What does Windows error code 84 (ERROR_OUT_OF_STRUCTURES) mean?

ERROR_OUT_OF_STRUCTURES

What ERROR_OUT_OF_STRUCTURES means

ERROR_OUT_OF_STRUCTURES is a Win32 system result whose documented message is: “Storage to process this request is not available.” In practical troubleshooting, it belongs to legacy subsystem bookkeeping where the operating system or compatibility environment has exhausted a fixed pool of internal structures.

Typical causes

• a 16-bit or emulated subsystem consumed its available task, file, queue, or control blocks
• a long-running legacy process leaked handles or subsystem objects
• the compatibility environment was configured with limits that are small relative to the workload

How to investigate the result

1. measure process handles and object counts before and after each repeated operation
2. restart only the affected compatibility subsystem and compare behavior
3. Reduce parallel jobs to determine whether the limit is global or per process

Developer guidance

Treat this as resource exhaustion, not ordinary memory pressure. Add bounds to object creation, close every compatibility handle on all error paths, and emit counters for the relevant pool.

Administrator and support guidance

A restart can temporarily recover service, but repeated recurrence indicates a leak or fixed legacy limit. Preserve a process dump and handle inventory before restarting.

Example

An old batch processor opens many concurrent jobs and never releases one subsystem record per job; later requests fail although the machine still has free RAM.

How it differs from related results

ERROR_NOT_ENOUGH_MEMORY concerns allocatable memory; it more often means a bounded internal table has no free entry.

References

• Microsoft: System error codes 0–499