Making sure AsyncEventHandlers are all run. Fixes issue #838.

[stebet]

Proposed Changes

Fixes #838 by making sure all asynchronous event handlers are run.

Types of Changes

• Bug fix (non-breaking change which fixes issue The implementation of the AsyncEventingBasicConsumer is not safe when there are multiple handlers attached #838)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

[lukebakken]

Thanks @stebet

[michaelklishin]

@stebet thank you for your ongoing contributions 🥇