What does Windows error code 4 (ERROR_TOO_MANY_OPEN_FILES) mean?

ERROR_TOO_MANY_OPEN_FILES

Too many file objects are open

ERROR_TOO_MANY_OPEN_FILES indicates exhaustion of a file-opening resource, often because handles are leaked or retained longer than intended. The name is historical, but the underlying issue is still usually lifetime management.

Investigation

• Measure the process handle count over time.
• Group open handles by type and call site.
• Check error paths that return before closing files, directories, or search handles.
• Review pools and caches that intentionally retain file handles.

Fix

Close handles deterministically and bound any cache that keeps files open. Increasing a limit may delay the symptom but does not correct a leak.

References

• Microsoft: System error codes 0–499
• Microsoft: File management