Problem

Starting in Bitbucket Server 7.4, hosting requests made via HTTP now perform request processing async on a separate thread. It also switches to use non-blocking I/O when handling requests. If you have any third-party App installed that has explicitly disabled async processing, you will see the following in atlassian-bitbucket.log:

Async handling for HTTP hosting is enabled, but async is not supported for the request. It may be have been blocked by a third-party app.

Note: In order to not flood the logs, this message will only be logged once per startup.

This will not prevent hosting operations from working, instead all HTTP hosting requests will fall back to blocking I/O and work as they did in previous versions. This has the side-affect of affecting performance and scalability as blocking I/O requests extra threads and overhead.

Cause

A third-party App has explicitly opted out of using async processing, likely because it needs additional work to support this. The offending App will have set a filter to not support async with <async-supported>false</async-supported>:

<servlet-filter name="My Filter" key="my-filter" class="com.atlassian.example.web.MyFilter"
                location="before-login">
    <async-supported>false</async-supported>
    <dispatcher>REQUEST</dispatcher>
    <url-pattern>*</url-pattern>
</servlet-filter>

Bitbucket Server is unable to tell which App is unable to determine which App has turned off async processing, so you will need to go through each App to determine if it is the cause.

Workaround

If possible, the App can be disabled to allow async requests.

If you choose to leave the App as-is, HTTP hosting requests will continue to work, but there is the performance impact mentioned above to be aware of.

Resolution

The App needs to be updated to support async processing. If this is an internally developed App, the API Changelog for Bitbucket Server 7.4 provides the needed changes for updating your App. If this is a third-party App, you will need to reach out and raise a request with the developer of that App.