KePulseEvent function (ntddk.h)

Article
04/18/2022

The KePulseEvent routine atomically sets an event object to a signaled state, attempts to satisfy as many waits as possible, and then resets the event object to a not-signaled state.

Syntax

LONG KePulseEvent(
  [in, out] PRKEVENT  Event,
  [in]      KPRIORITY Increment,
  [in]      BOOLEAN   Wait
);

Parameters

[in, out] Event

A pointer to a dispatcher object of type KEVENT.

[in] Increment

Specifies a boost to apply to the priority of threads which are readied as a result of pulsing the event. Typically set to zero but can be set to one.

[in] Wait

Specifies a Boolean value that signifies whether the call to KePulseEvent will be immediately followed by a call to one of the KeWaitXxx routines. If TRUE, the KePulseEvent call is immediately followed by a call to KeWaitForMultipleObjects, KeWaitForMutexObject, or KeWaitForSingleObject. For more information, see the following Remarks section.

Return value

The previous signal state of the event object.

Remarks

For more information about event objects, see Event Objects.

The KePulseEvent routine might temporarily raise the IRQL. If the Wait parameter is FALSE, the routine, before it returns, restores the IRQL to the original value that it had at the start of the call.

If Wait = TRUE, the routine returns without lowering the IRQL. In this case, the KePulseEvent call must be immediately followed by a KeWaitXxx call. By setting Wait = TRUE, the caller can prevent an unnecessary context switch from occurring between the KePulseEvent call and the KeWaitXxx call. The KeWaitXxx routine, before it returns, restores the IRQL to its original value at the start of the KePulseEvent call. Although the IRQL disables context switches between the two calls, these calls cannot reliably be used as the start and end of an atomic operation. For example, between these two calls, a thread that is running at the same time on another processor might change the state of the event object or of the target of the wait.

If the caller is executing at IRQL = DISPATCH_LEVEL or in an arbitrary thread context, the Timeout parameter to KeWaitXxx must be zero.

Warning

If a thread waiting for Event is currently running a kernel APC, then, when KePulseEvent is called, this thread's wait is not satisfied. After the kernel APC completes, the thread remains in the wait state.

Requirements

Requirement	Value
Minimum supported client	Available starting with Windows 2000.
Target Platform	Universal
Header	ntddk.h (include Ntddk.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe
IRQL	<= DISPATCH_LEVEL
DDI compliance rules	HwStorPortProhibitedDDIs(storport), IrqlKeDispatchLte(wdm)