#vulnerable code 
                              protected <T> Promise<T> execute(final Class<T> clazz, Command command) {
    final Promise<T> reply = new Promise<T>() {
      @Override
      public void set(T value) {
        // Check the type and fail if the wrong type
        if (!clazz.isInstance(value)) {
          setException(new RedisException("Incorrect type for " + value + " should be " + clazz.getName() + " but is " + value.getClass().getName()));
        } else {
          super.set(value);
        }
      }
    };
    if (subscribed.get()) {
      reply.setException(new RedisException("Already subscribed, cannot send this command"));
    } else {
      ChannelFuture write;
      synchronized (channel) {
        queue.add(reply);
        write = channel.write(command);
      }
      write.addListener(new ChannelFutureListener() {
        @Override
        public void operationComplete(ChannelFuture future) throws Exception {
          if (future.isSuccess()) {
            // Netty doesn't call these in order
          } else if (future.isCancelled()) {
            reply.cancel(true);
          } else {
            reply.setException(future.getCause());
          }
        }
      });
    }
    return reply;
  } 
                            #location 17 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                              protected <T> Promise<T> execute(final Class<T> clazz, Command command) {
    final Promise<T> reply = new Promise<T>() {
      @Override
      public void set(T value) {
        // Check the type and fail if the wrong type
        if (!clazz.isInstance(value)) {
          setException(new RedisException("Incorrect type for " + value + " should be " + clazz.getName() + " but is " + value.getClass().getName()));
        } else {
          super.set(value);
        }
      }
    };
    if (subscribed.get()) {
      reply.setException(new RedisException("Already subscribed, cannot send this command"));
    } else {
      ChannelFuture write;
      writerLock.acquireUninterruptibly();
      queue.add(reply);
      write = channel.write(command);
      write.addListener(new ChannelFutureListener() {
        @Override
        public void operationComplete(ChannelFuture future) throws Exception {
          writerLock.release();
          if (future.isSuccess()) {
            // Netty doesn't call these in order
          } else if (future.isCancelled()) {
            reply.cancel(true);
          } else {
            reply.setException(future.getCause());
          }
        }
      });
    }
    return reply;
  }