DISPATCHLEVEL

Dispatchlevel, denoted as DISPATCH_LEVEL, is a kernel-mode IRQL used in the Windows NT family of operating systems to indicate the priority at which certain code executes. It represents a mid-to-high level in the IRQL hierarchy, higher than passive and APC levels but lower than device-related IRQLs. Code running at this level is intended for quick, high-priority work, such as handling parts of interrupt processing or Deferred Procedure Calls (DPCs).

In practice, DISPATCH_LEVEL is most commonly associated with DPC routines. An interrupt service routine may schedule a DPC to run later, and that DPC executes at DISPATCH_LEVEL. While operating at this level, the code is expected to be non-blocking and non-paged, and it should avoid operations that could sleep or cause a page fault. The intent is to complete urgent work promptly and then lower the IRQL or queue additional work to a lower-priority context.

Because DISPATCH_LEVEL cannot suffer page faults and cannot block, code at this IRQL must avoid acquiring resources that might sleep or touch pageable memory. If longer or potentially blocking work is required, it should be deferred to a thread running at PASSIVE_LEVEL or queued to a worker pool. Proper use of DISPATCH_LEVEL helps ensure responsive interrupt handling while maintaining system stability.

See also: IRQL, DPC (Deferred Procedure Call), ISR, kernel synchronization primitives.