v0.30.0: Creating `google-cloud-pubsub==0.30.0` release. (#4619)

Notable Implementation Changes

• Dropping redundant Policy._paused data member (#4568).
• Removing redundant "active" check in policy (#4603).
• Adding a Consumer.active property (#4604).
• Making it impossible to call Policy.open() on an already opened
  policy (#4606).
• Bug fix (#4575): Fix bug with async publish for batches. There
  were two related bugs. The first: if a batch exceeds the max_messages
  from the batch settings, then the commit() will fail. The second:
  when a "monitor" worker calls commit() after max_latency seconds,
  a failure can occur if a new message is added to the batch during
  the commit. To fix, the following changes were implemented:
  • Adding a "STARTING" status for Batch.commit() (#4614). This
    fixes the issue when the batch exceeds max_messages.
  • Adding extra check in Batch.will_accept for the number of
    messages (#4612).
  • Moving will_accept() check out of PublisherClient.batch()
    factory (#4613).
  • Checking Batch.will_accept in thread-safe way (#4616).
• Breaking API change: As part of #4613, changing PublisherClient.batch()
  to no longer accept a message (since the will_accept check needs to
  happen in a more concurrency friendly way). In addition, changing the
  create argument so that it means "create even if batch already exists"
  rather than "create if missing".

Documentation

• Add more explicit documentation for Message.attributes (#4601).
• Make Message.__repr__ a bit prettier / more useful (#4602).

PyPI: https://pypi.org/project/google-cloud-pubsub/0.30.0/