How do you find what process is holding a file open in Windows?

Suppose a search index service has a file open for indexing but has gotten stuck temporarily and you want to delete the file, so you (unwisely) force the handle closed. The search index service opens its log file in order to record some information, and the handle to the deleted file is recycled as the handle to the log file. The stuck operation finally completes, and the search index service finally gets around to closing that handle it had open, but it ends up unwittingly closing the log file handle.

The search index service opens another file, say a configuration file for writing so it can update some persistent state. The handle for the log file gets recycled as the handle for the configuration file. The search index service wants to log some information, so it writes to its log file. Unfortunately, the log file handle was closed and the handle reused for its configuration file. The logged information goes into the configuration file, corrupting it.

Meanwhile, another handle you forced closed was reused as a mutex handle, which is used to help prevent data from being corrupted. When the original file handle is closed, the mutex handle is closed and the protections against data corruption are lost. The longer the service runs, the more corrupted its indexes become. Eventually, somebody notices the index is returning incorrect results. And when you try to restart the service, it fails because its configuration files have been corrupted.

You report the problem to the company that makes the search index service and they determine that the index has been corrupted, the log file has mysteriously stopped logging, and the configuration file was overwritten with garbage. Some poor technician is assigned the hopeless task of figuring out why the service corrupts its indexes and configuration files, unaware that the source of the corruption is that you forced a handle closed.