[HDFS-9616] libhdfs++ Add runtime hooks to allow a client application to add low level monitoring and tests.

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Component/s: hdfs-client
• Assignee: Bob Hansen
• Reporter: James Clampffer
• Created: 05/Jan/16 23:09
• Updated: 22/Mar/18 21:57
• Resolved: 24/Mar/16 04:21

Description

It would be nice to have a set of callable objects and corresponding event hooks in useful places that can be set by a client application at runtime.

This is intended to provide a scalable mechanism for implementing counters (#retries, #namenode requests) or application specific testing e.g. simulate a dropped connection when the test system running the client application requests.

Current implementation plan is a struct full of callbacks (std::functions) owned by the FileSystemImpl. A callback could be set (or left as a no-op) and when the code hits the corresponding event it will be invoked with a reference to the object (for context) and each method argument by reference. The callback returns a bool: true to continue execution or false to bail out of the calling method.