ISSUE-213: Racy access of partitionProducer.state

[sijie]

Original Issue: apache#213

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Expected behavior

No data race.

Actual behavior

Panic in TestDLQ test due to data race: https://github.com/apache/pulsar-client-go/pull/212/checks?check_run_id=579812410

WARNING: DATA RACE
Write at 0x00c0009a8960 by goroutine 187:
  github.com/apache/pulsar-client-go/pulsar.(*partitionProducer).internalClose()
      /pulsar-client-go/pulsar/producer_partition.go:454 +0x5e0
  github.com/apache/pulsar-client-go/pulsar.(*partitionProducer).runEventsLoop()
      /pulsar-client-go/pulsar/producer_partition.go:214 +0x35d

Previous read at 0x00c0009a8960 by goroutine 350:
  github.com/apache/pulsar-client-go/pulsar.(*partitionProducer).Close()
      /pulsar-client-go/pulsar/producer_partition.go:475 +0x56
  github.com/apache/pulsar-client-go/pulsar.(*producer).Close()
      /pulsar-client-go/pulsar/producer_impl.go:173 +0xd8
  github.com/apache/pulsar-client-go/pulsar/internal.(*ClientHandlers).Close()
      /pulsar-client-go/pulsar/internal/client_handlers.go:61 +0x30b
  github.com/apache/pulsar-client-go/pulsar.(*client).Close()
      /pulsar-client-go/pulsar/client_impl.go:165 +0x56
  github.com/apache/pulsar-client-go/pulsar.TestDLQ()
      /pulsar-client-go/pulsar/consumer_test.go:1041 +0xf80

The data access to partitionProducer.state is not thread-safe. internalClose() is writing it from a different goroutine than the readers.

Steps to reproduce

go test -race -count 100 -v -run 'TestDLQ$' .

System configuration

Pulsar version: 2.5