Hi there, I'm writing for knowledge about SerializationSchema/DeserializationSchema's concurrency safety.
The problem is, I've implemented my own KafkaSerializationSchema/KafkaDeserializationKafka which I have added some internal state and object cache as to avoid heavy object(memory) allocation. My question is, if the two classes are safe in the following two situations: 1. Multiple sub-tasks are running in the same JVM. 2. One sub-task is outputting to multiple Kafka partitions. Will there be shared instance (which lead to unsafe concurrency) or each sub-task/thread will have its own instance (safe)?
