HDDS-15080. DirectoryDeletingService is using single thread

[aryangupta1998]

What changes were proposed in this pull request?

Switched DirectoryDeletingService to consistently use a fixed-size parallel deletion pool instead of the previous core-0 setup.
Unified pool creation so constructor/start/restart all follow the same path and behave the same after reconfiguration.
Also fixed thread-count reconfig handling so updated values are actually used by worker creation and pool recreation.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-15080

How was this patch tested?

Tested Manually on a cluster.

2026-04-22 21:05:50,910 [pool-37-thread-2] INFO org.apache.hadoop.ozone.om.service.DirectoryDeletingService: Number of dirs deleted: 224, Number of sub-dir deleted: 0, Number of sub-files moved: 447 to DeletedTable, Number of sub-dirs moved 110 to DeletedDirectoryTable, iteration elapsed: 445ms,  totalRunCount: 1
2026-04-22 21:05:50,921 [pool-37-thread-8] INFO org.apache.hadoop.ozone.om.service.DirectoryDeletingService: Number of dirs deleted: 159, Number of sub-dir deleted: 0, Number of sub-files moved: 568 to DeletedTable, Number of sub-dirs moved 89 to DeletedDirectoryTable, iteration elapsed: 456ms,  totalRunCount: 1
2026-04-22 21:05:50,929 [pool-37-thread-7] INFO org.apache.hadoop.ozone.om.service.DirectoryDeletingService: Number of dirs deleted: 262, Number of sub-dir deleted: 0, Number of sub-files moved: 339 to DeletedTable, Number of sub-dirs moved 135 to DeletedDirectoryTable, iteration elapsed: 465ms,  totalRunCount: 1
2026-04-22 21:05:50,940 [pool-37-thread-6] INFO org.apache.hadoop.ozone.om.service.DirectoryDeletingService: Number of dirs deleted: 211, Number of sub-dir deleted: 0, Number of sub-files moved: 437 to DeletedTable, Number of sub-dirs moved 133 to DeletedDirectoryTable, iteration elapsed: 475ms,  totalRunCount: 1
2026-04-22 21:05:50,951 [pool-37-thread-9] INFO org.apache.hadoop.ozone.om.service.DirectoryDeletingService: Number of dirs deleted: 221, Number of sub-dir deleted: 0, Number of sub-files moved: 474 to DeletedTable, Number of sub-dirs moved 116 to DeletedDirectoryTable, iteration elapsed: 487ms,  totalRunCount: 1

[ptlrs]

Thanks for the patch @aryangupta1998. LGTM

[adoroszlai]

Thanks @aryangupta1998 for the patch.

[ashishkumar50]

@aryangupta1998 Thanks for working on this, can you also have a test to see if multiple threads are executing in parallel.

[ashishkumar50]

@aryangupta1998 Can you add a test if multiple threads are executing in parallel.

[ptlrs]

Thanks for the updates @aryangupta1998. LGTM

[ashishkumar50]

@aryangupta1998 Thanks for updating patch, LGTM.