too many ProduceAccmulators

[manfrid]

• Our program creates many DefaultMQProducer instances (for several clusters).
• After initializing DefaultMQProducer, we set the instanceName.
• Previously, in version 5.3.0, the ProduceAccumulator was created in its constructor at a time when the instanceName was still "DEFAULT". As a result, only one ProduceAccumulator was created.
• After upgrading to version 5.3.2, the creation of ProduceAccumulator was moved to the start method. This change caused the creation of many ProduceAccumulator instances (more than 80).
• Each ProduceAccumulator maintains two threads that continuously loop, consuming a significant amount of CPU resources.
• At the same time, it was discovered that libjvm.so.java_start is also consuming a significant amount of resources. It is suspected that this is related to frequent lock contention and thread context switching caused by the two threads inside ProduceAccumulator.