful when cleaning up the lock key.  If we took a really long
+        # time for some reason, and the lock expired, someone else may have it, and
+        # it's not safe for us to remove it.  Check how much time has passed since we
+        # wrote the lock key and only delete it if it hasn't expired (or we're not using
+        # lock expiration)
+        if @options[:expiration].nil? || expiration > Time.now.to_f
+          redis.del(key)
+        end
       end
+    end
+
+    def generate_expiration
+      @options[:expiration].nil? ? 1 : (Time.now + @options[:expiration].to_f + 1).to_f
     end
   end
 end
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