HBASE-29965: Unable to dynamically change readonly flag

[kgeisz]

https://issues.apache.org/jira/browse/HBASE-29965

Summary

This pull request fixes an issue where dynamic configuration for hbase.global.readonly.enabled was not working. If the user changed the boolean value for hbase.global.readonly.enabled in hbase-site.xml, saved the file, and then ran update_all_config, then the new config value was not being set in HBase. This was happening because the ConfigurationManager.notifyAllObservers() method was not getting the updated value for hbase.global.readonly.enabled. I was able to fix this by making sure CoprocessorConfigurationUtil.syncReadOnlyConfigurations() was not directly setting the conf value.

Key Changes

• Adds a read-only instance variable to HMaster, HRegionServer, and HRegion.
  • This is used to track whether the read-only mode has been changed when update_all_config triggers the onConfigurationChange() method for each ConfigurationObserver.
• Enabling/disabling read-only mode is now handled in the onConfigurationChange() method for HMaster, HRegionServer, and HRegion.
• Updated CoprocessorConfigurationUtil.syncReadOnlyConfigurations() to have it only handle updating coprocessor lists. It no longer handles updating hbase.global.readonly.enabled in the configuration.
• Updates when syncReadOnlyConfigurations() is run in the onConfigurationChange() methods. It is now run when the global read-only status has changed or when there has been a change in the coprocessor configuration.
• Removes the read-only variable from the syncReadOnlyConfigurations() method signature.
  • syncReadOnlyConfigurations() is now either used when initializing a master, region server, or region, or when a configuration change has occurred. This means the method is always using the "most up-to-date" version of the configuration, so it can get the read-only mode from the configuration itself.